I've been doing a bit more digging into this - trying to get my head around all the different components at work here. There is a good explanation on around the 6th post in this gentoo thread http://forums.gentoo.org/viewtopic-t...6-start-0.html .
That seems to suggest there was a problem in 2008 with AIGLX and Rage 128/Mach 64 cards. So I looked up the AIGLX documentation at Fedora http://fedoraproject.org/wiki/RenderingProject/aiglx and that still has the cards listed as not working.
So maybe the thing to do is add
to the xorg.conf as suggested at the bottom of the Fedora page?
Option "AIGLX" "off"
Option "Composite" "Disable"
We really need somebody with an r128 card to have a good experiment with all these options and report back.
I still can't work out how the framebuffers interact with all this. Do you need to manually set the framebuffer resolution to match the Xorg resolution? Also, the powerpcFAQ suggests in the tweak section that the UseFBDev option slows 3D performance for radeon cards https://wiki.ubuntu.com/PowerPCFAQ#A...eryl.2C_Compiz . This seems to contadict other advice regarding this option for the r128. Does this option impact the working of AIGLX???