Removing WORLD_SIZE, part 1.

Erased almost every instance of WORLD_SIZE and replaced it with a local
power of two, map_size_lg (which respects certain invariants; see
common/src/terrain/map.rs for more details about MapSizeLg).  This also
means we can avoid a dependency on the world crate from client, as
desired.

Now that the rest of the code is not expecting a fixed WORLD_SIZE, the
next step is to arrange for maps to store their world size, and to use
that world size as a basis prior to loading the map (as well, probably,
as prior to configuring some of the noise functions).

Cargo.lock

@@ -4565,7 +4565,6 @@ dependencies = [
  "uvth 3.1.1",
  "vek",
  "veloren-common",
- "veloren-world",
  "veloren_network",
 ]
 
@@ -4588,6 +4587,7 @@ dependencies = [
  "rand 0.7.3",
  "rayon",
  "ron",
+ "roots",
  "serde",
  "serde_json",
  "specs",
@@ -4733,7 +4733,6 @@ dependencies = [
  "rand_chacha 0.2.2",
  "rayon",
  "ron",
- "roots",
  "serde",
  "tracing",
  "tracing-subscriber",

client/Cargo.toml

@@ -6,7 +6,6 @@ edition = "2018"
 
 [dependencies]
 common = { package = "veloren-common", path = "../common", features = ["no-assets"] }
-world = { package = "veloren-world", path = "../world" }
 network = { package = "veloren_network", path = "../network", default-features = false }
 
 byteorder = "1.3.2"

client/src/lib.rs

@@ -28,7 +28,7 @@ use common::{
     recipe::RecipeBook,
     state::State,
     sync::{Uid, UidAllocator, WorldSyncExt},
-    terrain::{block::Block, TerrainChunk, TerrainChunkSize},
+    terrain::{block::Block, neighbors, TerrainChunk, TerrainChunkSize},
     vol::RectVolSize,
 };
 use futures_executor::block_on;
@@ -50,9 +50,6 @@ use std::{
 use tracing::{debug, error, trace, warn};
 use uvth::{ThreadPool, ThreadPoolBuilder};
 use vek::*;
-// TODO: remove world dependencies.  We should see if we
-// can pull out map drawing into common somehow.
-use world::sim::{neighbors, Alt};
 
 // The duration of network inactivity until the player is kicked
 // @TODO: in the future, this should be configurable on the server
@@ -187,8 +184,18 @@ impl Client {
                             let entity = state.ecs_mut().apply_entity_package(entity_package);
                             *state.ecs_mut().write_resource() = time_of_day;
 
-                            let map_size = world_map.dimensions;
+                            let map_size_lg = common::terrain::MapSizeLg::new(
+                                world_map.dimensions_lg,
+                            )
+                            .map_err(|_| {
+                                Error::Other(format!(
+                                    "Server sent bad world map dimensions: {:?}",
+                                    world_map.dimensions_lg,
+                                ))
+                            })?;
+                            let map_size = map_size_lg.chunks();
                             let max_height = world_map.max_height;
+                            let sea_level = world_map.sea_level;
                             let rgba = world_map.rgba;
                             let alt = world_map.alt;
                             let expected_size =
@@ -203,10 +210,9 @@ impl Client {
                             }
                             let [west, east] = world_map.horizons;
                             let scale_angle =
-                                |a: u8| (a as Alt / 255.0 * <Alt as FloatConst>::FRAC_PI_2()).tan();
+                                |a: u8| (a as f32 / 255.0 * <f32 as FloatConst>::FRAC_PI_2()).tan();
-                            let scale_height = |h: u8| h as Alt / 255.0 * max_height as Alt;
+                            let scale_height = |h: u8| h as f32 / 255.0 * max_height;
-                            let scale_height_big =
+                            let scale_height_big = |h: u32| (h >> 3) as f32 / 8191.0 * max_height;
-                                |h: u32| (h >> 3) as Alt / 8191.0 * max_height as Alt;
 
                             debug!("Preparing image...");
                             let unzip_horizons = |(angles, heights): &(Vec<_>, Vec<_>)| {
@@ -223,13 +229,15 @@ impl Client {
 
                             // Redraw map (with shadows this time).
                             let mut world_map = vec![0u32; rgba.len()];
-                            let mut map_config = world::sim::MapConfig::default();
+                            let mut map_config = common::terrain::map::MapConfig::orthographic(
-                            map_config.lgain = 1.0;
+                                map_size_lg,
-                            map_config.gain = max_height;
+                                core::ops::RangeInclusive::new(0.0, max_height),
+                            );
+                            // map_config.gain = max_height;
                             map_config.horizons = Some(&horizons);
                             // map_config.light_direction = Vec3::new(1.0, -1.0, 0.0);
-                            map_config.focus.z = 0.0;
+                            // map_config.focus.z = 0.0;
-                            let rescale_height = |h: Alt| (h / max_height as Alt) as f32;
+                            let rescale_height = |h: f32| h / max_height;
                             let bounds_check = |pos: Vec2<i32>| {
                                 pos.reduce_partial_min() >= 0
                                     && pos.x < map_size.x as i32
@@ -246,9 +254,7 @@ impl Client {
                                         let downhill = {
                                             let mut best = -1;
                                             let mut besth = alti;
-                                            // TODO: Fix to work for dynamic WORLD_SIZE (i.e.
+                                            for nposi in neighbors(map_size_lg, posi) {
-                                            // map_size).
-                                            for nposi in neighbors(posi) {
                                                 let nbh = alt[nposi];
                                                 if nbh < besth {
                                                     besth = nbh;
@@ -278,9 +284,9 @@ impl Client {
                                         wpos + TerrainChunkSize::RECT_SIZE.map(|e| e as i32),
                                     );
                                     let alt = rescale_height(scale_height_big(alt));
-                                    world::sim::MapSample {
+                                    common::terrain::map::MapSample {
                                         rgb: Rgb::from(rgba),
-                                        alt: alt as Alt,
+                                        alt: f64::from(alt),
                                         downhill_wpos,
                                         connections: None,
                                     }
@@ -326,10 +332,7 @@ impl Client {
                                 .collect::<Vec<_>>();
                             let lod_horizon = horizons; //make_raw(&horizons)?;
                             // TODO: Get sea_level from server.
-                            let map_bounds = Vec2::new(
+                            let map_bounds = Vec2::new(sea_level, max_height);
-                                /* map_config.focus.z */ world::CONFIG.sea_level,
-                                /* map_config.gain */ max_height,
-                            );
                             debug!("Done preparing image...");
 
                             break Ok((

common/Cargo.toml

@@ -11,6 +11,7 @@ no-assets = []
 arraygen = "0.1.13"
 specs-idvs = { git = "https://gitlab.com/veloren/specs-idvs.git", branch = "specs-git" }
 
+roots = "0.0.5"
 specs = { git = "https://github.com/amethyst/specs.git", features = ["serde", "storage-event-control"], rev = "7a2e348ab2223818bad487695c66c43db88050a5" }
 vek = { version = "0.11.0", features = ["serde"] }
 dot_vox = "4.0"

common/src/lib.rs

@@ -3,6 +3,8 @@
 #![type_length_limit = "1664759"]
 #![feature(
     arbitrary_enum_discriminant,
+    const_checked_int_methods,
+    const_if_match,
     option_unwrap_none,
     bool_to_option,
     label_break_value,

common/src/msg/server.rs

@@ -66,8 +66,12 @@ pub struct CharacterInfo {
 /// repeating the "small angles" optimization that works well on more detailed
 /// shadow maps intended for height maps.
 pub struct WorldMapMsg {
-    /// World map dimensions (width × height)
+    /// Log base 2 of world map dimensions (width × height) in chunks.
-    pub dimensions: Vec2<u16>,
+    ///
+    /// NOTE: Invariant: chunk count fits in a u16.
+    pub dimensions_lg: Vec2<u32>,
+    /// Sea level (used to provide a base altitude).
+    pub sea_level: f32,
     /// Max height (used to scale altitudes).
     pub max_height: f32,
     /// RGB+A; the alpha channel is currently unused, but will be used in the

