Initial claude dump

engine/src/shaders/sprite.vert

@@ -0,0 +1,31 @@
+#version 450
+
+// Per instance; layout must match SpriteRenderSystem::Instance.
+layout (location = 0) in mat4 model;  // Maps the unit quad to world space.
+layout (location = 4) in vec4 color;
+layout (location = 5) in vec4 uvRect;
+
+layout (location = 0) out vec4 fragColor;
+layout (location = 1) out vec2 fragUv;
+
+layout (push_constant) uniform Push {
+  mat4 viewProjection;
+} push;
+
+// Two triangles covering the unit quad (0,0)-(1,1).
+const vec2 CORNERS[6] = vec2[](
+  vec2(0.0, 0.0), vec2(1.0, 0.0), vec2(1.0, 1.0),
+  vec2(1.0, 1.0), vec2(0.0, 1.0), vec2(0.0, 0.0)
+);
+
+void main() {
+  vec2 corner = CORNERS[gl_VertexIndex];
+
+  gl_Position = push.viewProjection * model * vec4(corner, 0.0, 1.0);
+  // Draw order comes from the CPU-side sort, so flatten depth; sprites should
+  // never be clipped by the camera's near/far planes.
+  gl_Position.z = 0.0;
+
+  fragColor = color;
+  fragUv = mix(uvRect.xy, uvRect.zw, corner);
+}