CPEN 461/661, Spring 1997

OpenGL Tutorial

Typical OpenGL Program Organization

A typical program that uses OpenGL begins with calls to open a window into the frame buffer into which the program will draw. Then, calls are made to allocate a GL context and associate it with the window. Once a GL context is allocated, the programmer is free to issue OpenGL commands. Some calls are used to draw simple geometric objects (i.e. points, line segments, and polygons), while others affect the rendering of these primitives including how they are lit or colored and how they are mapped from the user's two- or three-dimensional model space to the two-dimensional screen. There are also calls to effect direct control of the frame buffer, such as reading and writing pixels.

 main:

     find GL visual and create window

     initialize GL states (e.g. viewing, color, lighting)

     initialize display lists

     loop

          check for events (and process them)

          if   window event (window moved, exposed, etc.)

               modify viewport, if needed

               redraw

          else if mouse or keyboard

               do something, e.g., change states and redraw

redraw:

     clear screen (to background color)

     change state(s), if needed

     render some graphics

     change more states

     render some more graphics

     .

     .

     .

     swap buffers