Why X server exposes multiple visuals with same depth/colormap ?

[Yann Droneaud]

Le jeudi 31 décembre 2009 à 08:17 +0100, patrick ficheux a écrit :
> Hello,
> 
> It seems that X server exposes several visuals with same caracteristics 
> (depth / color).
> 
> For example, on my Debian, xdpyinfo displays 4 identical Visuals: 
> TrueColor/24 planes (see output below) and only one visual TrueColor/32 
> planes.
> With window/cygwin, XWin (the X server) exposes 15 identical visuals 
> TrueColor / 24 planes
> 
> Is there a reason to expose several identical visuals ?
> If yes, could you give me an example ?
> 

I don't have a definitive answer for this, but from my humble
experience, those visuals have different render / OpenGL support:
there's an X visual for each specific OpenGL framebuffer configuration.

Try xdpyinfo -ext RENDER and you can see picture formats for each
visual.

Try glxinfo and you will get OpenGL framebuffer attributes.

Regards.

-- 
Yann Droneaud