Environment Variables
Mesa supports the following environment variables:
MESA_NO_ASM - if set, disables all assembly language optimizations
MESA_NO_MMX - if set, disables Intel MMX optimizations
MESA_NO_3DNOW - if set, disables AMD 3DNow! optimizations
MESA_NO_SSE - if set, disables Intel SSE optimizations
MESA_DEBUG - if set, error messages are printed to stderr.
If the value of MESA_DEBUG is "FP" floating point arithmetic errors will
generate exceptions.
MESA_NO_DITHER - if set, disables dithering, overriding glEnable(GL_DITHER)
The following environment variables are only applicable to the Xlib/X11
software driver.
See the 
README.X11README.X11  file for details.
MESA_RGB_VISUAL - specifies the X visual and depth for RGB mode
MESA_CI_VISUAL - specifies the X visual and depth for CI mode
MESA_BACK_BUFFER - specifies how to implement the back color buffer,
    either "pixmap" or "ximage"
MESA_GAMMA - gamma correction coefficients for red, green, blue channels
MESA_XSYNC - enable synchronous X behavior (for debugging only)
MESA_GLX_FORCE_CI - if set, force GLX to treat 8bpp visuals as CI visuals
MESA_GLX_FX - set to either "fullscreen" for full-screen rendering,
  "window" to render into a window, or "disable" to disable the Glide driver.
MESA_GLX_FORCE_ALPHA - if set, forces RGB windows to have an alpha channel.
MESA_GLX_DEPTH_BITS - specifies default number of bits for depth buffer.
