Feb 98 - Getting Started
Volume Number: 14 (1998)
Issue Number: 2
Column Tag: Getting Started
Window-Related Events
by Dave Mark, ©1997, All Rights Reserved.
How a Mac program handles windows
In last month's column, we covered the basics of event loop programming, focusing on four specific events: the mouseDown, mouseUp, keyDown, and autoKey events. If you haven't already, be sure to read through the Event Manager chapter in Inside Macintosh: Macintosh Toolbox Essentials. Pay specific attention to the sections that describe the mouseDown, mouseUp, keyDown, and autoKey events in detail. Finally, go back to last month's program and flesh it out a little. When a mouseDown occurs, draw a string in the event window that describes where and when the mouseDown occurred. For a keyDown, draw the character and key codes embedded in the EventRecord.
In this month's column, we're going to expand our event handling repertoire, focusing on activate, update, and suspend/resume events.
Activate Events
Every time your application creates a window, that window is added to a list maintained by the Window Manager. The windows in this list are in the order that they appear on the screen, from the frontmost to the rearmost.
The frontmost window is also known as the active window. In Figure 1, Window #1 starts off as the active window. Notice the difference between the title bars of the active and non-active window.
Figure 1. A mouse click in Window #2 brings it to the front.
When the mouse is clicked in the rear window, Window #1 is made inactive, then the rear window, Window #2, is made active. Since the front window is made inactive before another window is brought to the front, there will never be more than one active window at a time!
The Window Manager accomplishes this by sending your application a series of activate events. If a rear window is being brought to the front, your application will receive two activate events. The first tells you that the frontmost window is becoming inactive. This event is also known as a deactivate event. The second event tells your application that a window is becoming active. Both of these events set EventRecord.what to activateEvt.
If a window is created, and there are no currently open windows, the Window Manager only generates a single activate event, indicating that the newly created window is becoming active. In this case, no deactivate event is sent.
In general, you'll use activate events if you treat window contents differently for an active window than for an inactive window. For example, your application might highlight selected text in the active window, but not in an inactive window. Activate events are provided for your benefit. Use them as you see fit. You'll see how we discriminate between an activate and deactivate event when we get to our program later in the column.
Update Events
Next on our list of events is an event that tells your program to update the contents of a window. The updateEvt is generated when a window is created (after the activateEvt is generated) and when a new portion of a window is revealed. Figure 2 shows a typical sequence that generates an updateEvt. The first picture shows Window #1 partially obscuring Window #2. Next, Window #1 is dragged to the left, revealing a previously hidden section of the Window #2. The Window Manager sends an updateEvt to your application, telling it to update the contents of Window #2. The third picture shows the window, after the program responded to the update event.
Figure 2. When Window #1 is dragged to the left, more of Window #2 is exposed, causing an update event.
Figure 3 shows a slightly different sequence, involving update and activate events. This time, the mouse is clicked in Window #2, bringing it to the front. First, a deactivate event is generated for Window #1. Next, an activate event is generated for Window #2. Finally, an update event is generated, asking the program to update the contents of Window #2.
Figure 3. When Window #2 is moved to the front, two activate events and an update event are generated.
Once again, you'll see update and activate events in action in the program later in the column.
Suspend & Resume Events
When you click in a window belonging to a background application, the active application receives a suspend event, and the background application receives a resume event and is moved to the foreground.
You might use suspend and resume events to determine the actions taken by your program. For example, in the foreground, you might display a special tool palette, or perhaps run an animation. When your application moves into the background, you'll receive a suspend event and you might hide the tool palette, or discontinue the animation until you get a resume event.
It's important to note that your application can continue running, even if it receives a suspend event. It will still continue to receive update (and other appropriate events) while in the background. At the very least, it's a good idea to treat a suspend event as you would a deactivate event when it comes to the contents of your windows. For example, if you usually deselect any selected text when a window is deactivated, do the same thing for the active window when you receive a suspend event.
At Last! The Program!
As promised, here's a program that incorporates all the events described in this column. WindowMaster creates a single window and handles all the usual events relating to windows. Figure 4 shows the WindowMaster window in all its glory. Notice that this window sports a close box, a zoom box, a drag region (the title bar), and a grow box. Though this window doesn't support scroll bars, there is room for them. In most cases, if a window has a grow box, it has room for scroll bars.
