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Fix density computation.

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This commit is contained in:
Joshua Yanovski 2019-08-22 17:45:47 +02:00
parent aa4464d8f4
commit 5caed42e4f
1 changed files with 37 additions and 15 deletions
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52
world/src/sim/mod.rs
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@ -690,25 +690,38 @@ impl SimChunk {
let cliff = gen_ctx.cliff_nz.get((wposf.div(2048.0)).into_array()) as f32 + chaos * 0.2;
let tree_density =
(gen_ctx.tree_nz.get((wposf.div(1024.0)).into_array()) as f32)
// Logistic regression. Make sure x ∈ (0, 1).
let logit = |x: f32 | x.ln() - x.neg().ln_1p();
// 0.5 + 0.5 * tanh(ln(1 / (1 - 0.1) - 1) / (2 * (sqrt(3)/pi)))
let logistic_2_base = 3.0f32.sqrt().mul(f32::consts::FRAC_2_PI);
// Assumes μ = 0, σ = 1
let logistic_cdf = |x: f32| x.div(logistic_2_base).tanh().mul(0.5).add(0.5);
// Weighted logit sum.
let f = |humidity, density| logistic_cdf(logit(humidity) + 0.5 * logit(density));
// No trees in the ocean or with zero humidity (currently)
let tree_density = if alt <= CONFIG.sea_level + 5.0 { 0.0 } else {
let tree_density = (gen_ctx.tree_nz.get((wposf.div(1024.0)).into_array()) as f32)
.mul(1.5)
.add(1.0)
.mul(0.5)
.mul(1.2 - chaos * 0.95)
.add(0.05)
.max(0.0)
.min(1.0)
.min(1.0);
// Tree density should go (by a lot) with humidity.
if humidity <= 0.0 || tree_density <= 0.0 {
0.0
} else if humidity >= 1.0 || tree_density >= 1.0 {
1.0
} else {
logistic_cdf(logit(humidity) + 0.5 * logit(tree_density))
}
// rescale to (-0.9, 0.9)
.sub(0.5)
.mul(0.9)
// Tree density should go (by a lot) with humidity.
.powf(1.0 - humidity)
// No trees in the ocean (currently), no trees in true deserts.
.mul(if alt > CONFIG.sea_level + 5.0 && humidity > CONFIG.desert_hum {
1.0
} else {
0.0
})
.max(0.0);
.add(0.5)
};
Self {
chaos,
@ -736,10 +749,12 @@ impl SimChunk {
ForestKind::Palm
} else if humidity > CONFIG.forest_hum {
ForestKind::Palm
} else {
} else if humidity > CONFIG.desert_hum {
// Low but not desert humidity, so we should really have some other
// terrain...
ForestKind::Savannah
} else {
ForestKind::Savannah
}
} else if temp > CONFIG.tropical_temp {
if humidity > CONFIG.jungle_hum {
@ -747,9 +762,11 @@ impl SimChunk {
} else if humidity > CONFIG.forest_hum {
// NOTE: Probably the wrong kind of tree for this climate.
ForestKind::Oak
} else {
} else if humidity > CONFIG.desert_hum {
// Low but not desert... need something besides savannah.
ForestKind::Savannah
} else {
ForestKind::Savannah
}
} else {
if humidity > CONFIG.jungle_hum {
@ -761,10 +778,12 @@ impl SimChunk {
} else if humidity > CONFIG.forest_hum {
// Moderate climate, moderate humidity.
ForestKind::Oak
} else {
} else if humidity > CONFIG.desert_hum {
// With moderate temperature and low humidity, we should probably see
// something different from savannah, but oh well...
ForestKind::Savannah
} else {
ForestKind::Savannah
}
}
} else {
@ -772,7 +791,10 @@ impl SimChunk {
// should!) except that we make sure we only have snow pines when there is snow.
if temp <= CONFIG.snow_temp && humidity > CONFIG.forest_hum {
ForestKind::SnowPine
} else if humidity > CONFIG.desert_hum {
ForestKind::Pine
} else {
// Should really have something like tundra.
ForestKind::Pine
}
},