OpenGL Insights

328 IV Performance

Discards have another use with framebuffer objects, i.e., render-to-texture. When

rendering 3D geometry to a texture such as an environment map, a depth buffer is

needed during the rendering but does not need to be preserved a fterwards. The

application can inform the driver of this by calling glDiscardFramebufferEXT

after doing the rendering but before unbinding the framebuffer object, and a tile-

based GPU may use this as a hint that depth values need not be copied back from

the tile buffer to main memory. Although not yet available on desktop OpenGL,

EXT

discard framebuffer is likely to be useful for multisampled framebuffer

object ...