feat(physics): add voltex_physics crate with Collider and ContactPoint

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Cargo.toml

@@ -15,6 +15,7 @@ members = [
     "examples/multi_light_demo",
     "examples/shadow_demo",
     "examples/ibl_demo",
+    "crates/voltex_physics",
 ]
 
 [workspace.dependencies]
@@ -23,6 +24,7 @@ voltex_platform = { path = "crates/voltex_platform" }
 voltex_renderer = { path = "crates/voltex_renderer" }
 voltex_ecs = { path = "crates/voltex_ecs" }
 voltex_asset = { path = "crates/voltex_asset" }
+voltex_physics = { path = "crates/voltex_physics" }
 wgpu = "28.0"
 winit = "0.30"
 bytemuck = { version = "1", features = ["derive"] }

crates/voltex_physics/Cargo.toml

@@ -0,0 +1,8 @@
+[package]
+name = "voltex_physics"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+voltex_math.workspace = true
+voltex_ecs.workspace = true

crates/voltex_physics/src/collider.rs

@@ -0,0 +1,42 @@
+use voltex_math::{Vec3, AABB};
+
+#[derive(Debug, Clone, Copy)]
+pub enum Collider {
+    Sphere { radius: f32 },
+    Box { half_extents: Vec3 },
+}
+
+impl Collider {
+    pub fn aabb(&self, position: Vec3) -> AABB {
+        match self {
+            Collider::Sphere { radius } => {
+                let r = Vec3::new(*radius, *radius, *radius);
+                AABB::new(position - r, position + r)
+            }
+            Collider::Box { half_extents } => {
+                AABB::new(position - *half_extents, position + *half_extents)
+            }
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_sphere_aabb() {
+        let c = Collider::Sphere { radius: 2.0 };
+        let aabb = c.aabb(Vec3::new(1.0, 0.0, 0.0));
+        assert_eq!(aabb.min, Vec3::new(-1.0, -2.0, -2.0));
+        assert_eq!(aabb.max, Vec3::new(3.0, 2.0, 2.0));
+    }
+
+    #[test]
+    fn test_box_aabb() {
+        let c = Collider::Box { half_extents: Vec3::new(1.0, 2.0, 3.0) };
+        let aabb = c.aabb(Vec3::ZERO);
+        assert_eq!(aabb.min, Vec3::new(-1.0, -2.0, -3.0));
+        assert_eq!(aabb.max, Vec3::new(1.0, 2.0, 3.0));
+    }
+}

crates/voltex_physics/src/contact.rs

@@ -0,0 +1,12 @@
+use voltex_ecs::Entity;
+use voltex_math::Vec3;
+
+#[derive(Debug, Clone, Copy)]
+pub struct ContactPoint {
+    pub entity_a: Entity,
+    pub entity_b: Entity,
+    pub normal: Vec3,
+    pub depth: f32,
+    pub point_on_a: Vec3,
+    pub point_on_b: Vec3,
+}

crates/voltex_physics/src/lib.rs

@@ -0,0 +1,5 @@
+pub mod collider;
+pub mod contact;
+
+pub use collider::Collider;
+pub use contact::ContactPoint;