TweetFollow Us on Twitter

Windows in Action
Volume Number:1
Issue Number:5
Column Tag:C WORKSHOP

Windows in Action

By Robert B. Denny

Windows in Action

There is an initial “hill” that every Macintosh developer must climb before doing anything useful. Most applications require use of windows for presentation and control. Unfortunately for the developer, this fundamental requirement makes it necessary to understand a large part of the Mac’s internals. This information is presented piecemeal in Inside Macintosh (IM).

Last month, we covered the “static” aspects of windows, including data struc- tures and the functions of the Window Manager. Much of this information can be gleaned from IM relatively easily.

The dynamic aspects of windows, how- ever, are far more subtle. Most of what we learn about window dynamics comes from our experience implementing window-based applications. Take some time to observe how various Mac applications handle things like activating overlapped windows and dragging or re- sizing of windows. Some applications take an “overkill” approach, erasing the entire window and re-drawing everything. Others behave in a more refined fashion, updating only what’s necessary.

The goal of this month’s column is to provide you with some insights into window dynamics and how to apply that knowledge to avoid over-updating and ghost images.

In particular, we will cover creating, updating, dragging, re-sizing, activating and deactivating of windows. The details of scroll-bars, textEdit and other window “content” items will be covered in next month’s column.

Regions Again

Before we go any further, let’s quickly review the various regions involved in window construction and dynamics.

Fig 1.

Fig. 1 shows the various component regions of a common “edit” window. The terminology used here and in Inside Macintosh is confusing. The go-away, drag and grow regions aren’t really “regions” in the QuickDraw sense. They are areas within the window that are handled specially by the Window Manager. For the purposes of compatibility with IM, however, we will use the same termin- ology.

The structure and content regions are true regions. The structure region encloses the entire window, frame and all. The frame consists of the entire title bar and the border (even the drop-shadow, if any). The content region is that area inside the frame. Note that the scroll bars and size box are located within the content region. These regions change only when the window is moved or re-sized.

The Update Region

There is another region that we will be dealing with extensively, the update region. It’s not a structural part of the window as are the structure and content regions. Instead, it is a dynamic descrip- tion of the area(s) of the window which need updating at any given instant.

The update region, like the structure and content regions, is linked directly to the windowRecord. It is used by the Window Manager to control QuickDraw updates to the screen. We’ll look at this in more detail later.

When windows are shuffled front and back, or moved about the desktop, it can be confusing as to whom is responsible for re-drawing what parts of the window. What will the window manager do for you, and what must your application do itself? Here is a simple rule to remember:

The Window Manager handles the frame; your application must handle the contents.

The contents include any controls (e.g., scroll bars) and the “grow icon” in the grow region, as well as whatever you have placed elsewhere in the window area.

How a Window is Drawn

Let’s look at the process of creating a new window, neglecting the programming needed and concentrating on what actually happens. Keep in mind the rule presented above regarding who handles what.

First, the Window Manager calls the “definition procedure” (DefProc) for the window type and asks it to draw the frame. In doing this, the DefProc manipulates the desktop visRgn and clipRgn to make sure that only the visible portion of the frame will be actually drawn. The DefProc may also draw a go-away box in the title bar area. If you are unclear about DefProcs, refer to last month’s C Workshop.

When the DefProc returns to the Window Manager (with the frame drawn), the Window Manager posts an update event for the application that requested the window to be drawn, then returns control to the application.

It is important to understand just how this update event gets generated. The Window Manager determines which areas of the window’s content region need updating. This set of areas is accumu- lated into the window’s update region, which is now no longer empty. When the Toolbox Event Manager sees a window with a non-empty update region, it queues an update event for that window.

Note that drawing and updating is supported for any window on the desktop. the window being drawn need not be frontmost nor the “active” window. It might not be visible at all.

Sometime later, when the application de-queues the update event just posted, it must draw the window contents. This could be tricky, since all or part of the window could be obscured, and if it’s being re-drawn, some of the image might not need updating.

The proper method of handling update events involves use of two very important Window Manager services, BeginUpdate() and EndUpdate() as follows:

/*
 * Handle update event
 */
do_update(wp)
WindowPtr wp;    /* Update this window */
   {
   BeginUpdate(wp);
   ...            /* Draw everything */
   EndUpdate(wp);
   }

BeginUpdate() calculates the intersec- tion of the window’s visRgn and the update region. The result of this intersection is “the area that is visible and needs updating”. It then replaces the visRgn with this newly calculated region. Finally, it clears the update region so that the update event will not be repeated for the window. Then control is returned to the update event handler.

At this point your application may draw the entire window contents without fear. Actual drawing will be restricted to the (temporary) visRgn, which encloses only what may and should be drawn. Nothing else will be drawn.