Figure 4. The WindowMaster window
Creating the WindowMaster Resources
Create a folder in your development folder named WindowMaster. Launch ResEdit, then create a resource file named WindowMaster.rsrc in your WindowMaster folder. You'll create two resources in this file.
First, create a WIND resource according to the specifications shown in Figure 5. Next, select Set 'WIND' Characteristics... from the WIND menu and set the window's title to PICT 128. Next, copy a graphic from your scrapbook into the clipboard. If you don't have anything interesting in your scrapbook, go draw something. I'll wait.
If you are running Mac OS 8, you can give your window the Mac OS 8 appearance with a few extra steps. First we have to configure ResEdit to support a Mac OS 8 window. See the row of window icons across the top of Figure 5? These icons select the window's procID, which tells the system how to select and configure the WDEF that makes the window. Double click one of the icons containing a questionmark shown at the end of the row. In the resulting window, enter 1031 in one of the empty fields. Now one of your icons will contain 1031 as in Figure 5. Select this icon. If you are doing this under Mac OS 8, you will see a Mac OS 8-style window. You can experiment with other document window procIDs ranging from 1024 to 1031. These are all listed in Appearance.h of the Appearance Manager SDK.
Once you've got a graphic in the clipboard, return to ResEdit and select Paste from the Edit menu. ResEdit will place your picture in a PICT resource. Make sure the PICT resource has a resource ID of 128. Well, that's it for ResEdit. Quit, making sure you save your changes.
Figure 5. Specifications for WindowMaster's WIND resource.
Creating the WindowMaster Project
Once you're out of ResEdit, launch CodeWarrior and create a new project based on the MacOS:C/C++:Basic Toolbox 68k stationary. Turn off the Create Folder check box. Name the project WindowMaster.mcp and place it in your WindowMaster folder. Remove SillyBalls.c and SillyBalls.rsrc from the project; we will not be using these files. From the Finder, drag and drop your WindowMaster.rsrc file into the project window. You also can remove the ANSI Libraries group from the project, because we won't need them, either.
Select New from the File menu to create a new window. Save it under the name WindowMaster.c, Select Add Window from the Project menu to add WindowMaster.c to the project. Your project window should look something like Figure 6.
Figure 6. WindowMaster project window.
Rather than print the code here twice, we'll go straight to the walk-through. You can type in the code as we discuss it below and you will end up with the complete program, or you can save your fingures some effort and get the complete project from MacTech's ftp site ftp://ftp.mactech.com/src/mactech/volume14_1998/14.02.sit.
Walking Through the Source Code
Just like last month's program, WindowMaster is based on an event loop architecture. Also, like last month's column, the program starts off by including <Sounds.h> to access the SysBeep() system call. This month we add <limits.h> to define SHRT_MAX.
#include <limits.h>
#include <Sound.h>
#define kBaseResID 128
#define kMoveToFront (WindowPtr)-1L
#define kSleep 7
#define kScrollBarAdjust (16-1)
#define kLeaveWhereItIs false
#define kNormalUpdates true
#define kMinWindowHeight 50
#define kMinWindowWidth 80
gDone is initialized to false, then set to true when a click occurs in the window's close box. Note that this is not the way Mac applications normally exit, but we haven't got to menus yet, so a click in the close box will have to do for now.
/******************************** Globals *********/
Boolean gDone;
As always, the code includes prototypes for all functions.
/******************************** Function Prototypes ****/
void ToolBoxInit( void );
void WindowInit( void );
void EventLoop( void );
void DoEvent( EventRecord *eventPtr );
void HandleMouseDown( EventRecord *eventPtr );
void DoUpdate( EventRecord *eventPtr );
void DoPicture( WindowPtr window, PicHandle picture );
void DoActivate( WindowPtr window, Boolean becomingActive );
void DoSuspendResume( Boolean resuming );
void CenterPict( PicHandle picture, Rect *srcRectPtr,
Rect *destRectPtr );
main() initializes the Toolbox, creates a window, then enters the main event loop.
/******************************** main *********/
void main( void )
{
ToolBoxInit();
WindowInit();
EventLoop();
}
ToolBoxInit() is the same as it ever was.
