[Xorg] Pixmap 24/32 on dual videocard system

Keith Packard keithp at keithp.com
Mon Jul 5 17:29:19 PDT 2004

> Thomas Winischhofer wrote:

> If the latter, I would think that the pixmap depth should not matter at 
> all; the screens are entirely independent. With Xinerama, however, the 
> screens must be in sync wrt color depth, framebuffer depth and some 
> other criteria.

Alas, this is one place where the X server has some cross-screen 
dependencies.  X provides only one list of Z image formats for the entire 
X server, as such two screens which expose different formats for the same 
depth cannot be mixed.

This is a bit confusing to me though; the X server can "hide" the fact 
that a screen is 24bpp and instead offer 32bpp Z-format images; this works 
around numerous bugs in applications which can't deal with the odd 24bpp 
format.  At first blush, I would have guessed that with the server doing 
this there wouldn't be any trouble with screens using different internal 
formats as long as the exposed image format was the same.  That can 
probably be fixed if it is indeed a problem.


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