Re: [Linux-fbdev-devel] Alpha blending

[Sven L. <lu...@dp...>]

On Tue, Apr 03, 2001 at 10:24:25AM +0200, Geert Uytterhoeven wrote:
> On Tue, 3 Apr 2001, Sven LUTHER wrote:
> > On Tue, Apr 03, 2001 at 10:05:01AM +0200, Geert Uytterhoeven wrote:
> > > On Tue, 3 Apr 2001, Sven LUTHER wrote:
> > > > What about anti-aliasing ?
> > > 
> > > Anti-aliasing has nothing to do with transparency on non-transparent text
> > > consoles.
> > 
> > Err, it was my understanding that you use the alpha channel to do
> > anti-aliasing, even if in the end you don't support transparency, but then i
> > may be wrong, (mmm, maybe i am).
> 
> Yes, for an object that still has to be blended with a background image.
> 
> But since a text console has a solid background, you can calculate the
> resulting RGB values directly:
> 
>     [rgb]_res = [rgb] * a + [rgb]_bg * (1-a)
> 
> This is indeed equivalent with alpha blending a pixel with transparency a to a
> solid background pixel.

Ok, i see that, but what about hardware supported anti-aliasing/alpha
blending. will providing the value to the chip and let it do stuff not be
faster (especially as some more advanced chip don't know about 24bpp, treating
it as 32bpp and ignore the 8bit of the alpha channel ?

Friendly,

Sven Luther