common/src/terrain/map.rs

@@ -0,0 +1,719 @@
+use super::{
+    neighbors, quadratic_nearest_point, river_spline_coeffs, uniform_idx_as_vec2,
+    vec2_as_uniform_idx, TerrainChunkSize, NEIGHBOR_DELTA, TERRAIN_CHUNK_BLOCKS_LG,
+};
+use crate::vol::RectVolSize;
+use core::{f32, f64, iter, ops::RangeInclusive};
+use vek::*;
+
+/// Base two logarithm of the maximum size of the precomputed world, in meters,
+/// along the x (E/W) and y (N/S) dimensions.
+///
+/// NOTE: Each dimension is guaranteed to be a power of 2, so the logarithm is
+/// exact. This is so that it is possible (at least in theory) for compiler or
+/// runtime optimizations exploiting this are possible.  For example, division
+/// by the chunk size can turn into a bit shift.
+///
+/// NOTE: As an invariant, this value is at least [TERRAIN_CHUNK_BLOCKS_LG].
+///
+/// NOTE: As an invariant, `(1 << [MAX_WORLD_BLOCKS_LG])` fits in an i32.
+///
+/// TODO: Add static assertions for the above invariants.
+///
+/// Currently, we define the maximum to be 19 (corresponding to 2^19 m) for both
+/// directions. This value was derived by backwards reasoning from the following
+/// conservative estimate of the maximum landmass area (using an approximation
+/// of 1024 blocks / km instead of 1000 blocks / km, which will result in an
+/// estimate that is strictly lower than the real landmass):
+///
+/// Max area (km²)
+///     ≌ (2^19 blocks * 1 km / 1024 blocks)^2
+///     = 2^((19 - 10) * 2) km²
+///     = 2^18 km²
+///     = 262,144 km²
+///
+/// which is roughly the same area as the entire United Kingdom, and twice the
+/// horizontal extent of Dwarf Fortress's largest map.  Besides the comparison
+/// to other games without infinite or near-infinite maps (like Dwarf Fortress),
+/// there are other reasons to choose this as a good maximum size:
+///
+/// * It is large enough to include geological features of fairly realistic
+///   scale.  It may be hard to do justice to truly enormous features like the
+///   Amazon River, and natural temperature variation not related to altitude
+///   would probably not produce climate extremes on an Earth-like planet, but
+///   it can comfortably fit enormous river basins, Everest-scale mountains,
+///   large islands and inland lakes, vast forests and deserts, and so on.
+///
+/// * It is large enough that making it from one side of the map to another will
+///   take a *very* long time.  We show this with two examples.  In each
+///   example, travel is either purely horizontal or purely vertical (to
+///   minimize distance traveled) across the whole map, and we assume there are
+///   no obstacles or slopes.
+///
+///   In example 1, a human is walking at the (real-time) speed of the fastest
+/// marathon runners   (around 6 blocks / real-time s).  We assume the human can
+/// maintain this pace indefinitely   without stopping.  Then crossing the map
+/// will take about:
+///
+///   2^19 blocks * 1 real-time s / 6 blocks * 1 real-time min / 60 real-time s
+/// * 1 real-time hr / 60 real-time min * 1 real-time days / 24 hr = 2^19 / 6 /
+///   60 / 60 / 24 real-time days ≌ 1 real-time day.
+///
+///   That's right--it will take a full day of *real* time to cross the map at
+/// an apparent speed of   6 m / s.  Moreover, since in-game time passes at a
+/// rate of 1 in-game min / 1 in-game s, this   would also take *60 days* of
+/// in-game time.
+///
+///   Still though, this is the rate of an ordinary human.  And besides that, if
+/// we instead had a   marathon runner traveling at 6 m / in-game s, it would
+/// take just 1 day of in-game time for   the runner to cross the map, or a mere
+/// 0.4 hr of real time.   To show that this rate of travel is unrealistic (and
+/// perhaps make an eventual argument for   a slower real-time to in-game time
+/// conversion rate), our second example will consist of a   high-speed train
+/// running at 300 km / real-time h (the fastest real-world high speed train
+///   averages under 270 k m / h, with 300 km / h as the designed top speed).
+/// For a train   traveling at this apparent speed (in real time), crossing the
+/// map would take:
+///
+///   2^19 blocks * 1 km / 1000 blocks * 1 real-time hr / 300 km
+///   = 2^19 / 1000 / 300 real-time hr
+///   ≌ 1.75 real-time hr
+///
+///   = 2^19 / 1000 / 300 real-time hr * 60 in-game hr / real-time hr
+///     * 1 in-game days / 24 in-game hr
+///   = 2^19 / 1000 / 300 * 60 / 24 in-game days
+///   ≌ 4.37 in-game days
+///
+///   In other words, something faster in real-time than any existing high-speed
+/// train would be   over 4 times slower (in real-time) than our hypothetical
+/// top marathon runner running at 6 m /   s in in-game speed.  This suggests
+/// that the gap between in-game time and real-time is   probably much too large
+/// for most purposes; however, what it definitely shows is that even
+///   extremely fast in-game transport across the world will not trivialize its
+/// size.
+///
+///   It follows that cities or towns of realistic scale, player housing,
+/// fields, and so on, will   all fit comfortably on a map of this size, while
+/// at the same time still being reachable by   non-warping, in-game mechanisms
+/// (such as high-speed transit).  It also provides plenty of   room for mounts
+/// of varying speeds, which can help ensure that players don't feel cramped or
+///   deliberately slowed down by their own speed.
+///
+/// * It is small enough that it is (barely) plausible that we could still
+///   generate maps for a world of this size using detailed and realistic
+///   erosion algorithms.  At 1/4 of this map size along each dimension,
+///   generation currently takes around 5 hours on a good computer, and one
+///   could imagine (since the bottleneck step appears to be roughly O(n)) that
+///   with a smart implementation generation times of under a week could be
+///   achievable.
+///
+/// * The map extends further than the resolution of human eyesight under
+///   Earthlike conditions, even from tall mountains across clear landscapes.
+///   According to one calculation, even from Mt. Everest in the absence of
+///   cloud cover, you could only see for about 339 km before the Earth's
+///   horizon prevented you from seeing further, and other sources suggest that
+///   in practice the limit is closer to 160 km under realistic conditions. This
+///   implies that making the map much larger in a realistic way would require
+///   incorporating curvature, and also implies that any features that cannot
+///   fit on the map would not (under realistic atmospheric conditions) be fully
+///   visible from any point on Earth.  Therefore, even if we cannot represent
+///   features larger than this accurately, nothing should be amiss from a
+///   visual perspective, so this should not significantly impact the player
+///   experience.
+pub const MAX_WORLD_BLOCKS_LG: Vec2<u32> = Vec2 { x: 19, y: 19 };
+
+/// Base two logarithm of a world size, in chunks, per dimension
+/// (each dimension must be a power of 2, so the logarithm is exact).
+///
+/// NOTE: As an invariant, each dimension must be between 0 and
+/// `[MAX_WORLD_BLOCKS_LG] - [TERRAIN_CHUNK_BLOCKS_LG]`.
+///
+/// NOTE: As an invariant, `(1 << ([DEFAULT_WORLD_CHUNKS_LG] +
+/// [TERRAIN_CHUNK_BLOCKS_LG]))` fits in an i32 (derived from the invariant
+/// on [MAX_WORLD_BLOCKS_LG]).
+///
+/// NOTE: As an invariant, each dimension (in chunks) must fit in a u16.
+///
+/// NOTE: As an invariant, the product of dimensions (in chunks) must fit in a
+/// usize.
+///
+/// These invariants are all checked on construction of a `MapSizeLg`.
+#[derive(Clone, Copy, Debug)]
+pub struct MapSizeLg(Vec2<u32>);
+
+impl MapSizeLg {
+    /// Construct a new `MapSizeLg`, returning an error if the needed invariants
+    /// do not hold and the vector otherwise.
+    ///
+    /// TODO: In the future, we may use unsafe code to assert to the compiler
+    /// that these invariants indeed hold, safely opening up optimizations
+    /// that might not otherwise be available at runtime.
+    #[inline(always)]
+    pub const fn new(map_size_lg: Vec2<u32>) -> Result<Self, ()> {
+        // Assertion on dimensions: must be between
+        // 0 and MAX_WORLD_BLOCKS_LG] - [TERRAIN_CHUNK_BLOCKS_LG
+        let is_le_max = map_size_lg.x <= MAX_WORLD_BLOCKS_LG.x - TERRAIN_CHUNK_BLOCKS_LG
+            && map_size_lg.y <= MAX_WORLD_BLOCKS_LG.y - TERRAIN_CHUNK_BLOCKS_LG;
+        // Assertion on dimensions: chunks must fit in a u16.
+        let chunks_in_range =
+            /* 1u16.checked_shl(map_size_lg.x).is_some() &&
+            1u16.checked_shl(map_size_lg.y).is_some(); */
+            map_size_lg.x <= 16 &&
+            map_size_lg.y <= 16;
+        if is_le_max && chunks_in_range {
+            // Assertion on dimensions: blocks must fit in a i32.
+            let blocks_in_range =
+                /* 1i32.checked_shl(map_size_lg.x + TERRAIN_CHUNK_BLOCKS_LG).is_some() &&
+                1i32.checked_shl(map_size_lg.y + TERRAIN_CHUNK_BLOCKS_LG).is_some(); */
+                map_size_lg.x + TERRAIN_CHUNK_BLOCKS_LG < 32 &&
+                map_size_lg.y + TERRAIN_CHUNK_BLOCKS_LG < 32;
+            // Assertion on dimensions: product of dimensions must fit in a usize.
+            let chunks_product_in_range =
+                if let Some(_) = 1usize.checked_shl(map_size_lg.x + map_size_lg.y) {
+                    true
+                } else {
+                    false
+                };
+            if blocks_in_range && chunks_product_in_range {
+                // Cleared all invariants.
+                Ok(MapSizeLg(map_size_lg))
+            } else {
+                Err(())
+            }
+        } else {
+            Err(())
+        }
+    }
+
+    #[inline(always)]
+    /// Acquire the `MapSizeLg`'s inner vector.
+    pub const fn vec(self) -> Vec2<u32> { self.0 }
+
+    #[inline(always)]
+    /// Get the size of this map in chunks.
+    pub const fn chunks(self) -> Vec2<u16> { Vec2::new(1 << self.0.x, 1 << self.0.y) }
+
+    /// Get the size of an array of the correct size to hold all chunks.
+    pub const fn chunks_len(self) -> usize { 1 << (self.0.x + self.0.y) }
+}
+
+impl From<MapSizeLg> for Vec2<u32> {
+    #[inline(always)]
+    fn from(size: MapSizeLg) -> Self { size.vec() }
+}
+
+pub struct MapConfig<'a> {
+    /// Base two logarithm of the chunk dimensions of the base map.
+    /// Has no default; set explicitly during initial orthographic projection.
+    pub map_size_lg: MapSizeLg,
+    /// Dimensions of the window being written to.
+    ///
+    /// Defaults to `1 << [MapConfig::map_size_lg]`.
+    pub dimensions: Vec2<usize>,
+    /// x, y, and z of top left of map.
+    ///
+    /// Default x and y are 0.0; no reasonable default for z, so set during
+    /// initial orthographic projection.
+    pub focus: Vec3<f64>,
+    /// Altitude is divided by gain and clamped to [0, 1]; thus, decreasing gain
+    /// makes smaller differences in altitude appear larger.
+    ///
+    /// No reasonable default for z; set during initial orthographic projection.
+    pub gain: f32,
+    /// `fov` is used for shading purposes and refers to how much impact a
+    /// change in the z direction has on the perceived slope relative to the
+    /// same change in x and y.
+    ///
+    /// It is stored as cos θ in the range (0, 1\] where θ is the FOV
+    /// "half-angle" used for perspective projection.  At 1.0, we treat it
+    /// as the limit value for θ = 90 degrees, and use an orthographic
+    /// projection.
+    ///
+    /// Defaults to 1.0.
+    ///
+    /// FIXME: This is a hack that tries to incorrectly implement a variant of
+    /// perspective projection (which generates ∂P/∂x and ∂P/∂y for screen
+    /// coordinate P by using the hyperbolic function \[assuming frustum of
+    /// \[l, r, b, t, n, f\], rh coordinates, and output from -1 to 1 in
+    /// s/t, 0 to 1 in r, and NDC is left-handed \[so visible z ranges from
+    /// -n to -f\]\]):
+    ///
+    /// P.s(x, y, z) = -1 +  2(-n/z x -  l) / ( r -  l)
+    /// P.t(x, y, z) = -1 +  2(-n/z y -  b) / ( t -  b)
+    /// P.r(x, y, z) =  0 + -f(-n/z   -  1) / ( f -  n)
+    ///
+    /// Then arbitrarily using W_e_x = (r - l) as the width of the projected
+    /// image, we have W_e_x = 2 n_e tan θ ⇒ tan Θ = (r - l) / (2n_e), for a
+    /// perspective projection
+    ///
+    /// (where θ is the half-angle of the FOV).
+    ///
+    /// Taking the limit as θ → 90, we show that this degenrates to an
+    /// orthogonal projection:
+    ///
+    /// lim{n → ∞}(-f(-n / z - 1) / (f - n)) = -(z - -n) / (f - n).
+    ///
+    /// (Proof not currently included, but has been formalized for the P.r case
+    /// in Coq-tactic notation; the proof can be added on request, but is
+    /// large and probably not well-suited to Rust documentation).
+    ///
+    /// For this reason, we feel free to store `fov` as cos θ in the range (0,
+    /// 1\].
+    ///
+    /// However, `fov` does not actually work properly yet, so for now we just
+    /// treat it as a visual gimmick.
+    pub fov: f64,
+    /// Scale is like gain, but for x and y rather than z.
+    ///
+    /// Defaults to (1 << world_size_lg).x / dimensions.x (NOTE: fractional, not
+    /// integer, division!).
+    pub scale: f64,
+    /// Vector that indicates which direction light is coming from, if shading
+    /// is turned on.
+    ///
+    /// Right-handed coordinate system: light is going left, down, and
+    /// "backwards" (i.e. on the map, where we translate the y coordinate on
+    /// the world map to z in the coordinate system, the light comes from -y
+    /// on the map and points towards +y on the map).  In a right
+    /// handed coordinate system, the "camera" points towards -z, so positive z
+    /// is backwards "into" the camera.
+    ///
+    /// "In world space the x-axis will be pointing east, the y-axis up and the
+    /// z-axis will be pointing south"
+    ///
+    /// Defaults to (-0.8, -1.0, 0.3).
+    pub light_direction: Vec3<f64>,
+    /// If Some, uses the provided horizon map.
+    ///
+    /// Defaults to None.
+    pub horizons: Option<&'a [(Vec<f32>, Vec<f32>); 2]>,
+    /// If true, only the basement (bedrock) is used for altitude; otherwise,
+    /// the surface is used.
+    ///
+    /// Defaults to false.
+    pub is_basement: bool,
+    /// If true, water is rendered; otherwise, the surface without water is
+    /// rendered, even if it is underwater.
+    ///
+    /// Defaults to true.
+    pub is_water: bool,
+    /// If true, 3D lighting and shading are turned on.  Otherwise, a plain
+    /// altitude map is used.
+    ///
+    /// Defaults to true.
+    pub is_shaded: bool,
+    /// If true, the red component of the image is also used for temperature
+    /// (redder is hotter). Defaults to false.
+    pub is_temperature: bool,
+    /// If true, the blue component of the image is also used for humidity
+    /// (bluer is wetter).
+    ///
+    /// Defaults to false.
+    pub is_humidity: bool,
+    /// Record debug information.
+    ///
+    /// Defaults to false.
+    pub is_debug: bool,
+}
+
+pub const QUADRANTS: usize = 4;
+
+pub struct MapDebug {
+    pub quads: [[u32; QUADRANTS]; QUADRANTS],
+    pub rivers: u32,
+    pub lakes: u32,
+    pub oceans: u32,
+}
+
+/// Connection kind (per edge).  Currently just supports rivers, but may be
+/// extended to support paths or at least one other kind of connection.
+#[derive(Clone, Copy, Debug)]
+pub enum ConnectionKind {
+    /// Connection forms a visible river.
+    River,
+}
+
+/// Map connection (per edge).
+#[derive(Clone, Copy, Debug)]
+pub struct Connection {
+    /// The kind of connection this is (e.g. river or path).
+    pub kind: ConnectionKind,
+    /// Assumed to be the "b" part of a 2d quadratic function.
+    pub spline_derivative: Vec2<f32>,
+    /// Width of the connection.
+    pub width: f32,
+}
+
+/// Per-chunk data the map needs to be able to sample in order to correctly
+/// render.
+#[derive(Clone, Debug)]
+pub struct MapSample {
+    /// the base RGB color for a particular map pixel using the current settings
+    /// (i.e. the color *without* lighting).
+    pub rgb: Rgb<u8>,
+    /// Surface altitude information
+    /// (correctly reflecting settings like is_basement and is_water)
+    pub alt: f64,
+    /// Downhill chunk (may not be meaningful on ocean tiles, or at least edge
+    /// tiles)
+    pub downhill_wpos: Vec2<i32>,
+    /// Connection information about any connections to/from this chunk (e.g.
+    /// rivers).
+    ///
+    /// Connections at each index correspond to the same index in
+    /// NEIGHBOR_DELTA.
+    pub connections: Option<[Option<Connection>; 8]>,
+}
+
+impl<'a> MapConfig<'a> {
+    /// Constructs the configuration settings for an orthographic projection of
+    /// a map from the top down, rendering (by default) the complete map to
+    /// an image such that the chunk:pixel ratio is 1:1.
+    ///
+    /// Takes two arguments: the base two logarithm of the horizontal map extent
+    /// (in chunks), and the z bounds of the projection.
+    pub fn orthographic(map_size_lg: MapSizeLg, z_bounds: RangeInclusive<f32>) -> Self {
+        assert!(z_bounds.start() <= z_bounds.end());
+        // NOTE: Safe cast since map_size_lg is restricted by the prior assert.
+        let dimensions = map_size_lg.chunks().map(usize::from);
+        Self {
+            map_size_lg,
+            dimensions,
+            focus: Vec3::new(0.0, 0.0, f64::from(*z_bounds.start())),
+            gain: z_bounds.end() - z_bounds.start(),
+            fov: 1.0,
+            scale: 1.0,
+            light_direction: Vec3::new(-1.2, -1.0, 0.8),
+            horizons: None,
+
+            is_basement: false,
+            is_water: true,
+            is_shaded: true,
+            is_temperature: false,
+            is_humidity: false,
+            is_debug: false,
+        }
+    }
+
+    /// Get the base 2 logarithm of the underlying map size.
+    pub fn map_size_lg(&self) -> MapSizeLg { self.map_size_lg }
+
+    /// Generates a map image using the specified settings.  Note that it will
+    /// write from left to write from (0, 0) to dimensions - 1, inclusive,
+    /// with 4 1-byte color components provided as (r, g, b, a).  It is up
+    /// to the caller to provide a function that translates this information
+    /// into the correct format for a buffer and writes to it.
+    ///
+    /// sample_pos is a function that, given a chunk position, returns enough
+    /// information about the chunk to attempt to render it on the map.
+    /// When in doubt, try using `MapConfig::sample_pos` for this.
+    ///
+    /// sample_wpos is a simple function that, given a *column* position,
+    /// returns the approximate altitude at that column.  When in doubt, try
+    /// using `MapConfig::sample_wpos` for this.
+    #[allow(clippy::if_same_then_else)] // TODO: Pending review in #587
+    #[allow(clippy::unnested_or_patterns)] // TODO: Pending review in #587
+    #[allow(clippy::many_single_char_names)]
+    pub fn generate(
+        &self,
+        sample_pos: impl Fn(Vec2<i32>) -> MapSample,
+        sample_wpos: impl Fn(Vec2<i32>) -> f32,
+        mut write_pixel: impl FnMut(Vec2<usize>, (u8, u8, u8, u8)),
+    ) -> MapDebug {
+        let MapConfig {
+            map_size_lg,
+            dimensions,
+            focus,
+            gain,
+            fov,
+            scale,
+            light_direction,
+            horizons,
+
+            is_shaded,
+            // is_debug,
+            ..
+        } = *self;
+
+        let light_direction = Vec3::new(
+            light_direction.x,
+            light_direction.y,
+            0.0, // we currently ignore light_direction.z.
+        );
+        let light_shadow_dir = if light_direction.x >= 0.0 { 0 } else { 1 };
+        let horizon_map = horizons.map(|horizons| &horizons[light_shadow_dir]);
+        let light = light_direction.normalized();
+        let /*mut */quads = [[0u32; QUADRANTS]; QUADRANTS];
+        let /*mut */rivers = 0u32;
+        let /*mut */lakes = 0u32;
+        let /*mut */oceans = 0u32;
+
+        let focus_rect = Vec2::from(focus);
+
+        let chunk_size = TerrainChunkSize::RECT_SIZE.map(|e| e as f64);
+
+        /* // NOTE: Asserting this to enable LLVM optimizations.  Ideally we should come up
+        // with a principled way to do this (especially one with no runtime
+        // cost).
+        assert!(
+            map_size_lg
+                .vec()
+                .cmple(&(MAX_WORLD_BLOCKS_LG - TERRAIN_CHUNK_BLOCKS_LG))
+                .reduce_and()
+        ); */
+        let world_size = map_size_lg.chunks();
+
+        (0..dimensions.y * dimensions.x).for_each(|chunk_idx| {
+            let i = chunk_idx % dimensions.x as usize;
+            let j = chunk_idx / dimensions.x as usize;
+
+            let wposf = focus_rect + Vec2::new(i as f64, j as f64) * scale;
+            let pos = wposf.map(|e: f64| e as i32);
+            let wposf = wposf * chunk_size;
+
+            let chunk_idx = if pos.reduce_partial_min() >= 0
+                && pos.x < world_size.x as i32
+                && pos.y < world_size.y as i32
+            {
+                Some(vec2_as_uniform_idx(map_size_lg, pos))
+            } else {
+                None
+            };
+
+            let MapSample {
+                rgb,
+                alt,
+                downhill_wpos,
+                ..
+            } = sample_pos(pos);
+
+            let alt = alt as f32;
+            let wposi = pos * TerrainChunkSize::RECT_SIZE.map(|e| e as i32);
+            let mut rgb = rgb.map(|e| e as f64 / 255.0);
+
+            // Material properties:
+            //
+            // For each material in the scene,
+            //  k_s = (RGB) specular reflection constant
+            let mut k_s = Rgb::new(1.0, 1.0, 1.0);
+            //  k_d = (RGB) diffuse reflection constant
+            let mut k_d = rgb;
+            //  k_a = (RGB) ambient reflection constant
+            let mut k_a = rgb;
+            //  α = (per-material) shininess constant
+            let mut alpha = 4.0; // 4.0;
+
+            // Compute connections
+            let mut has_river = false;
+            // NOTE: consider replacing neighbors with local_cells, since it is more
+            // accurate (though I'm not sure if it can matter for these
+            // purposes).
+            chunk_idx
+                .map(|chunk_idx| neighbors(map_size_lg, chunk_idx).chain(iter::once(chunk_idx)))
+                .into_iter()
+                .flatten()
+                .for_each(|neighbor_posi| {
+                    let neighbor_pos = uniform_idx_as_vec2(map_size_lg, neighbor_posi);
+                    let neighbor_wpos = neighbor_pos.map(|e| e as f64) * chunk_size;
+                    let MapSample { connections, .. } = sample_pos(neighbor_pos);
+                    NEIGHBOR_DELTA
+                        .iter()
+                        .zip(
+                            connections
+                                .as_ref()
+                                .map(|e| e.iter())
+                                .into_iter()
+                                .flatten()
+                                .into_iter(),
+                        )
+                        .for_each(|(&delta, connection)| {
+                            let connection = if let Some(connection) = connection {
+                                connection
+                            } else {
+                                return;
+                            };
+                            let downhill_wpos = neighbor_wpos
+                                + Vec2::from(delta).map(|e: i32| e as f64) * chunk_size;
+                            let coeffs = river_spline_coeffs(
+                                neighbor_wpos,
+                                connection.spline_derivative,
+                                downhill_wpos,
+                            );
+                            let (_t, _pt, dist) = if let Some((t, pt, dist)) =
+                                quadratic_nearest_point(&coeffs, wposf)
+                            {
+                                (t, pt, dist)
+                            } else {
+                                let ndist = wposf.distance_squared(neighbor_wpos);
+                                let ddist = wposf.distance_squared(downhill_wpos);
+                                if ndist <= ddist {
+                                    (0.0, neighbor_wpos, ndist)
+                                } else {
+                                    (1.0, downhill_wpos, ddist)
+                                }
+                            };
+                            let connection_dist =
+                                (dist.sqrt() - (connection.width as f64 * 0.5).max(1.0)).max(0.0);
+                            if connection_dist == 0.0 {
+                                match connection.kind {
+                                    ConnectionKind::River => {
+                                        has_river = true;
+                                    },
+                                }
+                            }
+                        });
+                });
+
+            // Color in connectins.
+            let water_color_factor = 2.0;
+            let g_water = 32.0 * water_color_factor;
+            let b_water = 64.0 * water_color_factor;
+            if has_river {
+                let water_rgb = Rgb::new(0, ((g_water) * 1.0) as u8, ((b_water) * 1.0) as u8)
+                    .map(|e| e as f64 / 255.0);
+                rgb = water_rgb;
+                k_s = Rgb::new(1.0, 1.0, 1.0);
+                k_d = water_rgb;
+                k_a = water_rgb;
+                alpha = 0.255;
+            }
+
+            let downhill_alt = sample_wpos(downhill_wpos);
+            let cross_pos = wposi
+                + ((downhill_wpos - wposi)
+                    .map(|e| e as f32)
+                    .rotated_z(f32::consts::FRAC_PI_2)
+                    .map(|e| e as i32));
+            let cross_alt = sample_wpos(cross_pos);
+            // TODO: Fix use of fov to match proper perspective projection, as described in
+            // the doc comment.
+            // Pointing downhill, forward
+            // (index--note that (0,0,1) is backward right-handed)
+            let forward_vec = Vec3::new(
+                (downhill_wpos.x - wposi.x) as f64,
+                ((downhill_alt - alt) * gain) as f64 * fov,
+                (downhill_wpos.y - wposi.y) as f64,
+            );
+            // Pointing 90 degrees left (in horizontal xy) of downhill, up
+            // (middle--note that (1,0,0), 90 degrees CCW backward, is right right-handed)
+            let up_vec = Vec3::new(
+                (cross_pos.x - wposi.x) as f64,
+                ((cross_alt - alt) * gain) as f64 * fov,
+                (cross_pos.y - wposi.y) as f64,
+            );
+            // let surface_normal = Vec3::new(fov* (f.y * u.z - f.z * u.y), -(f.x * u.z -
+            // f.z * u.x), fov* (f.x * u.y - f.y * u.x)).normalized();
+            // Then cross points "to the right" (upwards) on a right-handed coordinate
+            // system. (right-handed coordinate system means (0, 0, 1.0) is
+            // "forward" into the screen).
+            let surface_normal = forward_vec.cross(up_vec).normalized();
+
+            // TODO: Figure out if we can reimplement debugging.
+            /* if is_debug {
+                let quad =
+                    |x: f32| ((x as f64 * QUADRANTS as f64).floor() as usize).min(QUADRANTS - 1);
+                if river_kind.is_none() || humidity != 0.0 {
+                    quads[quad(humidity)][quad(temperature)] += 1;
+                }
+                match river_kind {
+                    Some(RiverKind::River { .. }) => {
+                        rivers += 1;
+                    },
+                    Some(RiverKind::Lake { .. }) => {
+                        lakes += 1;
+                    },
+                    Some(RiverKind::Ocean { .. }) => {
+                        oceans += 1;
+                    },
+                    None => {},
+                }
+            } */
+
+            let shade_frac = horizon_map
+                .and_then(|(angles, heights)| {
+                    chunk_idx
+                        .and_then(|chunk_idx| angles.get(chunk_idx))
+                        .map(|&e| (e as f64, heights))
+                })
+                .and_then(|(e, heights)| {
+                    chunk_idx
+                        .and_then(|chunk_idx| heights.get(chunk_idx))
+                        .map(|&f| (e, f as f64))
+                })
+                .map(|(angle, height)| {
+                    let w = 0.1;
+                    let height = (height - f64::from(alt * gain)).max(0.0);
+                    if angle != 0.0 && light_direction.x != 0.0 && height != 0.0 {
+                        let deltax = height / angle;
+                        let lighty = (light_direction.y / light_direction.x * deltax).abs();
+                        let deltay = lighty - height;
+                        let s = (deltay / deltax / w).min(1.0).max(0.0);
+                        // Smoothstep
+                        s * s * (3.0 - 2.0 * s)
+                    } else {
+                        1.0
+                    }
+                })
+                .unwrap_or(1.0);
+
+            let rgb = if is_shaded {
+                // Phong reflection model with shadows:
+                //
+                // I_p = k_a i_a + shadow * Σ {m ∈ lights} (k_d (L_m ⋅ N) i_m,d + k_s (R_m ⋅
+                // V)^α i_m,s)
+                //
+                // where for the whole scene,
+                //  i_a = (RGB) intensity of ambient lighting component
+                let i_a = Rgb::new(0.1, 0.1, 0.1);
+                //  V = direction pointing towards the viewer (e.g. virtual camera).
+                let v = Vec3::new(0.0, 0.0, -1.0).normalized();
+                // let v = Vec3::new(0.0, -1.0, 0.0).normalized();
+                //
+                // for each light m,
+                //  i_m,d = (RGB) intensity of diffuse component of light source m
+                let i_m_d = Rgb::new(1.0, 1.0, 1.0);
+                //  i_m,s = (RGB) intensity of specular component of light source m
+                let i_m_s = Rgb::new(0.45, 0.45, 0.45);
+                // let i_m_s = Rgb::new(0.45, 0.45, 0.45);
+
+                // for each light m and point p,
+                //  L_m = (normalized) direction vector from point on surface to light source m
+                let l_m = light;
+                //  N = (normalized) normal at this point on the surface,
+                let n = surface_normal;
+                //  R_m = (normalized) direction a perfectly reflected ray of light from m would
+                // take from point p      = 2(L_m ⋅ N)N - L_m
+                let r_m = (-l_m).reflected(n); // 2 * (l_m.dot(n)) * n - l_m;
+                //
+                // and for each point p in the scene,
+                //  shadow = computed shadow factor at point p
+                // FIXME: Should really just be shade_frac, but with only ambient light we lose
+                // all local lighting detail... some sort of global illumination (e.g.
+                // radiosity) is of course the "right" solution, but maybe we can find
+                // something cheaper?
+                let shadow = 0.2 + 0.8 * shade_frac;
+
+                let lambertian = l_m.dot(n).max(0.0);
+                let spec_angle = r_m.dot(v).max(0.0);
+
+                let ambient = k_a * i_a;
+                let diffuse = k_d * lambertian * i_m_d;
+                let specular = k_s * spec_angle.powf(alpha) * i_m_s;
+                (ambient + shadow * (diffuse + specular)).map(|e| e.min(1.0))
+            } else {
+                rgb
+            }
+            .map(|e| (e * 255.0) as u8);
+
+            let rgba = (rgb.r, rgb.g, rgb.b, 255);
+            write_pixel(Vec2::new(i, j), rgba);
+        });
+
+        MapDebug {
+            quads,
+            rivers,
+            lakes,
+            oceans,
+        }
+    }
+}

common/src/terrain/mod.rs

@@ -1,14 +1,17 @@
 pub mod biome;
 pub mod block;
 pub mod chonk;
+pub mod map;
 pub mod structure;
 
 // Reexports
 pub use self::{
     biome::BiomeKind,
     block::{Block, BlockKind},
+    map::MapSizeLg,
     structure::Structure,
 };
+use roots::find_roots_cubic;
 use serde::{Deserialize, Serialize};
 
 use crate::{vol::RectVolSize, volumes::vol_grid_2d::VolGrid2d};
@@ -19,8 +22,24 @@ use vek::*;
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct TerrainChunkSize;
 
+/// Base two logarithm of the number of blocks along either horizontal axis of
+/// a chunk.
+///
+/// NOTE: (1 << CHUNK_SIZE_LG) is guaranteed to fit in a u32.
+///
+/// NOTE: A lot of code assumes that the two dimensions are equal, so we make it
+/// explicit here.
+///
+/// NOTE: It is highly unlikely that a value greater than 5 will work, as many
+/// frontend optimizations rely on being able to pack chunk horizontal
+/// dimensions into 5 bits each.
+pub const TERRAIN_CHUNK_BLOCKS_LG: u32 = 5;
+
 impl RectVolSize for TerrainChunkSize {
-    const RECT_SIZE: Vec2<u32> = Vec2 { x: 32, y: 32 };
+    const RECT_SIZE: Vec2<u32> = Vec2 {
+        x: (1 << TERRAIN_CHUNK_BLOCKS_LG),
+        y: (1 << TERRAIN_CHUNK_BLOCKS_LG),
+    };
 }
 
 // TerrainChunkMeta
@@ -50,3 +69,140 @@ impl TerrainChunkMeta {
 
 pub type TerrainChunk = chonk::Chonk<Block, TerrainChunkSize, TerrainChunkMeta>;
 pub type TerrainGrid = VolGrid2d<TerrainChunk>;
+
+// Terrain helper functions used across multiple crates.
+
+/// Computes the position Vec2 of a SimChunk from an index, where the index was
+/// generated by uniform_noise.
+///
+/// NOTE: Dimensions obey constraints on [map::MapConfig::map_size_lg].
+#[inline(always)]
+pub fn uniform_idx_as_vec2(map_size_lg: MapSizeLg, idx: usize) -> Vec2<i32> {
+    let x_mask = (1 << map_size_lg.vec().x) - 1;
+    Vec2::new((idx & x_mask) as i32, (idx >> map_size_lg.vec().x) as i32)
+}
+
+/// Computes the index of a Vec2 of a SimChunk from a position, where the index
+/// is generated by uniform_noise.  NOTE: Both components of idx should be
+/// in-bounds!
+#[inline(always)]
+pub fn vec2_as_uniform_idx(map_size_lg: MapSizeLg, idx: Vec2<i32>) -> usize {
+    ((idx.y as usize) << map_size_lg.vec().x) | idx.x as usize
+}
+
+// NOTE: want to keep this such that the chunk index is in ascending order!
+pub const NEIGHBOR_DELTA: [(i32, i32); 8] = [
+    (-1, -1),
+    (0, -1),
+    (1, -1),
+    (-1, 0),
+    (1, 0),
+    (-1, 1),
+    (0, 1),
+    (1, 1),
+];
+
+/// Iterate through all cells adjacent to a chunk.
+#[inline(always)]
+pub fn neighbors(map_size_lg: MapSizeLg, posi: usize) -> impl Clone + Iterator<Item = usize> {
+    let pos = uniform_idx_as_vec2(map_size_lg, posi);
+    let world_size = map_size_lg.chunks();
+    NEIGHBOR_DELTA
+        .iter()
+        .map(move |&(x, y)| Vec2::new(pos.x + x, pos.y + y))
+        .filter(move |pos| {
+            pos.x >= 0 && pos.y >= 0 && pos.x < world_size.x as i32 && pos.y < world_size.y as i32
+        })
+        .map(move |pos| vec2_as_uniform_idx(map_size_lg, pos))
+}
+
+pub fn river_spline_coeffs(
+    // _sim: &WorldSim,
+    chunk_pos: Vec2<f64>,
+    spline_derivative: Vec2<f32>,
+    downhill_pos: Vec2<f64>,
+) -> Vec3<Vec2<f64>> {
+    let dxy = downhill_pos - chunk_pos;
+    // Since all splines have been precomputed, we don't have to do that much work
+    // to evaluate the spline.  The spline is just ax^2 + bx + c = 0, where
+    //
+    // a = dxy - chunk.river.spline_derivative
+    // b = chunk.river.spline_derivative
+    // c = chunk_pos
+    let spline_derivative = spline_derivative.map(|e| e as f64);
+    Vec3::new(dxy - spline_derivative, spline_derivative, chunk_pos)
+}
+
+/// Find the nearest point from a quadratic spline to this point (in terms of t,
+/// the "distance along the curve" by which our spline is parameterized).  Note
+/// that if t < 0.0 or t >= 1.0, we probably shouldn't be considered "on the
+/// curve"... hopefully this works out okay and gives us what we want (a
+/// river that extends outwards tangent to a quadratic curve, with width
+/// configured by distance along the line).
+#[allow(clippy::let_and_return)] // TODO: Pending review in #587
+#[allow(clippy::many_single_char_names)]
+pub fn quadratic_nearest_point(
+    spline: &Vec3<Vec2<f64>>,
+    point: Vec2<f64>,
+) -> Option<(f64, Vec2<f64>, f64)> {
+    let a = spline.z.x;
+    let b = spline.y.x;
+    let c = spline.x.x;
+    let d = point.x;
+    let e = spline.z.y;
+    let f = spline.y.y;
+    let g = spline.x.y;
+    let h = point.y;
+    // This is equivalent to solving the following cubic equation (derivation is a
+    // bit annoying):
+    //
+    // A = 2(c^2 + g^2)
+    // B = 3(b * c + g * f)
+    // C = ((a - d) * 2 * c + b^2 + (e - h) * 2 * g + f^2)
+    // D = ((a - d) * b + (e - h) * f)
+    //
+    // Ax³ + Bx² + Cx + D = 0
+    //
+    // Once solved, this yield up to three possible values for t (reflecting minimal
+    // and maximal values).  We should choose the minimal such real value with t
+    // between 0.0 and 1.0.  If we fall outside those bounds, then we are
+    // outside the spline and return None.
+    let a_ = (c * c + g * g) * 2.0;
+    let b_ = (b * c + g * f) * 3.0;
+    let a_d = a - d;
+    let e_h = e - h;
+    let c_ = a_d * c * 2.0 + b * b + e_h * g * 2.0 + f * f;
+    let d_ = a_d * b + e_h * f;
+    let roots = find_roots_cubic(a_, b_, c_, d_);
+    let roots = roots.as_ref();
+
+    let min_root = roots
+        .iter()
+        .copied()
+        .filter_map(|root| {
+            let river_point = spline.x * root * root + spline.y * root + spline.z;
+            let river_zero = spline.z;
+            let river_one = spline.x + spline.y + spline.z;
+            if root > 0.0 && root < 1.0 {
+                Some((root, river_point))
+            } else if river_point.distance_squared(river_zero) < 0.5 {
+                Some((root, /*river_point*/ river_zero))
+            } else if river_point.distance_squared(river_one) < 0.5 {
+                Some((root, /*river_point*/ river_one))
+            } else {
+                None
+            }
+        })
+        .map(|(root, river_point)| {
+            let river_distance = river_point.distance_squared(point);
+            (root, river_point, river_distance)
+        })
+        // In the (unlikely?) case that distances are equal, prefer the earliest point along the
+        // river.
+        .min_by(|&(ap, _, a), &(bp, _, b)| {
+            (a, ap < 0.0 || ap > 1.0, ap)
+                .partial_cmp(&(b, bp < 0.0 || bp > 1.0, bp))
+                .unwrap()
+        });
+    min_root
+}

server/src/lib.rs

@@ -54,14 +54,14 @@ use std::{
     time::{Duration, Instant},
 };
 #[cfg(not(feature = "worldgen"))]
-use test_world::{World, WORLD_SIZE};
+use test_world::World;
 use tracing::{debug, error, info, warn};
 use uvth::{ThreadPool, ThreadPoolBuilder};
 use vek::*;
 #[cfg(feature = "worldgen")]
 use world::{
     civ::SiteKind,
-    sim::{FileOpts, WorldOpts, DEFAULT_WORLD_MAP, WORLD_SIZE},
+    sim::{FileOpts, WorldOpts, DEFAULT_WORLD_MAP},
     World,
 };
 
