3 files changed, 71 insertions, 33 deletions

diff --git a/src/sim/lib/mod.rs b/src/sim/lib/mod.rs
index a00d7e6..01373bc 100644
--- a/src/sim/lib/mod.rs
+++ b/src/sim/lib/mod.rs
@@ -1,2 +1,3 @@
 pub mod force;
 pub mod marching_squares;
+pub mod ray;
diff --git a/src/sim/lib/ray.rs b/src/sim/lib/ray.rs
new file mode 100644
index 0000000..52d5ba9
--- /dev/null
+++ b/src/sim/lib/ray.rs
@@ -0,0 +1,63 @@
+use glam::{IVec2, Vec2};
+
+// Amanatides and Woo's fast Voxel Traversal
+pub struct AwDda {
+    next: IVec2,
+    step_sign: IVec2,
+    step_delta: Vec2,
+    t_max: Vec2,
+}
+
+impl AwDda {
+    pub fn new(from: Vec2, to: Vec2) -> Self {
+        let first = from.round().as_ivec2();
+        // direction we step for each component on each iteration
+        let from_to_delta = to - from;
+        let step_sign = from_to_delta.signum().as_ivec2();
+
+        let step_delta = 1.0 / from_to_delta.abs();
+
+        let frac = Vec2::new(
+            if step_sign.x > 0 {
+                (first.x as f32 + 0.5) - from.x
+            } else {
+                from.x - (first.x as f32 - 0.5)
+            },
+            if step_sign.y > 0 {
+                (first.y as f32 + 0.5) - from.y
+            } else {
+                from.y - (first.y as f32 - 0.5)
+            },
+        );
+
+        let t_max = frac * step_delta;
+
+        AwDda {
+            next: first,
+            step_sign,
+            step_delta,
+            t_max,
+        }
+    }
+}
+
+impl Iterator for AwDda {
+    type Item = IVec2;
+    fn next(&mut self) -> Option<Self::Item> {
+        if self.t_max.min_element() >= 1.0 {
+            return None;
+        }
+
+        let cur = self.next;
+
+        if self.t_max.x < self.t_max.y {
+            self.next.x += self.step_sign.x;
+            self.t_max.x += self.step_delta.x;
+        } else {
+            self.next.y += self.step_sign.y;
+            self.t_max.y += self.step_delta.y;
+        }
+
+        Some(cur)
+    }
+}
diff --git a/src/sim/particle_sim/mod.rs b/src/sim/particle_sim/mod.rs
index 08febfb..4378d25 100644
--- a/src/sim/particle_sim/mod.rs
+++ b/src/sim/particle_sim/mod.rs
@@ -8,6 +8,7 @@ use crate::{
             materials::{MaterialForm, MaterialId},
         },
         cell_sim::world::World,
+        lib::ray::AwDda,
         particle_sim::particle::Particle,
     },
 };
@@ -35,46 +36,20 @@ impl ParticleManager {
             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 mut dda = AwDda::new(p.position, p.position + p.velocity * delta_time);
 
-                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(prev) = dda.next() {
                 if let Some(cell) = world.get_cell_from_game_position(prev.x, prev.y)
                     && [MaterialForm::Solid, MaterialForm::Powder]
                         .contains(&cell.material.def().form)
                 {
-                    // already occupied, die
+                    // the particle is already inside a collider, we should just kill it
                     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)
+
+                for cell in dda.map(|p| world.get_cell_from_game_position(p.x, p.y)) {
+                    if let Some(cell) = cell
                         && [MaterialForm::Solid, MaterialForm::Powder]
                             .contains(&cell.material.def().form)
                     {
@@ -88,7 +63,6 @@ impl ParticleManager {
                         self.particles.swap_remove(i);
                         continue 'outer;
                     }
-                    prev = cur;
                 }
             }