After this has been done, call EndUpdate() to restore the original visRgn. This completes the actions needed to service an update event.

So the steps are, restrict actual drawing by hacking the visRgn, draw everything, then restore the real visRgn. This approach to window content maintenance is absolutely basic to successful Mac application development.

Don’t be tempted to try analyzing the hacked visRgn calculated by BeginUpdate() and manually restrict your drawing to that region only. You may think you’re saving time by not drawing invisible areas, but you’re more likely to chew up at least that much time figuring out what you don’t want to do!

Deferred Drawing

Window contents must be updated whenever something happens to cause a portion of the window’s image to become visible after being obscured. The Window Manager will automatically accumulate areas into a window’s update region, and your application may manually add to the update region as well.

In either case, when the update event occurs, part or all of the window may need re-drawing. In order to do this properly, you must have a description of the window’s contents stored somewhere. Think about the implications of this.

Let’s say your application requests input of a set of 10 values that you use to draw a figure. You simply read the values and draw the figure as they are read in. Now let’s say you drag the window partially off-screen, release it, then drag it back on screen. You’ll get an update event for the area that was off-screen. How can you reproduce the figure? The values are gone.

You should have stored the values in an array so that they could be used by the update event handler to re-draw the figure as needed. And why draw any time except after an update event? This is a trivial example of an important rule in Mac programming:

Never “store” anything in the window’s image. Always maintain the data needed to re-draw the window and draw only in response to an update event.

If you change something in the window, change the descriptive data then force an update event by calling InvalRect() or InvalRgn() to put the changed area into the update region. Let the update event handler do the actual drawing. This method of window maintenance is called “deferred drawing” because the changes are made to the descriptive data and the actual drawing is deferred to the time of the update event.

If you follow the above rule, it will usually simplify your program’s logic, making it more reliable and less likely to leave “fossils” on the screen or blow holes in the window image.

Activation and Deactivation

The Macintosh User Interface Guideines specify that only one window on the screen may be “active”. What does active mean? Remember that any window on the screen can (and may) be updated at any time. But the user should be able to tell which window will react to keystrokes and/or mouse clicks. Which window is “hooked up” to the mouse and keyboard?

The active window is the one the user is “working in” at the moment. It is always the frontmost window (alerts and dialogs excepted) and has a distinctive highlighted appearance.

The Window Manager provides services to activate and deactivate windows. Also, the system delivers activation events to the the application so that it can make any changes to the window contents as a result of activation or deactivation. Remember, the Window Manager handles the frame and the application handles the contents.

Fig 2.

Fig. 2 shows a document window in its deactivated state. The title bar (drag region) has no stripes and the go-away box is not present. These items are controlled by the Window Manager. The scroll bars are hidden and the grow icon is gone. These items are controlled by the application’s deactivation event handler.

Fig 3.

Fig. 3 shows an activated document window. The title bar has stripes showing and the go-away box is visible. The Window Manager handles these items. The scroll bars and the grow icon are visible. The application’s activate event handler handles the latter items.

Fig. 4

Activation and deactivation are signalled by the same “activation” event being queued for the window. The application must decode which action to take.

What your application should do in response to update and activation events can become confusing. Servicing update and activation events is a simple matter if you keep the following rule in mind:

Drawing should be done only for update events. Activation and deactivation should cause only changes in appearance of activation dependent items such as controls and menus.

If you follow this rule, it will simplify the logic of your program and prevent unnecessary drawing. Do actual drawing only in response to update events. Use activation events to change the appearance of items.

Fig 5.

Putting it All Together

Let’s take the concepts we have learned and apply them to some common situations. Fig. 4 shows the sequence of events when a window is activated and brought to the front. Look at the steps involved and note the roles of the update and activation events, and the formation of the update region.

There are some fine-points of handling the scroll bars and grow icon that we will discuss next month, when we cover controls and textEdit.

The next illustration shows what happens when a window which is partially off-screen is dragged back on to the screen. It was this case which turned the light on for me personally.

Fig 6.

Interestingly enough, no update event is generated for a window which is dragged from one place to another on the screen. The window manager has a complete image of the window already on the screen, so it simply “bit-blits” (fast image copy) the image from one place to the other.

The surprise comes when you drag the window off-screen, release it, then drag it back on. Now part of the window must be re-constructed as if it was being drawn for the first time. An update event is posted and the application must re-draw the part that was off the screen.

The last “movie”, fig. 6, shows what happens when a window is re-sized. No activation events are posted for this action.

Note particularly the manual invalidation of the scroll bars by calling InvalRect() for each. This is needed because the window manager has no idea that the controls are going to be moved, invalidating the area covered by them.

