glClear sets the bitplane area of the window to values previously selected
by glClearColor , glClearIndex , glClearDepth ,
glClearStencil , and glClearAccum .
Multiple color buffers can be cleared simultaneously by selecting
more than one buffer at a time using glDrawBuffer .
The pixel ownership test,
the scissor test,
dithering, and the buffer writemasks affect the operation of glClear .
The scissor box bounds the cleared region.
Alpha function,
blend function,
logical operation,
stenciling,
texture mapping,
and depth-buffering are ignored by glClear .
glClear takes a single argument that is the bitwise OR of several
values indicating which buffer is to be cleared.
The values are as follows:
The value to which each buffer is cleared depends on the setting of the
clear value for that buffer.