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.

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

GraphicConverter 10.5.1 - $39.95
GraphicConverter is an all-purpose image-editing program that can import 200 different graphic-based formats, edit the image, and export it to any of 80 available file formats. The high-end editing... Read more
Delicious Library 3.7 - Import, browse a...
Delicious Library allows you to import, browse, and share all your books, movies, music, and video games with Delicious Library. Run your very own library from your home or office using our... Read more
Adobe Animate CC 2017 18.0.0.107 - Anima...
Animate CC 2018 is available as part of Adobe Creative Cloud for as little as $19.99/month (or $9.99/month if you're a previous Flash Professional customer). Animate CC 2018 (was Flash CC) lets you... Read more
Adobe After Effects CC 2018 15.0 - Creat...
After Effects CC 2018 is available as part of Adobe Creative Cloud for as little as $19.99/month (or $9.99/month if you're a previous After Effects customer). The new, more connected After Effects CC... Read more
Adobe Premiere Pro CC 2018 12.0.0 - Digi...
Premiere Pro CC 2018 is available as part of Adobe Creative Cloud for as little as $19.99/month (or $9.99/month if you're a previous Premiere Pro customer). Adobe Premiere Pro CC 2018 lets you edit... Read more
Alarm Clock Pro 10.3 - $19.95
Alarm Clock Pro isn't just an ordinary alarm clock. Use it to wake you up in the morning, send and compose e-mails, remind you of appointments, randomize the iTunes selection, control an internet... Read more
Adobe Lightroom 20170919-1412-ccb76bd] -...
Adobe Lightroom is available as part of Adobe Creative Cloud for as little as $9.99/month bundled with Photoshop CC as part of the photography package. Lightroom 6 is also available for purchase as a... Read more
Adobe Illustrator CC 2018 22.0.0 - Profe...
Illustrator CC 2018 is available as part of Adobe Creative Cloud for as little as $19.99/month (or $9.99/month if you're a previous Illustrator customer). Adobe Illustrator CC 2018 is the industry... Read more
Hopper Disassembler 4.3.0- - Binary disa...
Hopper Disassembler is a binary disassembler, decompiler, and debugger for 32- and 64-bit executables. It will let you disassemble any binary you want, and provide you all the information about its... Read more
Adobe InDesign CC 2018 13.0.0.125 - Prof...
InDesign CC 2018 is available as part of Adobe Creative Cloud for as little as $19.99/month (or $9.99/month if you're a previous InDesign customer). Adobe InDesign CC 2018 is part of Creative Cloud.... Read more

ICEY (Games)
ICEY 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: ICEY is a 2D side-scrolling action game. As you follow the narrator's omnipresent voice, you will see through ICEY's eyes and learn the... | Read more »
The best new games we played this week -...
We've made it, folks. Another weekend is upon us. It's time to sit back and relax with the best new releases of the week. Puzzles, strategy RPGs, and arcade games abound this week. There's a lot of quality stuff to unpack this week, so let's hop... | Read more »
Wheels of Aurelia (Games)
Wheels of Aurelia 1.0.1 Device: iOS Universal Category: Games Price: $3.99, Version: 1.0.1 (iTunes) Description: | Read more »
Halcyon 6: Starbase Commander guide - ti...
Halcyon 6 is a well-loved indie RPG with stellar tactical combat and some pretty good writing, too. It's now landed on the App Store, so mobile fans, if you're itching for a good intergalactic adventure, here's your game. Being a strategy RPG, the... | Read more »
Game of Thrones: Conquest guide - how to...
Fans of base building games might be excited to know that yet another entry in the genre has materialized - Game of Thrones: Conquest. Yes, you can now join the many kingdoms of the famed book series, or create your own, as you try to conquer... | Read more »
Halcyon 6: Starbase Commander (Games)
Halcyon 6: Starbase Commander 1.4.2.0 Device: iOS Universal Category: Games Price: $6.99, Version: 1.4.2.0 (iTunes) Description: An epic space strategy RPG with base building, deep tactical combat, crew management, alien diplomacy,... | Read more »
Legacy of Discord celebrates its 1 year...
It’s been a thrilling first year for fans of Legacy of Discord, the stunning PvP dungeon-crawling ARPG from YOOZOO Games, and now it’s time to celebrate the game’s first anniversary. The developers are amping up the festivities with some exciting... | Read more »
3 reasons to play Thunder Armada - the n...
The bygone days of the Battleship board game might have past, but naval combat simulators still find an audience on mobile. Thunder Armada is Chinese developer Chyogames latest entry into the genre, drawing inspiration from the explosive exchanges... | Read more »
Experience a full 3D fantasy MMORPG, as...
Those hoping to sink their teeth into a meaty hack and slash RPG that encourages you to fight with others might want to check out EZFun’s new Eternity Guardians. Available to download for iOS and Android, Eternity Guardians is an MMORPG that lets... | Read more »
Warhammer Quest 2 (Games)
Warhammer Quest 2 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: Dungeon adventures in the Warhammer World are back! | Read more »

