[pixel shader]
float4 main(uniform float2 u) : sv_target
{
    return float4(abs(u), abs(u.x - 0.5), abs(-0.4));
}

[test]
uniform 0 float4 0.1 0.7 0.0 0.0
draw quad
probe all rgba (0.1, 0.7, 0.4, 0.4)
uniform 0 float4 -0.7 0.1 0.0 0.0
draw quad
probe all rgba (0.7, 0.1, 1.2, 0.4)