TweetFollow Us on Twitter

March 96 - GRAPHICAL TRUFFLES: The Display Manager

GRAPHICAL TRUFFLES: The Display Manager

Mike Marinkovich

A major change is taking place on the screen, which your application might not even know about! With the help of the Display Manager, the user can use the Monitors control panel to rearrange displays, make resolution switches, add or remove a display, and move the menu bar from one display to another -- all without rebooting. However, the ease of changing a display for the user poses new challenges for the developer if an application relies on a graphics device's bounding rectangle to position, zoom, and grow its windows.

To meet this challenge, the Display Manager provides several new functions that make it easier to gather information about the display environment and implement changes. I'll describe some of the more commonly used functions in this column. I'll also discuss how to use a notification event to find out when a display has changed (an example is included on this issue's CD).

Two versions of the Display Manager are currently implemented in the system software. The information in this column applies to both versions. Display Manager version 1.0 is available on all PowerPC(TM) processor-based Macintosh computers and Color QuickDraw-capable Macintosh computers running System 7.5. Display Manager 2.0 is available on PCI-based computers running System 7.5.2. To determine whether the Display Manager is available, call Gestalt with the selector gestaltDisplayMgrAttr and check the gestaltDisplayMgrPresent bit of the response. To determine which version you have, call Gestalt with the selector gestaltDisplayMgrVers.

MORE FUNCTIONS, LESS CODE

The Display Manager includes several new functions that greatly simplify tasks that used to take a lot of code. For example, many applications need to query screen devices for bounding rectangles, pixel depths, and a variety of other things. Prior to the Display Manager, an application could use the GetDeviceList function to retrieve the first graphics device record in the device list and call GetNextDevice for subsequent devices in the list. The application would then need to use the Device Manager to determine whether the device was a screen device and whether it was active. With the Display Manager, you can do all this with two functions: DMGetFirstScreenDevice and DMGetNextScreenDevice.
GDHandle      aDevice;

aDevice = 
   DMGetFirstScreenDevice(dmOnlyActiveDisplays);
while (aDevice != nil) {
   // Do something with the device.
   ...
   // Get the next device in the list.
   aDevice = DMGetNextScreenDevice(aDevice, 
                        dmOnlyActiveDisplays);
}
The Display Manager also introduces two functions that make it easier to retrieve information about the attached displays and to change their characteristics: DMCheckDisplayMode and DMSetDisplayMode.

DMCheckDisplayMode determines whether a specific display mode and pixel depth are supported by the supplied graphics device. (A display mode is a combination of several interrelated display characteristics, such as resolution and scan timing.) This function has two output parameters: modeOk and switchFlags. If the Boolean modeOk parameter is true, the screen device supports the requested display mode. The switchFlags parameter contains two flag bits that should be checked with the constants kNoSwitchConfirmBit and kDepthNotAvailableBit.

  • If kNoSwitchConfirmBit isn't set, the requested mode is an optional mode and is only shown in the mode list of the Monitors control panel when the Option key is pressed (an optional mode requires confirmation from the user before it's allowed).

  • kDepthNotAvailableBit indicates whether the requested pixel depth is available with the requested display mode.
Once your application knows that the requested display mode and pixel depth are available, you can use the DMSetDisplayMode function to reconfigure the video display. If you pass 0 for the mode parameter, the Display Manager uses the device's current display mode.

If you like to change the display mode and pixel depth often, you can save the configuration and retrieve it at startup with the DMSaveScreenPrefs function. This function requires three parameters, which all take the value of NULL since they're private to the Display Manager. (Go figure.)

Identifying displays. Many of the Display Manager functions require a display ID (type DisplayIDType) as a parameter. A display ID is a long integer that uniquely identifies a screen display. Affiliating a display ID with a graphics device can be useful in cases where the graphics device might change or isn't available. You can obtain a display ID with the function DMGetDisplayIDByGDevice, which requires a graphics device as a parameter. Or you can retrieve the graphics device corresponding to a given display ID by calling DMGetGDeviceByDisplayID. Both functions require the Boolean parameter failToMain.

  • If you set failToMain to true and the routine can't find what it's looking for (either the graphics device or the display ID), the routine returns information about the main graphics device rather than returning an error.

  • If you set failToMain to false and the routine can't find what it's looking for, it will return kDMDisplayNotFoundErr. (For example, when a PowerBook goes to sleep, the display might be removed.)

KEEPING UP WITH THE CHANGES

Now that the user is able to change a screen display without restarting, your application may want to reposition and resize its windows, update internal display-related data structures, or update nonstandard window definitions on the fly.

If desired, the Display Manager can automatically adjust the positions of the windows that were onscreen before the change to keep them onscreen after the change, but it may not put them in the best possible positions. However, if you want to reposition and resize your windows yourself, you need to set the isDisplayManagerAware flag in your application's SIZE resource and install a callback procedure or an Apple event handler in your application so that you'll know when a display has changed.

