out vec2 uv;

void main() {
    // Calculate vertex position based on gl_VertexID
    vec2 positions[6] = vec2[6](
        vec2(-1.0,  1.0),  // Top-left
        vec2( 1.0,  1.0),  // Top-right
        vec2( 1.0, -1.0),  // Bottom-right
        vec2( 1.0, -1.0),  // Bottom-right (repeated)
        vec2(-1.0, -1.0),  // Bottom-left
        vec2(-1.0,  1.0)   // Top-left (repeated)
    );
    
    // Calculate UV coordinates based on gl_VertexID
    vec2 texCoords[6] = vec2[6](
        vec2(0.0, 1.0),  // Top-left
        vec2(1.0, 1.0),  // Top-right
        vec2(1.0, 0.0),  // Bottom-right
        vec2(1.0, 0.0),  // Bottom-right (repeated)
        vec2(0.0, 0.0),  // Bottom-left
        vec2(0.0, 1.0)   // Top-left (repeated)
    );

    gl_Position = vec4(positions[gl_VertexID], 0.0, 1.0);
    uv = texCoords[gl_VertexID];
}