@@ -200,7 +200,7 @@ impl Server {
             // complaining)
 
             // spawn in the chunk, that is in the middle of the world
-            let center_chunk: Vec2<i32> = WORLD_SIZE.map(|e| e as i32) / 2;
+            let center_chunk: Vec2<i32> = world.sim().map_size_lg().chunks().map(i32::from) / 2;
 
             // Find a town to spawn in that's close to the centre of the world
             let spawn_chunk = world

server/src/test_world.rs

@@ -1,13 +1,18 @@
 use common::{
     generation::{ChunkSupplement, EntityInfo, EntityKind},
-    terrain::{Block, BlockKind, TerrainChunk, TerrainChunkMeta, TerrainChunkSize},
+    terrain::{Block, BlockKind, MapSizeLg, TerrainChunk, TerrainChunkMeta, TerrainChunkSize},
     vol::{ReadVol, RectVolSize, Vox, WriteVol},
 };
 use rand::{prelude::*, rngs::SmallRng};
 use std::time::Duration;
 use vek::*;
 
-pub const WORLD_SIZE: Vec2<usize> = Vec2 { x: 1, y: 1 };
+const DEFAULT_WORLD_CHUNKS_LG: MapSizeLg =
+    if let Ok(map_size_lg) = MapSizeLg::new(Vec2 { x: 1, y: 1 }) {
+        map_size_lg
+    } else {
+        panic!("Default world chunk size does not satisfy required invariants.");
+    };
 
 pub struct World;
 
@@ -16,6 +21,9 @@ impl World {
 
     pub fn tick(&self, dt: Duration) {}
 
+    #[inline(always)]
+    pub const fn map_size_lg(&self) -> MapSizeLg { DEFAULT_WORLD_CHUNKS_LG }
+
     pub fn generate_chunk(
         &self,
         chunk_pos: Vec2<i32>,

world/Cargo.toml

@@ -23,7 +23,6 @@ rand_chacha = "0.2.1"
 arr_macro = "0.1.2"
 packed_simd = "0.3.3"
 rayon = "^1.3.0"
-roots = "0.0.5"
 serde = { version = "1.0.110", features = ["derive"] }
 ron = { version = "0.6", default-features = false }
 

world/examples/water.rs

@@ -1,16 +1,19 @@
-use common::{terrain::TerrainChunkSize, vol::RectVolSize};
+use common::{
+    terrain::{
+        map::{MapConfig, MapDebug, MapSample},
+        uniform_idx_as_vec2, vec2_as_uniform_idx, TerrainChunkSize,
+    },
+    vol::RectVolSize,
+};
 use rayon::prelude::*;
 use std::{f64, io::Write, path::PathBuf, time::SystemTime};
 use tracing::warn;
 use tracing_subscriber;
 use vek::*;
 use veloren_world::{
-    sim::{
+    sim::{self, get_horizon_map, sample_pos, sample_wpos, WorldOpts},
-        self, get_horizon_map, uniform_idx_as_vec2, vec2_as_uniform_idx, MapConfig, MapDebug,
-        MapSample, WorldOpts, WORLD_SIZE,
-    },
     util::Sampler,
-    World, CONFIG,
+    ColumnSample, World, CONFIG,
 };
 
 const W: usize = 1024;
@@ -41,31 +44,41 @@ fn main() {
     });
     tracing::info!("Sampling data...");
     let sampler = world.sim();
+    let map_size_lg = sampler.map_size_lg();
 
     let samples_data = {
         let column_sample = world.sample_columns();
-        (0..WORLD_SIZE.product())
+        (0..map_size_lg.chunks_len())
             .into_par_iter()
             .map(|posi| {
-                column_sample
+                column_sample.get(
-                    .get(uniform_idx_as_vec2(posi) * TerrainChunkSize::RECT_SIZE.map(|e| e as i32))
+                    uniform_idx_as_vec2(map_size_lg, posi)
+                        * TerrainChunkSize::RECT_SIZE.map(|e| e as i32),
+                )
             })
             .collect::<Vec<_>>()
             .into_boxed_slice()
     };
-    let refresh_map_samples = |config: &MapConfig| {
+    let refresh_map_samples = |config: &MapConfig, samples: Option<&[Option<ColumnSample>]>| {
-        (0..WORLD_SIZE.product())
+        (0..map_size_lg.chunks_len())
             .into_par_iter()
-            .map(|posi| config.sample_pos(sampler, uniform_idx_as_vec2(posi)))
+            .map(|posi| {
+                sample_pos(
+                    config,
+                    sampler,
+                    samples,
+                    uniform_idx_as_vec2(map_size_lg, posi),
+                )
+            })
             .collect::<Vec<_>>()
             .into_boxed_slice()
     };
     let get_map_sample = |map_samples: &[MapSample], pos: Vec2<i32>| {
         if pos.reduce_partial_min() >= 0
-            && pos.x < WORLD_SIZE.x as i32
+            && pos.x < map_size_lg.chunks().x as i32
-            && pos.y < WORLD_SIZE.y as i32
+            && pos.y < map_size_lg.chunks().y as i32
         {
-            map_samples[vec2_as_uniform_idx(pos)].clone()
+            map_samples[vec2_as_uniform_idx(map_size_lg, pos)].clone()
         } else {
             MapSample {
                 alt: 0.0,
@@ -76,26 +89,26 @@ fn main() {
         }
     };
 
-    let refresh_horizons = |lgain, is_basement, is_water| {
+    let refresh_horizons = |is_basement, is_water| {
         get_horizon_map(
-            lgain,
+            map_size_lg,
             Aabr {
                 min: Vec2::zero(),
-                max: WORLD_SIZE.map(|e| e as i32),
+                max: map_size_lg.chunks().map(|e| e as i32),
             },
-            CONFIG.sea_level as f64,
+            CONFIG.sea_level,
-            (CONFIG.sea_level + sampler.max_height) as f64,
+            CONFIG.sea_level + sampler.max_height,
             |posi| {
-                let sample = sampler.get(uniform_idx_as_vec2(posi)).unwrap();
+                let sample = sampler.get(uniform_idx_as_vec2(map_size_lg, posi)).unwrap();
                 if is_basement {
-                    sample.alt as f64
+                    sample.alt
                 } else {
-                    sample.basement as f64
+                    sample.basement
                 }
                 .max(if is_water {
-                    sample.water_alt as f64
+                    sample.water_alt
                 } else {
-                    -f64::INFINITY
+                    -f32::INFINITY
                 })
             },
             |a| a,
@@ -114,8 +127,8 @@ fn main() {
     // makes smaller differences in altitude appear larger.
     let mut gain = /*CONFIG.mountain_scale*/sampler.max_height;
     // The Z component during normal calculations is multiplied by gain; thus,
-    let mut lgain = 1.0;
+    let mut fov = 1.0;
-    let mut scale = WORLD_SIZE.x as f64 / W as f64;
+    let mut scale = map_size_lg.chunks().x as f64 / W as f64;
 
     // Right-handed coordinate system: light is going left, down, and "backwards"
     // (i.e. on the map, where we translate the y coordinate on the world map to
@@ -133,21 +146,21 @@ fn main() {
     let mut is_temperature = true;
     let mut is_humidity = true;
 
-    let mut horizons = refresh_horizons(lgain, is_basement, is_water);
+    let mut horizons = refresh_horizons(is_basement, is_water);
     let mut samples = None;
 
     let mut samples_changed = true;
     let mut map_samples: Box<[_]> = Box::new([]);
     while win.is_open() {
         let config = MapConfig {
+            map_size_lg,
             dimensions: Vec2::new(W, H),
             focus,
             gain,
-            lgain,
+            fov,
             scale,
             light_direction,
             horizons: horizons.as_ref(), /* .map(|(a, b)| (&**a, &**b)) */
-            samples,
 
             is_basement,
             is_water,
@@ -158,7 +171,7 @@ fn main() {
         };
 
         if samples_changed {
-            map_samples = refresh_map_samples(&config);
+            map_samples = refresh_map_samples(&config, samples);
         };
 
         let mut buf = vec![0; W * H];
@@ -169,7 +182,7 @@ fn main() {
             quads,
         } = config.generate(
             |pos| get_map_sample(&map_samples, pos),
-            |pos| config.sample_wpos(sampler, pos),
+            |pos| sample_wpos(&config, sampler, pos),
             |pos, (r, g, b, a)| {
                 let i = pos.x;
                 let j = pos.y;
@@ -187,7 +200,7 @@ fn main() {
             {
                 let x = (W as f64 * scale) as usize;
                 let y = (H as f64 * scale) as usize;
-                let config = sim::MapConfig {
+                let config = MapConfig {
                     dimensions: Vec2::new(x, y),
                     scale: 1.0,
                     ..config
@@ -195,7 +208,7 @@ fn main() {
                 let mut buf = vec![0u8; 4 * len];
                 config.generate(
                     |pos| get_map_sample(&map_samples, pos),
-                    |pos| config.sample_wpos(sampler, pos),
+                    |pos| sample_wpos(&config, sampler, pos),
                     |pos, (r, g, b, a)| {
                         let i = pos.x;
                         let j = pos.y;
@@ -233,7 +246,7 @@ fn main() {
                  Land(adjacent): (X = temp, Y = humidity): {:?}\nRivers: {:?}\nLakes: \
                  {:?}\nOceans: {:?}\nTotal water: {:?}\nTotal land(adjacent): {:?}",
                 gain,
-                lgain,
+                fov,
                 scale,
                 focus,
                 light_direction,
@@ -272,7 +285,7 @@ fn main() {
         if win.is_key_down(minifb::Key::B) {
             is_basement ^= true;
             samples_changed = true;
-            horizons = horizons.and_then(|_| refresh_horizons(lgain, is_basement, is_water));
+            horizons = horizons.and_then(|_| refresh_horizons(is_basement, is_water));
         }
         if win.is_key_down(minifb::Key::H) {
             is_humidity ^= true;
@@ -285,7 +298,7 @@ fn main() {
         if win.is_key_down(minifb::Key::O) {
             is_water ^= true;
             samples_changed = true;
-            horizons = horizons.and_then(|_| refresh_horizons(lgain, is_basement, is_water));
+            horizons = horizons.and_then(|_| refresh_horizons(is_basement, is_water));
         }
         if win.is_key_down(minifb::Key::L) {
             if is_camera {
@@ -293,7 +306,7 @@ fn main() {
                 horizons = if horizons.is_some() {
                     None
                 } else {
-                    refresh_horizons(lgain, is_basement, is_water)
+                    refresh_horizons(is_basement, is_water)
                 };
                 samples_changed = true;
             } else {
@@ -335,10 +348,8 @@ fn main() {
         }
         if win.is_key_down(minifb::Key::Q) {
             if is_camera {
-                if (lgain * 2.0).is_normal() {
+                if (fov * 2.0).is_normal() {
-                    lgain *= 2.0;
+                    fov *= 2.0;
-                    horizons =
-                        horizons.and_then(|_| refresh_horizons(lgain, is_basement, is_water));
                 }
             } else {
                 gain += 64.0;
@@ -346,10 +357,8 @@ fn main() {
         }
         if win.is_key_down(minifb::Key::E) {
             if is_camera {
-                if (lgain / 2.0).is_normal() {
+                if (fov / 2.0).is_normal() {
-                    lgain /= 2.0;
+                    fov /= 2.0;
-                    horizons =
-                        horizons.and_then(|_| refresh_horizons(lgain, is_basement, is_water));
                 }
             } else {
                 gain = (gain - 64.0).max(64.0);

world/src/civ/mod.rs

@@ -14,7 +14,7 @@ use common::{
     path::Path,
     spiral::Spiral2d,
     store::{Id, Store},
-    terrain::TerrainChunkSize,
+    terrain::{MapSizeLg, TerrainChunkSize},
     vol::RectVolSize,
 };
 use core::{
@@ -29,7 +29,11 @@ use rand_chacha::ChaChaRng;
 use tracing::{debug, info, warn};
 use vek::*;
 
-const INITIAL_CIV_COUNT: usize = (crate::sim::WORLD_SIZE.x * crate::sim::WORLD_SIZE.y * 3) / 65536; //48 at default scale
+const fn initial_civ_count(map_size_lg: MapSizeLg) -> u32 {
+    // NOTE: since map_size_lg's dimensions must fit in a u16, we can safely add
+    // them here. NOTE: N48 at "default" scale of 10 × 10 bits.
+    (3 << (map_size_lg.vec().x + map_size_lg.vec().y)) >> 16
+}
 
 #[allow(clippy::type_complexity)] // TODO: Pending review in #587
 #[derive(Default)]
@@ -74,17 +78,17 @@ impl Civs {
     pub fn generate(seed: u32, sim: &mut WorldSim) -> Self {
         let mut this = Self::default();
         let rng = ChaChaRng::from_seed(seed_expan::rng_state(seed));
+        let initial_civ_count = initial_civ_count(sim.map_size_lg());
         let mut ctx = GenCtx { sim, rng };
-
+        for _ in 0..initial_civ_count {
-        for _ in 0..INITIAL_CIV_COUNT {
             debug!("Creating civilisation...");
             if this.birth_civ(&mut ctx.reseed()).is_none() {
                 warn!("Failed to find starting site for civilisation.");
             }
         }
-        info!(?INITIAL_CIV_COUNT, "all civilisations created");
+        info!(?initial_civ_count, "all civilisations created");
 
-        for _ in 0..INITIAL_CIV_COUNT * 3 {
+        for _ in 0..initial_civ_count * 3 {
             attempt(5, || {
                 let loc = find_site_loc(&mut ctx, None)?;
                 this.establish_site(&mut ctx.reseed(), loc, |place| Site {

world/src/column/mod.rs

@@ -1,13 +1,18 @@
 use crate::{
     all::ForestKind,
     block::StructureMeta,
-    sim::{local_cells, uniform_idx_as_vec2, vec2_as_uniform_idx, RiverKind, SimChunk, WorldSim},
+    sim::{local_cells, RiverKind, SimChunk, WorldSim},
     util::Sampler,
     CONFIG,
 };
-use common::{terrain::TerrainChunkSize, vol::RectVolSize};
+use common::{
+    terrain::{
+        quadratic_nearest_point, river_spline_coeffs, uniform_idx_as_vec2, vec2_as_uniform_idx,
+        TerrainChunkSize,
+    },
+    vol::RectVolSize,
+};
 use noise::NoiseFn;
-use roots::find_roots_cubic;
 use std::{
     cmp::Reverse,
     f32, f64,
@@ -74,97 +79,6 @@ impl<'a> ColumnGen<'a> {
     }
 }
 
-pub fn river_spline_coeffs(
-    // _sim: &WorldSim,
-    chunk_pos: Vec2<f64>,
-    spline_derivative: Vec2<f32>,
-    downhill_pos: Vec2<f64>,
-) -> Vec3<Vec2<f64>> {
-    let dxy = downhill_pos - chunk_pos;
-    // Since all splines have been precomputed, we don't have to do that much work
-    // to evaluate the spline.  The spline is just ax^2 + bx + c = 0, where
-    //
-    // a = dxy - chunk.river.spline_derivative
-    // b = chunk.river.spline_derivative
-    // c = chunk_pos
-    let spline_derivative = spline_derivative.map(|e| e as f64);
-    Vec3::new(dxy - spline_derivative, spline_derivative, chunk_pos)
-}
-
-/// Find the nearest point from a quadratic spline to this point (in terms of t,
-/// the "distance along the curve" by which our spline is parameterized).  Note
-/// that if t < 0.0 or t >= 1.0, we probably shouldn't be considered "on the
-/// curve"... hopefully this works out okay and gives us what we want (a
-/// river that extends outwards tangent to a quadratic curve, with width
-/// configured by distance along the line).
-#[allow(clippy::let_and_return)] // TODO: Pending review in #587
-#[allow(clippy::many_single_char_names)]
-pub fn quadratic_nearest_point(
-    spline: &Vec3<Vec2<f64>>,
-    point: Vec2<f64>,
-) -> Option<(f64, Vec2<f64>, f64)> {
-    let a = spline.z.x;
-    let b = spline.y.x;
-    let c = spline.x.x;
-    let d = point.x;
-    let e = spline.z.y;
-    let f = spline.y.y;
-    let g = spline.x.y;
-    let h = point.y;
-    // This is equivalent to solving the following cubic equation (derivation is a
-    // bit annoying):
-    //
-    // A = 2(c^2 + g^2)
-    // B = 3(b * c + g * f)
-    // C = ((a - d) * 2 * c + b^2 + (e - h) * 2 * g + f^2)
-    // D = ((a - d) * b + (e - h) * f)
-    //
-    // Ax³ + Bx² + Cx + D = 0
-    //
-    // Once solved, this yield up to three possible values for t (reflecting minimal
-    // and maximal values).  We should choose the minimal such real value with t
-    // between 0.0 and 1.0.  If we fall outside those bounds, then we are
-    // outside the spline and return None.
-    let a_ = (c * c + g * g) * 2.0;
-    let b_ = (b * c + g * f) * 3.0;
-    let a_d = a - d;
-    let e_h = e - h;
-    let c_ = a_d * c * 2.0 + b * b + e_h * g * 2.0 + f * f;
-    let d_ = a_d * b + e_h * f;
-    let roots = find_roots_cubic(a_, b_, c_, d_);
-    let roots = roots.as_ref();
-
-    let min_root = roots
-        .iter()
-        .copied()
-        .filter_map(|root| {
-            let river_point = spline.x * root * root + spline.y * root + spline.z;
-            let river_zero = spline.z;
-            let river_one = spline.x + spline.y + spline.z;
-            if root > 0.0 && root < 1.0 {
-                Some((root, river_point))
-            } else if river_point.distance_squared(river_zero) < 0.5 {
-                Some((root, /*river_point*/ river_zero))
-            } else if river_point.distance_squared(river_one) < 0.5 {
-                Some((root, /*river_point*/ river_one))
-            } else {
-                None
-            }
-        })
-        .map(|(root, river_point)| {
-            let river_distance = river_point.distance_squared(point);
-            (root, river_point, river_distance)
-        })
-        // In the (unlikely?) case that distances are equal, prefer the earliest point along the
-        // river.
-        .min_by(|&(ap, _, a), &(bp, _, b)| {
-            (a, ap < 0.0 || ap > 1.0, ap)
-                .partial_cmp(&(b, bp < 0.0 || bp > 1.0, bp))
-                .unwrap()
-        });
-    min_root
-}
-
 impl<'a> Sampler<'a> for ColumnGen<'a> {
     type Index = Vec2<i32>;
     type Sample = Option<ColumnSample<'a>>;
@@ -196,12 +110,13 @@ impl<'a> Sampler<'a> for ColumnGen<'a> {
         let chunk_warp_factor = sim.get_interpolated_monotone(wpos, |chunk| chunk.warp_factor)?;
         let sim_chunk = sim.get(chunk_pos)?;
         let neighbor_coef = TerrainChunkSize::RECT_SIZE.map(|e| e as f64);
-        let my_chunk_idx = vec2_as_uniform_idx(chunk_pos);
+        let my_chunk_idx = vec2_as_uniform_idx(self.sim.map_size_lg(), chunk_pos);
-        let neighbor_river_data = local_cells(my_chunk_idx).filter_map(|neighbor_idx: usize| {
+        let neighbor_river_data =
-            let neighbor_pos = uniform_idx_as_vec2(neighbor_idx);
+            local_cells(self.sim.map_size_lg(), my_chunk_idx).filter_map(|neighbor_idx: usize| {
-            let neighbor_chunk = sim.get(neighbor_pos)?;
+                let neighbor_pos = uniform_idx_as_vec2(self.sim.map_size_lg(), neighbor_idx);
-            Some((neighbor_pos, neighbor_chunk, &neighbor_chunk.river))
+                let neighbor_chunk = sim.get(neighbor_pos)?;
-        });
+                Some((neighbor_pos, neighbor_chunk, &neighbor_chunk.river))
+            });
         let lake_width = (TerrainChunkSize::RECT_SIZE.x as f64 * (2.0f64.sqrt())) + 12.0;
         let neighbor_river_data = neighbor_river_data.map(|(posj, chunkj, river)| {
             let kind = match river.river_kind {

world/src/lib.rs

@@ -1,7 +1,13 @@
 #![deny(unsafe_code)]
 #![allow(incomplete_features)]
 #![allow(clippy::option_map_unit_fn)]
-#![feature(arbitrary_enum_discriminant, const_generics, label_break_value)]
+#![feature(
+    arbitrary_enum_discriminant,
+    const_if_match,
+    const_generics,
+    const_panic,
+    label_break_value
+)]
 
 mod all;
 mod block;
@@ -16,9 +22,10 @@ pub mod util;
 // Reexports
 pub use crate::config::CONFIG;
 pub use block::BlockGen;
+pub use column::ColumnSample;
 
 use crate::{
-    column::{ColumnGen, ColumnSample},
+    column::ColumnGen,
     util::{Grid, Sampler},
 };
 use common::{

world/src/sim/erosion.rs

@@ -1,9 +1,12 @@
-use super::{
+use super::{diffusion, downhill, uphill};
-    diffusion, downhill, neighbors, uniform_idx_as_vec2, uphill, vec2_as_uniform_idx,
-    NEIGHBOR_DELTA, WORLD_SIZE,
-};
 use crate::{config::CONFIG, util::RandomField};
-use common::{terrain::TerrainChunkSize, vol::RectVolSize};
+use common::{
+    terrain::{
+        neighbors, uniform_idx_as_vec2, vec2_as_uniform_idx, MapSizeLg, TerrainChunkSize,
+        NEIGHBOR_DELTA,
+    },
+    vol::RectVolSize,
+};
 use tracing::{debug, error, warn};
 // use faster::*;
 use itertools::izip;
@@ -27,7 +30,12 @@ pub type Computex8 = [Compute; 8];
 
