In the device section of your /etc/X11/xorg.conf file)
Option "DigitalVibrance" "64"
Option "DisableGLXRootClipping" "True"
Option "XvmcUsesTextures" "true"
Option "AllowGLXWithComposite" "true"
Option "Coolbits" "1"
Option "RenderAccel" "true"
Option "NoLogo" "true"
Option "AddARGBGLXVisuals" "True"
