How do I obtain the address of the OpenGL framebuffer, so I can write directly to it?
OpenGL doesn’t provide a standard mechanism to let an application obtain the address of the framebuffer. If an implementation allows this, it’s through an extension. Typically, programmers who write graphics programs for a single standard graphics hardware format, such as the VGA standard under Microsoft Windows, will want the framebuffer’s address. The programmers need to understand that OpenGL is designed to run on a wide variety of graphics hardware, many of which don’t run on Microsoft Windows and therefore, don’t support any kind of standard framebuffer format. Because a programmer will likely be unfamiliar with this proprietary framebuffer layout, writing directly to it would produce unpredictable results. Furthermore, some OpenGL devices might not have a framebuffer that the CPU can address. You can read the contents of the color, depth, and stencil buffers with the glReadPixels() command. Likewise, glDrawPixels() and glCopyPixels() are available for sending images to and BLTing
