Re: Alpha compositing in gnustep-back

[Adam Fedor]

Thanks. I added this.

Jeff Teunissen wrote:
> XGBitmap's _pixmap_combine_alpha() and _bitmap_combine_alpha() functions
> don't quite work right. Specifically, the colors are all wrong.
>
> For some reason, the colors seem to be scaled by the value of alpha
> (127/127/127/127 becomes 63/63/63/127 somewhere). In my spare time, I've
> been working on them to make them generate correct output.

Well, colors are supposed to be scaled by alpha. Thats how alpha works. 
But perhaps when you combine two colors together they need to be unscaled.

> As part of trying to understand the functions, I partially rewrote the
> fast paths for them. The code is shorter, but it may be slower since the
> math is done in floating point.

It's about 10% slower in my tests. But that may not be accurate.

--
Adam Fedor, Digital Optics Corp.      | I'm glad I hate spinach, because
http://www.doc.com                    | if I didn't, I'd eat it, and you
                                      | know how I hate the stuff.