veloren/common/src/sys/phys.rs

use crate::{
    comp::{Collider, Gravity, Mass, Mounting, Ori, PhysicsState, Pos, Scale, Sticky, Vel},
    event::{EventBus, ServerEvent},
    state::DeltaTime,
    sync::Uid,
    terrain::{Block, BlockKind, TerrainGrid},
    vol::ReadVol,
};
use specs::{Entities, Join, Read, ReadExpect, ReadStorage, System, WriteStorage};
use vek::*;

pub const GRAVITY: f32 = 9.81 * 5.0;
const BOUYANCY: f32 = 0.0;
// Friction values used for linear damping. They are unitless quantities. The
// value of these quantities must be between zero and one. They represent the
// amount an object will slow down within 1/60th of a second. Eg. if the frction
// is 0.01, and the speed is 1.0, then after 1/60th of a second the speed will
// be 0.99. after 1 second the speed will be 0.54, which is 0.99 ^ 60.
const FRIC_GROUND: f32 = 0.15;
const FRIC_AIR: f32 = 0.0125;
const FRIC_FLUID: f32 = 0.2;

// Integrates forces, calculates the new velocity based off of the old velocity
// dt = delta time
// lv = linear velocity
// damp = linear damping
// Friction is a type of damping.
fn integrate_forces(dt: f32, mut lv: Vec3<f32>, grav: f32, damp: f32) -> Vec3<f32> {
    // this is not linear damping, because it is proportional to the original
    // velocity this "linear" damping in in fact, quite exponential. and thus
    // must be interpolated accordingly
    let linear_damp = (1.0 - damp.min(1.0)).powf(dt * 60.0);

    lv.z = (lv.z - grav * dt).max(-80.0);
    lv * linear_damp
}

/// This system applies forces and calculates new positions and velocities.
pub struct Sys;
impl<'a> System<'a> for Sys {
    type SystemData = (
        Entities<'a>,
        ReadStorage<'a, Uid>,
        ReadExpect<'a, TerrainGrid>,
        Read<'a, DeltaTime>,
        Read<'a, EventBus<ServerEvent>>,
        ReadStorage<'a, Scale>,
        ReadStorage<'a, Sticky>,
        ReadStorage<'a, Mass>,
        ReadStorage<'a, Collider>,
        ReadStorage<'a, Gravity>,
        WriteStorage<'a, PhysicsState>,
        WriteStorage<'a, Pos>,
        WriteStorage<'a, Vel>,
        WriteStorage<'a, Ori>,
        ReadStorage<'a, Mounting>,
    );

    fn run(
        &mut self,
        (
            entities,
            uids,
            terrain,
            dt,
            event_bus,
            scales,
            stickies,
            masses,
            colliders,
            gravities,
            mut physics_states,
            mut positions,
            mut velocities,
            mut orientations,
            mountings,
        ): Self::SystemData,
    ) {
        let mut event_emitter = event_bus.emitter();

        // Apply movement inputs
        for (entity, scale, sticky, collider, mut pos, mut vel, _ori, _) in (
            &entities,
            scales.maybe(),
            stickies.maybe(),
            &colliders,
            &mut positions,
            &mut velocities,
            &mut orientations,
            !&mountings,
        )
            .join()
        {
            let mut physics_state = physics_states.get(entity).cloned().unwrap_or_default();

            if sticky.is_some()
                && (physics_state.on_ground
                    || physics_state.on_ceiling
                    || physics_state.on_wall.is_some())
            {
                vel.0 = Vec3::zero();
                continue;
            }

            let scale = scale.map(|s| s.0).unwrap_or(1.0);

            let old_vel = *vel;
            // Integrate forces
            // Friction is assumed to be a constant dependent on location
            let friction = FRIC_AIR
                .max(if physics_state.on_ground {
                    FRIC_GROUND
                } else {
                    0.0
                })
                .max(if physics_state.in_fluid {
                    FRIC_FLUID
                } else {
                    0.0
                });
            let downward_force = if physics_state.in_fluid {
                (1.0 - BOUYANCY) * GRAVITY
            } else {
                GRAVITY
            } * gravities.get(entity).map(|g| g.0).unwrap_or_default();
            vel.0 = integrate_forces(dt.0, vel.0, downward_force, friction);

