osx man page for glreadbuffer

GLREADBUFFER(3G)														  GLREADBUFFER(3G)

NAME
       glReadBuffer - select a color buffer source for pixels

C SPECIFICATION
       void glReadBuffer( GLenum mode )

PARAMETERS
       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.

DESCRIPTION
       glReadBuffer specifies a color buffer as the source for subsequent glReadPixels, glCopyTexImage1D,  glCopyTexImage2D,  glCopyTexSubImage1D,
       glCopyTexSubImage2D,  glCopyTexSubImage3D,  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.

ERRORS
       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.

ASSOCIATED GETS
       glGet with argument GL_READ_BUFFER

SEE ALSO
       glCopyPixels, glCopyTexImage1D, glCopyTexImage2D, glCopyTexSubImage1D, glCopyTexSubImage2D, glCopyTexSubImage3D, glDrawBuffer, glReadPixels

																  GLREADBUFFER(3G)