DEFINE_UI_PARAMS(useAlpha, Dissolve Alpha Channel, DCTLUI_CHECK_BOX, 1)

__DEVICE__ float4 transition(int p_Width, int p_Height, int p_X, int p_Y, __TEXTURE__ p_FromTexR, __TEXTURE__ p_FromTexG, __TEXTURE__ p_FromTexB, __TEXTURE__ p_FromTexA, __TEXTURE__ p_ToTexR, __TEXTURE__ p_ToTexG, __TEXTURE__ p_ToTexB, __TEXTURE__ p_ToTexA)
{
    const float alphaWeightFrom = _tex2D(p_FromTexA, p_X, p_Y) * (1.0f - TRANSITION_PROGRESS);
    const float alphaWeightTo   = _tex2D(p_ToTexA, p_X, p_Y) * TRANSITION_PROGRESS;

    // Dissolve RGB channels
    const float r = alphaWeightFrom * _tex2D(p_FromTexR, p_X, p_Y) + alphaWeightTo * _tex2D(p_ToTexR, p_X, p_Y);
    const float g = alphaWeightFrom * _tex2D(p_FromTexG, p_X, p_Y) + alphaWeightTo * _tex2D(p_ToTexG, p_X, p_Y);
    const float b = alphaWeightFrom * _tex2D(p_FromTexB, p_X, p_Y) + alphaWeightTo * _tex2D(p_ToTexB, p_X, p_Y);

    // Dissolve alpha channel
    const float a = useAlpha ? (alphaWeightFrom + alphaWeightTo) : 1.0f;
    return make_float4(r, g, b, a);
}