libGL.so serves two primary functions: GLX protocol generation for indirect
rendering and loading/management of hardware drivers for direct rendering.
When libGL.so initializes itself it uses the DRI to determine the
appropriate hardware driver for each screen on the local X display.
The hardware drivers are expected to be in the /usr/X11R6/lib/modules/dri/
directory. Drivers are named with the convention <name>_dri.so where
<name> is a driver such as "tdfx", "i810", "gamma", etc.
The LIBGL_DRIVERS_DIR environment variable may be used to specify a
different DRI modules directory, overriding /usr/X11R6/lib/modules/dri/.
This environment variable is ignored in setuid programs for security
When libGL.so is unable to locate appropriate hardware drivers it will
fall back to using indirect GLX rendering.
To aid in solving problems, libGL.so will print diagnostic messages to
stderr if the LIBGL_DEBUG environment variable is defined.