particles

1 files changed, 101 insertions, 0 deletions

diff --git a/src/sim/particle_sim/mod.rs b/src/sim/particle_sim/mod.rs
new file mode 100644
index 0000000..8bad61d
--- /dev/null
+++ b/src/sim/particle_sim/mod.rs
@@ -0,0 +1,101 @@
+use glam::{IVec2, Vec2};
+
+use crate::{
+    config::PIXELS_TO_METRES,
+    sim::{
+        cell::{cell::Cell, materials::MaterialId},
+        cell_sim::world::World,
+        particle_sim::particle::Particle,
+    },
+};
+
+pub mod particle;
+
+pub struct ParticleManager {
+    pub particles: Vec<Particle>,
+}
+
+const PARTICLE_GRAVITY: f32 = 9.81 * PIXELS_TO_METRES;
+
+impl ParticleManager {
+    pub fn particle_tick(&mut self, world: &mut World, delta_time: f32) {
+        let mut i = 0;
+        'outer: while i < self.particles.len() {
+            let p = &mut self.particles[i];
+
+            p.life -= delta_time;
+            if p.life <= 0.0 {
+                self.particles.swap_remove(i);
+                continue 'outer;
+            }
+
+            p.velocity.y += PARTICLE_GRAVITY * delta_time;
+            let dt_velocity = p.velocity * delta_time;
+
+            // Amanatides and Woo's fast Voxel Traversal
+            {
+                let mut cur = IVec2::new(p.position.x.round() as i32, p.position.y.round() as i32);
+                // direction we step for each component on each iteration
+                let step_sign =
+                    IVec2::new(dt_velocity.x.signum() as i32, dt_velocity.y.signum() as i32);
+                let delta = Vec2::new(1.0 / dt_velocity.x.abs(), 1.0 / dt_velocity.y.abs());
+
+                let frac = Vec2::new(
+                    if step_sign.x > 0 {
+                        (cur.x as f32 + 0.5) - p.position.x
+                    } else {
+                        p.position.x - (cur.x as f32 - 0.5)
+                    },
+                    if step_sign.y > 0 {
+                        (cur.y as f32 + 0.5) - p.position.y
+                    } else {
+                        p.position.y - (cur.y as f32 - 0.5)
+                    },
+                );
+                let mut t_max = frac * delta;
+
+                let mut prev = cur;
+                if let Some(cell) = world.get_cell_from_game_position(prev.x, prev.y)
+                    && cell.material != MaterialId::Void
+                {
+                    // already occupied, die
+                    self.particles.swap_remove(i);
+                    continue 'outer;
+                }
+                while t_max.min_element() <= 1.0 {
+                    if t_max.x < t_max.y {
+                        cur.x += step_sign.x;
+                        t_max.x += delta.x;
+                    } else {
+                        cur.y += step_sign.y;
+                        t_max.y += delta.y;
+                    }
+                    if let Some(cell) = world.get_cell_from_game_position(cur.x, cur.y)
+                        && cell.material != MaterialId::Void
+                    {
+                        // write ourselves to the board
+                        world.set_cell_from_game_position(
+                            prev.x,
+                            prev.y,
+                            Cell::from_material(p.material),
+                            false,
+                        );
+                        self.particles.swap_remove(i);
+                        continue 'outer;
+                    }
+                    prev = cur;
+                }
+            }
+
+            // no collision, just move
+            p.position = p.position + dt_velocity;
+            i += 1;
+        }
+    }
+
+    pub fn new() -> Self {
+        ParticleManager {
+            particles: Vec::new(),
+        }
+    }
+}