Working with GUI APIs - Essentials of Interactive Computer Graphics - page 54

event services are predefined by the MFC CDialog , and we override the
OnScroll() functions to customize the services. The definition of event
service routines can be found at labels C3 and C7. Notice that if our appli-
cation has more than one horizontal scroll bar, all horizontal scroll events
will be serviced by the the same OnHScroll() function. This means, as
illustrated by the if statement in C3, that when servicing horizontal scroll
events, we must identify which of the scroll bars triggered the event. At
label C4, we call the GetPos() function on the control variable to obtain
the up-to-date knob value, which is updated in the echo control variable at
C5 and flushed to the corresponding GUI element at label C6.

Tutorial 2.4. Application-Defined Events

Tutorial 2.4.
Project Name
MFC _ MouseAndTimer

• Goal. Experience events triggered by the application; experience working
with servicing events from the mouse.

• Approach. Work with GUI timer event; service all events from the mouse
and echo all relevant information to the application window.

Figure 2.8 is a screenshot of running Tutorial 2.4. The source code of this appli-
cation is based on that from Tutorial 2.3. When compared to the main application
window from Tutorial 2.3, we can see two extra sets of outputs.

• Mouse echo. When the mouse pointer is inside the application window,
this echo prints out the position of the mouse and the status (e.g., clicked)
of the mouse buttons.

Figure 2.8. Tutorial 2.4.

• Timer echo. We will enable the timer alarm to trigger an event for our
application every second. This echo will print out the number of seconds
elapsed since we started running this application.

class CTutorialDlg : public CDialog {
. // removed content similar to that from Listing 2.7 (Tutorial 2.3) .
A1: int m _ Seconds;
B1: CString m _ MouseEcho, m _ TimerEcho; Source file.

TutorialDlg.h/cpp
file in the Source and
Header file folders of the
MFC _ MouseAndTimer project.

C1: afx _ msg void OnTimer(UINT nIDEvent);
D1: afx _ msg void OnLButtonDown(UINT nFlags, CPoint point);
afx _ msg void OnMouseMove(UINT nFlags, CPoint point);
afx _ msg void OnRButtonDown(UINT nFlags, CPoint point);

};

Listing 2.8. CTutorialDlg class (Tutorial 2.4).