<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