   Stencil efficient?
  If I have large areas inside an OpenGL window I don't need to draw on because there will be large things overlayed, such other viewports, what's the most efficient way to do it?  I'm using a 3.0 forward context so I assume I can't use the fixed-function stencil buffer test (after I mask the areas drawing the overlays front to back while setting the stencil); what's the fastest way to do it in the shader then?   
  stenciling should be supported in 3.0 forward compatible.   ;  glColorMask(0,0,0,0);glDepthRange(1,1);draw area(s)glColorMask(1,1,1,1);glDepthRange(0,1);the areas wont be drawn over later on (provided depth etc is working)