Pat's Log
Tue, 15 Aug 2006

High Resolution AIGLX, Low Video Memory
After playing with XGL (and loving it) for a while on my home desktop (ATI Radeon 9800), I thought that it needed a relatively powerful card to work. However, at LinuxSymposium, I noticed a beat-up old ThinkPad R-series laptop running it. I was told that the requirements to run AIGLX are much less demanding.

Intrigued, I tried running AIGLX on my laptop, a Dell D600 (600m) with a 32 megabyte ATI Radeon 9000 M9; by no means powerful 3D hardware. At a resolution of 1024x768, it worked very, very well, doing the same compiz effects I could do under XGL on a much more powerful card with proprietary drivers. However, running at my LCD's native resolution of 1400x1050, the desktop didn't draw completely: it clipped at 1024x1024.

At first, I figured the old hardware had a texture limitation of 1024x1024. Thankfully, since this was LinuxSymposium, I ran right to the man who knows my hardware best, Adam Jackson. He told me that the 1K-texture limit was artificial, and has to do with memory resources. Using glxinfo -l, he showed me that GL_MAX_RECTANGLE_TEXTURE_SIZE_NV is the texture size that would fit in the video texture memory, so that the card could hold a certain number of textures, also listed in glxinfo. This value could be overridden by telling the card to support large texture sizes in a mysterious /etc/drirc XML file:

<driconf> <device screen="0" driver="r200"> <application name="all"> <option name="allow_large_textures" value="2" /> </application> </device> </driconf>

This allowed textures to easily draw the full 1400x1050 I needed. However, because of the sheer size of the textures and the small amount of video memory I have, the number of textures that could be stored on the chip went down significantly. Having a few large windows open (Desktop, Firefox, Thunderbird) resulted in an extremely slow desktop experience, as the textures had to be swapped in and out of the video memory for every frame drawn.

So, while it didn't work out for me, perhaps this information will be useful for people who have a little more video memory than I.

[] | posted @ 22:06 | link

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