<li>MESA_GAMMA - gamma correction coefficients for red, green, blue channels
<li>MESA_XSYNC - enable synchronous X behavior (for debugging only)
<li>MESA_GLX_FORCE_CI - if set, force GLX to treat 8bpp visuals as CI visuals
-<li>MESA_GLX_FX - set to either "fullscreen" for full-screen rendering,
- "window" to render into a window, or "disable" to disable the Glide driver.
<li>MESA_GLX_FORCE_ALPHA - if set, forces RGB windows to have an alpha channel.
<li>MESA_GLX_DEPTH_BITS - specifies default number of bits for depth buffer.
<li>MESA_GLX_ALPHA_BITS - specifies default number of bits for alpha channel.