Hi,
Here is the latest version of my OpenGL scaling backend for SDL. The
purpose if this backed is to scale SDL 2D games using OpenGL. Nice,
isn’t it ? 
To use it, patch your SDL source tree, compile, install and then set the
environment variable SDL_VIDEODRIVER :
export SDL_VIDEODRIVER=glscale
It scales the picture by a factor 2 by default, but you can set your own
window size using the two env variables SDL_VIDEODRIVER_GLSCALE_X and
SDL_VIDEODRIVER_GLSCALE_Y.
This latest version avoids pixel copy/conversion most of the time, so
it’s faster than the previous one (most games are playable even on my
radeon 7000 card with the free dri drivers
The patch is there :
http://icps.u-strasbg.fr/~marchesin/sdl/sdl_glscale.patch
Stephane