            // Don't move if we're not in a loaded chunk
            let mut pos_delta = if terrain
                .get_key(terrain.pos_key(pos.0.map(|e| e.floor() as i32)))
                .is_some()
            {
                // this is an approximation that allows most framerates to
                // behave in a similar manner.
                let dt_lerp = 0.2;
                (vel.0 * dt_lerp + old_vel.0 * (1.0 - dt_lerp)) * dt.0
            } else {
                Vec3::zero()
            };

            match collider {
                Collider::Box {
                    radius,
                    z_min,
                    z_max,
                } => {
                    // Scale collider
                    let radius = *radius * scale;
                    let z_min = *z_min * scale;
                    let z_max = *z_max * scale;

                    // Probe distances
                    let hdist = radius.ceil() as i32;
                    // Neighbouring blocks iterator
                    let near_iter = (-hdist..hdist + 1)
                        .map(move |i| {
                            (-hdist..hdist + 1).map(move |j| {
                                (1 - BlockKind::MAX_HEIGHT.ceil() as i32 + z_min.floor() as i32
                                    ..z_max.ceil() as i32 + 1)
                                    .map(move |k| (i, j, k))
                            })
                        })
                        .flatten()
                        .flatten();

                    // Function for determining whether the player at a specific position collides
                    // with the ground
                    let collision_with = |pos: Vec3<f32>,
                                          hit: &dyn Fn(&Block) -> bool,
                                          near_iter| {
                        for (i, j, k) in near_iter {
                            let block_pos = pos.map(|e| e.floor() as i32) + Vec3::new(i, j, k);

                            if let Some(block) = terrain.get(block_pos).ok().copied().filter(hit) {
                                let player_aabb = Aabb {
                                    min: pos + Vec3::new(-radius, -radius, z_min),
                                    max: pos + Vec3::new(radius, radius, z_max),
                                };
                                let block_aabb = Aabb {
                                    min: block_pos.map(|e| e as f32),
                                    max: block_pos.map(|e| e as f32)
                                        + Vec3::new(1.0, 1.0, block.get_height()),
                                };

                                if player_aabb.collides_with_aabb(block_aabb) {
                                    return true;
                                }
                            }
                        }
                        false
                    };

                    let was_on_ground = physics_state.on_ground;
                    physics_state.on_ground = false;

                    let mut on_ground = false;
                    let mut on_ceiling = false;
                    let mut attempts = 0; // Don't loop infinitely here

                    // Don't jump too far at once
                    let increments = (pos_delta.map(|e| e.abs()).reduce_partial_max() / 0.3)
                        .ceil()
                        .max(1.0);
                    let old_pos = pos.0;
                    for _ in 0..increments as usize {
                        pos.0 += pos_delta / increments;

                        const MAX_ATTEMPTS: usize = 16;

                        // While the player is colliding with the terrain...
                        while collision_with(pos.0, &|block| block.is_solid(), near_iter.clone())
                            && attempts < MAX_ATTEMPTS
                        {
                            // Calculate the player's AABB
                            let player_aabb = Aabb {
                                min: pos.0 + Vec3::new(-radius, -radius, z_min),
                                max: pos.0 + Vec3::new(radius, radius, z_max),
                            };

                            // Determine the block that we are colliding with most (based on minimum
                            // collision axis)
                            let (_block_pos, block_aabb, block_height) = near_iter
                                .clone()
                                // Calculate the block's position in world space
                                .map(|(i, j, k)| pos.0.map(|e| e.floor() as i32) + Vec3::new(i, j, k))
                                // Make sure the block is actually solid
                                .filter_map(|block_pos| {
                                    if let Some(block) = terrain
                                        .get(block_pos)
                                        .ok()
                                        .filter(|block| block.is_solid())
                                    {
                                        // Calculate block AABB
                                        Some((
                                            block_pos,
                                            Aabb {
                                                min: block_pos.map(|e| e as f32),
                                                max: block_pos.map(|e| e as f32) + Vec3::new(1.0, 1.0, block.get_height()),
                                            },
                                            block.get_height(),
                                        ))
                                    } else {
                                        None
                                    }
                                })
                                // Determine whether the block's AABB collides with the player's AABB
                                .filter(|(_, block_aabb, _)| block_aabb.collides_with_aabb(player_aabb))
                                // Find the maximum of the minimum collision axes (this bit is weird, trust me that it works)
                                .min_by_key(|(_, block_aabb, _)| {
                                    ((block_aabb.center() - player_aabb.center() - Vec3::unit_z() * 0.5)
                                        .map(|e| e.abs())
                                        .sum()
                                        * 1_000_000.0) as i32
                                })
                                .expect("Collision detected, but no colliding blocks found!");

