void image_colour_at(const ImageData *image, DBL xcoor, DBL ycoor, RGBFTColour& colour, int *index, bool premul)
{
*index = -1;
bool doProperTransmitAll = image->data->HasTransparency() &&
!image->AllTransmitLegacyMode &&
!image->data->IsIndexed() && ( (image->AllTransmit != 0.0) || (image->AllFilter != 0.0) );
// If either source or destination uses premultiplied alpha, make sure interpolation is done in premultiplied space
// as it makes the mathematical operations cleaner -- unless the alpha channel is modulated by "transmit all" or
// "filter all", in which case we prefer non-premultiplied space.
bool getPremul = doProperTransmitAll ? (premul && image->data->IsPremultiplied()) :
(premul || image->data->IsPremultiplied());
switch(image->Interpolation_Type)
{
case NO_INTERPOLATION:
no_interpolation(image, xcoor, ycoor, colour, index, getPremul);
break;
case BICUBIC:
InterpolateBicubic(image, xcoor, ycoor, colour, index, getPremul);
break;
default:
Interp(image, xcoor, ycoor, colour, index, getPremul);
break;
}
bool havePremul = getPremul;
if (!premul && havePremul)
{
// We fetched premultiplied data, but caller expects it non-premultiplied, so we need to fix that.
// As "transmit/filter all" handling also works best on non-premultiplied data, we're doing this now.
AlphaUnPremultiply(colour.rgb(), colour.FTtoA());
havePremul = false;
}
if (doProperTransmitAll)
{
COLC imageAlpha = colour.FTtoA();
if (imageAlpha != 0.0) // No need to apply "filter/transmit all" if the image is fully transparent here anyway.
{
colour.transm() += image->AllTransmit * imageAlpha;
colour.filter() += image->AllFilter * imageAlpha;
if (havePremul)
{
// We have premultiplied data here, and the caller expects it to stay that way (otherwise we'd already
// have converted to non-premultiplied by now), so we need to fix the premultiplication of the colour
// according to our modifications to the transparency components.
COLC alphaCorrection = colour.FTtoA() / imageAlpha;
AlphaPremultiply(colour.rgb(), alphaCorrection);
}
}
}
if (premul && !havePremul)
{
// We have non-premultiplied data here, but caller expects it premultiplied, so we need to fix that
// As "transmit/filter all" handling works best on non-premultiplied data, we haven't done this earlier.
AlphaPremultiply(colour.rgb(), colour.FTtoA());
}
}
