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

Spotify 1.0.57.474. - Stream music, crea...
Spotify is a streaming music service that gives you on-demand access to millions of songs. Whether you like driving rock, silky R&B, or grandiose classical music, Spotify's massive catalogue puts... Read more
VOX 2.8.26 - Music player that supports...
VOX just sounds better! The beauty is in its simplicity, yet behind the minimal exterior lies a powerful music player with a ton of features and support for all audio formats you should ever need.... Read more
beaTunes 5.0.1 - Organize your music col...
beaTunes is a full-featured music player and organizational tool for music collections. How well organized is your music library? Are your artists always spelled the same way? Any R.E.M. vs REM?... Read more
LibreOffice 5.3.4.2 - Free, open-source...
LibreOffice is an office suite (word processor, spreadsheet, presentations, drawing tool) compatible with other major office suites. The Document Foundation is coordinating development and... Read more
Sparkle Pro 2.2 - $79.99
Sparkle Pro will change your mind if you thought building websites wasn't for you. Sparkle is the intuitive site builder that lets you create sites for your online portfolio, team or band pages, or... Read more
calibre 3.1.1 - Complete e-book library...
Calibre is a complete e-book library manager. Organize your collection, convert your books to multiple formats, and sync with all of your devices. Let Calibre be your multi-tasking digital librarian... Read more
calibre 3.1.1 - Complete e-book library...
Calibre is a complete e-book library manager. Organize your collection, convert your books to multiple formats, and sync with all of your devices. Let Calibre be your multi-tasking digital librarian... Read more
Sparkle Pro 2.2 - $79.99
Sparkle Pro will change your mind if you thought building websites wasn't for you. Sparkle is the intuitive site builder that lets you create sites for your online portfolio, team or band pages, or... Read more
Spotify 1.0.57.474. - Stream music, crea...
Spotify is a streaming music service that gives you on-demand access to millions of songs. Whether you like driving rock, silky R&B, or grandiose classical music, Spotify's massive catalogue puts... Read more
beaTunes 5.0.1 - Organize your music col...
beaTunes is a full-featured music player and organizational tool for music collections. How well organized is your music library? Are your artists always spelled the same way? Any R.E.M. vs REM?... Read more

Latest Forum Discussions

See All

This War of Mine gets a new ending and m...
This War of Mine just got a big new update, featuring free DLC that adds a new ending to the game, among other exciting changes. The update is celebrating the game's two-year release anniversary. Apart from the new ending, which will be quite... | Read more »
Summon eight new heroes in Fire Emblem H...
Nintendo keeps coming at us with Fire Emblem Heroes updates, and it doesn't look like that trend is stopping anytime soon. The folks behind the game have just announced the new War of the Clerics Voting Gauntlet, expected to start next Tuesday. [... | Read more »
The best deals on the App Store this wee...
iOS publishers are pulling out all the stops this week -- there's a huge number of seriously great games at discounted prices this week. Let's not waste any time and get right down to business. [Read more] | Read more »
The House of da Vinci (Games)
The House of da Vinci 1.0.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0.0 (iTunes) Description: Enter The House of Da Vinci, a new must-try 3D puzzle adventure game. Solve mechanical puzzles, discover hidden... | Read more »
Solve the disappearance of history’s gre...
Blue Brain Games invites you to indulge in an immersive hands-on 3D puzzle adventure in similar vein to The Room series, with its debut release The House of Da Vinci. Set during the historic period of the Italian Renaissance (when Leonardo himself... | Read more »
Age of Rivals (Games)
Age of Rivals 3.3 Device: iOS Universal Category: Games Price: $.99, Version: 3.3 (iTunes) Description: Deep civilization-building strategy in a fast-paced card game! | Read more »
Panthera Frontier (Games)
Panthera Frontier 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: | Read more »
Angry Birds Evolution beginner's gu...
Angry Birds changes things up a fair bit in its latest iteration, Angry Birds Evolution. The familiar sling-shot physics mechanics are still there, but the game now features team-based gameplay, RPG elements, and a new top-down view. With all of... | Read more »
Sega Forever is for the retro game fans
Sega is launching a new retro games service titled Sega Forever, in a move that's sure to delight games enthusiasts with a bit of nostalgia. Sega's releasing five classic games for free. The titles include Sonic the Hedgehog, Phantasy Star II,... | Read more »
The Little Acre (Games)
The Little Acre 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: | Read more »