/*********************************** ToolBoxInit */
void ToolBoxInit( void )
{
InitGraf( &qd.thePort );
InitFonts();
InitWindows();
InitMenus();
TEInit();
InitDialogs( nil );
InitCursor();
}
WindowInit() calls GetNewWindow() to load the WIND resource from the resource file.
/******************************** WindowInit *********/
void WindowInit( void )
{
WindowPtr window;
window = GetNewWindow( kBaseResID, nil, kMoveToFront );
If the resource wasn't found, beep once, then exit.
if ( window == nil )
{
SysBeep( 10 ); /* Couldn't load the WIND resource!!!*/
ExitToShell();
}
Once the window is created, make it visible, then make it the current port. Notice that this routine does not do any drawing. We'll draw our picture in response to an update event.
ShowWindow( window );
SetPort( window );
}
EventLoop() sets gDone to false, then loops around a call to WaitNextEvent(). If WaitNextEvent() returns true, the event is passed to DoEvent().
/******************************** EventLoop *********/
void EventLoop( void )
{
EventRecord event;
gDone = false;
while ( gDone == false )
{
if ( WaitNextEvent( everyEvent, &event, kSleep, nil ) )
DoEvent( &event );
}
}
DoEvent() switches on the event's what field.
/************************************* DoEvent */
void DoEvent( EventRecord *eventPtr )
{
Boolean becomingActive, resuming;
switch ( eventPtr->what )
{
A mouseDown event is passed to HandleMouseDown(). An updateEvt is passed on to DoUpdate().
case mouseDown:
HandleMouseDown( eventPtr );
break;
case updateEvt:
DoUpdate( eventPtr );
break;
In the case of an activate event, the event's modifiers field holds the key to whether the event is an activate or deactivate event. activeFlag is a mask that designates one of the bits in the modifiers field. If the bit is set, the event is an activate event. If the bit is clear, the event is a deactivate event. The Boolean becomingActive is true if the event is an activate event. Once becomingActive is set, it is passed on to DoActivate(). The event's message field holds a pointer to the window being activated or deactivated.
case activateEvt:
becomingActive = ( (eventPtr->modifiers & activeFlag)
== activeFlag );
DoActivate( (WindowPtr)eventPtr->message,
becomingActive );
break;
Similarly, an osEvt is used to indicate either a suspend or resume event. suspendResumeMessage is a predefined constant that designates the suspend/resume bit in the message field. resuming is set to true if the event is a resume event. Once set, resuming is passed on to DoSuspendResume().
case osEvt:
resuming = ( eventPtr->message & suspendResumeMessage )
== resumeFlag;
DoSuspendResume( resuming );
break;
}
}
HandleMouseDown() handles the mouseDown event.
/************************************* HandleMouseDown */
void HandleMouseDown( EventRecord *eventPtr )
{
WindowPtr window;
short thePart;
GrafPtr oldPort;
long windSize;
Rect growRect;
FindWindow() takes the event's where field and returns the window at those coordinates. thePart indicates the part of the window the mouse click occurred in.
thePart = FindWindow( eventPtr->where, &window );
If the click was in a portion of the screen not belonging to our application (like a desk accessory window), thePart is set to inSysWindow and we'll pass the event back to the system with SystemClick().
switch ( thePart )
{
case inSysWindow :
SystemClick( eventPtr, window );
break;
If the event was in the content region of the window, we'll typically call SelectWindow() to bring the window to the front. Since we only have one window, this line isn't particularly useful. Later on though, you'll add another window to this program and you'll want to keep this code in here.
As your windows get more complex, you'll want to do more with inContent clicks than just select the window. You might have a button or scroll bar in the window that needs action, or you might have some text that needs selection. This is the jumping off point for all clicks that occur in the window. Eventually, we'll add a routine named DoContentClick() to process clicks in a window's content region.
case inContent:
SelectWindow( window );
break;
If the click was in the window's drag region (title bar), we'll pass the window (retrieved by FindWindow()), and the mouse click coordinates to the Toolbox routine DragWindow(). The third parameter is a bounding rectangle that determines where on the screen the window may be dragged. screenBits.bounds is a System global variable that defines the boundaries of the main display.
