<li>MESA_EXTENSION_OVERRIDE - can be used to enable/disable extensions.
A value such as "GL_EXT_foo -GL_EXT_bar" will enable the GL_EXT_foo extension
and disable the GL_EXT_bar extension.
+<li>MESA_EXTENSION_MAX_YEAR - The GL_EXTENSIONS string returned by Mesa is sorted
+by extension year.
+If this variable is set to year X, only extensions defined on or before year
+X will be reported.
+This is to work-around a bug in some games where the extension string is
+copied into a fixed-size buffer without truncating.
+If the extension string is too long, the buffer overrun can cause the game
+to crash.
+This is a work-around for that.
+<li>MESA_GL_VERSION_OVERRIDE - changes the value returned by
+glGetString(GL_VERSION). Valid values are point-separated version numbers,
+such as "3.0". Mesa will not really implement all the features of the given
+version if it's higher than what's normally reported.
+<li>MESA_GLSL_VERSION_OVERRIDE - changes the value returned by
+glGetString(GL_SHADING_LANGUAGE_VERSION). Valid values are integers, such as
+"130". Mesa will not really implement all the features of the given language version
+if it's higher than what's normally reported. (for developers only)
<li>MESA_GLSL - <a href="shading.html#envvars">shading language compiler options</a>
</ul>
<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.
<li>SOFTPIPE_DUMP_GS - if set, the softpipe driver will print geometry shaders
to stderr
<li>SOFTPIPE_NO_RAST - if set, rasterization is no-op'd. For profiling purposes.
+<li>SOFTPIPE_USE_LLVM - if set, the softpipe driver will try to use LLVM JIT for
+ vertex shading procesing.
</ul>