ABAP programs calling the graphics function modules and the utility function modules can provide the online user with extensive interactive capabilities. The online user can open multiple windows, each with a different graphics program running in it, and enter input to any of them.

To make these interactions possible, the function modules perform all the communications tasks needed to carry on the dialog between the application program and the graphics program. In addition, the modules execute the following operations:

• open a window on the user's desktop

• start up the graphics program in the window

• send data to the running graphics program

• receive messages from the graphics program

• report the messages back to the ABAP program

Thus, the function module is the mediator (see the following figure) in all communication between the ABAP program and the graphics program.

When reading this guide, it is important to keep the above diagram in mind. The sections in this guide make continual reference to the three participants (ABAP program, function module, and graphics program) in the story. Keeping firmly in mind which programs are responsible for which actions will greatly ease your programming efforts.