Constant USER_COMP_VERTEX 

const USER_COMP_VERTEX: &str = r#"
struct VertexOutput {
    @builtin(position) position: vec4<f32>,
    @location(0) uv: vec2<f32>,
}

@vertex
fn vs_main(@builtin(vertex_index) idx: u32) -> VertexOutput {
    let x = f32(idx & 1u) * 4.0 - 1.0;
    let y = f32((idx >> 1u) & 1u) * 4.0 - 1.0;
    var out: VertexOutput;
    out.position = vec4<f32>(x, y, 0.0, 1.0);
    out.uv = vec2<f32>((x + 1.0) * 0.5, 1.0 - (y + 1.0) * 0.5);
    return out;
}
"#;