[pixel shader]
void main(out float4 ret : sv_target)
{
    ret = float4(0.1, 0.2, 0.3, 0.4);
    return;
    ret = float4(0.5, 0.6, 0.7, 0.8);
}

[test]
draw quad
todo probe all rgba (0.1, 0.2, 0.3, 0.4)