[Xorg] Pixmap 24/32 on dual videocard system

Thomas Winischhofer thomas at winischhofer.net
Mon Jul 5 17:45:51 PDT 2004

Keith Packard wrote:
>>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.

I think Nils' problem boils down to the fact that I, a while back, 
removed the "Convert24To32..." flags from fb init and put them back 
immediately after a user of a SiS6326 reported problems with an older 
application. Seems this short period was exactly when the X.org tree was 
forked from XFree86 and 6.7.0 was released.

> 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.

I am curiously awaiting his results with the current driver.

(However, the "nv" driver doesn't set these flags either. If the sis 
driver works with these flags set and both settings for the Pixmap "24" 
and "32", I'd say it's about time to fix the nv driver to do the same.)


Thomas Winischhofer
thomas AT winischhofer DOT net          http://www.winischhofer.net/
twini AT xfree86 DOT org

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