                            // Find the intrusion vector of the collision
                            let dir = player_aabb.collision_vector_with_aabb(block_aabb);

                            // Determine an appropriate resolution vector (i.e: the minimum distance
                            // needed to push out of the block)
                            let max_axis = dir.map(|e| e.abs()).reduce_partial_min();
                            let resolve_dir = -dir.map(|e| {
                                if e.abs().to_bits() == max_axis.to_bits() {
                                    e
                                } else {
                                    0.0
                                }
                            });

                            // When the resolution direction is pointing upwards, we must be on the
                            // ground
                            if resolve_dir.z > 0.0 && vel.0.z <= 0.0 {
                                on_ground = true;

                                if !was_on_ground {
                                    event_emitter
                                        .emit(ServerEvent::LandOnGround { entity, vel: vel.0 });
                                }
                            } else if resolve_dir.z < 0.0 && vel.0.z >= 0.0 {
                                on_ceiling = true;
                            }

                            // When the resolution direction is non-vertical, we must be colliding
                            // with a wall If the space above is free...
                            if !collision_with(Vec3::new(pos.0.x, pos.0.y, (pos.0.z + 0.1).ceil()), &|block| block.is_solid(), near_iter.clone())
                                // ...and we're being pushed out horizontally...
                                && resolve_dir.z == 0.0
                                // ...and the vertical resolution direction is sufficiently great...
                                && -dir.z > 0.1
                                // ...and we're falling/standing OR there is a block *directly* beneath our current origin (note: not hitbox)...
                                && (vel.0.z <= 0.0 || terrain
                                    .get((pos.0 - Vec3::unit_z() * 0.1).map(|e| e.floor() as i32))
                                    .map(|block| block.is_solid())
                                    .unwrap_or(false))
                                // ...and there is a collision with a block beneath our current hitbox...
                                && collision_with(
                                    pos.0 + resolve_dir - Vec3::unit_z() * 1.05,
                                    &|block| block.is_solid(),
                                    near_iter.clone(),
                                )
                            {
                                // ...block-hop!
                                pos.0.z = (pos.0.z + 0.1).floor() + block_height;
                                vel.0.z = 0.0;
                                on_ground = true;
                                break;
                            } else {
                                // Correct the velocity
                                vel.0 = vel.0.map2(resolve_dir, |e, d| {
                                    if d * e.signum() < 0.0 { 0.0 } else { e }
                                });
                                pos_delta *= resolve_dir.map(|e| if e != 0.0 { 0.0 } else { 1.0 });
                            }

                            // Resolve the collision normally
                            pos.0 += resolve_dir;

                            attempts += 1;
                        }

                        if attempts == MAX_ATTEMPTS {
                            pos.0 = old_pos;
                            break;
                        }
                    }

                    if on_ceiling {
                        physics_state.on_ceiling = true;
                    }

                    if on_ground {
                        physics_state.on_ground = true;
                    // If the space below us is free, then "snap" to the ground
                    } else if collision_with(
                        pos.0 - Vec3::unit_z() * 1.05,
                        &|block| block.is_solid(),
                        near_iter.clone(),
                    ) && vel.0.z < 0.0
                        && vel.0.z > -1.5
                        && was_on_ground
                        && !collision_with(
                            pos.0 - Vec3::unit_z() * 0.05,
                            &|block| {
                                block.is_solid()
                                    && block.get_height() >= (pos.0.z - 0.05).rem_euclid(1.0)
                            },
                            near_iter.clone(),
                        )
                    {
                        let snap_height = terrain
                            .get(
                                Vec3::new(pos.0.x, pos.0.y, pos.0.z - 0.05)
                                    .map(|e| e.floor() as i32),
                            )
                            .ok()
                            .filter(|block| block.is_solid())
                            .map(|block| block.get_height())
                            .unwrap_or(0.0);
                        pos.0.z = (pos.0.z - 0.05).floor() + snap_height;
                        physics_state.on_ground = true;
                    }