 /// Compute the water flux at all chunks, given a list of chunk indices sorted
 /// by increasing height.
-pub fn get_drainage(newh: &[u32], downhill: &[isize], _boundary_len: usize) -> Box<[f32]> {
+pub fn get_drainage(
+    map_size_lg: MapSizeLg,
+    newh: &[u32],
+    downhill: &[isize],
+    _boundary_len: usize,
+) -> Box<[f32]> {
     // FIXME: Make the below work.  For now, we just use constant flux.
     // Initially, flux is determined by rainfall.  We currently treat this as the
     // same as humidity, so we just use humidity as a proxy.  The total flux
@@ -35,10 +43,10 @@ pub fn get_drainage(newh: &[u32], downhill: &[isize], _boundary_len: usize) -> B
     // to be 0.5.  To figure out how far from normal any given chunk is, we use
     // its logit. NOTE: If there are no non-boundary chunks, we just set
     // base_flux to 1.0; this should still work fine because in that case
-    // there's no erosion anyway. let base_flux = 1.0 / ((WORLD_SIZE.x *
+    // there's no erosion anyway. let base_flux = 1.0 / ((map_size_lg.chunks_len())
-    // WORLD_SIZE.y) as f32);
+    // as f32);
     let base_flux = 1.0;
-    let mut flux = vec![base_flux; WORLD_SIZE.x * WORLD_SIZE.y].into_boxed_slice();
+    let mut flux = vec![base_flux; map_size_lg.chunks_len()].into_boxed_slice();
     newh.iter().rev().for_each(|&chunk_idx| {
         let chunk_idx = chunk_idx as usize;
         let downhill_idx = downhill[chunk_idx];
@@ -52,6 +60,7 @@ pub fn get_drainage(newh: &[u32], downhill: &[isize], _boundary_len: usize) -> B
 /// Compute the water flux at all chunks for multiple receivers, given a list of
 /// chunk indices sorted by increasing height and weights for each receiver.
 pub fn get_multi_drainage(
+    map_size_lg: MapSizeLg,
     mstack: &[u32],
     mrec: &[u8],
     mwrec: &[Computex8],
@@ -66,12 +75,12 @@ pub fn get_multi_drainage(
     // base_flux to 1.0; this should still work fine because in that case
     // there's no erosion anyway.
     let base_area = 1.0;
-    let mut area = vec![base_area; WORLD_SIZE.x * WORLD_SIZE.y].into_boxed_slice();
+    let mut area = vec![base_area; map_size_lg.chunks_len()].into_boxed_slice();
     mstack.iter().for_each(|&ij| {
         let ij = ij as usize;
         let wrec_ij = &mwrec[ij];
         let area_ij = area[ij];
-        mrec_downhill(mrec, ij).for_each(|(k, ijr)| {
+        mrec_downhill(map_size_lg, mrec, ij).for_each(|(k, ijr)| {
             area[ijr] += area_ij * wrec_ij[k];
         });
     });
@@ -226,6 +235,7 @@ impl RiverData {
 /// liberties with the constant factors etc. in order to make it more likely
 /// that we draw rivers at all.
 pub fn get_rivers<F: fmt::Debug + Float + Into<f64>, G: Float + Into<f64>>(
+    map_size_lg: MapSizeLg,
     newh: &[u32],
     water_alt: &[F],
     downhill: &[isize],
@@ -236,7 +246,7 @@ pub fn get_rivers<F: fmt::Debug + Float + Into<f64>, G: Float + Into<f64>>(
     // to build up the derivatives from the top down.  Fortunately this
     // computation seems tractable.
 
-    let mut rivers = vec![RiverData::default(); WORLD_SIZE.x * WORLD_SIZE.y].into_boxed_slice();
+    let mut rivers = vec![RiverData::default(); map_size_lg.chunks_len()].into_boxed_slice();
     let neighbor_coef = TerrainChunkSize::RECT_SIZE.map(|e| e as f64);
     // (Roughly) area of a chunk, times minutes per second.
     // NOTE: Clearly, this should "actually" be 1/60 (or maybe 1/64, if you want to
@@ -262,8 +272,8 @@ pub fn get_rivers<F: fmt::Debug + Float + Into<f64>, G: Float + Into<f64>>(
             return;
         }
         let downhill_idx = downhill_idx as usize;
-        let downhill_pos = uniform_idx_as_vec2(downhill_idx);
+        let downhill_pos = uniform_idx_as_vec2(map_size_lg, downhill_idx);
-        let dxy = (downhill_pos - uniform_idx_as_vec2(chunk_idx)).map(|e| e as f64);
+        let dxy = (downhill_pos - uniform_idx_as_vec2(map_size_lg, chunk_idx)).map(|e| e as f64);
         let neighbor_dim = neighbor_coef * dxy;
         // First, we calculate the river's volumetric flow rate.
         let chunk_drainage = drainage[chunk_idx].into();
@@ -382,10 +392,16 @@ pub fn get_rivers<F: fmt::Debug + Float + Into<f64>, G: Float + Into<f64>>(
                     // This is a pass, so set our flow direction to point to the neighbor pass
                     // rather than downhill.
                     // NOTE: Safe because neighbor_pass_idx >= 0.
-                    (uniform_idx_as_vec2(downhill_idx), river_spline_derivative)
+                    (
+                        uniform_idx_as_vec2(map_size_lg, downhill_idx),
+                        river_spline_derivative,
+                    )
                 } else {
                     // Try pointing towards the lake side of the pass.
-                    (uniform_idx_as_vec2(pass_idx), river_spline_derivative)
+                    (
+                        uniform_idx_as_vec2(map_size_lg, pass_idx),
+                        river_spline_derivative,
+                    )
                 };
                 let mut lake = &mut rivers[chunk_idx];
                 lake.spline_derivative = river_spline_derivative;
@@ -427,12 +443,12 @@ pub fn get_rivers<F: fmt::Debug + Float + Into<f64>, G: Float + Into<f64>>(
             error!(
                 "Our chunk (and downhill, lake, pass, neighbor_pass): {:?} (to {:?}, in {:?} via \
                  {:?} to {:?}), chunk water alt: {:?}, lake water alt: {:?}",
-                uniform_idx_as_vec2(chunk_idx),
+                uniform_idx_as_vec2(map_size_lg, chunk_idx),
-                uniform_idx_as_vec2(downhill_idx),
+                uniform_idx_as_vec2(map_size_lg, downhill_idx),
-                uniform_idx_as_vec2(lake_idx),
+                uniform_idx_as_vec2(map_size_lg, lake_idx),
-                uniform_idx_as_vec2(pass_idx),
+                uniform_idx_as_vec2(map_size_lg, pass_idx),
                 if neighbor_pass_idx >= 0 {
-                    Some(uniform_idx_as_vec2(neighbor_pass_idx as usize))
+                    Some(uniform_idx_as_vec2(map_size_lg, neighbor_pass_idx as usize))
                 } else {
                     None
                 },
@@ -550,6 +566,7 @@ pub fn get_rivers<F: fmt::Debug + Float + Into<f64>, G: Float + Into<f64>>(
 /// TODO: See if allocating in advance is worthwhile.
 #[allow(clippy::let_and_return)] // TODO: Pending review in #587
 fn get_max_slope(
+    map_size_lg: MapSizeLg,
     h: &[Alt],
     rock_strength_nz: &(impl NoiseFn<Point3<f64>> + Sync),
     height_scale: impl Fn(usize) -> Alt + Sync,
@@ -560,7 +577,7 @@ fn get_max_slope(
     h.par_iter()
         .enumerate()
         .map(|(posi, &z)| {
-            let wposf = uniform_idx_as_vec2(posi).map(|e| e as f64)
+            let wposf = uniform_idx_as_vec2(map_size_lg, posi).map(|e| e as f64)
                 * TerrainChunkSize::RECT_SIZE.map(|e| e as f64);
             let height_scale = height_scale(posi);
             let wposz = z as f64 / height_scale as f64;
@@ -685,6 +702,8 @@ fn get_max_slope(
 #[allow(clippy::many_single_char_names)]
 #[allow(clippy::too_many_arguments)]
 fn erode(
+    // Underlying map dimensions.
+    map_size_lg: MapSizeLg,
     // Height above sea level of topsoil
     h: &mut [Alt],
     // Height above sea level of bedrock
@@ -733,8 +752,8 @@ fn erode(
     // at the cost of less interesting erosion behavior (linear vs. nonlinear).
     let q_ = 1.5;
     let k_da = 2.5 * k_da_scale(q);
-    let nx = WORLD_SIZE.x;
+    let nx = usize::from(map_size_lg.chunks().x);
-    let ny = WORLD_SIZE.y;
+    let ny = usize::from(map_size_lg.chunks().y);
     let dx = TerrainChunkSize::RECT_SIZE.x as f64;
     let dy = TerrainChunkSize::RECT_SIZE.y as f64;
 
@@ -795,11 +814,17 @@ fn erode(
     let g_fs_mult_sed = 1.0;
     let ((dh, newh, maxh, mrec, mstack, mwrec, area), (mut max_slopes, h_t)) = rayon::join(
         || {
-            let mut dh = downhill(|posi| h[posi], |posi| is_ocean(posi) && h[posi] <= 0.0);
+            let mut dh = downhill(
+                map_size_lg,
+                |posi| h[posi],
+                |posi| is_ocean(posi) && h[posi] <= 0.0,
+            );
             debug!("Computed downhill...");
-            let (boundary_len, _indirection, newh, maxh) = get_lakes(|posi| h[posi], &mut dh);
+            let (boundary_len, _indirection, newh, maxh) =
+                get_lakes(map_size_lg, |posi| h[posi], &mut dh);
             debug!("Got lakes...");
             let (mrec, mstack, mwrec) = get_multi_rec(
+                map_size_lg,
                 |posi| h[posi],
                 &dh,
                 &newh,
@@ -813,16 +838,17 @@ fn erode(
             debug!("Got multiple receivers...");
             // TODO: Figure out how to switch between single-receiver and multi-receiver
             // drainage, as the former is much less computationally costly.
-            // let area = get_drainage(&newh, &dh, boundary_len);
+            // let area = get_drainage(map_size_lg, &newh, &dh, boundary_len);
-            let area = get_multi_drainage(&mstack, &mrec, &*mwrec, boundary_len);
+            let area = get_multi_drainage(map_size_lg, &mstack, &mrec, &*mwrec, boundary_len);
             debug!("Got flux...");
             (dh, newh, maxh, mrec, mstack, mwrec, area)
         },
         || {
             rayon::join(
                 || {
-                    let max_slope =
+                    let max_slope = get_max_slope(map_size_lg, h, rock_strength_nz, |posi| {
-                        get_max_slope(h, rock_strength_nz, |posi| height_scale(n_f(posi)));
+                        height_scale(n_f(posi))
+                    });
                     debug!("Got max slopes...");
                     max_slope
                 },
@@ -870,9 +896,10 @@ fn erode(
                         let m = m_f(posi) as f64;
 
                         let mwrec_i = &mwrec[posi];
-                        mrec_downhill(&mrec, posi).for_each(|(kk, posj)| {
+                        mrec_downhill(map_size_lg, &mrec, posi).for_each(|(kk, posj)| {
-                            let dxy = (uniform_idx_as_vec2(posi) - uniform_idx_as_vec2(posj))
+                            let dxy = (uniform_idx_as_vec2(map_size_lg, posi)
-                                .map(|e| e as f64);
+                                - uniform_idx_as_vec2(map_size_lg, posj))
+                            .map(|e| e as f64);
                             let neighbor_distance = (neighbor_coef * dxy).magnitude();
                             let knew = (k
                                 * (p as f64
@@ -919,7 +946,7 @@ fn erode(
                         let k_da = k_da * kd_factor;
 
                         let mwrec_i = &mwrec[posi];
-                        mrec_downhill(&mrec, posi).for_each(|(kk, posj)| {
+                        mrec_downhill(map_size_lg, &mrec, posi).for_each(|(kk, posj)| {
                             let mwrec_kk = mwrec_i[kk] as f64;
 
                             #[rustfmt::skip]
@@ -965,8 +992,9 @@ fn erode(
                             let k = (mwrec_kk * (uplift_i + max_uplift as f64 * g_i / p as f64))
                                 / (1.0 + k_da * (mwrec_kk * chunk_neutral_area).powf(q))
                                 / max_slope.powf(q_);
-                            let dxy = (uniform_idx_as_vec2(posi) - uniform_idx_as_vec2(posj))
+                            let dxy = (uniform_idx_as_vec2(map_size_lg, posi)
-                                .map(|e| e as f64);
+                                - uniform_idx_as_vec2(map_size_lg, posj))
+                            .map(|e| e as f64);
                             let neighbor_distance = (neighbor_coef * dxy).magnitude();
 
                             let knew = (k
@@ -984,11 +1012,10 @@ fn erode(
 
     debug!("Computed stream power factors...");
 
-    let mut lake_water_volume =
+    let mut lake_water_volume = vec![0.0 as Compute; map_size_lg.chunks_len()].into_boxed_slice();
-        vec![0.0 as Compute; WORLD_SIZE.x * WORLD_SIZE.y].into_boxed_slice();
+    let mut elev = vec![0.0 as Compute; map_size_lg.chunks_len()].into_boxed_slice();
-    let mut elev = vec![0.0 as Compute; WORLD_SIZE.x * WORLD_SIZE.y].into_boxed_slice();
+    let mut h_p = vec![0.0 as Compute; map_size_lg.chunks_len()].into_boxed_slice();
-    let mut h_p = vec![0.0 as Compute; WORLD_SIZE.x * WORLD_SIZE.y].into_boxed_slice();
+    let mut deltah = vec![0.0 as Compute; map_size_lg.chunks_len()].into_boxed_slice();
-    let mut deltah = vec![0.0 as Compute; WORLD_SIZE.x * WORLD_SIZE.y].into_boxed_slice();
 
     // calculate the elevation / SPL, including sediment flux
     let tol1 = 1.0e-4 as Compute * (maxh as Compute + 1.0);
@@ -1022,8 +1049,8 @@ fn erode(
 
     // Gauss-Seidel iteration
 
-    let mut lake_silt = vec![0.0 as Compute; WORLD_SIZE.x * WORLD_SIZE.y].into_boxed_slice();
+    let mut lake_silt = vec![0.0 as Compute; map_size_lg.chunks_len()].into_boxed_slice();
-    let mut lake_sill = vec![-1isize; WORLD_SIZE.x * WORLD_SIZE.y].into_boxed_slice();
+    let mut lake_sill = vec![-1isize; map_size_lg.chunks_len()].into_boxed_slice();
 
     let mut n_gs_stream_power_law = 0;
     // NOTE: Increasing this can theoretically sometimes be necessary for
@@ -1120,7 +1147,7 @@ fn erode(
                         }
                     }
                     let mwrec_i = &mwrec[posi];
-                    mrec_downhill(&mrec, posi).for_each(|(k, posj)| {
+                    mrec_downhill(map_size_lg, &mrec, posi).for_each(|(k, posj)| {
                         let stack_posj = mstack_inv[posj];
                         deltah[stack_posj] += deltah_i * mwrec_i[k];
                     });
@@ -1269,7 +1296,7 @@ fn erode(
                         if (n - 1.0).abs() <= 1.0e-3 && (q_ - 1.0).abs() <= 1.0e-3 {
                             let mut f = h0;
                             let mut df = 1.0;
-                            mrec_downhill(&mrec, posi).for_each(|(kk, posj)| {
+                            mrec_downhill(map_size_lg, &mrec, posi).for_each(|(kk, posj)| {
                                 let posj_stack = mstack_inv[posj];
                                 let h_j = h_stack[posj_stack] as f64;
                                 // This can happen in cases where receiver kk is neither uphill of
@@ -1295,7 +1322,7 @@ fn erode(
                             let mut errp = 2.0 * tolp;
                             let mut rec_heights = [0.0; 8];
                             let mut mask = [MaskType::new(false); 8];
-                            mrec_downhill(&mrec, posi).for_each(|(kk, posj)| {
+                            mrec_downhill(map_size_lg, &mrec, posi).for_each(|(kk, posj)| {
                                 let posj_stack = mstack_inv[posj];
                                 let h_j = h_stack[posj_stack];
                                 // NOTE: Fastscape does h_t[posi] + uplift(posi) as f64 >= h_t[posj]
@@ -1383,8 +1410,9 @@ fn erode(
                             // of wh_j.
                             new_h_i = wh_j;
                         } else if compute_stats && new_h_i > 0.0 {
-                            let dxy = (uniform_idx_as_vec2(posi) - uniform_idx_as_vec2(posj))
+                            let dxy = (uniform_idx_as_vec2(map_size_lg, posi)
-                                .map(|e| e as f64);
+                                - uniform_idx_as_vec2(map_size_lg, posj))
+                            .map(|e| e as f64);
                             let neighbor_distance = (neighbor_coef * dxy).magnitude();
                             let dz = (new_h_i - wh_j).max(0.0);
                             let mag_slope = dz / neighbor_distance;
@@ -1479,7 +1507,9 @@ fn erode(
             } else {
                 let posj = posj as usize;
                 let h_j = h[posj];
-                let dxy = (uniform_idx_as_vec2(posi) - uniform_idx_as_vec2(posj)).map(|e| e as f64);
+                let dxy = (uniform_idx_as_vec2(map_size_lg, posi)
+                    - uniform_idx_as_vec2(map_size_lg, posj))
+                .map(|e| e as f64);
                 let neighbor_distance_squared = (neighbor_coef * dxy).magnitude_squared();
                 let dh = (h_i - h_j) as f64;
                 // H_i_fact = (h_i - h_j) / (||p_i - p_j||^2 + (h_i - h_j)^2)
@@ -1608,7 +1638,9 @@ fn erode(
                 // redistribute uplift to other neighbors.
                 let (posk, h_k) = (posj, h_j);
                 let (posk, h_k) = if h_k < h_j { (posk, h_k) } else { (posj, h_j) };
-                let dxy = (uniform_idx_as_vec2(posi) - uniform_idx_as_vec2(posk)).map(|e| e as f64);
+                let dxy = (uniform_idx_as_vec2(map_size_lg, posi)
+                    - uniform_idx_as_vec2(map_size_lg, posk))
+                .map(|e| e as f64);
                 let neighbor_distance = (neighbor_coef * dxy).magnitude();
                 let dz = (new_h_i - h_k).max(0.0);
                 let mag_slope = dz / neighbor_distance;
@@ -1706,6 +1738,7 @@ fn erode(
 ///
 /// See https://github.com/mewo2/terrain/blob/master/terrain.js
 pub fn fill_sinks<F: Float + Send + Sync>(
+    map_size_lg: MapSizeLg,
     h: impl Fn(usize) -> F + Sync,
     is_ocean: impl Fn(usize) -> bool + Sync,
 ) -> Box<[F]> {
@@ -1713,7 +1746,7 @@ pub fn fill_sinks<F: Float + Send + Sync>(
     // but doesn't change altitudes.
     let epsilon = F::zero();
     let infinity = F::infinity();
-    let range = 0..WORLD_SIZE.x * WORLD_SIZE.y;
+    let range = 0..map_size_lg.chunks_len();
     let oldh = range
         .into_par_iter()
         .map(|posi| h(posi))
@@ -1742,7 +1775,7 @@ pub fn fill_sinks<F: Float + Send + Sync>(
             if nh == oh {
                 return;
             }
-            for nposi in neighbors(posi) {
+            for nposi in neighbors(map_size_lg, posi) {
                 let onbh = newh[nposi];
                 let nbh = onbh + epsilon;
                 // If there is even one path downhill from this node's original height, fix
@@ -1793,6 +1826,7 @@ pub fn fill_sinks<F: Float + Send + Sync>(
 ///   indirection vector.
 #[allow(clippy::filter_next)] // TODO: Pending review in #587
 pub fn get_lakes<F: Float>(
+    map_size_lg: MapSizeLg,
     h: impl Fn(usize) -> F,
     downhill: &mut [isize],
 ) -> (usize, Box<[i32]>, Box<[u32]>, F) {
@@ -1817,7 +1851,7 @@ pub fn get_lakes<F: Float>(
     // node, so we should access that entry and increment it, then set our own
     // entry to it.
     let mut boundary = Vec::with_capacity(downhill.len());
-    let mut indirection = vec![/*-1i32*/0i32; WORLD_SIZE.x * WORLD_SIZE.y].into_boxed_slice();
+    let mut indirection = vec![/*-1i32*/0i32; map_size_lg.chunks_len()].into_boxed_slice();
 
     let mut newh = Vec::with_capacity(downhill.len());
 
