+
+<h2>Gallium environment variables</h2>
+
+<ul>
+<li>GALLIUM_HUD - draws various information on the screen, like framerate,
+ cpu load, driver statistics, performance counters, etc.
+ Set GALLIUM_HUD=help and run e.g. glxgears for more info.
+<li>GALLIUM_HUD_PERIOD - sets the hud update rate in seconds (float). Use zero
+ to update every frame. The default period is 1/2 second.
+<li>GALLIUM_HUD_VISIBLE - control default visibility, defaults to true.
+<li>GALLIUM_HUD_TOGGLE_SIGNAL - toggle visibility via user specified signal.
+ Especially useful to toggle hud at specific points of application and
+ disable for unencumbered viewing the rest of the time. For example, set
+ GALLIUM_HUD_VISIBLE to false and GALLIUM_HUD_TOGGLE_SIGNAL to 10 (SIGUSR1).
+ Use kill -10 <pid> to toggle the hud as desired.
+<li>GALLIUM_HUD_DUMP_DIR - specifies a directory for writing the displayed
+ hud values into files.
+<li>GALLIUM_DRIVER - useful in combination with LIBGL_ALWAYS_SOFTWARE=1 for
+ choosing one of the software renderers "softpipe", "llvmpipe" or "swr".
+<li>GALLIUM_LOG_FILE - specifies a file for logging all errors, warnings, etc.
+ rather than stderr.
+<li>GALLIUM_PRINT_OPTIONS - if non-zero, print all the Gallium environment
+ variables which are used, and their current values.
+<li>GALLIUM_DUMP_CPU - if non-zero, print information about the CPU on start-up
+<li>TGSI_PRINT_SANITY - if set, do extra sanity checking on TGSI shaders and
+ print any errors to stderr.
+<LI>DRAW_FSE - ???
+<LI>DRAW_NO_FSE - ???
+<li>DRAW_USE_LLVM - if set to zero, the draw module will not use LLVM to execute
+ shaders, vertex fetch, etc.
+<li>ST_DEBUG - controls debug output from the Mesa/Gallium state tracker.
+Setting to "tgsi", for example, will print all the TGSI shaders.
+See src/mesa/state_tracker/st_debug.c for other options.
+</ul>
+
+<h3>Clover state tracker environment variables</h3>
+
+<ul>
+<li>CLOVER_EXTRA_BUILD_OPTIONS - allows specifying additional compiler and linker
+ options. Specified options are appended after the options set by the OpenCL
+ program in clBuildProgram.
+<li>CLOVER_EXTRA_COMPILE_OPTIONS - allows specifying additional compiler
+ options. Specified options are appended after the options set by the OpenCL
+ program in clCompileProgram.
+<li>CLOVER_EXTRA_LINK_OPTIONS - allows specifying additional linker
+ options. Specified options are appended after the options set by the OpenCL
+ program in clLinkProgram.
+</ul>
+
+
+<h3>Softpipe driver environment variables</h3>
+<ul>
+<li>SOFTPIPE_DUMP_FS - if set, the softpipe driver will print fragment shaders
+ to stderr
+<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 processing.
+</ul>
+
+
+<h3>LLVMpipe driver environment variables</h3>
+<ul>
+<li>LP_NO_RAST - if set LLVMpipe will no-op rasterization
+<li>LP_DEBUG - a comma-separated list of debug options is accepted. See the
+ source code for details.
+<li>LP_PERF - a comma-separated list of options to selectively no-op various
+ parts of the driver. See the source code for details.
+<li>LP_NUM_THREADS - an integer indicating how many threads to use for rendering.
+ Zero turns off threading completely. The default value is the number of CPU
+ cores present.
+</ul>
+
+<h3>VMware SVGA driver environment variables</h3>
+<ul>
+<li>SVGA_FORCE_SWTNL - force use of software vertex transformation
+<li>SVGA_NO_SWTNL - don't allow software vertex transformation fallbacks
+(will often result in incorrect rendering).
+<li>SVGA_DEBUG - for dumping shaders, constant buffers, etc. See the code
+for details.
+<li>See the driver code for other, lesser-used variables.
+</ul>
+
+
+<h3>VA-API state tracker environment variables</h3>
+<ul>
+<li>VAAPI_MPEG4_ENABLED - enable MPEG4 for VA-API, disabled by default.
+</ul>
+
+
+<h3>VC4 driver environment variables</h3>
+<ul>
+<li>VC4_DEBUG - a comma-separated list of named flags, which do various things:
+<ul>
+ <li>cl - dump command list during creation</li>
+ <li>qpu - dump generated QPU instructions</li>
+ <li>qir - dump QPU IR during program compile</li>
+ <li>nir - dump NIR during program compile</li>
+ <li>tgsi - dump TGSI during program compile</li>
+ <li>shaderdb - dump program compile information for shader-db analysis</li>
+ <li>perf - print during performance-related events</li>
+ <li>norast - skip actual hardware execution of commands</li>
+ <li>always_flush - flush after each draw call</li>
+ <li>always_sync - wait for finish after each flush</li>
+ <li>dump - write a GPU command stream trace file (VC4 simulator only)</li>
+</ul>
+</ul>
+
+
+<p>
+Other Gallium drivers have their own environment variables. These may change
+frequently so the source code should be consulted for details.
+</p>
+
+</div>
+</body>
+</html>