If you have two monitors, this code works fine, however. DragWindow() checks for screenBits.bounds as a parameter and, if it finds it, allows dragging anywhere on any monitor attached to the system.
case inDrag :
DragWindow( window, eventPtr->where,
&qd.screenBits.bounds );
break;
If the mouseDown was in the close box, we'll call TrackGoAway() to see if the mouse was released while still inside the close box. If so, gDone is set to true. TrackGoAway() is the routine that does the little animation in the close box.
case inGoAway :
if ( TrackGoAway( window, eventPtr->where ) )
gDone = true;
break;
If the click was in the grow box, we set up a rectangle that defines how large and how small the window is allowed to grow. Basically, it's good policy to put a limit on how small a window can get, but, unless you've got a pressing reason, you should allow windows to get as large as the user wants.
case inGrow:
growRect.top = kMinWindowHeight;
growRect.left = kMinWindowWidth;
growRect.bottom = SHRT_MAX;
growRect.right = SHRT_MAX;
Next, this rectangle is passed on to GrowWindow(), which tracks the mouse, allowing the user to specify the new window size.
windSize = GrowWindow( window, eventPtr->where,
&growRect );
The return value contains two 2-byte values, indicating the new height and width of the window. If both are zero, the user has not changed the window size.
if ( windSize != 0 )
{
First, we'll save the current port (in case it's not this window), then make this window the current port. Next, we erase the entire window and change the window's size by calling SizeWindow(). The last parameter tells the system we want this resizing to generate an update event.
GetPort( &oldPort );
SetPort( window );
EraseRect( &window->portRect );
SizeWindow( window, LoWord( windSize ),
HiWord( windSize ), kNormalUpdates );
Next, we call InvalRect() to tell the system that the entire window should be redrawn with the next update event, not just the new area revealed by the grow box. In fact, this call will force an update even if the window was shrunk.
InvalRect( &window->portRect );
Because we center our picture in the window, we need to redraw the window contents whenever the window changes size. To see why this is true, try commenting out the previous line of code.
Update events are tricky. It is definitely worth reading the section of Inside Macintosh: Macintosh Toolbox Essentials that covers the Window Manager. You might also check out Chapter 4's Updater program in Volume I of the Mac Primer.
Once the window is resized, the port is set back to its old value. Since InvalRect() applies to the current port, it was important that we make the window being grown the current port.
SetPort( oldPort );
}
break;
Finally, a click in the zoom box follows a similar strategy. Again, TrackBox() is called to verify that the mouse was released inside the zoom box. If so, ZoomWindow() is called to zoom the window, or return it to its old position, depending on its current state.
case inZoomIn:
case inZoomOut:
if ( TrackBox( window, eventPtr->where, thePart ) )
{
GetPort( &oldPort );
SetPort( window );
EraseRect( &window->portRect );
ZoomWindow( window, thePart, kLeaveWhereItIs );
InvalRect( &window->portRect );
SetPort( oldPort );
}
break;
}
}
DoUpdate() is called whenever an update event occurs. First, the window is retrieved from the event's message field. Next, BeginUpdate() is called, telling the Window Manager that we're handling updates for this window. BeginUpdate() will restrict drawing to the region of the window that needs updating, also known as the update region. If you call InvalRect() on the whole window, the whole window is available for drawing.
/************************************* DoUpdate */
void DoUpdate( EventRecord *eventPtr )
{
PicHandle picture;
WindowPtr window;
window = (WindowPtr)eventPtr->message;
BeginUpdate( window );
Next, we load the picture and pass it on to DoPicture().
picture = GetPicture( kBaseResID );
if ( picture == nil )
{
SysBeep( 10 ); /* Couldn't load the PICT resource!!! */
ExitToShell();
}
DoPicture( window, picture );
EndUpdate( window );
}
DoPicture() makes the window the current port, then erases the entire window. Note that this will already have been done if the update event was caused by a resize or zoom, but there's no harm in this minor duplication of code.