@@ -1855,7 +1889,7 @@ pub fn get_lakes<F: Float>(
             let mut cur = start;
             while cur < newh.len() {
                 let node = newh[cur as usize];
-                uphill(downhill, node as usize).for_each(|child| {
+                uphill(map_size_lg, downhill, node as usize).for_each(|child| {
                     // lake_idx is the index of our lake root.
                     indirection[child] = chunk_idx as i32;
                     indirection_[child] = indirection_idx;
@@ -1896,7 +1930,7 @@ pub fn get_lakes<F: Float>(
         // our own lake's entry list.  If the maximum of the heights we get out
         // from this process is greater than the maximum of this chunk and its
         // neighbor chunk, we switch to this new edge.
-        neighbors(chunk_idx).for_each(|neighbor_idx| {
+        neighbors(map_size_lg, chunk_idx).for_each(|neighbor_idx| {
             let neighbor_height = h(neighbor_idx);
             let neighbor_lake_idx_ = indirection_[neighbor_idx];
             let neighbor_lake_idx = neighbor_lake_idx_ as usize;
@@ -1962,24 +1996,33 @@ pub fn get_lakes<F: Float>(
                             "For edge {:?} between lakes {:?}, couldn't find partner for pass \
                              {:?}. Should never happen; maybe forgot to set both edges?",
                             (
-                                (chunk_idx, uniform_idx_as_vec2(chunk_idx as usize)),
+                                (
-                                (neighbor_idx, uniform_idx_as_vec2(neighbor_idx as usize))
+                                    chunk_idx,
+                                    uniform_idx_as_vec2(map_size_lg, chunk_idx as usize)
+                                ),
+                                (
+                                    neighbor_idx,
+                                    uniform_idx_as_vec2(map_size_lg, neighbor_idx as usize)
+                                )
                             ),
                             (
                                 (
                                     lake_chunk_idx,
-                                    uniform_idx_as_vec2(lake_chunk_idx as usize),
+                                    uniform_idx_as_vec2(map_size_lg, lake_chunk_idx as usize),
                                     lake_idx_
                                 ),
                                 (
                                     neighbor_lake_chunk_idx,
-                                    uniform_idx_as_vec2(neighbor_lake_chunk_idx as usize),
+                                    uniform_idx_as_vec2(
+                                        map_size_lg,
+                                        neighbor_lake_chunk_idx as usize
+                                    ),
                                     neighbor_lake_idx_
                                 )
                             ),
                             (
-                                (pass.0, uniform_idx_as_vec2(pass.0 as usize)),
+                                (pass.0, uniform_idx_as_vec2(map_size_lg, pass.0 as usize)),
-                                (pass.1, uniform_idx_as_vec2(pass.1 as usize))
+                                (pass.1, uniform_idx_as_vec2(map_size_lg, pass.1 as usize))
                             ),
                         );
                     }
@@ -2068,7 +2111,7 @@ pub fn get_lakes<F: Float>(
         downhill[lake_chunk_idx] = neighbor_idx as isize;
         // Also set the indirection of the lake bottom to the negation of the
         // lake side of the chosen pass (chunk_idx).
-        // NOTE: This can't overflow i32 because WORLD_SIZE.x * WORLD_SIZE.y should fit
+        // NOTE: This can't overflow i32 because map_size_lg.chunks_len() should fit
         // in an i32.
         indirection[lake_chunk_idx] = -(chunk_idx as i32);
         // Add this edge to the sorted list.
@@ -2114,7 +2157,7 @@ pub fn get_lakes<F: Float>(
         InQueue,
         WithRcv,
     }
-    let mut tag = vec![Tag::UnParsed; WORLD_SIZE.x * WORLD_SIZE.y];
+    let mut tag = vec![Tag::UnParsed; map_size_lg.chunks_len()];
     // TODO: Combine with adding to vector.
     let mut filling_queue = Vec::with_capacity(downhill.len());
 
@@ -2182,17 +2225,17 @@ pub fn get_lakes<F: Float>(
                     tag[neighbor_pass_idx] = Tag::WithRcv;
                     tag[pass_idx] = Tag::InQueue;
 
-                    let outflow_coords = uniform_idx_as_vec2(neighbor_pass_idx);
+                    let outflow_coords = uniform_idx_as_vec2(map_size_lg, neighbor_pass_idx);
                     let elev = h(neighbor_pass_idx).max(h(pass_idx));
 
                     while let Some(node) = filling_queue.pop() {
-                        let coords = uniform_idx_as_vec2(node);
+                        let coords = uniform_idx_as_vec2(map_size_lg, node);
 
                         let mut rcv = -1;
                         let mut rcv_cost = -f64::INFINITY; /*f64::EPSILON;*/
                         let outflow_distance = (outflow_coords - coords).map(|e| e as f64);
 
-                        neighbors(node).for_each(|ineighbor| {
+                        neighbors(map_size_lg, node).for_each(|ineighbor| {
                             if indirection[ineighbor] != chunk_idx as i32
                                 && ineighbor != chunk_idx
                                 && ineighbor != neighbor_pass_idx
@@ -2200,7 +2243,8 @@ pub fn get_lakes<F: Float>(
                             {
                                 return;
                             }
-                            let dxy = (uniform_idx_as_vec2(ineighbor) - coords).map(|e| e as f64);
+                            let dxy = (uniform_idx_as_vec2(map_size_lg, ineighbor) - coords)
+                                .map(|e| e as f64);
                             let neighbor_distance = /*neighbor_coef * */dxy;
                             let tag = &mut tag[ineighbor];
                             match *tag {
@@ -2242,7 +2286,7 @@ pub fn get_lakes<F: Float>(
             let mut cur = start;
             let mut node = first_idx;
             loop {
-                uphill(downhill, node as usize).for_each(|child| {
+                uphill(map_size_lg, downhill, node as usize).for_each(|child| {
                     // lake_idx is the index of our lake root.
                     // Check to make sure child (flowing into us) is in the same lake.
                     if indirection[child] == chunk_idx as i32 || child == chunk_idx {
@@ -2263,10 +2307,11 @@ pub fn get_lakes<F: Float>(
 
 /// Iterate through set neighbors of multi-receiver flow.
 pub fn mrec_downhill<'a>(
+    map_size_lg: MapSizeLg,
     mrec: &'a [u8],
     posi: usize,
 ) -> impl Clone + Iterator<Item = (usize, usize)> + 'a {
-    let pos = uniform_idx_as_vec2(posi);
+    let pos = uniform_idx_as_vec2(map_size_lg, posi);
     let mrec_i = mrec[posi];
     NEIGHBOR_DELTA
         .iter()
@@ -2275,13 +2320,14 @@ pub fn mrec_downhill<'a>(
         .map(move |(k, &(x, y))| {
             (
                 k,
-                vec2_as_uniform_idx(Vec2::new(pos.x + x as i32, pos.y + y as i32)),
+                vec2_as_uniform_idx(map_size_lg, Vec2::new(pos.x + x as i32, pos.y + y as i32)),
             )
         })
 }
 
 /// Algorithm for computing multi-receiver flow.
 ///
+/// * `map_size_lg`: Size of the underlying map.
 /// * `h`: altitude
 /// * `downhill`: single receiver
 /// * `newh`: single receiver stack
@@ -2299,6 +2345,7 @@ pub fn mrec_downhill<'a>(
 #[allow(clippy::too_many_arguments)]
 #[allow(clippy::type_complexity)] // TODO: Pending review in #587
 pub fn get_multi_rec<F: fmt::Debug + Float + Sync + Into<Compute>>(
+    map_size_lg: MapSizeLg,
     h: impl Fn(usize) -> F + Sync,
     downhill: &[isize],
     newh: &[u32],
@@ -2379,18 +2426,15 @@ pub fn get_multi_rec<F: fmt::Debug + Float + Sync + Into<Compute>>(
             let mut mrec_ij = 0u8;
             let mut ndon_ij = 0u8;
             let neighbor_iter = |posi| {
-                let pos = uniform_idx_as_vec2(posi);
+                let pos = uniform_idx_as_vec2(map_size_lg, posi);
                 NEIGHBOR_DELTA
                     .iter()
                     .map(move |&(x, y)| Vec2::new(pos.x + x, pos.y + y))
                     .enumerate()
                     .filter(move |&(_, pos)| {
-                        pos.x >= 0
+                        pos.x >= 0 && pos.y >= 0 && pos.x < nx as i32 && pos.y < ny as i32
-                            && pos.y >= 0
-                            && pos.x < WORLD_SIZE.x as i32
-                            && pos.y < WORLD_SIZE.y as i32
                     })
-                    .map(move |(k, pos)| (k, vec2_as_uniform_idx(pos)))
+                    .map(move |(k, pos)| (k, vec2_as_uniform_idx(map_size_lg, pos)))
             };
 
             neighbor_iter(ij).for_each(|(k, ijk)| {
@@ -2417,9 +2461,10 @@ pub fn get_multi_rec<F: fmt::Debug + Float + Sync + Into<Compute>>(
                     let mut sumweight = czero;
                     let mut wrec = [czero; 8];
                     let mut nrec = 0;
-                    mrec_downhill(&mrec, ij).for_each(|(k, ijk)| {
+                    mrec_downhill(map_size_lg, &mrec, ij).for_each(|(k, ijk)| {
-                        let lrec_ijk = ((uniform_idx_as_vec2(ijk) - uniform_idx_as_vec2(ij))
+                        let lrec_ijk = ((uniform_idx_as_vec2(map_size_lg, ijk)
-                            .map(|e| e as Compute)
+                            - uniform_idx_as_vec2(map_size_lg, ij))
+                        .map(|e| e as Compute)
                             * dxdy)
                             .magnitude();
                         let wrec_ijk = (wh[ij] - wh[ijk]).into() / lrec_ijk;
@@ -2464,7 +2509,7 @@ pub fn get_multi_rec<F: fmt::Debug + Float + Sync + Into<Compute>>(
                 while let Some(ijn) = parse.pop() {
                     // we add the node to the stack
                     stack.push(ijn as u32);
-                    mrec_downhill(&mrec, ijn).for_each(|(_, ijr)| {
+                    mrec_downhill(map_size_lg, &mrec, ijn).for_each(|(_, ijr)| {
                         let (_, ref mut vis_ijr) = don_vis[ijr];
                         if *vis_ijr >= 1 {
                             *vis_ijr -= 1;
@@ -2492,6 +2537,7 @@ pub fn get_multi_rec<F: fmt::Debug + Float + Sync + Into<Compute>>(
 #[allow(clippy::many_single_char_names)]
 #[allow(clippy::too_many_arguments)]
 pub fn do_erosion(
+    map_size_lg: MapSizeLg,
     _max_uplift: f32,
     n_steps: usize,
     seed: &RandomField,
@@ -2513,59 +2559,59 @@ pub fn do_erosion(
     k_da_scale: impl Fn(f64) -> f64,
 ) -> (Box<[Alt]>, Box<[Alt]> /* , Box<[Alt]> */) {
     debug!("Initializing erosion arrays...");
-    let oldh_ = (0..WORLD_SIZE.x * WORLD_SIZE.y)
+    let oldh_ = (0..map_size_lg.chunks_len())
         .into_par_iter()
         .map(|posi| oldh(posi) as Alt)
         .collect::<Vec<_>>()
         .into_boxed_slice();
     // Topographic basement (The height of bedrock, not including sediment).
-    let mut b = (0..WORLD_SIZE.x * WORLD_SIZE.y)
+    let mut b = (0..map_size_lg.chunks_len())
         .into_par_iter()
         .map(|posi| oldb(posi) as Alt)
         .collect::<Vec<_>>()
         .into_boxed_slice();
     // Stream power law slope exponent--link between channel slope and erosion rate.
-    let n = (0..WORLD_SIZE.x * WORLD_SIZE.y)
+    let n = (0..map_size_lg.chunks_len())
         .into_par_iter()
         .map(|posi| n(posi))
         .collect::<Vec<_>>()
         .into_boxed_slice();
     // Stream power law concavity index (θ = m/n), turned into an exponent on
     // drainage (which is a proxy for discharge according to Hack's Law).
-    let m = (0..WORLD_SIZE.x * WORLD_SIZE.y)
+    let m = (0..map_size_lg.chunks_len())
         .into_par_iter()
         .map(|posi| theta(posi) * n[posi])
         .collect::<Vec<_>>()
         .into_boxed_slice();
     // Stream power law erodability constant for fluvial erosion (bedrock)
-    let kf = (0..WORLD_SIZE.x * WORLD_SIZE.y)
+    let kf = (0..map_size_lg.chunks_len())
         .into_par_iter()
         .map(|posi| kf(posi))
         .collect::<Vec<_>>()
         .into_boxed_slice();
     // Stream power law erodability constant for hillslope diffusion (bedrock)
-    let kd = (0..WORLD_SIZE.x * WORLD_SIZE.y)
+    let kd = (0..map_size_lg.chunks_len())
         .into_par_iter()
         .map(|posi| kd(posi))
         .collect::<Vec<_>>()
         .into_boxed_slice();
     // Deposition coefficient
-    let g = (0..WORLD_SIZE.x * WORLD_SIZE.y)
+    let g = (0..map_size_lg.chunks_len())
         .into_par_iter()
         .map(|posi| g(posi))
         .collect::<Vec<_>>()
         .into_boxed_slice();
-    let epsilon_0 = (0..WORLD_SIZE.x * WORLD_SIZE.y)
+    let epsilon_0 = (0..map_size_lg.chunks_len())
         .into_par_iter()
         .map(|posi| epsilon_0(posi))
         .collect::<Vec<_>>()
         .into_boxed_slice();
-    let alpha = (0..WORLD_SIZE.x * WORLD_SIZE.y)
+    let alpha = (0..map_size_lg.chunks_len())
         .into_par_iter()
         .map(|posi| alpha(posi))
         .collect::<Vec<_>>()
         .into_boxed_slice();
-    let mut wh = vec![0.0; WORLD_SIZE.x * WORLD_SIZE.y].into_boxed_slice();
+    let mut wh = vec![0.0; map_size_lg.chunks_len()].into_boxed_slice();
     // TODO: Don't do this, maybe?
     // (To elaborate, maybe we should have varying uplift or compute it some other
     // way).
@@ -2613,6 +2659,7 @@ pub fn do_erosion(
     (0..n_steps).for_each(|i| {
         debug!("Erosion iteration #{:?}", i);
         erode(
+            map_size_lg,
             &mut h,
             &mut b,
             &mut wh,

world/src/sim/map.rs

@@ -1,712 +1,264 @@
 use crate::{
-    column::{quadratic_nearest_point, river_spline_coeffs, ColumnSample},
+    column::ColumnSample,
-    sim::{
+    sim::{RiverKind, WorldSim},
-        neighbors, uniform_idx_as_vec2, vec2_as_uniform_idx, Alt, RiverKind, WorldSim,
-        NEIGHBOR_DELTA, WORLD_SIZE,
-    },
     CONFIG,
 };
-use common::{terrain::TerrainChunkSize, vol::RectVolSize};
+use common::{
-use std::{f32, f64, iter};
+    terrain::{
+        map::{Connection, ConnectionKind, MapConfig, MapSample},
+        vec2_as_uniform_idx, TerrainChunkSize, NEIGHBOR_DELTA,
+    },
+    vol::RectVolSize,
+};
+use std::{f32, f64};
 use vek::*;
 
-pub struct MapConfig<'a> {
+/// A sample function that grabs the connections at a chunk.
-    /// Dimensions of the window being written to.  Defaults to WORLD_SIZE.
+///
-    pub dimensions: Vec2<usize>,
+/// Currently this just supports rivers, but ideally it can be extended past
-    /// x, y, and z of top left of map (defaults to (0.0, 0.0,
+/// that.
-    /// CONFIG.sea_level)).
+///
-    pub focus: Vec3<f64>,
+/// A sample function that grabs surface altitude at a column.
-    /// Altitude is divided by gain and clamped to [0, 1]; thus, decreasing gain
+/// (correctly reflecting settings like is_basement and is_water).
-    /// makes smaller differences in altitude appear larger.
+///
-    ///
+/// The altitude produced by this function at a column corresponding to a
-    /// Defaults to CONFIG.mountain_scale.
+/// particular chunk should be identical to the altitude produced by
-    pub gain: f32,
+/// sample_pos at that chunk.
-    /// lgain is used for shading purposes and refers to how much impact a
+///
-    /// change in the z direction has on the perceived slope relative to the
+/// You should generally pass a closure over this function into generate
-    /// same change in x and y.
+/// when constructing a map for the first time.
-    ///
+/// However, if repeated construction is needed, or alternate base colors
-    /// Defaults to TerrainChunkSize::RECT_SIZE.x.
+/// are to be used for some reason, one should pass a custom function to
-    pub lgain: f64,
+/// generate instead (e.g. one that just looks up the height in a cached
-    /// Scale is like gain, but for x and y rather than z.
+/// array).
-    ///
+pub fn sample_wpos(config: &MapConfig, sampler: &WorldSim, wpos: Vec2<i32>) -> f32 {
-    /// Defaults to WORLD_SIZE.x / dimensions.x (NOTE: fractional, not integer,
+    let MapConfig {
-    /// division!).
+        focus,
-    pub scale: f64,
+        gain,
-    /// Vector that indicates which direction light is coming from, if shading
-    /// is turned on.
-    ///
-    /// Right-handed coordinate system: light is going left, down, and
-    /// "backwards" (i.e. on the map, where we translate the y coordinate on
-    /// the world map to z in the coordinate system, the light comes from -y
-    /// on the map and points towards +y on the map).  In a right
-    /// handed coordinate system, the "camera" points towards -z, so positive z
-    /// is backwards "into" the camera.
-    ///
-    /// "In world space the x-axis will be pointing east, the y-axis up and the
-    /// z-axis will be pointing south"
-    ///
-    /// Defaults to (-0.8, -1.0, 0.3).
-    pub light_direction: Vec3<f64>,
-    /// If Some, uses the provided horizon map.
-    ///
-    /// Defaults to None.
-    pub horizons: Option<&'a [(Vec<Alt>, Vec<Alt>); 2]>,
-    /// If Some, uses the provided column samples to determine surface color.
-    ///
-    /// Defaults to None.
-    pub samples: Option<&'a [Option<ColumnSample<'a>>]>,
-    /// If true, only the basement (bedrock) is used for altitude; otherwise,
-    /// the surface is used.
-    ///
-    /// Defaults to false.
-    pub is_basement: bool,
-    /// If true, water is rendered; otherwise, the surface without water is
-    /// rendered, even if it is underwater.
-    ///
-    /// Defaults to true.
-    pub is_water: bool,
-    /// If true, 3D lighting and shading are turned on.  Otherwise, a plain
-    /// altitude map is used.
-    ///
-    /// Defaults to true.
-    pub is_shaded: bool,
-    /// If true, the red component of the image is also used for temperature
-    /// (redder is hotter). Defaults to false.
-    pub is_temperature: bool,
-    /// If true, the blue component of the image is also used for humidity
-    /// (bluer is wetter).
-    ///
-    /// Defaults to false.
-    pub is_humidity: bool,
-    /// Record debug information.
-    ///
-    /// Defaults to false.
-    pub is_debug: bool,
-}
 
-pub const QUADRANTS: usize = 4;
+        is_basement,
+        is_water,
+        ..
+    } = *config;
 
-pub struct MapDebug {
+    (sampler
-    pub quads: [[u32; QUADRANTS]; QUADRANTS],
+        .get_wpos(wpos)
-    pub rivers: u32,
+        .map(|s| {
-    pub lakes: u32,
+            if is_basement { s.basement } else { s.alt }.max(if is_water {
-    pub oceans: u32,
+                s.water_alt
-}
+            } else {
-
+                -f32::INFINITY
-impl<'a> Default for MapConfig<'a> {
-    fn default() -> Self {
-        let dimensions = WORLD_SIZE;
-        Self {
-            dimensions,
-            focus: Vec3::new(0.0, 0.0, CONFIG.sea_level as f64),
-            gain: CONFIG.mountain_scale,
-            lgain: TerrainChunkSize::RECT_SIZE.x as f64,
-            scale: WORLD_SIZE.x as f64 / dimensions.x as f64,
-            light_direction: Vec3::new(-1.2, -1.0, 0.8),
-            horizons: None,
-            samples: None,
-
-            is_basement: false,
-            is_water: true,
-            is_shaded: true,
-            is_temperature: false,
-            is_humidity: false,
-            is_debug: false,
-        }
-    }
-}
-
-/// Connection kind (per edge).  Currently just supports rivers, but may be
-/// extended to support paths or at least one other kind of connection.
-#[derive(Clone, Copy, Debug)]
-pub enum ConnectionKind {
-    /// Connection forms a visible river.
-    River,
-}
-
-/// Map connection (per edge).
-#[derive(Clone, Copy, Debug)]
-pub struct Connection {
-    /// The kind of connection this is (e.g. river or path).
-    pub kind: ConnectionKind,
-    /// Assumed to be the "b" part of a 2d quadratic function.
-    pub spline_derivative: Vec2<f32>,
-    /// Width of the connection.
-    pub width: f32,
-}
-
-/// Per-chunk data the map needs to be able to sample in order to correctly
-/// render.
-#[derive(Clone, Debug)]
-pub struct MapSample {
-    /// the base RGB color for a particular map pixel using the current settings
-    /// (i.e. the color *without* lighting).
-    pub rgb: Rgb<u8>,
-    /// Surface altitude information
-    /// (correctly reflecting settings like is_basement and is_water)
-    pub alt: f64,
-    /// Downhill chunk (may not be meaningful on ocean tiles, or at least edge
-    /// tiles)
-    pub downhill_wpos: Vec2<i32>,
-    /// Connection information about any connections to/from this chunk (e.g.
-    /// rivers).
-    ///
-    /// Connections at each index correspond to the same index in
-    /// NEIGHBOR_DELTA.
-    pub connections: Option<[Option<Connection>; 8]>,
-}
-
-impl<'a> MapConfig<'a> {
-    /// A sample function that grabs the connections at a chunk.
-    ///
-    /// Currently this just supports rivers, but ideally it can be extended past
-    /// that.
-    ///
-    /// A sample function that grabs surface altitude at a column.
-    /// (correctly reflecting settings like is_basement and is_water).
-    ///
-    /// The altitude produced by this function at a column corresponding to a
-    /// particular chunk should be identical to the altitude produced by
-    /// sample_pos at that chunk.
-    ///
-    /// You should generally pass a closure over this function into generate
-    /// when constructing a map for the first time.
-    /// However, if repeated construction is needed, or alternate base colors
-    /// are to be used for some reason, one should pass a custom function to
-    /// generate instead (e.g. one that just looks up the height in a cached
-    /// array).
-    pub fn sample_wpos(&self, sampler: &WorldSim, wpos: Vec2<i32>) -> f32 {
-        let MapConfig {
-            focus,
-            gain,
-
-            is_basement,
-            is_water,
-            ..
-        } = *self;
-
-        (sampler
-            .get_wpos(wpos)
-            .map(|s| {
-                if is_basement { s.basement } else { s.alt }.max(if is_water {
-                    s.water_alt
-                } else {
-                    -f32::INFINITY
-                })
             })
-            .unwrap_or(CONFIG.sea_level)
+        })
-            - focus.z as f32)
+        .unwrap_or(CONFIG.sea_level)
-            / gain as f32
+        - focus.z as f32)
-    }
+        / gain as f32
+}
 
