Re: [Linux-fbdev-devel] Alpha blending

[Geert U. <ge...@li...>]

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.

Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- ge...@li...

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
							    -- Linus Torvalds