Simple collisions

src/collision/collider.rs

@@ -0,0 +1,21 @@
+use bevy::{math::FloatPow, prelude::*};
+
+/// Two-dimensional collider that detects collisions with another colliders
+///
+/// Composite colliders are not yet supported
+#[derive(Component)]
+#[require(Transform)]
+pub enum Collider {
+    Circle(f32),
+}
+
+impl Collider {
+    /// Function that checks collision between two colliders
+    ///
+    /// Algorithm is specific for each collider type
+    pub fn detect_collision(&self, self_center: Vec2, other: &Self, other_center: Vec2) -> bool {
+        match (self, other) {
+            (Collider::Circle(self_radius), Collider::Circle(other_radius)) => {(other_center-self_center).length_squared() <= (self_radius+other_radius).squared()}
+        }
+    }
+}

src/collision/event.rs

@@ -0,0 +1,8 @@
+use bevy::prelude::*;
+
+/// Event that triggers every frame collision occurs
+#[derive(EntityEvent)]
+pub struct Collided {
+    pub entity: Entity,
+    pub with: Entity,
+}

src/collision/mod.rs

@@ -1,9 +1,37 @@
 use bevy::prelude::*;
 
+use collider::Collider;
+use event::Collided;
+
+mod collider;
+mod event;
+
 pub struct CollisionPlugin;
 
 impl Plugin for CollisionPlugin {
     fn build(&self, app: &mut App) {
-        //todo!()
+        app.add_systems(Update, detect_collision_system);
+    }
+}
+
+fn detect_collision_system(mut commands: Commands, query: Query<(Entity, &Transform, &Collider)>) {
+    for (first_entity, first_transform, first_collider) in query {
+        for (second_entity, second_transform, second_collider) in query {
+            if first_entity == second_entity {
+                continue;
+            }
+
+            if first_collider.detect_collision(
+                first_transform.translation.truncate(), 
+                &second_collider, 
+                second_transform.translation.truncate()
+                ){
+                commands.trigger(
+                    Collided {
+                        entity:first_entity,
+                        with:second_entity
+                    });
+            }
+        }
     }
 }