-    /// Samples a MapSample at a chunk.
+/// Samples a MapSample at a chunk.
-    ///
+///
-    /// You should generally pass a closure over this function into generate
+/// You should generally pass a closure over this function into generate
-    /// when constructing a map for the first time.
+/// when constructing a map for the first time.
-    /// However, if repeated construction is needed, or alternate base colors
+/// However, if repeated construction is needed, or alternate base colors
-    /// are to be used for some reason, one should pass a custom function to
+/// are to be used for some reason, one should pass a custom function to
-    /// generate instead (e.g. one that just looks up the color in a cached
+/// generate instead (e.g. one that just looks up the color in a cached
-    /// array).
+/// array).
-    pub fn sample_pos(&self, sampler: &WorldSim, pos: Vec2<i32>) -> MapSample {
+pub fn sample_pos(
-        let MapConfig {
+    config: &MapConfig,
-            focus,
+    sampler: &WorldSim,
-            gain,
+    samples: Option<&[Option<ColumnSample>]>,
-            samples,
+    pos: Vec2<i32>,
+) -> MapSample {
+    let map_size_lg = config.map_size_lg();
+    let MapConfig {
+        focus,
+        gain,
 
-            is_basement,
+        is_basement,
-            is_water,
+        is_water,
-            is_shaded,
+        is_shaded,
-            is_temperature,
+        is_temperature,
-            is_humidity,
+        is_humidity,
-            // is_debug,
+        // is_debug,
-            ..
+        ..
-        } = *self;
+    } = *config;
 
-        let true_sea_level = (CONFIG.sea_level as f64 - focus.z) / gain as f64;
+    let true_sea_level = (CONFIG.sea_level as f64 - focus.z) / gain as f64;
 
-        let (
+    let (
-            chunk_idx,
+        chunk_idx,
-            alt,
+        alt,
-            basement,
+        basement,
-            water_alt,
+        water_alt,
-            humidity,
+        humidity,
-            temperature,
+        temperature,
-            downhill,
+        downhill,
-            river_kind,
+        river_kind,
-            spline_derivative,
+        spline_derivative,
-            is_path,
+        is_path,
-            near_site,
+        near_site,
-        ) = sampler
+    ) = sampler
-            .get(pos)
+        .get(pos)
-            .map(|sample| {
+        .map(|sample| {
-                (
+            (
-                    Some(vec2_as_uniform_idx(pos)),
+                Some(vec2_as_uniform_idx(map_size_lg, pos)),
-                    sample.alt,
+                sample.alt,
-                    sample.basement,
+                sample.basement,
-                    sample.water_alt,
+                sample.water_alt,
-                    sample.humidity,
+                sample.humidity,
-                    sample.temp,
+                sample.temp,
-                    sample.downhill,
+                sample.downhill,
-                    sample.river.river_kind,
+                sample.river.river_kind,
-                    sample.river.spline_derivative,
+                sample.river.spline_derivative,
-                    sample.path.is_path(),
+                sample.path.is_path(),
-                    sample.sites.iter().any(|site| {
+                sample.sites.iter().any(|site| {
-                        site.get_origin()
+                    site.get_origin()
-                            .distance_squared(pos * TerrainChunkSize::RECT_SIZE.x as i32)
+                        .distance_squared(pos * TerrainChunkSize::RECT_SIZE.x as i32)
-                            < 64i32.pow(2)
+                        < 64i32.pow(2)
-                    }),
+                }),
-                )
+            )
-            })
+        })
-            .unwrap_or((
+        .unwrap_or((
-                None,
+            None,
-                CONFIG.sea_level,
+            CONFIG.sea_level,
-                CONFIG.sea_level,
+            CONFIG.sea_level,
-                CONFIG.sea_level,
+            CONFIG.sea_level,
-                0.0,
+            0.0,
-                0.0,
+            0.0,
-                None,
+            None,
-                None,
+            None,
-                Vec2::zero(),
+            Vec2::zero(),
-                false,
+            false,
-                false,
+            false,
-            ));
+        ));
 
-        let humidity = humidity.min(1.0).max(0.0);
+    let humidity = humidity.min(1.0).max(0.0);
-        let temperature = temperature.min(1.0).max(-1.0) * 0.5 + 0.5;
+    let temperature = temperature.min(1.0).max(-1.0) * 0.5 + 0.5;
-        let wpos = pos * TerrainChunkSize::RECT_SIZE.map(|e| e as i32);
+    let wpos = pos * TerrainChunkSize::RECT_SIZE.map(|e| e as i32);
-        let column_rgb = samples
+    let column_rgb = samples
-            .and_then(|samples| {
+        .and_then(|samples| {
-                chunk_idx
-                    .and_then(|chunk_idx| samples.get(chunk_idx))
-                    .map(Option::as_ref)
-                    .flatten()
-            })
-            .map(|sample| {
-                // TODO: Eliminate the redundancy between this and the block renderer.
-                let alt = sample.alt;
-                let basement = sample.basement;
-                let grass_depth = (1.5 + 2.0 * sample.chaos).min(alt - basement);
-                let wposz = if is_basement { basement } else { alt };
-                if is_basement && wposz < alt - grass_depth {
-                    Lerp::lerp(
-                        sample.sub_surface_color,
-                        sample.stone_col.map(|e| e as f32 / 255.0),
-                        (alt - grass_depth - wposz as f32) * 0.15,
-                    )
-                    .map(|e| e as f64)
-                } else {
-                    Lerp::lerp(
-                        sample.sub_surface_color,
-                        sample.surface_color,
-                        ((wposz as f32 - (alt - grass_depth)) / grass_depth).powf(0.5),
-                    )
-                    .map(|e| e as f64)
-                }
-            });
-
-        let downhill_wpos = downhill
-            .map(|downhill_pos| downhill_pos)
-            .unwrap_or(wpos + TerrainChunkSize::RECT_SIZE.map(|e| e as i32));
-        let alt = if is_basement { basement } else { alt };
-
-        let true_water_alt = (alt.max(water_alt) as f64 - focus.z) / gain as f64;
-        let true_alt = (alt as f64 - focus.z) / gain as f64;
-        let water_depth = (true_water_alt - true_alt).min(1.0).max(0.0);
-        let alt = true_alt.min(1.0).max(0.0);
-
-        let water_color_factor = 2.0;
-        let g_water = 32.0 * water_color_factor;
-        let b_water = 64.0 * water_color_factor;
-        let default_rgb = Rgb::new(
-            if is_shaded || is_temperature {
-                1.0
-            } else {
-                0.0
-            },
-            if is_shaded { 1.0 } else { alt },
-            if is_shaded || is_humidity { 1.0 } else { 0.0 },
-        );
-        let column_rgb = column_rgb.unwrap_or(default_rgb);
-        let mut connections = [None; 8];
-        let mut has_connections = false;
-        // TODO: Support non-river connections.
-        // TODO: Support multiple connections.
-        let river_width = river_kind.map(|river| match river {
-            RiverKind::River { cross_section } => cross_section.x,
-            RiverKind::Lake { .. } | RiverKind::Ocean => TerrainChunkSize::RECT_SIZE.x as f32,
-        });
-        if let (Some(river_width), true) = (river_width, is_water) {
-            let downhill_pos = downhill_wpos.map2(TerrainChunkSize::RECT_SIZE, |e, f| e / f as i32);
-            NEIGHBOR_DELTA
-                .iter()
-                .zip((&mut connections).iter_mut())
-                .filter(|&(&offset, _)| downhill_pos - pos == Vec2::from(offset))
-                .for_each(|(_, connection)| {
-                    has_connections = true;
-                    *connection = Some(Connection {
-                        kind: ConnectionKind::River,
-                        spline_derivative,
-                        width: river_width,
-                    });
-                });
-        };
-        let rgb = match (river_kind, (is_water, true_alt >= true_sea_level)) {
-            (_, (false, _)) | (None, (_, true)) | (Some(RiverKind::River { .. }), _) => {
-                let (r, g, b) = (
-                    (column_rgb.r
-                        * if is_temperature {
-                            temperature as f64
-                        } else {
-                            column_rgb.r
-                        })
-                    .sqrt(),
-                    column_rgb.g,
-                    (column_rgb.b
-                        * if is_humidity {
-                            humidity as f64
-                        } else {
-                            column_rgb.b
-                        })
-                    .sqrt(),
-                );
-                Rgb::new((r * 255.0) as u8, (g * 255.0) as u8, (b * 255.0) as u8)
-            },
-            (None, _) | (Some(RiverKind::Lake { .. }), _) | (Some(RiverKind::Ocean), _) => {
-                Rgb::new(
-                    0,
-                    ((g_water - water_depth * g_water) * 1.0) as u8,
-                    ((b_water - water_depth * b_water) * 1.0) as u8,
-                )
-            },
-        };
-        // TODO: Make principled.
-        let rgb = if near_site {
-            Rgb::new(0x57, 0x39, 0x33)
-        } else if is_path {
-            Rgb::new(0x37, 0x29, 0x23)
-        } else {
-            rgb
-        };
-
-        MapSample {
-            rgb,
-            alt: if is_water {
-                true_alt.max(true_water_alt)
-            } else {
-                true_alt
-            },
-            downhill_wpos,
-            connections: if has_connections {
-                Some(connections)
-            } else {
-                None
-            },
-        }
-    }
-
-    /// Generates a map image using the specified settings.  Note that it will
-    /// write from left to write from (0, 0) to dimensions - 1, inclusive,
-    /// with 4 1-byte color components provided as (r, g, b, a).  It is up
-    /// to the caller to provide a function that translates this information
-    /// into the correct format for a buffer and writes to it.
-    ///
-    /// sample_pos is a function that, given a chunk position, returns enough
-    /// information about the chunk to attempt to render it on the map.
-    /// When in doubt, try using `MapConfig::sample_pos` for this.
-    ///
-    /// sample_wpos is a simple function that, given a *column* position,
-    /// returns the approximate altitude at that column.  When in doubt, try
-    /// using `MapConfig::sample_wpos` for this.
-    #[allow(clippy::if_same_then_else)] // TODO: Pending review in #587
-    #[allow(clippy::unnested_or_patterns)] // TODO: Pending review in #587
-    #[allow(clippy::many_single_char_names)]
-    pub fn generate(
-        &self,
-        sample_pos: impl Fn(Vec2<i32>) -> MapSample,
-        sample_wpos: impl Fn(Vec2<i32>) -> f32,
-        // sampler: &WorldSim,
-        mut write_pixel: impl FnMut(Vec2<usize>, (u8, u8, u8, u8)),
-    ) -> MapDebug {
-        let MapConfig {
-            dimensions,
-            focus,
-            gain,
-            lgain,
-            scale,
-            light_direction,
-            horizons,
-
-            is_shaded,
-            // is_debug,
-            ..
-        } = *self;
-
-        let light_direction = Vec3::new(
-            light_direction.x,
-            light_direction.y,
-            0.0, // we currently ignore light_direction.z.
-        );
-        let light_shadow_dir = if light_direction.x >= 0.0 { 0 } else { 1 };
-        let horizon_map = horizons.map(|horizons| &horizons[light_shadow_dir]);
-        let light = light_direction.normalized();
-        let /*mut */quads = [[0u32; QUADRANTS]; QUADRANTS];
-        let /*mut */rivers = 0u32;
-        let /*mut */lakes = 0u32;
-        let /*mut */oceans = 0u32;
-
-        let focus_rect = Vec2::from(focus);
-
-        let chunk_size = TerrainChunkSize::RECT_SIZE.map(|e| e as f64);
-
-        (0..dimensions.y * dimensions.x).for_each(|chunk_idx| {
-            let i = chunk_idx % dimensions.x as usize;
-            let j = chunk_idx / dimensions.x as usize;
-
-            let wposf = focus_rect + Vec2::new(i as f64, j as f64) * scale;
-            let pos = wposf.map(|e: f64| e as i32);
-            let wposf = wposf * chunk_size;
-
-            let chunk_idx = if pos.reduce_partial_min() >= 0
-                && pos.x < WORLD_SIZE.x as i32
-                && pos.y < WORLD_SIZE.y as i32
-            {
-                Some(vec2_as_uniform_idx(pos))
-            } else {
-                None
-            };
-
-            let MapSample {
-                rgb,
-                alt,
-                downhill_wpos,
-                ..
-            } = sample_pos(pos);
-
-            let alt = alt as f32;
-            let wposi = pos * TerrainChunkSize::RECT_SIZE.map(|e| e as i32);
-            let mut rgb = rgb.map(|e| e as f64 / 255.0);
-
-            // Material properties:
-            //
-            // For each material in the scene,
-            //  k_s = (RGB) specular reflection constant
-            let mut k_s = Rgb::new(1.0, 1.0, 1.0);
-            //  k_d = (RGB) diffuse reflection constant
-            let mut k_d = rgb;
-            //  k_a = (RGB) ambient reflection constant
-            let mut k_a = rgb;
-            //  α = (per-material) shininess constant
-            let mut alpha = 4.0; // 4.0;
-
-            // Compute connections
-            let mut has_river = false;
-            // NOTE: consider replacing neighbors with local_cells, since it is more
-            // accurate (though I'm not sure if it can matter for these
-            // purposes).
             chunk_idx
-                .map(|chunk_idx| neighbors(chunk_idx).chain(iter::once(chunk_idx)))
+                .and_then(|chunk_idx| samples.get(chunk_idx))
-                .into_iter()
+                .map(Option::as_ref)
                 .flatten()
-                .for_each(|neighbor_posi| {
+        })
-                    let neighbor_pos = uniform_idx_as_vec2(neighbor_posi);
+        .map(|sample| {
-                    let neighbor_wpos = neighbor_pos.map(|e| e as f64) * chunk_size;
+            // TODO: Eliminate the redundancy between this and the block renderer.
-                    let MapSample { connections, .. } = sample_pos(neighbor_pos);
+            let alt = sample.alt;
-                    NEIGHBOR_DELTA
+            let basement = sample.basement;
-                        .iter()
+            let grass_depth = (1.5 + 2.0 * sample.chaos).min(alt - basement);
-                        .zip(
+            let wposz = if is_basement { basement } else { alt };
-                            connections
+            if is_basement && wposz < alt - grass_depth {
-                                .as_ref()
+                Lerp::lerp(
-                                .map(|e| e.iter())
+                    sample.sub_surface_color,
-                                .into_iter()
+                    sample.stone_col.map(|e| e as f32 / 255.0),
-                                .flatten()
+                    (alt - grass_depth - wposz as f32) * 0.15,
-                                .into_iter(),
+                )
-                        )
+                .map(|e| e as f64)
-                        .for_each(|(&delta, connection)| {
-                            let connection = if let Some(connection) = connection {
-                                connection
-                            } else {
-                                return;
-                            };
-                            let downhill_wpos = neighbor_wpos
-                                + Vec2::from(delta).map(|e: i32| e as f64) * chunk_size;
-                            let coeffs = river_spline_coeffs(
-                                neighbor_wpos,
-                                connection.spline_derivative,
-                                downhill_wpos,
-                            );
-                            let (_t, _pt, dist) = if let Some((t, pt, dist)) =
-                                quadratic_nearest_point(&coeffs, wposf)
-                            {
-                                (t, pt, dist)
-                            } else {
-                                let ndist = wposf.distance_squared(neighbor_wpos);
-                                let ddist = wposf.distance_squared(downhill_wpos);
-                                if ndist <= ddist {
-                                    (0.0, neighbor_wpos, ndist)
-                                } else {
-                                    (1.0, downhill_wpos, ddist)
-                                }
-                            };
-                            let connection_dist =
-                                (dist.sqrt() - (connection.width as f64 * 0.5).max(1.0)).max(0.0);
-                            if connection_dist == 0.0 {
-                                match connection.kind {
-                                    ConnectionKind::River => {
-                                        has_river = true;
-                                    },
-                                }
-                            }
-                        });
-                });
-
-            // Color in connectins.
-            let water_color_factor = 2.0;
-            let g_water = 32.0 * water_color_factor;
-            let b_water = 64.0 * water_color_factor;
-            if has_river {
-                let water_rgb = Rgb::new(0, ((g_water) * 1.0) as u8, ((b_water) * 1.0) as u8)
-                    .map(|e| e as f64 / 255.0);
-                rgb = water_rgb;
-                k_s = Rgb::new(1.0, 1.0, 1.0);
-                k_d = water_rgb;
-                k_a = water_rgb;
-                alpha = 0.255;
-            }
-
-            let downhill_alt = sample_wpos(downhill_wpos);
-            let cross_pos = wposi
-                + ((downhill_wpos - wposi)
-                    .map(|e| e as f32)
-                    .rotated_z(f32::consts::FRAC_PI_2)
-                    .map(|e| e as i32));
-            let cross_alt = sample_wpos(cross_pos);
-            // Pointing downhill, forward
-            // (index--note that (0,0,1) is backward right-handed)
-            let forward_vec = Vec3::new(
-                (downhill_wpos.x - wposi.x) as f64,
-                ((downhill_alt - alt) * gain) as f64 * lgain,
-                (downhill_wpos.y - wposi.y) as f64,
-            );
-            // Pointing 90 degrees left (in horizontal xy) of downhill, up
-            // (middle--note that (1,0,0), 90 degrees CCW backward, is right right-handed)
-            let up_vec = Vec3::new(
-                (cross_pos.x - wposi.x) as f64,
-                ((cross_alt - alt) * gain) as f64 * lgain,
-                (cross_pos.y - wposi.y) as f64,
-            );
-            // let surface_normal = Vec3::new(lgain * (f.y * u.z - f.z * u.y), -(f.x * u.z -
-            // f.z * u.x), lgain * (f.x * u.y - f.y * u.x)).normalized();
-            // Then cross points "to the right" (upwards) on a right-handed coordinate
-            // system. (right-handed coordinate system means (0, 0, 1.0) is
-            // "forward" into the screen).
-            let surface_normal = forward_vec.cross(up_vec).normalized();
-
-            // TODO: Figure out if we can reimplement debugging.
-            /* if is_debug {
-                let quad =
-                    |x: f32| ((x as f64 * QUADRANTS as f64).floor() as usize).min(QUADRANTS - 1);
-                if river_kind.is_none() || humidity != 0.0 {
-                    quads[quad(humidity)][quad(temperature)] += 1;
-                }
-                match river_kind {
-                    Some(RiverKind::River { .. }) => {
-                        rivers += 1;
-                    },
-                    Some(RiverKind::Lake { .. }) => {
-                        lakes += 1;
-                    },
-                    Some(RiverKind::Ocean { .. }) => {
-                        oceans += 1;
-                    },
-                    None => {},
-                }
-            } */
-
-            let shade_frac = horizon_map
-                .and_then(|(angles, heights)| {
-                    chunk_idx
-                        .and_then(|chunk_idx| angles.get(chunk_idx))
-                        .map(|&e| (e as f64, heights))
-                })
-                .and_then(|(e, heights)| {
-                    chunk_idx
-                        .and_then(|chunk_idx| heights.get(chunk_idx))
-                        .map(|&f| (e, f as f64))
-                })
-                .map(|(angle, height)| {
-                    let w = 0.1;
-                    let height = (height - alt as Alt * gain as Alt).max(0.0);
-                    if angle != 0.0 && light_direction.x != 0.0 && height != 0.0 {
-                        let deltax = height / angle;
-                        let lighty = (light_direction.y / light_direction.x * deltax).abs();
-                        let deltay = lighty - height;
-                        let s = (deltay / deltax / w).min(1.0).max(0.0);
-                        // Smoothstep
-                        s * s * (3.0 - 2.0 * s)
-                    } else {
-                        1.0
-                    }
-                })
-                .unwrap_or(1.0);
-
-            let rgb = if is_shaded {
-                // Phong reflection model with shadows:
-                //
-                // I_p = k_a i_a + shadow * Σ {m ∈ lights} (k_d (L_m ⋅ N) i_m,d + k_s (R_m ⋅
-                // V)^α i_m,s)
-                //
-                // where for the whole scene,
-                //  i_a = (RGB) intensity of ambient lighting component
-                let i_a = Rgb::new(0.1, 0.1, 0.1);
-                //  V = direction pointing towards the viewer (e.g. virtual camera).
-                let v = Vec3::new(0.0, 0.0, -1.0).normalized();
-                // let v = Vec3::new(0.0, -1.0, 0.0).normalized();
-                //
-                // for each light m,
-                //  i_m,d = (RGB) intensity of diffuse component of light source m
-                let i_m_d = Rgb::new(1.0, 1.0, 1.0);
-                //  i_m,s = (RGB) intensity of specular component of light source m
-                let i_m_s = Rgb::new(0.45, 0.45, 0.45);
-                // let i_m_s = Rgb::new(0.45, 0.45, 0.45);
-
-                // for each light m and point p,
-                //  L_m = (normalized) direction vector from point on surface to light source m
-                let l_m = light;
-                //  N = (normalized) normal at this point on the surface,
-                let n = surface_normal;
-                //  R_m = (normalized) direction a perfectly reflected ray of light from m would
-                // take from point p      = 2(L_m ⋅ N)N - L_m
-                let r_m = (-l_m).reflected(n); // 2 * (l_m.dot(n)) * n - l_m;
-                //
-                // and for each point p in the scene,
-                //  shadow = computed shadow factor at point p
-                // FIXME: Should really just be shade_frac, but with only ambient light we lose
-                // all local lighting detail... some sort of global illumination (e.g.
-                // radiosity) is of course the "right" solution, but maybe we can find
-                // something cheaper?
-                let shadow = 0.2 + 0.8 * shade_frac;
-
-                let lambertian = l_m.dot(n).max(0.0);
-                let spec_angle = r_m.dot(v).max(0.0);
-
-                let ambient = k_a * i_a;
-                let diffuse = k_d * lambertian * i_m_d;
-                let specular = k_s * spec_angle.powf(alpha) * i_m_s;
-                (ambient + shadow * (diffuse + specular)).map(|e| e.min(1.0))
             } else {
-                rgb
+                Lerp::lerp(
+                    sample.sub_surface_color,
+                    sample.surface_color,
+                    ((wposz as f32 - (alt - grass_depth)) / grass_depth).powf(0.5),
+                )
+                .map(|e| e as f64)
             }
-            .map(|e| (e * 255.0) as u8);
-
-            let rgba = (rgb.r, rgb.g, rgb.b, 255);
-            write_pixel(Vec2::new(i, j), rgba);
         });
 
