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
$103.22
Apple Inc.
+0.72
MSFT
$44.88
Microsoft Corpora
-0.55
GOOG
$574.15
Google Inc.
+2.55

MacTech Search:
Community Search:

Software Updates via MacUpdate

NetShade 6.0.2 - Browse privately using...
NetShade is an Internet security tool that conceals your IP address on the web. NetShade routes your Web connection through either a public anonymous proxy server, or one of NetShade's own dedicated... Read more
Mac DVDRipper Pro 5.0 - Copy, backup, an...
Mac DVDRipper Pro is the DVD backup solution that lets you protect your DVDs from scratches, save your batteries by reading your movies from your hard disk, manage your collection with just a few... Read more
pwSafe 3.1 - Secure password management...
pwSafe provides simple and secure password management across devices and computers. pwSafe uses iCloud to keep your password databases backed-up and synced between Macs and iOS devices. It is... Read more
StatsBar 1.8 - Monitor system processes...
StatsBar gives you a comprehensive and detailed analysis of the following areas of your Mac: CPU usage Memory usage Disk usage Network and bandwidth usage Battery power and health (MacBooks only)... Read more
Path Finder 6.5.5 - Powerful, award-winn...
Path Finder is a file browser that combines the familiar Finder interface with the powerful utilities and innovative features. Just a small selection of the Path Finder 6 feature set: Dual pane... Read more
QuarkXPress 10.2.1 - Desktop publishing...
With QuarkXPress, you can communicate in all the ways you need to -- and always look professional -- in print and digital media, all in a single tool. Features include: Easy to Use -- QuarkXPress is... Read more
Skype 6.19.0.450 - Voice-over-internet p...
Skype allows you to talk to friends, family and co-workers across the Internet without the inconvenience of long distance telephone charges. Using peer-to-peer data transmission technology, Skype... Read more
VueScan 9.4.41 - Scanner software with a...
VueScan is a scanning program that works with most high-quality flatbed and film scanners to produce scans that have excellent color fidelity and color balance. VueScan is easy to use, and has... Read more
Cloud 3.0.0 - File sharing from your men...
Cloud is simple file sharing for the Mac. Drag a file from your Mac to the CloudApp icon in the menubar and we take care of the rest. A link to the file will automatically be copied to your clipboard... Read more
LibreOffice 4.3.1.2 - Free Open Source o...
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

Latest Forum Discussions

See All

Function Space, a Social Network App for...
Function Space, a Social Network App for Science, Launches on iOS Posted by Ellis Spice on September 2nd, 2014 [ permalink ] | Read more »
Treasure Tombs: Ra Deal Coming from Bulk...
Treasure Tombs: Ra Deal Coming from Bulkypix and Dark Tonic This Fall Posted by Jessica Fisher on September 2nd, 2014 [ permalink ] Dark Tonic and | Read more »
Tiny Tower Vegas Review
Tiny Tower Vegas Review By Jennifer Allen on September 2nd, 2014 Our Rating: :: STEADY DEVELOPMENTUniversal App - Designed for iPhone and iPad Build a huge tower again but Vegas-style in Tiny Tower Vegas.   | Read more »
The Manhattan Project Review
The Manhattan Project Review By Andrew Fisher on September 2nd, 2014 Our Rating: :: ROCKET SCIENCEUniversal App - Designed for iPhone and iPad The Manhattan Project offers a great Euro-style gameplay experience, but it is totally... | Read more »
Rhonna Designs Magic (Photography)
Rhonna Designs Magic 1.0 Device: iOS Universal Category: Photography Price: $1.99, Version: 1.0 (iTunes) Description: Want to sprinkle *magic* on your photos? With RD Magic, you can add colors, filters, light leaks, bokeh, edges,... | Read more »
This Week at 148Apps: August 25-29, 2014
Shiny Happy App Reviews   | Read more »
Qube Kingdom – Tips, Tricks, Strategies,...
Qube Kingdom is a tower defense game from DeNA. You rally your troops – magicians, archers, knights, barbarians, and others – and fight against an evil menace looking to dominate your kingdom of tiny squares. Planning a war isn’t easy, so here are a... | Read more »
Qube Kingdom Review
Qube Kingdom Review By Nadia Oxford on August 29th, 2014 Our Rating: :: KIND OF A SQUARE KINGDOMUniversal App - Designed for iPhone and iPad Qube Kingdom has cute visuals, but it’s a pretty basic tower defense game at heart.   | Read more »
Fire in the Hole Review
Fire in the Hole Review By Rob Thomas on August 29th, 2014 Our Rating: :: WALK THE PLANKUniversal App - Designed for iPhone and iPad Seafoam’s Fire in the Hole looks like a bright, 8-bit throwback, but there’s not enough booty to... | Read more »
Alien Creeps TD is Now Available Worldwi...
Alien Creeps TD is Now Available Worldwide Posted by Ellis Spice on August 29th, 2014 [ permalink ] Universal App - Designed for iPhone and iPad | Read more »

Price Scanner via MacPrices.net

Apple refurbished iPads available for up to $...
Apple is offering Certified Refurbished iPad Airs for up to $140 off MSRP. Apple’s one-year warranty is included with each model, and shipping is free. Stock tends to come and go with some of these... Read more
Are We Now In The Post-Post-PC Era?
A longtime and thoroughgoing laptop aficionado, I was more than a little dismayed by Steve Jobs’s declaration back in 2010 when he sprang the iPad on an unsuspecting world. that we’d entered a “post-... Read more
PC Outlook Improves, But 2014 Shipments Still...
According to the International Data Corporation (IDC) Worldwide Quarterly PC Tracker, worldwide PC shipments are expected to fall by -3.7 percent in 2014. To hat’s actually an improvement from the... Read more
IDC Lowers Tablet Sales Projections for 2014...
Following a second consecutive quarter of softer than expected demand, International Data Corporation (IDC) has lowered its worldwide tablet plus 2-in-1 forecast for 2014 to 233.1 million units. The... Read more
Apple now offering refurbished 21-inch 1.4GHz...
The Apple Store is now offering Apple Certified Refurbished 21″ 1.4GHz iMacs for $929 including free shipping plus Apple’s standard one-year warranty. Their price is $170 off the cost of new models,... Read more
Save $50 on the 2.5GHz Mac mini, on sale for...
B&H Photo has the 2.5GHz Mac mini on sale for $549.99 including free shipping. That’s $50 off MSRP, and B&H will also include a free copy of Parallels Desktop software. NY sales tax only. Read more
Save up to $300 on an iMac with Apple refurbi...
The Apple Store has Apple Certified Refurbished iMacs available for up to $300 off the cost of new models. Apple’s one-year warranty is standard, and shipping is free. These are the best prices on... Read more
The Rise of Phablets
Carlisle & Gallagher Consulting Group, a businesses and technology consulting firm focused solely on the financial services industry, has released an infographic depicting the convergence of... Read more
Bad Driver Database App Allows Good Drivers t...
Bad Driver Database 1.4 by Facile Group is a new iOS and Android app that lets users instantly input and see how many times a careless, reckless or just plain stupid driver has been added to the... Read more
Eddy – Cloud Music Player for iPhone/iPad Fre...
Ukraine based CapableBits announces the release of Eddy, its tiny, but smart and powerful cloud music player for iPhone and iPad that allows users to stream or download music directly from cloud... Read more

Jobs Board

*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
*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
*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
*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.