Final Words

Next month, we’ll finish up the treatment of windows with a description of controls and textEdit. By treating these two subjects together, we’ll learn a lot from their interrelatedness. I’ll also include some C routines for handling update, activate, deactivate, drag and grow actions for windows.

In the near future, The C Workshop will contain a complete application written in C which supports multiple windows of two types, one of which supports fully functional scroll bars and textEdit. The other window type supports a crude “blackboard” which does not remember the blackboard contents. We hope you’ll find this useful as a basis for non-trivial applications.

For now, please be patient. I have not included much C in the last few columns, since the template application. I feel that there is so much to know before one can write even a trivial application that it’s best to hold off until the foundation is complete.

 
AAPL
$100.41
Apple Inc.
-0.17
MSFT
$45.11
Microsoft Corpora
+0.16
GOOG
$583.46
Google Inc.
-1.03

MacTech Search:
Community Search:

Software Updates via MacUpdate

Videobox 4.1.1 - Download Flash video th...
Videobox allows you to quickly and easily download Flash video from most all of the popular video sites on the internet. Videobox will convert the video into a native Quicktime format so it's ready... Read more
Web Snapper 3.3.5 - Capture entire Web p...
Web Snapper lets you capture Web pages exactly as they appear in your browser. You can send them to a file as images or vector-based, multi-page PDFs. It captures the whole Web page - eliminating... Read more
Picasa 3.9.138 - Organize, edit, and sha...
Picasa and Picasa Web Albums allows you to organize, edit, and upload your photos to the Web from your computer in quick, simple steps. Arrange your photos into folders and albums and erase their... Read more
Tidy Up 3.0.15.0 - Find duplicate files...
Tidy Up is a complete duplicate finder and disk-tidiness utility. With Tidy Up you can search for duplicate files and packages by the owner application, content, type, creator, extension, time... Read more
Parallels Desktop 10.0 - Run Windows app...
Parallels Desktop is simply the world's bestselling, top-rated, and most trusted solution for running Windows applications on your Mac. With Parallels Desktop for Mac, you can seamlessly run both... Read more
Apple Final Cut Pro X 10.1.3 - Professio...
Apple Final Cut Pro X is a professional video editing solution.Completely redesigned from the ground up, Final Cut Pro adds extraordinary speed, quality, and flexibility to every part of the post-... Read more
Apple Compressor 4.1.3 - Adds power and...
Compressor adds power and flexibility to Final Cut Pro X export. Customize output settings, work faster with distributed encoding, and tap into a comprehensive set of delivery features. Powerful... Read more
Chromium 36.0.1985.143 - Fast and stable...
Chromium is an open-source browser project that aims to build a safer, faster, and more stable way for all Internet users to experience the web. FreeSMUG-Free OpenSource Mac User Group build is... Read more
Macgo Blu-ray Player 2.10.6.1691 - Blu-r...
Macgo Mac Blu-ray Player can bring you the most unforgettable Blu-ray experience on your Mac. Overview Macgo Mac Blu-ray Player can satisfy just about every need you could possibly have in a Blu-ray... Read more
Apple Motion 5.1.2 - Create and customiz...
Apple Motion is designed for video editors, Motion 5 lets you customize Final Cut Pro titles, transitions, and effects. Or create your own dazzling animations in 2D or 3D space, with real-time... Read more