Price Scanner via MacPrices.net

12″ iPad Pros on sale for $50 off MSRP, no ta...
Adorama has 12″ iPad Pros on sale today for $50 off MSRP. Shipping is free, and Adorama charges sales tax in NY & NJ only: – 12″ 64GB iPad Pro: $749, save $50 – 12″ 256GB iPad Pro: $899, save $50... Read more
9″ iPads on sale for $30 off, starting at $29...
MacMall has 9″ iPads on sale for $30 off including free shipping: – 9″ 32GB iPad: $299 – 9″ 128GB iPad: $399 Read more
Apple restocks full line of refurbished 13″ M...
Apple has restocked a full line of Apple Certified Refurbished 2017 13″ MacBook Pros for $200-$300 off MSRP. A standard Apple one-year warranty is included with each MacBook, and shipping is free.... Read more
13″ 3.1GHz/256GB MacBook Pro on sale for $167...
Amazon has the 2017 13″ 3.1GHz/256GB Space Gray MacBook Pro on sale today for $121 off MSRP including free shipping: – 13″ 3.1GHz/256GB Space Gray MacBook Pro (MPXV2LL/A): $1678 $121 off MSRP Keep an... Read more
13″ MacBook Pros on sale for up to $120 off M...
B&H Photo has 2017 13″ MacBook Pros in stock today and on sale for up to $120 off MSRP, each including free shipping plus NY & NJ sales tax only: – 13-inch 2.3GHz/128GB Space Gray MacBook... Read more
15″ MacBook Pros on sale for up to $200 off M...
B&H Photo has 15″ MacBook Pros on sale for up to $200 off MSRP. Shipping is free, and B&H charges sales tax in NY & NJ only: – 15″ 2.8GHz MacBook Pro Space Gray (MPTR2LL/A): $2249, $150... Read more
Roundup of Apple Certified Refurbished iMacs,...
Apple has a full line of Certified Refurbished 2017 21″ and 27″ iMacs available starting at $1019 and ranging up to $350 off original MSRP. Apple’s one-year warranty is standard, and shipping is free... Read more
Sale! 27″ 3.8GHz 5K iMac for $2098, save $201...
Amazon has the 27″ 3.8GHz 5K iMac (MNED2LL/A) on sale today for $2098 including free shipping. Their price is $201 off MSRP, and it’s the lowest price available for this model (Apple’s $1949... Read more
Sale! 10″ Apple WiFi iPad Pros for up to $100...
B&H Photo has 10.5″ WiFi iPad Pros in stock today and on sale for $50-$100 off MSRP. Each iPad includes free shipping, and B&H charges sales tax in NY & NJ only: – 10.5″ 64GB iPad Pro: $... Read more
Apple iMacs on sale for up to $130 off MSRP w...
B&H Photo has 21-inch and 27-inch iMacs in stock and on sale for up to $130 off MSRP including free shipping. B&H charges sales tax in NY & NJ only: – 27″ 3.8GHz iMac (MNED2LL/A): $2179 $... Read more

Jobs Board

Engineering Manager, *Apple* Retail Enginee...
# Engineering Manager, Apple Retail Engineering Job Number: 58139948 Santa Clara Valley, California, United States Posted: 20-Oct-2017 Weekly Hours: 40.00 **Job Read more
*Apple* Retail - Multiple Positions - Apple,...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
Commerce Engineer, *Apple* Media Products -...
Commerce Engineer, Apple Media Products (New York City) Job Number: 113028813New York City, New York, United StatesPosted: Sep. 20, 2017Weekly Hours: 40.00 Job Read more
US- *Apple* Store Leader Program - Apple (Un...
US- Apple Store Leader Program Job Number: VariousUnited StatesPosted: Oct. 19, 2017Retail Store Job Summary Learn and grow as you explore the art of leadership at Read more
Product Manager - *Apple* Pay on the *Appl...
Job Summary Apple is looking for a talented product manager to drive the expansion of Apple Pay on the Apple Online Store. This position includes a unique Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.