OpenGL Programming Guide

Chapter 10The Framebuffer

Buffers and Their Uses

Selecting Color Buffers for Writing

The results of a drawing operation can go into any of the color buffers: front, back, front-left, back-left, front-right, back-right, or any of the auxiliary buffers. You can choose an individual buffer to be the drawing target, or you can also set the target to be a combination of these buffers. In a double-buffered application, for example, you might want to draw a common background into both the back and front buffers; from then on, you want to draw only in the back buffer (and swap the buffers when you're finished drawing). In some cases, however, you might want to treat part of a particular double-buffered window as though it were single-buffered by drawing to both front and back buffers. You use the glDrawBuffer() command to select the buffers to be written. void glDrawBuffer(GLenum mode);

Selects the buffers enabled for writing or clearing. The value of mode can be one of the following:

GL_FRONT
GL_BACK
GL_RIGHT
GL_LEFT
GL_FRONT_RIGHT
GL_FRONT_LEFT
GL_BACK_RIGHT
GL_BACK_LEFT
GL_AUXi
GL_FRONT_AND_BACK
GL_NONE

Arguments that omit RIGHT or LEFT refer to both the left and right buffers; similarly, arguments that omit FRONT or BACK refer to both. The i in GL_AUXi is a digit identifying a particular auxiliary buffer.

You can enable drawing to nonexistent buffers as long as you enable drawing to at least one buffer that does exist. If none of the specified buffers exist, an error results.

OpenGL Programming Guide