RGB Shift

kernel vec4 RGBEffect(sampler image, vec2 offset)
{
    vec2 coord = destCoord();
    float r = sample(image, samplerTransform(image, coord - offset)).r;
    vec2 ga = sample(image, samplerTransform(image, coord)).ga;
    float b = sample(image, samplerTransform(image, coord + offset)).b;
    return vec4(r, ga[0], b, ga[1]);
}

function myROIFunction(samplerIndex, dstRect, offset)
{
    var roiRect = new Vec(dstRect);
    var extra = new Vec(Math.abs(offset.x), Math.abs(offset.y));
    if (dstRect.x > extra.x)
        roiRect.x -= extra.x;
    if (dstRect.y > extra.y)
        roiRect.y -= extra.y;
    roiRect.z += extra.x;
    roiRect.w += extra.y;
    return roiRect;
}

RGBEffect.ROIHandler = myROIFunction;

function __image main(__image image, __number amount, __number angle)
{
    s = amount / 2;
    offset = new Vec(s * Math.cos(angle), s * Math.sin(angle));
    return RGBEffect.apply(image.definition, offset, image, offset);
}