The Model-View-Controller Architecture - Essentials of Interactive Computer Graphics - page 107

Listing 5.2 shows the CApplicationView class supporting the two main func-
tionalities of a view component: coordinate space transformation and initial-
ization for redraw. As discussed earlier, the controller is responsible for call-
ing the HardwareToModelXform() function to communicate user input points to
the model component. The CUIDrawArea class is introduced to encapsulate the
highly API-dependent device initialization and drawing procedures.

5.2.3 The Controllers

We can improve the solution of Listing 1.7 to better support the specified function-
ality of the ball-shooting program. Recall that the application window depicted in
Figure I.2 has two distinct regions for interpreting events: the upper application
drawing area where mouse button events are associated with defining/selecting the
HeroBall and the lower GUI element area where mouse button events on the GUI
elements have different meanings (e.g., mouse button events on the slider bars
generate SliderBarChange events). We also notice that the upper application
drawing area is the exact same area where the CApplicationView must direct
the drawings of the CApplicationModel state. Listing 5.3 introduces two types
of controller classes: a CViewController and the CMainAppController . Each
controller class is dedicated to receiving input events from the corresponding re-
gion on the application window. The CViewController creates a CApplication
View during initialization such that the view can be tightly paired for drawing of
the CApplicationModel state in the same area. In addition, the CViewControl
ler class also defines the appropriate mouse event service routines to support the
interaction with the HeroBall .The CMainAppController is meant to contain
GUI elements for interacting with the application state.
The bottom of Listing 5.3 illustrates that the GUI API MainEventLoop()
will still call the SystemInitialization() function to initialize the application.
In this case, we create one instance each of CViewController and CMainApp
Controller .The CViewController is initialized to monitor mouse button events
in the drawing area of the application window (e.g., left mouse button click to de-
fine HeroBall ), whereas the CMainAppController is initialized to monitor the
GUI element state changes (e.g., left mouse button dragging of a slider bar). No-
tice that the service of the timer event is global to the entire application and should
be defined in only one of the controllers (either one will do).
In practice, the GUI API MainEventLoop() dispatches events to the con-
trollers based on the context of the event. The context of an event is typically
defined by the location of the mouse pointer or the current focus of the GUI