+<h2 id="envvars">Environment Variables</h2>
+
+<p>
+The <b>MESA_GLSL</b> environment variable can be set to a comma-separated
+list of keywords to control some aspects of the GLSL compiler and shader
+execution. These are generally used for debugging.
+</p>
+<ul>
+<li><b>dump</b> - print GLSL shader code to stdout at link time
+<li><b>log</b> - log all GLSL shaders to files.
+ The filenames will be "shader_X.vert" or "shader_X.frag" where X
+ the shader ID.
+<li><b>nopt</b> - disable compiler optimizations
+<li><b>opt</b> - force compiler optimizations
+<li><b>uniform</b> - print message to stdout when glUniform is called
+<li><b>nopvert</b> - force vertex shaders to be a simple shader that just transforms
+ the vertex position with ftransform() and passes through the color and
+ texcoord[0] attributes.
+<li><b>nopfrag</b> - force fragment shader to be a simple shader that passes
+ through the color attribute.
+<li><b>useprog</b> - log glUseProgram calls to stderr
+</ul>
+<p>
+Example: export MESA_GLSL=dump,nopt
+</p>
+
+<p>
+Shaders can be dumped and replaced on runtime for debugging purposes. Mesa
+needs to be configured with '--with-sha1' to enable this functionality. This
+feature is not currently supported by SCons build.
+
+This is controlled via following environment variables:
+<ul>
+<li><b>MESA_SHADER_DUMP_PATH</b> - path where shader sources are dumped
+<li><b>MESA_SHADER_READ_PATH</b> - path where replacement shaders are read
+</ul>
+Note, path set must exist before running for dumping or replacing to work.
+When both are set, these paths should be different so the dumped shaders do
+not clobber the replacement shaders.
+</p>
+
+<h2 id="support">GLSL Version</h2>