[Mesa-dev] Mesa + glxPixmaps problems

Ian Molton ian.molton at collabora.co.uk
Fri Aug 27 02:24:52 PDT 2010

On 27/08/10 08:53, Michel Dänzer wrote:
> Note that it's XGet*Window*Attributes. This call seems totally
> inappropriate for pixmaps and it might be pure luck if it ever does
> anything other than fail in that case.

Indeed - but there it is...

It does in fact work on any X drawable - but not on glxPixmaps which 
appear not to count as X drawables

>> >  Sadly, however, it appears that there are many more similar looking bugs
>> >  in Mesa. Has anyone actually used Mesa to render to glxPixmaps? are
>> >  there patches available to make this stuff work?
> The Mesa demos rendering to GLXPixmaps and gnubg have been working for
> me at least basically.

I have a simple testcase which highlights the above problem. I can send 
it to anyone who wants it.

The problem, I expect, is much worse though. glxPixmap support was added 
later to Mesa and I think has had little 'hard' use. as a result, only a 
few code paths have got tested.

My program is redirecting calls from multiple applications that would 
normally have rendered to a window onto glxpixmaps. As a result, there 
is a LOT of GL context switching going on. I am starting to see a lot of 
BadDrawable errors cropping up and I suspect its no co-incidence.

If the code is modified to use offscreen *windows* instead of 
glxPixmaps, it works much better.


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