                    let dirs = [
                        Vec3::unit_x(),
                        Vec3::unit_y(),
                        -Vec3::unit_x(),
                        -Vec3::unit_y(),
                    ];

                    if let (wall_dir, true) =
                        dirs.iter().fold((Vec3::zero(), false), |(a, hit), dir| {
                            if collision_with(
                                pos.0 + *dir * 0.01,
                                &|block| block.is_solid(),
                                near_iter.clone(),
                            ) {
                                (a + dir, true)
                            } else {
                                (a, hit)
                            }
                        })
                    {
                        physics_state.on_wall = Some(wall_dir);
                    } else {
                        physics_state.on_wall = None;
                    }

                    // Figure out if we're in water
                    physics_state.in_fluid =
                        collision_with(pos.0, &|block| block.is_fluid(), near_iter.clone());
                },
                Collider::Point => {
                    let (dist, block) = terrain.ray(pos.0, pos.0 + pos_delta).ignore_error().cast();

                    pos.0 += pos_delta.try_normalized().unwrap_or(Vec3::zero()) * dist;

                    // Can't fair since we do ignore_error above
                    if block.unwrap().is_some() {
                        let block_center = pos.0.map(|e| e.floor()) + 0.5;
                        let block_rpos = (pos.0 - block_center)
                            .try_normalized()
                            .unwrap_or(Vec3::zero());

                        // See whether we're on the top/bottom of a block, or the side
                        if block_rpos.z.abs()
                            > block_rpos.xy().map(|e| e.abs()).reduce_partial_max()
                        {
                            if block_rpos.z > 0.0 {
                                physics_state.on_ground = true;
                            } else {
                                physics_state.on_ceiling = true;
                            }
                            vel.0.z = 0.0;
                        } else {
                            physics_state.on_wall =
                                Some(if block_rpos.x.abs() > block_rpos.y.abs() {
                                    vel.0.x = 0.0;
                                    Vec3::unit_x() * -block_rpos.x.signum()
                                } else {
                                    vel.0.y = 0.0;
                                    Vec3::unit_y() * -block_rpos.y.signum()
                                });
                        }
                    }
                },
            }

            let _ = physics_states.insert(entity, physics_state);
        }

        // Apply pushback
        for (pos, scale, mass, vel, _, _, _, physics) in (
            &positions,
            scales.maybe(),
            masses.maybe(),
            &mut velocities,
            &colliders,
            !&mountings,
            stickies.maybe(),
            &mut physics_states,
        )
            .join()
            .filter(|(_, _, _, _, _, _, sticky, physics)| {
                sticky.is_none() || (physics.on_wall.is_none() && !physics.on_ground)
            })
        {
            physics.touch_entity = None;

            let scale = scale.map(|s| s.0).unwrap_or(1.0);
            let mass = mass.map(|m| m.0).unwrap_or(scale);

            for (other, pos_other, scale_other, mass_other, _, _) in (
                &uids,
                &positions,
                scales.maybe(),
                masses.maybe(),
                &colliders,
                !&mountings,
            )
                .join()
            {
                let scale_other = scale_other.map(|s| s.0).unwrap_or(1.0);

                let mass_other = mass_other.map(|m| m.0).unwrap_or(scale_other);
                if mass_other == 0.0 {
                    continue;
                }

                let diff = Vec2::<f32>::from(pos.0 - pos_other.0);

                let collision_dist = 0.95 * (scale + scale_other);

                if diff.magnitude_squared() > 0.0
                    && diff.magnitude_squared() < collision_dist.powf(2.0)
                    && pos.0.z + 1.6 * scale > pos_other.0.z
                    && pos.0.z < pos_other.0.z + 1.6 * scale_other
                {
                    let force = (collision_dist - diff.magnitude()) * 2.0 * mass_other
                        / (mass + mass_other);
                    vel.0 += Vec3::from(diff.normalized()) * force;
                    physics.touch_entity = Some(*other);
                }
            }
        }
    }
}