uniform half a, b, c;
uniform half4 d, e;

half4 main(float2) {
    // Ensure that constant-evaluation is safe in the presence of very large values.
    half4 result = refract(6e26, 2, 2).xxxx;

    result.x = refract(a, b, c);
    result = refract(d, e, c);

    result.xy   = refract(half2(1,0),     half2(0,1),     0.5);
    result.xyz  = refract(half3(1,0,0),   half3(0,0,1),   0.5);
    result.xyzw = refract(half4(1,0,0,0), half4(0,0,0,1), 0.5);
    return result;
}