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shaders/video-cube/shader.slang

@@ -17,6 +17,8 @@ bool intersectCube(float3 rayOrigin, float3 rayDirection, float halfExtent, out
 	float3 boxMin = float3(-halfExtent, -halfExtent, -halfExtent);
 	float3 boxMax = float3(halfExtent, halfExtent, halfExtent);
 
+	// Slab intersection: find the ray interval that overlaps all three box
+	// axes, then keep the nearest positive hit.
 	float3 invDir = 1.0 / rayDirection;
 	float3 t0 = (boxMin - rayOrigin) * invDir;
 	float3 t1 = (boxMax - rayOrigin) * invDir;
@@ -43,6 +45,8 @@ float2 cubeFaceUv(float3 hitPoint, float halfExtent, float zoom)
 	float2 uv = float2(0.5, 0.5);
 	float safeZoom = max(zoom, 0.001);
 
+	// The dominant coordinate tells which face was hit; the other two axes
+	// become that face's local UVs.
 	if (face.x >= face.y && face.x >= face.z)
 	{
 		uv = hitPoint.x > 0.0
@@ -79,6 +83,8 @@ float4 shadeVideo(ShaderContext context)
 	float yaw = spin;
 	float pitch = spin * 0.61 + 0.35;
 
+	// Rotate the camera ray into cube-local space instead of rotating the cube
+	// geometry, which keeps the intersection math axis-aligned.
 	float3 localOrigin = rotateY(rotateX(rayOrigin, -pitch), -yaw);
 	float3 localDirection = rotateY(rotateX(rayDirection, -pitch), -yaw);
 
@@ -96,6 +102,8 @@ float4 shadeVideo(ShaderContext context)
 
 	float3 normal;
 	float3 face = abs(localHit);
+	// Reconstruct the face normal from the hit point so lighting follows the
+	// same face choice used for UV lookup.
 	if (face.x >= face.y && face.x >= face.z)
 		normal = float3(sign(localHit.x), 0.0, 0.0);
 	else if (face.y >= face.x && face.y >= face.z)