attempt to not be twash

src/cuwusions.rs

@@ -0,0 +1,76 @@
+// assume collision resolution takes place before velocity resolution
+
+pub fn rects_collision_resolution_pos(
+    pos: (f64, f64),
+    vel: (f64, f64),
+    rect: (f64, f64),
+    other_pos: (f64, f64),
+    other_rect: (f64, f64),
+) -> (f64, f64) {
+    'top_left: {
+        let Some((intersection, dist)) =
+            closest_point_rect_intersection(pos, vel, other_pos, other_rect)
+        else {
+            let (x, y) = pos;
+            break 'top_left (x + vel.0, y + vel.1);
+        };
+
+        intersection
+    }
+}
+
+fn point_distance(a: (f64, f64), b: (f64, f64)) -> f64 {
+    ((a.0 - b.0).abs().powi(2) + (a.1 - b.1).abs().powi(2)).sqrt()
+}
+
+fn horizontal_line_intersect(p0: (f64, f64), vel: (f64, f64), line_y: f64) -> Option<(f64, f64)> {
+    if vel.1 == 0.0 {
+        // exclusively going left or right, ergo there's no collision with a horizontal line
+        return None;
+    } else if vel.0 == 0.0 {
+        // no change in x, ergo the intersect must be at p0_x
+        return Some((p0.0, line_y));
+    }
+    // y = ax + b
+    let a = vel.1 / vel.0;
+    let b = p0.1 - p0.0 * a;
+
+    let x = (line_y - b) / a;
+    Some((x, line_y))
+}
+
+fn vertical_line_intersect(p0: (f64, f64), vel: (f64, f64), line_x: f64) -> Option<(f64, f64)> {
+    if vel.0 == 0.0 {
+        // exclusively going up or down, ergo there's no collision with a vertical line
+        return None;
+    } else if vel.1 == 0.0 {
+        // no change in y, ergo the intersect must be at p0_y
+        return Some((line_x, p0.1));
+    }
+    //
+    // y = ax + b
+    let a = vel.1 / vel.0;
+    let b = p0.1 - p0.0 * a;
+
+    let y = a * line_x + b;
+    Some((line_x, y))
+}
+
+fn closest_point_rect_intersection(
+    p0: (f64, f64),
+    vel: (f64, f64),
+    pos: (f64, f64),
+    rect: (f64, f64),
+) -> Option<((f64, f64), f64)> {
+    [
+        horizontal_line_intersect(p0, vel, pos.1),
+        horizontal_line_intersect(p0, vel, pos.1 + rect.1),
+        vertical_line_intersect(p0, vel, pos.0 + rect.0),
+        vertical_line_intersect(p0, vel, pos.0),
+    ]
+    .into_iter()
+    .flatten()
+    .map(|point| (point, point_distance(p0, point)))
+    .filter(|(_, dist)| *dist <= point_distance((0.0, 0.0), vel))
+    .min_by(|(_, dist_a), (_, dist_b)| dist_a.total_cmp(dist_b))
+}

src/main.rs

@@ -1,5 +1,6 @@
 #![allow(dead_code)]
 
+mod cuwusions;
 mod engine;
 
 use engine::{Component, System};
@@ -9,7 +10,7 @@ struct Sprite {
     sprite: engine::Sprite,
 }
 
-#[derive(Component, Default, Clone)]
+#[derive(Component, Default, Clone, Debug)]
 struct RigidBody {
     pos: (f64, f64),
     vel: (f64, f64),
@@ -22,8 +23,8 @@ impl System for VelocitySystem {
     fn on_update(&self, ctx: &mut engine::Context, delta: f64) -> Result<(), engine::Error> {
         for id in query!(ctx, RigidBody) {
             let body = ctx.entity_component::<RigidBody>(id);
-            body.pos.0 += body.vel.0 * delta;
-            body.pos.1 += body.vel.1 * delta;
+            // body.pos.0 += body.vel.0 * delta;
+            // body.pos.1 += body.vel.1 * delta;
         }
         Ok(())
     }
@@ -154,51 +155,16 @@ impl System for CollisionSystem {
                     continue;
                 }
                 let other_body = ctx.entity_component::<RigidBody>(other_id).clone();
-                if rects_collide(body.rect, body.pos, other_body.rect, other_body.pos) {
-                    let last_pos = (
-                        body.pos.0 - body.vel.0 * delta,
-                        body.pos.1 - body.vel.1 * delta,
-                    );
-                    if rects_collide(body.rect, last_pos, other_body.rect, other_body.pos) {
-                        panic!()
-                    }
-                    let closest_surface = [
-                        (last_pos.0, last_pos.1),
-                        (last_pos.0, last_pos.1 + body.rect.1),
-                        (last_pos.0 + body.rect.0, last_pos.1),
-                        (last_pos.0 + body.rect.0, last_pos.1 + body.rect.1),
-                    ]
-                    .into_iter()
-                    .filter_map(|p0| {
-                        point_rect_closest_surface(p0, body.vel, other_body.pos, other_body.rect)
-                    })
-                    .min_by(|(dist_a, _), (dist_b, _)| dist_a.total_cmp(dist_b))
-                    .map(|(_, surface)| surface)
-                    .ok_or("we already checked if collision happens")?;
+                let new_pos = cuwusions::rects_collision_resolution_pos(
+                    body.pos,
+                    (body.vel.0 * delta, body.vel.1 * delta),
+                    body.rect,
+                    other_body.pos,
+                    other_body.rect,
+                );
 
-                    let collider = ctx.entity_component::<Collider>(id);
-                    collider.colliding_surface = Some(closest_surface.clone());
-                    let body = ctx.entity_component::<RigidBody>(id);
-                    println!("closest: {closest_surface:?} | vel: {:?}", body.vel);
-                    match closest_surface {
-                        Surface::Top => {
-                            body.vel.1 = 0.0;
-                            body.pos.1 = other_body.pos.1 - body.rect.1;
-                        }
-                        Surface::Bottom => {
-                            body.vel.1 = 0.0;
-                            body.pos.1 = other_body.pos.1 + other_body.rect.1;
-                        }
-                        Surface::Left => {
-                            body.vel.0 = 0.0;
-                            body.pos.0 = other_body.pos.0 - body.rect.0;
-                        }
-                        Surface::Right => {
-                            body.vel.0 = 0.0;
-                            body.pos.0 = other_body.pos.0 + other_body.rect.0;
-                        }
-                    }
-                }
+                let body = ctx.entity_component::<RigidBody>(id);
+                body.pos = new_pos;
             }
         }
         Ok(())