On Tue, 14 Apr 2015 17:15:10 +0100 "Ben Avison" <bavi...@riscosopen.org> wrote:
> On Tue, 14 Apr 2015 09:36:38 +0100, > Pekka Paalanen <ppaala...@gmail.com> wrote: > > > On Mon, 13 Apr 2015 18:42:45 +0100 > > "Ben Avison" <bavi...@riscosopen.org> wrote: > > > >> On Mon, 13 Apr 2015 12:31:35 +0100, > >> Pekka Paalanen <ppaala...@gmail.com> wrote: > >> > None of the existing tests has a solid mask for CA tests. I'm not > >> > sure how much it makes sense. > >> > >> When you're in component alpha mode, mathematically the source and mask > >> images are interchangeable. So you could implement over_8888_n_8888_ca > >> by calling over_n_8888_8888_ca, and we already have a number of fast > >> paths for operations of the latter form. (I'm not aware that Pixman is > >> - yet - aware that it can make such substitutions, but I'm sure it > >> could be added.) > > > > Hmm, yes, interesting, at least in the cases where the operator indeed > > allows it... I don't know the operators by heart so I don't know if > > there are any that wouldn't work like that. An idea to remember. > > Having thought about it some more, and checked the source code (it's > clearer in pixman-combine-float.c because the maths isn't obfuscated by > the need to work in fixed-point) I'm going to retract the claim. Or at > least restrict its applicability. (This demonstrates the danger of there > not being anyone around to contradict me!) > > The problem is that although alpha is considered independently for each > colour component of the mask - so you just multiply the source red by the > mask red and so on, I'd neglected the alpha component in the source > image. Yes, because Pixman premultiplies the alpha into the RGB > components, it doesn't directly affect the RGB output of the combined > source+mask image, but there's a secondary output, a per-channel alpha, > which affects the Porter-Duff operation. For example, with an OVER > operation, the inverse of the per-channel alpha is multiplied into the > existing value from the destination buffer before you add-saturate the > combined source+mask into it. Heh, I had a feeling there might be something like that, but couldn't put a finger down where. :-) > > So, can I take it that you gave your Reviewed-by for the whole series? > > Yes. Thanks! So that said, I will land this series on Thursday if no-one complains. Thanks, pq _______________________________________________ Pixman mailing list Pixman@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/pixman
