If the displacement map has some alpha values (not 0xFF),
then the blending should take this alpha into account. This
part is fine.
BUT, since Evas relies on premultiplied colors... we have a
problem: R (dx) and G (dy) have already been scaled down.
Actually we would need to load the map in non premultiplied RGBA,
otherwise we'll lose precision on dx,dy as soon as A != 0xFF.
Well... I guess this will be a limitation of this filter, for now
at least. Most displacement maps shouldn't even have any alpha
anyways.
Jean-Philippe Andre