-        MapDebug {
+    let downhill_wpos = downhill
-            quads,
+        .map(|downhill_pos| downhill_pos)
-            rivers,
+        .unwrap_or(wpos + TerrainChunkSize::RECT_SIZE.map(|e| e as i32));
-            lakes,
+    let alt = if is_basement { basement } else { alt };
-            oceans,
+
-        }
+    let true_water_alt = (alt.max(water_alt) as f64 - focus.z) / gain as f64;
+    let true_alt = (alt as f64 - focus.z) / gain as f64;
+    let water_depth = (true_water_alt - true_alt).min(1.0).max(0.0);
+    let alt = true_alt.min(1.0).max(0.0);
+
+    let water_color_factor = 2.0;
+    let g_water = 32.0 * water_color_factor;
+    let b_water = 64.0 * water_color_factor;
+    let default_rgb = Rgb::new(
+        if is_shaded || is_temperature {
+            1.0
+        } else {
+            0.0
+        },
+        if is_shaded { 1.0 } else { alt },
+        if is_shaded || is_humidity { 1.0 } else { 0.0 },
+    );
+    let column_rgb = column_rgb.unwrap_or(default_rgb);
+    let mut connections = [None; 8];
+    let mut has_connections = false;
+    // TODO: Support non-river connections.
+    // TODO: Support multiple connections.
+    let river_width = river_kind.map(|river| match river {
+        RiverKind::River { cross_section } => cross_section.x,
+        RiverKind::Lake { .. } | RiverKind::Ocean => TerrainChunkSize::RECT_SIZE.x as f32,
+    });
+    if let (Some(river_width), true) = (river_width, is_water) {
+        let downhill_pos = downhill_wpos.map2(TerrainChunkSize::RECT_SIZE, |e, f| e / f as i32);
+        NEIGHBOR_DELTA
+            .iter()
+            .zip((&mut connections).iter_mut())
+            .filter(|&(&offset, _)| downhill_pos - pos == Vec2::from(offset))
+            .for_each(|(_, connection)| {
+                has_connections = true;
+                *connection = Some(Connection {
+                    kind: ConnectionKind::River,
+                    spline_derivative,
+                    width: river_width,
+                });
+            });
+    };
+    let rgb = match (river_kind, (is_water, true_alt >= true_sea_level)) {
+        (_, (false, _)) | (None, (_, true)) | (Some(RiverKind::River { .. }), _) => {
+            let (r, g, b) = (
+                (column_rgb.r
+                    * if is_temperature {
+                        temperature as f64
+                    } else {
+                        column_rgb.r
+                    })
+                .sqrt(),
+                column_rgb.g,
+                (column_rgb.b
+                    * if is_humidity {
+                        humidity as f64
+                    } else {
+                        column_rgb.b
+                    })
+                .sqrt(),
+            );
+            Rgb::new((r * 255.0) as u8, (g * 255.0) as u8, (b * 255.0) as u8)
+        },
+        (None, _) | (Some(RiverKind::Lake { .. }), _) | (Some(RiverKind::Ocean), _) => Rgb::new(
+            0,
+            ((g_water - water_depth * g_water) * 1.0) as u8,
+            ((b_water - water_depth * b_water) * 1.0) as u8,
+        ),
+    };
+    // TODO: Make principled.
+    let rgb = if near_site {
+        Rgb::new(0x57, 0x39, 0x33)
+    } else if is_path {
+        Rgb::new(0x37, 0x29, 0x23)
+    } else {
+        rgb
+    };
+
+    MapSample {
+        rgb,
+        alt: if is_water {
+            true_alt.max(true_water_alt)
+        } else {
+            true_alt
+        },
+        downhill_wpos,
+        connections: if has_connections {
+            Some(connections)
+        } else {
+            None
+        },
     }
 }

world/src/sim/mod.rs

@@ -14,12 +14,11 @@ pub use self::{
         get_rivers, mrec_downhill, Alt, RiverData, RiverKind,
     },
     location::Location,
-    map::{MapConfig, MapDebug, MapSample},
+    map::{sample_pos, sample_wpos},
     path::PathData,
     util::{
         cdf_irwin_hall, downhill, get_horizon_map, get_oceans, local_cells, map_edge_factor,
-        neighbors, uniform_idx_as_vec2, uniform_noise, uphill, vec2_as_uniform_idx, InverseCdf,
+        uniform_noise, uphill, InverseCdf, ScaleBias,
-        ScaleBias, NEIGHBOR_DELTA,
     },
 };
 
@@ -36,7 +35,10 @@ use common::{
     assets,
     msg::server::WorldMapMsg,
     store::Id,
-    terrain::{BiomeKind, TerrainChunkSize},
+    terrain::{
+        map::MapConfig, uniform_idx_as_vec2, vec2_as_uniform_idx, BiomeKind, MapSizeLg,
+        TerrainChunkSize,
+    },
     vol::RectVolSize,
 };
 use noise::{
@@ -58,6 +60,18 @@ use std::{
 use tracing::{debug, warn};
 use vek::*;
 
+/// Default base two logarithm of the world size, in chunks, per dimension.
+///
+/// Currently, our default map dimensions are 2^10 × 2^10 chunks,
+/// mostly for historical reasons.  It is likely that we will increase this
+/// default at some point.
+const DEFAULT_WORLD_CHUNKS_LG: MapSizeLg =
+    if let Ok(map_size_lg) = MapSizeLg::new(Vec2 { x: 10, y: 10 }) {
+        map_size_lg
+    } else {
+        panic!("Default world chunk size does not satisfy required invariants.");
+    };
+
 // NOTE: I suspect this is too small (1024 * 16 * 1024 * 16 * 8 doesn't fit in
 // an i32), but we'll see what happens, I guess!  We could always store sizes >>
 // 3.  I think 32 or 64 is the absolute limit though, and would require
@@ -67,9 +81,9 @@ use vek::*;
 // don't think we actually cast a chunk id to float, just coordinates... could
 // be wrong though!
 #[allow(clippy::identity_op)] // TODO: Pending review in #587
-pub const WORLD_SIZE: Vec2<usize> = Vec2 {
+const WORLD_SIZE: Vec2<usize> = Vec2 {
-    x: 1024 * 1,
+    x: 1 << DEFAULT_WORLD_CHUNKS_LG.vec().x,
-    y: 1024 * 1,
+    y: 1 << DEFAULT_WORLD_CHUNKS_LG.vec().y,
 };
 
 /// A structure that holds cached noise values and cumulative distribution
@@ -296,6 +310,8 @@ impl WorldFile {
 
 pub struct WorldSim {
     pub seed: u32,
+    /// Base 2 logarithm of the map size.
+    map_size_lg: MapSizeLg,
     /// Maximum height above sea level of any chunk in the map (not including
     /// post-erosion warping, cliffs, and other things like that).
     pub max_height: f32,
@@ -449,16 +465,17 @@ impl WorldSim {
         // Assumes μ = 0, σ = 1
         let logistic_cdf = |x: f64| (x / logistic_2_base).tanh() * 0.5 + 0.5;
 
-        let min_epsilon =
+        let map_size_lg = DEFAULT_WORLD_CHUNKS_LG;
-            1.0 / (WORLD_SIZE.x as f64 * WORLD_SIZE.y as f64).max(f64::EPSILON as f64 * 0.5);
+        let map_size_chunks_len_f64 = map_size_lg.chunks().map(f64::from).product();
-        let max_epsilon = (1.0 - 1.0 / (WORLD_SIZE.x as f64 * WORLD_SIZE.y as f64))
+        let min_epsilon = 1.0 / map_size_chunks_len_f64.max(f64::EPSILON as f64 * 0.5);
-            .min(1.0 - f64::EPSILON as f64 * 0.5);
+        let max_epsilon =
+            (1.0 - 1.0 / map_size_chunks_len_f64).min(1.0 - f64::EPSILON as f64 * 0.5);
 
         // No NaNs in these uniform vectors, since the original noise value always
         // returns Some.
         let ((alt_base, _), (chaos, _)) = rayon::join(
             || {
-                uniform_noise(|_, wposf| {
+                uniform_noise(map_size_lg, |_, wposf| {
                     // "Base" of the chunk, to be multiplied by CONFIG.mountain_scale (multiplied
                     // value is from -0.35 * (CONFIG.mountain_scale * 1.05) to
                     // 0.35 * (CONFIG.mountain_scale * 0.95), but value here is from -0.3675 to
@@ -475,7 +492,7 @@ impl WorldSim {
                 })
             },
             || {
-                uniform_noise(|_, wposf| {
+                uniform_noise(map_size_lg, |_, wposf| {
                     // From 0 to 1.6, but the distribution before the max is from -1 and 1.6, so
                     // there is a 50% chance that hill will end up at 0.3 or
                     // lower, and probably a very high change it will be exactly
@@ -548,7 +565,7 @@ impl WorldSim {
         //
         // No NaNs in these uniform vectors, since the original noise value always
         // returns Some.
-        let (alt_old, _) = uniform_noise(|posi, wposf| {
+        let (alt_old, _) = uniform_noise(map_size_lg, |posi, wposf| {
             // This is the extension upwards from the base added to some extra noise from -1
             // to 1.
             //
@@ -612,11 +629,11 @@ impl WorldSim {
             // = [-0.946, 1.067]
             Some(
                 ((alt_base[posi].1 + alt_main.mul((chaos[posi].1 as f64).powf(1.2)))
-                    .mul(map_edge_factor(posi) as f64)
+                    .mul(map_edge_factor(map_size_lg, posi) as f64)
                     .add(
                         (CONFIG.sea_level as f64)
                             .div(CONFIG.mountain_scale as f64)
-                            .mul(map_edge_factor(posi) as f64),
+                            .mul(map_edge_factor(map_size_lg, posi) as f64),
                     )
                     .sub((CONFIG.sea_level as f64).div(CONFIG.mountain_scale as f64)))
                     as f32,
@@ -624,12 +641,12 @@ impl WorldSim {
         });
 
         // Calculate oceans.
-        let is_ocean = get_oceans(|posi: usize| alt_old[posi].1);
+        let is_ocean = get_oceans(map_size_lg, |posi: usize| alt_old[posi].1);
         // NOTE: Uncomment if you want oceans to exclusively be on the border of the
         // map.
-        /* let is_ocean = (0..WORLD_SIZE.x * WORLD_SIZE.y)
+        /* let is_ocean = (0..map_size_lg.chunks())
         .into_par_iter()
-        .map(|i| map_edge_factor(i) == 0.0)
+        .map(|i| map_edge_factor(map_size_lg, i) == 0.0)
         .collect::<Vec<_>>(); */
         let is_ocean_fn = |posi: usize| is_ocean[posi];
 
@@ -650,14 +667,14 @@ impl WorldSim {
 
         // Recalculate altitudes without oceans.
         // NaNs in these uniform vectors wherever is_ocean_fn returns true.
-        let (alt_old_no_ocean, _) = uniform_noise(|posi, _| {
+        let (alt_old_no_ocean, _) = uniform_noise(map_size_lg, |posi, _| {
             if is_ocean_fn(posi) {
                 None
             } else {
                 Some(old_height(posi))
             }
         });
-        let (uplift_uniform, _) = uniform_noise(|posi, _wposf| {
+        let (uplift_uniform, _) = uniform_noise(map_size_lg, |posi, _wposf| {
             if is_ocean_fn(posi) {
                 None
             } else {
@@ -717,7 +734,7 @@ impl WorldSim {
             }
         };
         let g_func = |posi| {
-            if map_edge_factor(posi) == 0.0 {
+            if map_edge_factor(map_size_lg, posi) == 0.0 {
                 return 0.0;
             }
             // G = d* v_s / p_0, where
@@ -743,8 +760,9 @@ impl WorldSim {
                 let epsilon_0_i = 2.078e-3 / 4.0;
                 return epsilon_0_i * epsilon_0_scale_i;
             }
-            let wposf = (uniform_idx_as_vec2(posi) * TerrainChunkSize::RECT_SIZE.map(|e| e as i32))
+            let wposf = (uniform_idx_as_vec2(map_size_lg, posi)
-                .map(|e| e as f64);
+                * TerrainChunkSize::RECT_SIZE.map(|e| e as i32))
+            .map(|e| e as f64);
             let turb_wposf = wposf
                 .mul(5_000.0 / continent_scale)
                 .div(TerrainChunkSize::RECT_SIZE.map(|e| e as f64))
@@ -797,8 +815,9 @@ impl WorldSim {
                 // marine: α = 3.7e-2
                 return 3.7e-2 * alpha_scale_i;
             }
-            let wposf = (uniform_idx_as_vec2(posi) * TerrainChunkSize::RECT_SIZE.map(|e| e as i32))
+            let wposf = (uniform_idx_as_vec2(map_size_lg, posi)
-                .map(|e| e as f64);
+                * TerrainChunkSize::RECT_SIZE.map(|e| e as i32))
+            .map(|e| e as f64);
             let turb_wposf = wposf
                 .mul(5_000.0 / continent_scale)
                 .div(TerrainChunkSize::RECT_SIZE.map(|e| e as f64))
@@ -963,10 +982,11 @@ impl WorldSim {
 
         // Perform some erosion.
 
-        let (alt, basement) = if let Some(map) = parsed_world_file {
+        let (alt, basement, map_size_lg) = if let Some(map) = parsed_world_file {
-            (map.alt, map.basement)
+            (map.alt, map.basement, DEFAULT_WORLD_CHUNKS_LG)
         } else {
             let (alt, basement) = do_erosion(
+                map_size_lg,
                 max_erosion_per_delta_t as f32,
                 n_steps,
                 &river_seed,
@@ -992,7 +1012,8 @@ impl WorldSim {
             );
 
             // Quick "small scale" erosion cycle in order to lower extreme angles.
-            do_erosion(
+            let (alt, basement) = do_erosion(
+                map_size_lg,
                 1.0f32,
                 n_small_steps,
                 &river_seed,
@@ -1011,7 +1032,9 @@ impl WorldSim {
                 height_scale,
                 k_d_scale(n_approx),
                 k_da_scale,
-            )
+            );
+
+            (alt, basement, map_size_lg)
         };
 
         // Save map, if necessary.
@@ -1060,6 +1083,7 @@ impl WorldSim {
             (alt, basement)
         } else {
             do_erosion(
+                map_size_lg,
                 1.0f32,
                 n_post_load_steps,
                 &river_seed,
@@ -1081,28 +1105,31 @@ impl WorldSim {
             )
         };
 
-        let is_ocean = get_oceans(|posi| alt[posi]);
+        let is_ocean = get_oceans(map_size_lg, |posi| alt[posi]);
         let is_ocean_fn = |posi: usize| is_ocean[posi];
-        let mut dh = downhill(|posi| alt[posi], is_ocean_fn);
+        let mut dh = downhill(map_size_lg, |posi| alt[posi], is_ocean_fn);
-        let (boundary_len, indirection, water_alt_pos, maxh) = get_lakes(|posi| alt[posi], &mut dh);
+        let (boundary_len, indirection, water_alt_pos, maxh) =
+            get_lakes(map_size_lg, |posi| alt[posi], &mut dh);
         debug!(?maxh, "Max height");
         let (mrec, mstack, mwrec) = {
-            let mut wh = vec![0.0; WORLD_SIZE.x * WORLD_SIZE.y];
+            let mut wh = vec![0.0; map_size_lg.chunks_len()];
             get_multi_rec(
+                map_size_lg,
                 |posi| alt[posi],
                 &dh,
                 &water_alt_pos,
                 &mut wh,
-                WORLD_SIZE.x,
+                usize::from(map_size_lg.chunks().x),
-                WORLD_SIZE.y,
+                usize::from(map_size_lg.chunks().y),
                 TerrainChunkSize::RECT_SIZE.x as Compute,
                 TerrainChunkSize::RECT_SIZE.y as Compute,
                 maxh,
             )
         };
-        let flux_old = get_multi_drainage(&mstack, &mrec, &*mwrec, boundary_len);
+        let flux_old = get_multi_drainage(map_size_lg, &mstack, &mrec, &*mwrec, boundary_len);
-        // let flux_rivers = get_drainage(&water_alt_pos, &dh, boundary_len);
+        // let flux_rivers = get_drainage(map_size_lg, &water_alt_pos, &dh,
-        // TODO: Make rivers work with multi-direction flux as well.
+        // boundary_len); TODO: Make rivers work with multi-direction flux as
+        // well.
         let flux_rivers = flux_old.clone();
 
         let water_height_initial = |chunk_idx| {
@@ -1153,13 +1180,20 @@ impl WorldSim {
         // may comment out this line and replace it with the commented-out code
         // below; however, there are no guarantees that this
         // will work correctly.
-        let water_alt = fill_sinks(water_height_initial, is_ocean_fn);
+        let water_alt = fill_sinks(map_size_lg, water_height_initial, is_ocean_fn);
-        /* let water_alt = (0..WORLD_SIZE.x * WORLD_SIZE.y)
+        /* let water_alt = (0..map_size_lg.chunks_len())
         .into_par_iter()
         .map(|posi| water_height_initial(posi))
         .collect::<Vec<_>>(); */
 
-        let rivers = get_rivers(&water_alt_pos, &water_alt, &dh, &indirection, &flux_rivers);
+        let rivers = get_rivers(
+            map_size_lg,
+            &water_alt_pos,
+            &water_alt,
+            &dh,
+            &indirection,
+            &flux_rivers,
+        );
 
         let water_alt = indirection
             .par_iter()
@@ -1198,11 +1232,15 @@ impl WorldSim {
         // Check whether any tiles around this tile are not water (since Lerp will
         // ensure that they are included).
         let pure_water = |posi: usize| {
-            let pos = uniform_idx_as_vec2(posi);
+            let pos = uniform_idx_as_vec2(map_size_lg, posi);
             for x in pos.x - 1..(pos.x + 1) + 1 {
                 for y in pos.y - 1..(pos.y + 1) + 1 {
-                    if x >= 0 && y >= 0 && x < WORLD_SIZE.x as i32 && y < WORLD_SIZE.y as i32 {
+                    if x >= 0
-                        let posi = vec2_as_uniform_idx(Vec2::new(x, y));
+                        && y >= 0
+                        && x < map_size_lg.chunks().x as i32
+                        && y < map_size_lg.chunks().y as i32
+                    {
+                        let posi = vec2_as_uniform_idx(map_size_lg, Vec2::new(x, y));
                         if !is_underwater(posi) {
                             return false;
                         }
@@ -1217,7 +1255,7 @@ impl WorldSim {
             || {
                 rayon::join(
                     || {
-                        uniform_noise(|posi, _| {
+                        uniform_noise(map_size_lg, |posi, _| {
                             if pure_water(posi) {
                                 None
                             } else {
@@ -1228,7 +1266,7 @@ impl WorldSim {
                         })
                     },
                     || {
-                        uniform_noise(|posi, _| {
+                        uniform_noise(map_size_lg, |posi, _| {
                             if pure_water(posi) {
                                 None
                             } else {
@@ -1241,7 +1279,7 @@ impl WorldSim {
             || {
                 rayon::join(
                     || {
-                        uniform_noise(|posi, wposf| {
+                        uniform_noise(map_size_lg, |posi, wposf| {
                             if pure_water(posi) {
                                 None
                             } else {
@@ -1251,7 +1289,7 @@ impl WorldSim {
                         })
                     },
                     || {
-                        uniform_noise(|posi, wposf| {
+                        uniform_noise(map_size_lg, |posi, wposf| {
                             // Check whether any tiles around this tile are water.
                             if pure_water(posi) {
                                 None
@@ -1283,13 +1321,14 @@ impl WorldSim {
             rivers,
         };
 
-        let chunks = (0..WORLD_SIZE.x * WORLD_SIZE.y)
+        let chunks = (0..map_size_lg.chunks_len())
             .into_par_iter()
-            .map(|i| SimChunk::generate(i, &gen_ctx, &gen_cdf))
+            .map(|i| SimChunk::generate(map_size_lg, i, &gen_ctx, &gen_cdf))
             .collect::<Vec<_>>();
 
         let mut this = Self {
             seed,
+            map_size_lg,
             max_height: maxh as f32,
             chunks,
             locations: Vec::new(),
@@ -1304,13 +1343,18 @@ impl WorldSim {
         this
     }
 
-    pub fn get_size(&self) -> Vec2<u32> { WORLD_SIZE.map(|e| e as u32) }
+    #[inline(always)]
+    pub const fn map_size_lg(&self) -> MapSizeLg { self.map_size_lg }
+
+    pub fn get_size(&self) -> Vec2<u32> { self.map_size_lg().chunks().map(u32::from) }
 
     /// Draw a map of the world based on chunk information.  Returns a buffer of
     /// u32s.
     pub fn get_map(&self) -> WorldMapMsg {
-        let mut map_config = MapConfig::default();
+        let mut map_config = MapConfig::orthographic(
-        map_config.lgain = 1.0;
+            DEFAULT_WORLD_CHUNKS_LG,
+            core::ops::RangeInclusive::new(CONFIG.sea_level, CONFIG.sea_level + self.max_height),
+        );
         // Build a horizon map.
         let scale_angle = |angle: Alt| {
             (/* 0.0.max( */angle /* ) */
@@ -1325,14 +1369,14 @@ impl WorldSim {
 
         let samples_data = {
             let column_sample = ColumnGen::new(self);
-            (0..WORLD_SIZE.product())
+            (0..self.map_size_lg().chunks_len())
                 .into_par_iter()
                 .map_init(
                     || Box::new(BlockGen::new(ColumnGen::new(self))),
                     |block_gen, posi| {
-                        let wpos = uniform_idx_as_vec2(posi);
+                        let wpos = uniform_idx_as_vec2(self.map_size_lg(), posi);
                         let mut sample = column_sample.get(
-                            uniform_idx_as_vec2(posi) * TerrainChunkSize::RECT_SIZE.map(|e| e as i32),
+                            uniform_idx_as_vec2(self.map_size_lg(), posi) * TerrainChunkSize::RECT_SIZE.map(|e| e as i32),
                         )?;
                         let alt = sample.alt;
                         /* let z_cache = block_gen.get_z_cache(wpos);
@@ -1353,7 +1397,7 @@ impl WorldSim {
                 )
                 /* .map(|posi| {
                     let mut sample = column_sample.get(
-                        uniform_idx_as_vec2(posi) * TerrainChunkSize::RECT_SIZE.map(|e| e as i32),
+                        uniform_idx_as_vec2(self.map_size_lg(), posi) * TerrainChunkSize::RECT_SIZE.map(|e| e as i32),
                     );
                 }) */
                 .collect::<Vec<_>>()
@@ -1361,55 +1405,53 @@ impl WorldSim {
         };
 
         let horizons = get_horizon_map(
-            map_config.lgain,
+            self.map_size_lg(),
             Aabr {
                 min: Vec2::zero(),
-                max: WORLD_SIZE.map(|e| e as i32),
+                max: self.map_size_lg().chunks().map(|e| e as i32),
             },
-            CONFIG.sea_level as Alt,
+            CONFIG.sea_level,
-            (CONFIG.sea_level + self.max_height) as Alt,
+            CONFIG.sea_level + self.max_height,
             |posi| {
                 /* let chunk = &self.chunks[posi];
                 chunk.alt.max(chunk.water_alt) as Alt */
                 let sample = samples_data[posi].as_ref();
                 sample
                     .map(|s| s.alt.max(s.water_level))
-                    .unwrap_or(CONFIG.sea_level) as Alt
+                    .unwrap_or(CONFIG.sea_level)
             },
-            |a| scale_angle(a),
+            |a| scale_angle(a.into()),
-            |h| scale_height(h),
+            |h| scale_height(h.into()),
         )
         .unwrap();
 