Price Scanner via MacPrices.net

ABBYY TextGrabber 6 for iOS Implements Instan...
ABBYY has announced the release of TextGrabber 6.0.0, an important feature update to the company’s productivity app developed for iOS and Android devices. TextGrabber 6.0 now offers Real-Time... Read more
vPhone, First Smartphone That Can’t Be Lost,...
Austin, Texas based Hypori has introduced the vPhone, a virtual smartphone that affords every business user the benefits of separate work and personal phones, conveniently delivered on a single... Read more
Save this weekend with 2016 refurbished MacBo...
Apple has dropped prices on Certified Refurbished 2016 15″ and 13″ MacBook Pros by as much as $590 off original MSRP. An Apple one-year warranty is included with each model, and shipping is free: -... Read more
New 27-inch 3.4GHz iMac on sale for $1699, sa...
MacMall has the new 2017 27″ 3.4GHz iMac (MNE92LL/A) in stock and on sale for $1699 including free shipping. Their price is $100 off MSRP. Read more
Clearance 2016 MacBook Pros available for up...
B&H Photo has clearance 2016 13″ and 15″ MacBook Pros in stock today and on sale for up to $400 off original MSRP. Shipping is free, and B&H charges NY & NJ sales tax only: - 15″ 2.7GHz... Read more
Apple Ranks 9th In comScore Top 50 U.S. Digit...
comScore, Inc. has released its monthly ranking of U.S. online activity at the top digital media properties for May 2017 based on data from comScore Media Metrix Multi-Platform. * Entity has... Read more
10.5-inch iPad Pros available for up to $20 o...
B&H Photo has the new 2017 10.5″ iPad Pros available for up to $20 off MSRP including free shipping plus NY & NJ sales tax only: - 64GB iPad Pro WiFi: $649 - 256GB iPad Pro WiFi: $749 - 512GB... Read more
Three Off-The-Beaten-Track iOS Apps That Dese...
One of the great things about using iPads and iPhones is the vast selection of apps available for most anything you want or need to do. The three outlined in this article have been in my core app... Read more
Apple No. 1 Spot In Gartner Top 100 Vendors i...
Gartner, Inc. has unveiled the top global 100 vendors in IT in 2016 based on their revenue across IT (excluding communication services) and component market segments. In the Gartner Global Top 100:... Read more
Clearance iMacs available for up to $300 off...
B&H Photo has clearance 21″ and 27″ Apple iMacs available starting at $949, each including free shipping plus NY & NJ sales tax only: - 27″ 3.3GHz iMac 5K: $1999 $300 off original MSRP - 27″... Read more

Jobs Board

*Apple* News Product Marketing Mgr., Publish...
…organizational consensus on strategy and vision for publisher tools, authoring, and Apple News Format.Carries this strategy and vision across the organization to 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
Security Data Analyst - *Apple* Information...
…data sources need to be collected to allow Information Security to better protect Apple employees and customers from a wide range of threats.Act as the subject matter Read more
Lead *Apple* Solutions Consultant - Apple I...
…integrity, and trust.Success Metrics/Key Performance Indicators:Quantitative* Year over Year growth in Apple Product and Beyond the Box sales in the assigned Point of Read more
*Apple* Solutions Consultant till v%u00E5r...
…ethics, integrity, and trust.Success Metrics/Key Performance Indicators:QuantitativeYear over Year growth in Apple Product and Beyond the Box sales in the assigned Point Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.