OpenGL Programming Guide

Appendix AOrder of Operations

Overview

This section gives an overview of the order of operations, as shown in Figure A-1 . Geometric data (vertices, lines, and polygons) follows the path through the row of boxes that includes evaluators and per-vertex operations, while pixel data (pixels, images, and bitmaps) is treated differently for part of the process. Both types of data undergo the rasterization and per-fragment operations before the final pixel data is written into the framebuffer.

Figure A-1 : Order of Operations

All data, whether it describes geometry or pixels, can be saved in a display list or processed immediately. When a display list is executed, the data is sent from the display list just as if it were sent by the application.

All geometric primitives are eventually described by vertices. If evaluators are used, that data is converted to vertices and treated as vertices from then on. Per-vertex calculations are performed on each vertex, followed by rasterization to fragments. For pixel data, pixel operations are performed, and the results are either stored in the texture memory, used for polygon stippling, or rasterized to fragments.

Finally, the fragments are subjected to a series of per-fragment operations, after which the final pixel values are drawn into the framebuffer.

OpenGL Programming Guide