-        let mut v = vec![0u32; WORLD_SIZE.x * WORLD_SIZE.y];
+        let mut v = vec![0u32; self.map_size_lg().chunks_len()];
-        let mut alts = vec![0u32; WORLD_SIZE.x * WORLD_SIZE.y];
+        let mut alts = vec![0u32; self.map_size_lg().chunks_len()];
         // TODO: Parallelize again.
-        let config = MapConfig {
+        map_config.is_shaded = false;
-            gain: self.max_height,
-            samples: Some(&samples_data),
-            is_shaded: false,
-            ..map_config
-        };
 
-        config.generate(
+        map_config.generate(
-            |pos| config.sample_pos(self, pos),
+            |pos| sample_pos(&map_config, self, Some(&samples_data), pos),
-            |pos| config.sample_wpos(self, pos),
+            |pos| sample_wpos(&map_config, self, pos),
             |pos, (r, g, b, _a)| {
                 // We currently ignore alpha and replace it with the height at pos, scaled to
                 // u8.
-                let alt = config.sample_wpos(
+                let alt = sample_wpos(
+                    &map_config,
                     self,
                     pos.map(|e| e as i32) * TerrainChunkSize::RECT_SIZE.map(|e| e as i32),
                 );
                 let a = 0; //(alt.min(1.0).max(0.0) * 255.0) as u8;
 
-                let posi = pos.y * WORLD_SIZE.x + pos.x;
+                // NOTE: Safe by invariants on map_size_lg.
+                let posi = (pos.y << self.map_size_lg().vec().x) | pos.x;
                 v[posi] = u32::from_le_bytes([r, g, b, a]);
                 alts[posi] = (((alt.min(1.0).max(0.0) * 8191.0) as u32) & 0x1FFF) << 3;
             },
         );
         WorldMapMsg {
-            dimensions: WORLD_SIZE.map(|e| e as u16),
+            dimensions_lg: self.map_size_lg().vec(),
+            sea_level: CONFIG.sea_level,
             max_height: self.max_height,
             rgba: v,
             alt: alts,
@@ -1422,7 +1464,7 @@ impl WorldSim {
         let mut rng = self.rng.clone();
 
         let cell_size = 16;
-        let grid_size = WORLD_SIZE / cell_size;
+        let grid_size = self.map_size_lg().chunks().map(usize::from) / cell_size;
         let loc_count = 100;
 
         let mut loc_grid = vec![None; grid_size.product()];
@@ -1490,7 +1532,7 @@ impl WorldSim {
             .par_iter_mut()
             .enumerate()
             .for_each(|(ij, chunk)| {
-                let chunk_pos = uniform_idx_as_vec2(ij);
+                let chunk_pos = uniform_idx_as_vec2(self.map_size_lg(), ij);
                 let i = chunk_pos.x as usize;
                 let j = chunk_pos.y as usize;
                 let block_pos = Vec2::new(
@@ -1530,10 +1572,10 @@ impl WorldSim {
         // Create waypoints
         const WAYPOINT_EVERY: usize = 16;
         let this = &self;
-        let waypoints = (0..WORLD_SIZE.x)
+        let waypoints = (0..this.map_size_lg().chunks().x)
             .step_by(WAYPOINT_EVERY)
             .map(|i| {
-                (0..WORLD_SIZE.y)
+                (0..this.map_size_lg().chunks().y)
                     .step_by(WAYPOINT_EVERY)
                     .map(move |j| (i, j))
             })
@@ -1576,10 +1618,10 @@ impl WorldSim {
 
     pub fn get(&self, chunk_pos: Vec2<i32>) -> Option<&SimChunk> {
         if chunk_pos
-            .map2(WORLD_SIZE, |e, sz| e >= 0 && e < sz as i32)
+            .map2(self.map_size_lg().chunks(), |e, sz| e >= 0 && e < sz as i32)
             .reduce_and()
         {
-            Some(&self.chunks[vec2_as_uniform_idx(chunk_pos)])
+            Some(&self.chunks[vec2_as_uniform_idx(self.map_size_lg(), chunk_pos)])
         } else {
             None
         }
@@ -1607,11 +1649,12 @@ impl WorldSim {
     }
 
     pub fn get_mut(&mut self, chunk_pos: Vec2<i32>) -> Option<&mut SimChunk> {
+        let map_size_lg = self.map_size_lg();
         if chunk_pos
-            .map2(WORLD_SIZE, |e, sz| e >= 0 && e < sz as i32)
+            .map2(map_size_lg.chunks(), |e, sz| e >= 0 && e < sz as i32)
             .reduce_and()
         {
-            Some(&mut self.chunks[vec2_as_uniform_idx(chunk_pos)])
+            Some(&mut self.chunks[vec2_as_uniform_idx(map_size_lg, chunk_pos)])
         } else {
             None
         }
@@ -1619,16 +1662,18 @@ impl WorldSim {
 
     pub fn get_base_z(&self, chunk_pos: Vec2<i32>) -> Option<f32> {
         if !chunk_pos
-            .map2(WORLD_SIZE, |e, sz| e > 0 && e < sz as i32 - 2)
+            .map2(self.map_size_lg().chunks(), |e, sz| {
+                e > 0 && e < sz as i32 - 2
+            })
             .reduce_and()
         {
             return None;
         }
 
-        let chunk_idx = vec2_as_uniform_idx(chunk_pos);
+        let chunk_idx = vec2_as_uniform_idx(self.map_size_lg(), chunk_pos);
-        local_cells(chunk_idx)
+        local_cells(self.map_size_lg(), chunk_idx)
             .flat_map(|neighbor_idx| {
-                let neighbor_pos = uniform_idx_as_vec2(neighbor_idx);
+                let neighbor_pos = uniform_idx_as_vec2(self.map_size_lg(), neighbor_idx);
                 let neighbor_chunk = self.get(neighbor_pos);
                 let river_kind = neighbor_chunk.and_then(|c| c.river.river_kind);
                 let has_water = river_kind.is_some() && river_kind != Some(RiverKind::Ocean);
@@ -1904,11 +1949,10 @@ pub struct RegionInfo {
 impl SimChunk {
     #[allow(clippy::if_same_then_else)] // TODO: Pending review in #587
     #[allow(clippy::unnested_or_patterns)] // TODO: Pending review in #587
-    fn generate(posi: usize, gen_ctx: &GenCtx, gen_cdf: &GenCdf) -> Self {
+    fn generate(map_size_lg: MapSizeLg, posi: usize, gen_ctx: &GenCtx, gen_cdf: &GenCdf) -> Self {
-        let pos = uniform_idx_as_vec2(posi);
+        let pos = uniform_idx_as_vec2(map_size_lg, posi);
         let wposf = (pos * TerrainChunkSize::RECT_SIZE.map(|e| e as i32)).map(|e| e as f64);
 
-        let _map_edge_factor = map_edge_factor(posi);
         let (_, chaos) = gen_cdf.chaos[posi];
         let alt_pre = gen_cdf.alt[posi] as f32;
         let basement_pre = gen_cdf.basement[posi] as f32;
@@ -1929,7 +1973,7 @@ impl SimChunk {
         // can always add a small x component).
         //
         // Not clear that we want this yet, let's see.
-        let latitude_uniform = (pos.y as f32 / WORLD_SIZE.y as f32).sub(0.5).mul(2.0);
+        let latitude_uniform = (pos.y as f32 / f32::from(self.map_size_lg().chunks().y)).sub(0.5).mul(2.0);
 
         // Even less granular--if this matters we can make the sign affect the quantiy slightly.
         let abs_lat_uniform = latitude_uniform.abs(); */
@@ -1962,7 +2006,7 @@ impl SimChunk {
             panic!("Uh... shouldn't this never, ever happen?");
         } else {
             Some(
-                uniform_idx_as_vec2(downhill_pre as usize)
+                uniform_idx_as_vec2(map_size_lg, downhill_pre as usize)
                     * TerrainChunkSize::RECT_SIZE.map(|e| e as i32),
             )
         };

world/src/sim/util.rs

@@ -1,6 +1,8 @@
-use super::WORLD_SIZE;
 use bitvec::prelude::{bitbox, BitBox};
-use common::{terrain::TerrainChunkSize, vol::RectVolSize};
+use common::{
+    terrain::{neighbors, uniform_idx_as_vec2, vec2_as_uniform_idx, MapSizeLg, TerrainChunkSize},
+    vol::RectVolSize,
+};
 use noise::{MultiFractal, NoiseFn, Perlin, Point2, Point3, Point4, Seedable};
 use num::Float;
 use rayon::prelude::*;
@@ -8,14 +10,15 @@ use std::{f32, f64, ops::Mul, u32};
 use vek::*;
 
 /// Calculates the smallest distance along an axis (x, y) from an edge of
-/// the world.  This value is maximal at WORLD_SIZE / 2 and minimized at the
+/// the world.  This value is maximal at map_size_lg.chunks() / 2 and
-/// extremes (0 or WORLD_SIZE on one or more axes).  It then divides the
+/// minimized at the
-/// quantity by cell_size, so the final result is 1 when we are not in a cell
+/// extremes (0 or map_size_lg.chunks() on one or more axes).  It then divides
-/// along the edge of the world, and ranges between 0 and 1 otherwise (lower
+/// the quantity by cell_size, so the final result is 1 when we are not in a
-/// when the chunk is closer to the edge).
+/// cell along the edge of the world, and ranges between 0 and 1 otherwise
-pub fn map_edge_factor(posi: usize) -> f32 {
+/// (lower when the chunk is closer to the edge).
-    uniform_idx_as_vec2(posi)
+pub fn map_edge_factor(map_size_lg: MapSizeLg, posi: usize) -> f32 {
-        .map2(WORLD_SIZE.map(|e| e as i32), |e, sz| {
+    uniform_idx_as_vec2(map_size_lg, posi)
+        .map2(map_size_lg.chunks().map(i32::from), |e, sz| {
             (sz / 2 - (e - sz / 2).abs()) as f32 / (16.0 / 1024.0 * sz as f32)
         })
         .reduce_partial_min()
@@ -118,8 +121,6 @@ pub fn cdf_irwin_hall<const N: usize>(weights: &[f32; N], samples: [f32; N]) ->
 /// returned by the noise function applied to every chunk in the game).  Second
 /// component is the cached value of the noise function that generated the
 /// index.
-///
-/// NOTE: Length should always be WORLD_SIZE.x * WORLD_SIZE.y.
 pub type InverseCdf<F = f32> = Box<[(f32, F)]>;
 
 /// NOTE: First component is estimated horizon angles at each chunk; second
@@ -127,19 +128,6 @@ pub type InverseCdf<F = f32> = Box<[(f32, F)]>;
 /// for making shadows volumetric).
 pub type HorizonMap<A, H> = (Vec<A>, Vec<H>);
 
-/// Computes the position Vec2 of a SimChunk from an index, where the index was
-/// generated by uniform_noise.
-pub fn uniform_idx_as_vec2(idx: usize) -> Vec2<i32> {
-    Vec2::new((idx % WORLD_SIZE.x) as i32, (idx / WORLD_SIZE.x) as i32)
-}
-
-/// Computes the index of a Vec2 of a SimChunk from a position, where the index
-/// is generated by uniform_noise.  NOTE: Both components of idx should be
-/// in-bounds!
-pub fn vec2_as_uniform_idx(idx: Vec2<i32>) -> usize {
-    (idx.y as usize * WORLD_SIZE.x + idx.x as usize) as usize
-}
-
 /// Compute inverse cumulative distribution function for arbitrary function f,
 /// the hard way.  We pre-generate noise values prior to worldgen, then sort
 /// them in order to determine the correct position in the sorted order.  That
@@ -178,15 +166,17 @@ pub fn vec2_as_uniform_idx(idx: Vec2<i32>) -> usize {
 /// value actually uses the same one we were using here easier).  Also returns
 /// the "inverted index" pointing from a position to a noise.
 pub fn uniform_noise<F: Float + Send>(
+    map_size_lg: MapSizeLg,
     f: impl Fn(usize, Vec2<f64>) -> Option<F> + Sync,
 ) -> (InverseCdf<F>, Box<[(usize, F)]>) {
-    let mut noise = (0..WORLD_SIZE.x * WORLD_SIZE.y)
+    let mut noise = (0..map_size_lg.chunks_len())
         .into_par_iter()
         .filter_map(|i| {
             f(
                 i,
-                (uniform_idx_as_vec2(i) * TerrainChunkSize::RECT_SIZE.map(|e| e as i32))
+                (uniform_idx_as_vec2(map_size_lg, i)
-                    .map(|e| e as f64),
+                    * TerrainChunkSize::RECT_SIZE.map(|e| e as i32))
+                .map(|e| e as f64),
             )
             .map(|res| (i, res))
         })
@@ -202,7 +192,7 @@ pub fn uniform_noise<F: Float + Send>(
     // position of the noise in the sorted vector (divided by the vector length).
     // This guarantees a uniform distribution among the samples (excluding those
     // that returned None, which will remain at zero).
-    let mut uniform_noise = vec![(0.0, F::nan()); WORLD_SIZE.x * WORLD_SIZE.y].into_boxed_slice();
+    let mut uniform_noise = vec![(0.0, F::nan()); map_size_lg.chunks_len()].into_boxed_slice();
     // NOTE: Consider using try_into here and elsewhere in this function, since
     // i32::MAX technically doesn't fit in an f32 (even if we should never reach
     // that limit).
@@ -223,8 +213,8 @@ pub fn uniform_noise<F: Float + Send>(
 /// its top-right/down-right/down neighbors, the twelve chunks surrounding this
 /// box (its "perimeter") are also inspected.
 #[allow(clippy::useless_conversion)] // TODO: Pending review in #587
-pub fn local_cells(posi: usize) -> impl Clone + Iterator<Item = usize> {
+pub fn local_cells(map_size_lg: MapSizeLg, posi: usize) -> impl Clone + Iterator<Item = usize> {
-    let pos = uniform_idx_as_vec2(posi);
+    let pos = uniform_idx_as_vec2(map_size_lg, posi);
     // NOTE: want to keep this such that the chunk index is in ascending order!
     let grid_size = 3i32;
     let grid_bounds = 2 * grid_size + 1;
@@ -236,51 +226,35 @@ pub fn local_cells(posi: usize) -> impl Clone + Iterator<Item = usize> {
                 pos.y + (index / grid_bounds) - grid_size,
             )
         })
-        .filter(|pos| {
+        .filter(move |pos| {
-            pos.x >= 0 && pos.y >= 0 && pos.x < WORLD_SIZE.x as i32 && pos.y < WORLD_SIZE.y as i32
+            pos.x >= 0
+                && pos.y >= 0
+                && pos.x < map_size_lg.chunks().x as i32
+                && pos.y < map_size_lg.chunks().y as i32
         })
-        .map(vec2_as_uniform_idx)
+        .map(move |e| vec2_as_uniform_idx(map_size_lg, e))
-}
-
-// NOTE: want to keep this such that the chunk index is in ascending order!
-pub const NEIGHBOR_DELTA: [(i32, i32); 8] = [
-    (-1, -1),
-    (0, -1),
-    (1, -1),
-    (-1, 0),
-    (1, 0),
-    (-1, 1),
-    (0, 1),
-    (1, 1),
-];
-
-/// Iterate through all cells adjacent to a chunk.
-pub fn neighbors(posi: usize) -> impl Clone + Iterator<Item = usize> {
-    let pos = uniform_idx_as_vec2(posi);
-    NEIGHBOR_DELTA
-        .iter()
-        .map(move |&(x, y)| Vec2::new(pos.x + x, pos.y + y))
-        .filter(|pos| {
-            pos.x >= 0 && pos.y >= 0 && pos.x < WORLD_SIZE.x as i32 && pos.y < WORLD_SIZE.y as i32
-        })
-        .map(vec2_as_uniform_idx)
 }
 
 // Note that we should already have okay cache locality since we have a grid.
-pub fn uphill<'a>(dh: &'a [isize], posi: usize) -> impl Clone + Iterator<Item = usize> + 'a {
+pub fn uphill<'a>(
-    neighbors(posi).filter(move |&posj| dh[posj] == posi as isize)
+    map_size_lg: MapSizeLg,
+    dh: &'a [isize],
+    posi: usize,
+) -> impl Clone + Iterator<Item = usize> + 'a {
+    neighbors(map_size_lg, posi).filter(move |&posj| dh[posj] == posi as isize)
 }
 
 /// Compute the neighbor "most downhill" from all chunks.
 ///
 /// TODO: See if allocating in advance is worthwhile.
 pub fn downhill<F: Float>(
+    map_size_lg: MapSizeLg,
     h: impl Fn(usize) -> F + Sync,
     is_ocean: impl Fn(usize) -> bool + Sync,
 ) -> Box<[isize]> {
     // Constructs not only the list of downhill nodes, but also computes an ordering
     // (visiting nodes in order from roots to leaves).
-    (0..WORLD_SIZE.x * WORLD_SIZE.y)
+    (0..map_size_lg.chunks_len())
         .into_par_iter()
         .map(|posi| {
             let nh = h(posi);
@@ -289,7 +263,7 @@ pub fn downhill<F: Float>(
             } else {
                 let mut best = -1;
                 let mut besth = nh;
-                for nposi in neighbors(posi) {
+                for nposi in neighbors(map_size_lg, posi) {
                     let nbh = h(nposi);
                     if nbh < besth {
                         besth = nbh;
@@ -354,37 +328,37 @@ fn get_interpolated_bilinear<T, F>(&self, pos: Vec2<i32>, mut f: F) -> Option<T>
 /// - posi is at the side of the world (map_edge_factor(posi) == 0.0)
 /// - posi has a neighboring ocean tile, and has a height below sea level
 ///   (oldh(posi) <= 0.0).
-pub fn get_oceans<F: Float>(oldh: impl Fn(usize) -> F + Sync) -> BitBox {
+pub fn get_oceans<F: Float>(map_size_lg: MapSizeLg, oldh: impl Fn(usize) -> F + Sync) -> BitBox {
     // We can mark tiles as ocean candidates by scanning row by row, since the top
     // edge is ocean, the sides are connected to it, and any subsequent ocean
     // tiles must be connected to it.
-    let mut is_ocean = bitbox![0; WORLD_SIZE.x * WORLD_SIZE.y];
+    let mut is_ocean = bitbox![0; map_size_lg.chunks_len()];
     let mut stack = Vec::new();
     let mut do_push = |pos| {
-        let posi = vec2_as_uniform_idx(pos);
+        let posi = vec2_as_uniform_idx(map_size_lg, pos);
         if oldh(posi) <= F::zero() {
             stack.push(posi);
         }
     };
-    for x in 0..WORLD_SIZE.x as i32 {
+    for x in 0..map_size_lg.chunks().x as i32 {
         do_push(Vec2::new(x, 0));
-        do_push(Vec2::new(x, WORLD_SIZE.y as i32 - 1));
+        do_push(Vec2::new(x, map_size_lg.chunks().y as i32 - 1));
     }
-    for y in 1..WORLD_SIZE.y as i32 - 1 {
+    for y in 1..map_size_lg.chunks().y as i32 - 1 {
         do_push(Vec2::new(0, y));
-        do_push(Vec2::new(WORLD_SIZE.x as i32 - 1, y));
+        do_push(Vec2::new(map_size_lg.chunks().x as i32 - 1, y));
     }
     while let Some(chunk_idx) = stack.pop() {
-        // println!("Ocean chunk {:?}: {:?}", uniform_idx_as_vec2(chunk_idx),
+        // println!("Ocean chunk {:?}: {:?}", uniform_idx_as_vec2(map_size_lg,
-        // oldh(chunk_idx));
+        // chunk_idx), oldh(chunk_idx));
         let mut is_ocean = is_ocean.get_mut(chunk_idx).unwrap();
         if *is_ocean {
             continue;
         }
         *is_ocean = true;
-        stack.extend(neighbors(chunk_idx).filter(|&neighbor_idx| {
+        stack.extend(neighbors(map_size_lg, chunk_idx).filter(|&neighbor_idx| {
-            // println!("Ocean neighbor: {:?}: {:?}", uniform_idx_as_vec2(neighbor_idx),
+            // println!("Ocean neighbor: {:?}: {:?}", uniform_idx_as_vec2(map_size_lg,
-            // oldh(neighbor_idx));
+            // neighbor_idx), oldh(neighbor_idx));
             oldh(neighbor_idx) <= F::zero()
         }));
     }
@@ -393,7 +367,7 @@ pub fn get_oceans<F: Float>(oldh: impl Fn(usize) -> F + Sync) -> BitBox {
 
 /// Finds the horizon map for sunlight for the given chunks.
 pub fn get_horizon_map<F: Float + Sync, A: Send, H: Send>(
-    lgain: F,
+    map_size_lg: MapSizeLg,
     bounds: Aabr<i32>,
     minh: F,
     maxh: F,
@@ -416,7 +390,7 @@ pub fn get_horizon_map<F: Float + Sync, A: Send, H: Send>(
     };
     // let epsilon = F::epsilon() * if let x = F::from(map_size.x) { x } else {
     // return Err(()) };
-    let march = |dx: isize, maxdx: fn(isize) -> isize| {
+    let march = |dx: isize, maxdx: fn(isize, map_size_lg: MapSizeLg) -> isize| {
         let mut angles = Vec::with_capacity(map_len);
         let mut heights = Vec::with_capacity(map_len);
         (0..map_len)
@@ -425,14 +399,14 @@ pub fn get_horizon_map<F: Float + Sync, A: Send, H: Send>(
                 let wposi =
                     bounds.min + Vec2::new((posi % map_size.x) as i32, (posi / map_size.x) as i32);
                 if wposi.reduce_partial_min() < 0
-                    || wposi.x as usize >= WORLD_SIZE.x
+                    || wposi.x as usize >= usize::from(map_size_lg.chunks().x)
-                    || wposi.y as usize >= WORLD_SIZE.y
+                    || wposi.y as usize >= usize::from(map_size_lg.chunks().y)
                 {
                     return (to_angle(F::zero()), to_height(F::zero()));
                 }
-                let posi = vec2_as_uniform_idx(wposi);
+                let posi = vec2_as_uniform_idx(map_size_lg, wposi);
                 // March in the given direction.
-                let maxdx = maxdx(wposi.x as isize);
+                let maxdx = maxdx(wposi.x as isize, map_size_lg);
                 let mut slope = F::zero();
                 let h0 = h(posi);
                 let h = if h0 < minh {
@@ -458,14 +432,16 @@ pub fn get_horizon_map<F: Float + Sync, A: Send, H: Send>(
                     }
                     h0 - minh + max_height
                 };
-                let a = slope * lgain;
+                let a = slope;
                 (to_angle(a), to_height(h))
             })
             .unzip_into_vecs(&mut angles, &mut heights);
         (angles, heights)
     };
-    let west = march(-1, |x| x);
+    let west = march(-1, |x, _| x);
-    let east = march(1, |x| (WORLD_SIZE.x - x as usize) as isize);
+    let east = march(1, |x, map_size_lg| {
+        (usize::from(map_size_lg.chunks().x) - x as usize) as isize
+    });
     Ok([west, east])
 }