/******************************** DoPicture *********/
void DoPicture( WindowPtr window, PicHandle picture )
{
Rect drawingClipRect, destRect;
RgnHandle tempRgn;
SetPort( window );
EraseRect( &window->portRect );
Next, a new region is created. We pass this region handle on to GetClip(), which places a copy of the window's clipping region in tempRgn. The clipping region defines which parts of the window can be drawn in and which parts can't. Again, it is a good idea to read the entire Window Manager chapter in Inside Macintosh: Macintosh Toolbox Essentials, as there's not enough space to cover all of it in this column.
tempRgn = NewRgn();
GetClip( tempRgn );
Since we want to center the picture in the part of the window not covered by the grow region and scroll bar areas, we'll subtract those areas from the window's portRect. Next, we'll pass this rectangle on to ClipRect() making it the new clip region.
drawingClipRect = window->portRect;
drawingClipRect.right -= kScrollBarAdjust;
drawingClipRect.bottom -= kScrollBarAdjust;
ClipRect( &drawingClipRect );
Next, we'll call CenterPict() to center the picture in drawingClipRect, returning the rectangle the picture should be drawn in as its third parameter. We then draw the picture with DrawPicture().
CenterPict( picture, &drawingClipRect, &destRect );
DrawPicture( picture, &destRect );
Next, the clipping region is set back to its old value and the grow icon is redrawn, completing our update.
SetClip( tempRgn );
DisposeRgn( tempRgn );
DrawGrowIcon( window );
}
It's important to remember that your application can receive update events even if it's running in the background. If a foreground application's window covers your application's windows and is then moved, the Window Manager will send your application update events asking you to redraw the affected windows.
DoActivate() is pretty simple. It redraws the grow icon in the specified window. DrawGrowIcon() will draw a different grow icon, depending on whether your window is frontmost or not. When your application starts handling more than one window, you'll start making use of the second parameter, becomingActive. For now, we use the CodeWarrior #pragma unused directive to let the compiler know we intentionally are not using this variable. If we didn't add this line, CodeWarrior would warn us that the variable was never used.
/************************************* DoActivate */
void DoActivate( WindowPtr window, Boolean becomingActive )
{
#pragma unused ( becomingActive )
DrawGrowIcon( window );
}
DoSuspendResume() is also pretty simple. This time the frontmost window's grow icon is redrawn. A front window, which has been suspended gets the same grow icon as any other window. DrawGrowIcon() is smart enough to know the state of your application.
Once again, as your programs get more complex, you'll make use of the second parameter, resuming.
/************************************* DoSuspendResume */
void DoSuspendResume( Boolean resuming )
{
#pragma unused ( resuming )
WindowPtr window;
window = FrontWindow();
DrawGrowIcon( window );
}
CenterPict() centers the picture in the rectangle pointed to by srcRectPtr, returning the result in the rectangle pointed to by destRectPtr.
/****************** CenterPict ********************/
void CenterPict( PicHandle picture, Rect *srcRectPtr,
Rect *destRectPtr )
{
Rect pictRect;
pictRect = (**( picture )).picFrame;
OffsetRect( &pictRect, srcRectPtr->left - pictRect.left,
srcRectPtr->top - pictRect.top);
OffsetRect( &pictRect,
(srcRectPtr->right - pictRect.right)/2,
(srcRectPtr->bottom - pictRect.bottom)/2);
*destRectPtr = pictRect;
}
Running WindowMaster
Select Run from the Project menu to run WindowMaster. A single window, like the one shown in Figure 4 should appear. Click the mouse in the title bar and drag the window around on the screen. Next, click in the grow box and resize the window. Try making it tall and skinny, then short and fat. Notice that there is a limit to how small you can make the window. Next, click the zoom box in the upper-right corner of the window. The window should expand to fill the main screen. Click the zoom-box again to return the window to its previous size.
Next, drag the window downwards, so it is halfway off the screen, obscuring part of the picture. Now drag it back up. The picture will be redrawn in full. Finally, click in the window's close box to exit the program.
Till Next Month
There's a lot going on in this program. As I've said before, do yourself a favor and read the Window Manager chapter in Inside Macintosh: Macintosh Toolbox Essentials. If a concept in this program seems fuzzy, try commenting out some of the code to see what happens. This is especially useful with the code that affects or handles update events. You might also try commenting out the calls to DrawGrowIcon() just to see what happens.
Finally, try adding another window to the program. Add a second WIND and a second PICT resource to the resource file, then create the new window in WindowInit(). You'll be amazed how easy it is to add a second window. Go ahead, try it!
