Performing Selection and Feedback
Selection, feedback, and rendering are mutually exclusive modes of operation. Rendering is the normal, default mode during which fragments are produced by rasterization.
In selection and feedback modes, no fragments are produced; therefore, no framebuffer modification occurs. In selection mode, you can determine which primitives will be drawn into some region of a window; in feedback mode, information about primitives that will be rasterized is fed back to the application.
You select among these three modes with glRenderMode.
Build date: 3/6/2012