#version 450
layout(location=0) out vec2 v_uv;
void main() {
    // Full-screen triangle from vertex index (no vertex buffer needed)
    // NDC/UV mapping matches the MSL version (SDL3 GPU normalizes Y-up on all backends)
    vec2 positions[3] = vec2[3](vec2(-1.0,-1.0), vec2(3.0,-1.0), vec2(-1.0,3.0));
    vec2 uvs[3]       = vec2[3](vec2(0.0, 1.0),  vec2(2.0, 1.0), vec2(0.0,-1.0));
    gl_Position = vec4(positions[gl_VertexIndex], 0.0, 1.0);
    v_uv = uvs[gl_VertexIndex];
}