This may or may not be specific to the Quake 3 engine.

Ubuntu Linux (Breezy), Mesa 6.4.2 (compiled from source, though the 6.3 in the
package repository exhibits this behavior), Intel 855GM.

In both Quake 3 (commercial release 1.32) and the open-source ioquake3
(icculus.org/quake3), nothing will render until glScissor is called with
arguments specifying an area different from the viewport. This happens whether
ioquake3 uses SDL or GLX for window management. (The commercial engine uses GLX.)

The following engine hack is presented to illustrate the problem:

   // set the window clipping
   qglViewport(backEnd.viewParms.viewportX, backEnd.viewParms.viewportY,
       backEnd.viewParms.viewportWidth, backEnd.viewParms.viewportHeight);

   if (!i915hack) // static qboolean
   {
       i915hack = qtrue;
       qglScissor(backEnd.viewParms.viewportX, backEnd.viewParms.viewportY,
           backEnd.viewParms.viewportWidth, backEnd.viewParms.viewportHeight - 1);
   }
   else
   {
       qglScissor(backEnd.viewParms.viewportX, backEnd.viewParms.viewportY,
           backEnd.viewParms.viewportWidth, backEnd.viewParms.viewportHeight);
   }

i915hack is a static variable - that is, doing this hack call to glScissor only
ONCE fixes the problem until the application is unloaded.

Steps to duplicate:

1) Install Quake 3
2) Run Quake 3, load a map, drop the console, type "cg_draw2d 0"
3) Reload Quake 3 from the command line with +devmap <some map>

Nothing should draw on step 3. Setting cg_draw2d to 0 keeps Quake 3 from
rendering a small scene containing the player's head model, which is scissored
around the model.

The status of this on other Quake 3 engine games is unknown.