[vertex shader]
void main(out float tex : texcoord, inout float4 pos : sv_position)
{
    tex = pos.x;
}

[pixel shader]
float4 main(float tex : texcoord) : SV_TARGET
{
    if (tex > 0.0)
        return float4(0.1, 0.2, 0.3, 0.4);
    else
        return float4(0.9, 0.8, 0.7, 0.6);
}

[test]
draw quad
probe (  0, 0, 319, 480) rgba (0.9, 0.8, 0.7, 0.6)
probe (321, 0, 640, 480) rgba (0.1, 0.2, 0.3, 0.4)