Re: [AD] 5.0 and 5.1 branches

[Peter Wang <novalazy@xxxxxxxxxx>]

On 2010-11-16, Elias Pschernig <elias.pschernig@xxxxxxxxxx> wrote:
> On Tue, 2010-11-16 at 13:08 +0100, Elias Pschernig wrote:
> > I think the flag for load_bitmap to premultiply alpha should still be
> > added. It's more a bugfix anyway, as ex_premulalpha shows - without it
> > it's hard to get rid of dark outlines around all sprites. I just have
> > to figure out how to fix the platform specific bitmap loaders. The
> > iphone one actually always premultiples right now according to Trent
> > (something which needs to be fixed). Not sure about OSX.
> 
> Hm, OSX has this:
> 
> CGContextRef context = CGBitmapContextCreate(pixels, w, h, 8, w * 4,
> colour_space, kCGImageAlphaPremultipliedLast);
> 
> I'm not sure what it means, but sounds like it also pre-multiplies?

 From googling around, yes, it seems CGBitmapContextCreate only supports
pre-multiplied alpha, and you have to make a post-pass to demultiply
(with loss in precision, I suppose).  I seem to remember a colleague
telling me about this, too.

Peter