Latest Forum Discussions

See All

BoxPop Review
BoxPop Review By Jennifer Allen on August 21st, 2014 Our Rating: :: UNTAXING PUZZLESUniversal App - Designed for iPhone and iPad Move from tile to tile to clear the board in this slightly too simple and easy puzzle game.   | Read more »
Breakdown Buddy Review
Breakdown Buddy Review By Jennifer Allen on August 21st, 2014 Our Rating: :: FLAWED CONCEPTiPhone App - Designed for the iPhone, compatible with the iPad There’s a good idea here, but Breakdown Buddy isn’t as useful as it tries to... | Read more »
jamstik, the Guitar You Can Take Everywh...
jamstik, the Guitar You Can Take Everywhere, is Now Available for Purchase Posted by Jessica Fisher on August 21st, 2014 [ permalink ] Zivix has announced that their guitar-in-your-pocket, | Read more »
Star Walk 2 - Guide to the Sky Day and N...
Star Walk 2 - Guide to the Sky Day and Night 1.0.0 Device: iOS Universal Category: Education Price: $2.99, Version: 1.0.0 (iTunes) Description: The next generation of the best-selling Star Walk, winner of Apple Design Award, used by... | Read more »
Forks Over Knives Review
Forks Over Knives Review By Jennifer Allen on August 21st, 2014 Our Rating: :: TASTY AND HEALTHYUniversal App - Designed for iPhone and iPad Want some tasty new recipe ideas but want to keep it healthy? Forks Over Knives is the... | Read more »
Invaders! From Outer Space (Games)
Invaders! From Outer Space 1.0 Device: iOS Universal Category: Games Price: $.99, Version: 1.0 (iTunes) Description: | Read more »
Dementia: Book of the Dead (Games)
Dementia: Book of the Dead 1.00 Device: iOS Universal Category: Games Price: $2.99, Version: 1.00 (iTunes) Description: EXCLUSIVE CONTENT ONLY ON THE APP STORE. Medieval England. Times of knights, witches and hunters. What other... | Read more »
Wan Nyan Slash (Games)
Wan Nyan Slash 1.0 Device: iOS Universal Category: Games Price: $.99, Version: 1.0 (iTunes) Description: Wan Nyan Slash is an infinite adorable demon slaying slashing action game! Play as the wandering samurai Wan and Nyan as they... | Read more »
Fallin Love - The Game of Love (Games)
Fallin Love - The Game of Love 1.0 Device: iOS Universal Category: Games Price: $.99, Version: 1.0 (iTunes) Description: GRAVITATE AROUND LOVE | Read more »
Ancient Battle: Hannibal (Games)
Ancient Battle: Hannibal 1.0 Device: iOS Universal Category: Games Price: $.99, Version: 1.0 (iTunes) Description: | Read more »

Price Scanner via MacPrices.net

21-inch iMacs on sale for up to $150 off MSRP
B&H Photo has 21″ iMacs on sale for up to $150 off MSRP including free shipping plus NY sales tax only. B&H will also include a free copy of Parallels Desktop software: - 21″ 2.7GHz iMac: $... Read more
27-inch 3.2GHz iMac on sale for $1698, save $...
Abt has the 27″ 3.2GHz iMac on sale for $1698 including free shipping. Their price is $101 off MSRP. Read more
Mac Backup Guru 2.0 Drive Backup/Cloneing Uti...
Mac Backup Guru developer MacDaddy has released Mac Backup Guru 2.0, offering new and enhanced advanced features, such as bootable backups, synchronised volumes and folders, and a Snapshot mode that... Read more
Operate GE’s New Free-Standing KItchen Range...
Think you accidentally left the oven on? Switch it off while on the go. The new free-standing Profile™ Series gas and electric ranges are GE’s second cooking appliances, following their wall oven, to... Read more
Parallels Announces Parallels Desktop 10 for...
The no. 1-selling software for running Windows applications on a Mac becomes an even easier choice for millions of consumers and IT professionals worldwide with the launch of the most powerful... Read more
Apple now offering certified refurbished 2014...
 The Apple Store is now offering Apple Certified Refurbished 2014 MacBook Airs for up to $180 off the cost of new models. An Apple one-year warranty is included with each MacBook, and shipping is... Read more
Best Buy’s College Student Deals: $100 off Ma...
Take an additional $100 off all MacBooks and iMacs, $50 off iPad Airs and iPad minis, at Best Buy Online with their College Students Deals Savings, valid through September 6th. Anyone with a valid .... Read more
MacBook Airs on sale for $100 off MSRP, free...
B&H Photo has three 2014 MacBook Airs on sale for $100 off MSRP. Shipping is free, and B&H charges NY sales tax only. They also include free copies of Parallels Desktop and LoJack for Laptops... Read more
Razer Taipan Mouse For Gamers And Non-Gamers...
If you’re a serious gamer on either Mac or Windows PCs, a serious gaming mouse is a necessity for first-tier performance. However, even if like me you’re not much of a gamer, there’s still a strong... Read more
15-inch 2.2GHz MacBook Pro on sale for $1899,...
Adorama has the new 15″ 2.2GHz Retina MacBook Pro on sale for $1899 including free shipping plus NY & NJ sales tax only. Their price is $100 off MSRP, and it’s the lowest price available for this... Read more

Jobs Board

Project Manager, *Apple* Financial Services...
**Job Summary** Apple Financial Services (AFS) offers consumers, businesses and educational institutions ways to finance Apple purchases. We work with national and Read more
*Apple* Solutions Consultant (ASC)- Retail S...
**Job Summary** The ASC is an Apple employee who serves as an Apple brand ambassador and influencer in a Reseller's store. The ASC's role is to grow Apple Read more
Position Opening at *Apple* - Apple (United...
…customers purchase our products, you're the one who helps them get more out of their new Apple technology. Your day in the Apple Store is filled with a range of Read more
*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
Senior Event Manager, *Apple* Retail Market...
…This senior level position is responsible for leading and imagining the Apple Retail Team's global event strategy. Delivering an overarching brand story; in-store, Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.