OpenGL

OpenGL is a stated system for inputing information. This somewhat goes back to the turtle graphics view. In building an object, you step through calls to add one part at at time. The next item picks up with the transformation matrix left by the previous calls and the modes left by previous calls (ie color).

The primary way the system works is callbacks. For example, you may build a drawing routine called mydraw. You tell OpenGL to use mydraw to display the information. Then mydraw is called by OpenGL at the times you specified.

     Your code       the OpenGL engine          your callback routines

----------------       _______________          _____________________
| pass name    |name  |              |         |                    |
| of routine   |=====>|              |-------->|                    |
|              |      |              | call    |                    |
| call OpenGL  |----->|              | return  |                    |
---------------- call  _______________          _____________________
                 return