#version 450

// Shared fullscreen-triangle vertex shader for the SDL3 GPU backend.
// Emits vUV in Shadertoy convention: (0,0) bottom-left, (1,1) top-right.
// Y flipped in NDC because Vulkan/Metal point Y down by default.

layout(location = 0) out vec2 vUV;

void main() {
    const vec2 positions[3] = vec2[3](
        vec2(-1.0, -1.0),
        vec2( 3.0, -1.0),
        vec2(-1.0,  3.0)
    );
    vec2 pos = positions[gl_VertexIndex];
    vUV = pos * 0.5 + 0.5;
    gl_Position = vec4(pos.x, -pos.y, 0.0, 1.0);
}