From 35cfbf5ae470ef1b65a425b2f78d698dc9976ec9 Mon Sep 17 00:00:00 2001
From: Willow Sparks <willow.sparks@stfc.ac.uk>
Date: Tue, 27 Jan 2026 13:49:33 +0000
Subject: [PATCH] Add StaticCollider struct and Plane collider variant

- Add Collider::Plane variant for infinite plane colliders
- Add StaticCollider struct with collider, material fields
- Export StaticCollider from rust4d_physics

Phase 4 (Wave 1): Static Colliders foundation

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
---
 crates/rust4d_physics/src/body.rs   | 46 ++++++++++++++++++++++++++++-
 crates/rust4d_physics/src/lib.rs    |  2 +-
 crates/rust4d_physics/src/shapes.rs | 11 +++++++
 3 files changed, 57 insertions(+), 2 deletions(-)

diff --git a/crates/rust4d_physics/src/body.rs b/crates/rust4d_physics/src/body.rs
index f2f6f80..da0518c 100644
--- a/crates/rust4d_physics/src/body.rs
+++ b/crates/rust4d_physics/src/body.rs
@@ -1,7 +1,7 @@
 //! Rigid body types for 4D physics simulation
 
 use crate::material::PhysicsMaterial;
-use crate::shapes::Collider;
+use crate::shapes::{Collider, Plane4D};
 use rust4d_math::Vec4;
 use slotmap::new_key_type;
 
@@ -127,6 +127,50 @@ impl RigidBody4D {
     }
 }
 
+/// A collider that doesn't move (floors, walls, platforms)
+///
+/// Static colliders are checked for collision with all dynamic bodies
+/// but never move themselves.
+#[derive(Clone, Debug)]
+pub struct StaticCollider {
+    /// The collision shape
+    pub collider: Collider,
+    /// Physics material (friction and restitution)
+    pub material: PhysicsMaterial,
+}
+
+impl StaticCollider {
+    /// Create a new static collider with the given shape and material
+    pub fn new(collider: Collider, material: PhysicsMaterial) -> Self {
+        Self { collider, material }
+    }
+
+    /// Create a plane collider
+    pub fn plane(normal: Vec4, distance: f32, material: PhysicsMaterial) -> Self {
+        Self {
+            collider: Collider::Plane(Plane4D::new(normal, distance)),
+            material,
+        }
+    }
+
+    /// Create a horizontal floor plane at the given Y height
+    pub fn floor(y: f32, material: PhysicsMaterial) -> Self {
+        Self {
+            collider: Collider::Plane(Plane4D::floor(y)),
+            material,
+        }
+    }
+
+    /// Create an AABB static collider
+    pub fn aabb(center: Vec4, half_extents: Vec4, material: PhysicsMaterial) -> Self {
+        use crate::shapes::AABB4D;
+        Self {
+            collider: Collider::AABB(AABB4D::from_center_half_extents(center, half_extents)),
+            material,
+        }
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
diff --git a/crates/rust4d_physics/src/lib.rs b/crates/rust4d_physics/src/lib.rs
index f7e865e..5e93c65 100644
--- a/crates/rust4d_physics/src/lib.rs
+++ b/crates/rust4d_physics/src/lib.rs
@@ -14,7 +14,7 @@ pub mod shapes;
 pub mod world;
 
 // Re-export commonly used types
-pub use body::{BodyKey, RigidBody4D};
+pub use body::{BodyKey, RigidBody4D, StaticCollider};
 pub use collision::{aabb_vs_aabb, aabb_vs_plane, sphere_vs_aabb, sphere_vs_plane, Contact};
 pub use material::PhysicsMaterial;
 pub use player::{PlayerPhysics, DEFAULT_JUMP_VELOCITY, DEFAULT_PLAYER_RADIUS};
diff --git a/crates/rust4d_physics/src/shapes.rs b/crates/rust4d_physics/src/shapes.rs
index a56a4c8..9731c94 100644
--- a/crates/rust4d_physics/src/shapes.rs
+++ b/crates/rust4d_physics/src/shapes.rs
@@ -168,22 +168,33 @@ impl Plane4D {
 pub enum Collider {
     Sphere(Sphere4D),
     AABB(AABB4D),
+    Plane(Plane4D),
 }
 
 impl Collider {
     /// Get the center of the collider
+    ///
+    /// For planes, returns a point on the plane at the origin offset.
     pub fn center(&self) -> Vec4 {
         match self {
             Collider::Sphere(s) => s.center,
             Collider::AABB(b) => b.center(),
+            Collider::Plane(p) => p.normal * p.distance,
         }
     }
 
     /// Translate the collider by a delta
+    ///
+    /// For planes, this adjusts the distance from origin.
     pub fn translated(&self, delta: Vec4) -> Self {
         match self {
             Collider::Sphere(s) => Collider::Sphere(Sphere4D::new(s.center + delta, s.radius)),
             Collider::AABB(b) => Collider::AABB(b.translated(delta)),
+            Collider::Plane(p) => {
+                // Moving a plane by delta means the distance changes by normal · delta
+                let new_distance = p.distance + p.normal.dot(delta);
+                Collider::Plane(Plane4D::new(p.normal, new_distance))
+            }
         }
     }
 }
-- 
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