glReadBuffer - select	a color	buffer source for pixels

glReadBuffer
	glReadBuffer(mode) -> None

void glReadBuffer( GLenum mode )

mode	Specifies a color buffer.  Accepted values are
      GL_FRONT_LEFT, GL_FRONT_RIGHT, GL_BACK_LEFT,
      GL_BACK_RIGHT, GL_FRONT, GL_BACK, GL_LEFT, GL_RIGHT,
      and GL_AUXi, where i is	between	0 and GL_AUX_BUFFERS
      -1.

glReadBuffer specifies a color buffer	as the source for
subsequent glReadPixels, glCopyTexImage1D, glCopyTexImage2D,
glCopyTexSubImage1D, glCopyTexSubImage2D, and	glCopyPixels
commands. mode accepts one of	twelve or more predefined
values.  (GL_AUX0 through GL_AUX3 are	always defined.)  In a
fully	configured system, GL_FRONT, GL_LEFT, and
GL_FRONT_LEFT	all name the front left	buffer,	GL_FRONT_RIGHT
and GL_RIGHT name the	front right buffer, and	GL_BACK_LEFT
and GL_BACK name the back left buffer.

Nonstereo double-buffered configurations have	only a front
left and a back left buffer.	Single-buffered	configurations
have a front left and	a front	right buffer if	stereo,	and
only a front left buffer if nonstereo.  It is	an error to
specify a nonexistent	buffer to glReadBuffer.

mode is initially GL_FRONT in	single-buffered
configurations, and GL_BACK in double-buffered
configurations.

GL_INVALID_ENUM is generated if mode is not one of the
twelve (or more) accepted values.

GL_INVALID_OPERATION is generated if mode specifies a	buffer
that does not	exist.

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

glGet	with argument GL_READ_BUFFER

glCopyPixels,	glCopyTexImage1D, glCopyTexImage2D,
glCopyTexSubImage1D, glCopyTexSubImage2D, glDrawBuffer,
glReadPixels