feat(shaders): Add Möller-Trumbore ray-triangle intersection

Implements ray-triangle intersection algorithm for future mesh raytracing support.

Changes:
- Add ray_triangle.wgsl with TriangleHit struct and intersection function
- Register shader snippet in asset system (SHADER_RAY_TRIANGLE)
- Add shader composer registration for #include "ray_triangle" support

Returns:
- hit.uv: Barycentric coordinates (for texture mapping)
- hit.z: Parametric distance along ray
- hit.N: Triangle face normal
- hit.hit: Boolean indicating intersection

Task: Progress on SDF for mesh (related to Task #18)
Algorithm: Fast, Minimum Storage Ray-Triangle Intersection (Möller-Trumbore)
Size: ~30 lines WGSL, negligible binary impact

1 files changed, 30 insertions, 0 deletions

diff --git a/assets/final/shaders/ray_triangle.wgsl b/assets/final/shaders/ray_triangle.wgsl
new file mode 100644
index 0000000..13341c8
--- /dev/null
+++ b/assets/final/shaders/ray_triangle.wgsl
@@ -0,0 +1,30 @@
+// This file is part of the 64k demo project.
+// Möller-Trumbore ray-triangle intersection algorithm.
+// Reference: "Fast, Minimum Storage Ray-Triangle Intersection"
+
+struct TriangleHit {
+  uv: vec2<f32>,
+  z: f32,
+  N: vec3<f32>,
+  hit: bool,
+};
+
+fn ray_triangle_intersection(
+  orig: vec3<f32>,
+  dir: vec3<f32>,
+  p0: vec3<f32>,
+  p1: vec3<f32>,
+  p2: vec3<f32>
+) -> TriangleHit {
+  let d10 = p1 - p0;
+  let d20 = p2 - p0;
+  let N = cross(d10, d20);
+  let det = -dot(dir, N);
+  let invdet = 1.0 / det;
+  let d0 = orig - p0;
+  let nd = cross(d0, dir);
+  let uv = vec2<f32>(dot(d20, nd), -dot(d10, nd)) * invdet;
+  let z = dot(d0, N) * invdet;
+  let hit = det > 0.0 && z >= 0.0 && uv.x >= 0.0 && uv.y >= 0.0 && (uv.x + uv.y) < 1.0;
+  return TriangleHit(uv, z, N, hit);
+}