To select the buffer into which color values are written, use glDrawBuffer. You use four different functions to mask the writing of bits to each of the logical frame buffers after all per-fragment operations have been performed:
The glAccum function controls the operation of the accumulation buffer. Finally, glClear sets every pixel in a specified subset of the buffers to the value specified with glClearColor, glClearIndex, glClearDepth, glClearStencil, or glClearAccum.