Comment 34 for bug 146859

This is most noticeable when you're trying to use Compiz and a dual-head screen, where the desktop size exceeds 2048 pixels in at least one direction. The desktop window exceeds the Mesa texture limit and fails to draw.

Keith Packard floated a patch to increase the Mesa texture size limit to 4096x4096 on the xorg mailing list in April: http://lists.freedesktop.org/archives/xorg/2008-April/034707.html

With that patch applied I can use Compiz with dual-head.

The bug is also reported in Ubuntu as https://bugs.launchpad.net/ubuntu/+source/mesa/+bug/146859