glFinish - block until all GL	execution is complete

glFinish
	glFinish() -> None

void glFinish( void )

glFinish does	not return until the effects of	all previously
called GL commands are complete.  Such effects include all
changes to GL	state, all changes to connection state,	and
all changes to the frame buffer contents.

glFinish requires a round trip to the	server.

GL_INVALID_OPERATION is generated if glFinish	is executed
between the execution	of glBegin and the corresponding
execution of glEnd.

glFlush