Depth testing is done in the fragment shader so it shouldn't be done
in the a-buffer shader for the first pixel, or until the depth is updated.
Fixes flashlight and lightstorm effects in Alone in the Dark
90deg CC screen rotation option for some arcade games
Fix scissoring and clipping when screen scaling/stretching/rotating
Clear shader cache when screen rotation changes
Properly delete all gl programs and shaders when needed
implement screen scaling for per-pixel renderer
fix output FBO not being freed/recreated when GL context is reset
refactor DrawQuad on per-pixel renderer
scribam