@vertex
fn vs_main(@builtin(vertex_index) vertex_index: u32) -> @builtin(position) vec4<f32> {
    let pos = vec2<f32>(
        f32(vertex_index == 0u) * 4.0 - 1.0,
        f32(vertex_index == 1u) * 4.0 - 1.0
    );
    return vec4<f32>(pos, 0.0, 1.0);
}

@fragment
fn fs_main() -> @location(0) vec4<f32> {
    return vec4<f32>(1.0, 0.0, 0.0, 1.0);
}