Your application registers a callback procedure with the Display Manager function DMRegisterNotifyProc. The display notification procedure takes a Display Notice Apple event parameter describing the changes that were made to the display. The notification callback is especially useful for control panels and other instances where high-level event handling in an event loop isn't possible. Another benefit of the notification callback is that your application is informed on a more timely basis than through a high-level event, thus giving the appearance of seamless integration with the Display Manager.

    If you're using Display Manager 1.0, you're not notified about depth changes, and A5 isn't restored when you receive the notification callback.*
You can also receive and process Display Notice events through an Apple event handler. Display Notice event handlers are installed like any other Apple event handlers, with the AEInstallEventHandler function:
err = AEInstallEventHandler(kCoreEventClass, 
   kAESystemConfigNotice,
   NewAEEventHandlerProc(DoAEDisplayConfigChange),
   0, false);
To enable high-level events in your application, you need to set the isHighLevelEventAware flag in the SIZE resource. (You'll also need to support the required Apple events described in Inside Macintosh: Interapplication Communication.)

Whether your application uses a notification callback or a high-level event handler, a Display Notice Apple event is passed to your routine. You can obtain a list of descriptor records (an AEDescList) from the Display Notice event with the AEGetParamDesc function. Each descriptor record holds two additional keyword-specific descriptor records:

  • keyDisplayOldConfig, which is a record of the display's previous state

  • keyDisplayNewConfig, which is a record of the display's current state
You can obtain these records one at a time with the function AEGetNthDesc.

To move and resize your application's windows, you need to know which graphics device was affected, the old and new bounding rectangles of the device, and possibly the pixel depth. All the information about the affected graphics device can be obtained from the descriptor list with keyword-specific descriptor constants, which are defined in the Displays.h universal header file. You call AEGetKeyPtr with the various descriptor constants to extract the information you need. In particular, the constant keyDeviceRect extracts the bounding rectangle, and keyDisplayID extracts the display ID. As previously mentioned, you can convert a display ID to a graphics device with the function DMGetGDeviceByDisplayID.

Listing 1 shows an example of what to do after receiving a Display Notice event from a notification callback or a high-level event handler.

Listing 1. Handling the Display Notice event

OSErr HandleNotification(AppleEvent *event)
{
   OSErr           err;
   GrafPtr         oldPort;
   AEDescList      displayList, aDisplay;
   AERecord        oldConfig, newConfig;
   AEKeyword       tempWord;
   DisplayIDType   displayID;
   unsigned long   returnType;
   long            count;
   Rect            oldRect, newRect;

   GetPort(&oldPort);

   // Get a list of the displays from the Display Notice Apple event.
   err = AEGetParamDesc(event, kAEDisplayNotice, typeWildCard,
             &DisplayList);

   // How many items in the list?
   err = AECountItems(&displayList, &count);

   while (count > 0) {
      // Loop through the list.
      err = AEGetNthDesc(&displayList, count, typeWildCard,
               &tempWord, &aDisplay);

      // Get the old rect. 
      err = AEGetNthDesc(&aDisplay, 1, typeWildCard, &tempWord,
               &oldConfig);
      err = AEGetKeyPtr(&oldConfig, keyDeviceRect, typeWildCard,
               &returnType, &oldRect, 8, nil);

      // Get the display ID so that we can get the GDevice later.
      err = AEGetKeyPtr(&oldConfig, keyDisplayID, typeWildCard,
               &returnType, &displayID, 8, nil);

      // Get the new rect.
      err = AEGetNthDesc(&aDisplay, 2, typeWildCard, &tempWord,
               &newConfig);
      err = AEGetKeyPtr(&newConfig, keyDeviceRect, typeWildCard,
               &returnType, &newRect, 8, nil);

      // If the new and old rects are not the same, we can assume
      // that the GDevice has changed, and the windows need to be
      // rearranged.
      if (err == noErr && !EqualRect(&newRect, &oldRect))
         HandleDeviceChange(displayID, &newRect);

      count--;
      err = AEDisposeDesc(&aDisplay);
      err = AEDisposeDesc(&oldConfig);
      err = AEDisposeDesc(&newConfig);
   }

   err = AEDisposeDesc(&displayList);
   SetPort(oldPort);

   return err;
}

WHAT TO DO NOW

The sample code on this issue's CD should provide a starting point for how to handle display notification events in your application. Additional documentation and sample code for the Display Manager are provided in the Display Manager Development Kit, which is also on the CD.
    The Mac OS Software Developer's Kit incudes the Display Manager Development Kit along with a lot of other development software. The Mac OSSDK is now part of the Developer CD Series (included in the Apple Developer Mailing, which is available through the Apple Developer Catalog).*
To learn more about what the Display Manager can do for you, you should also take a look at the Displays.h universal header file.

Now there's no excuse for your application to be in the dark about changes taking place on the screen. So why not keep your users happy and take advantage of the help that the Display Manager can give you?

MIKE MARINKOVICH (marink@apple.com) is a member of the Printing, Imaging, and Graphics (PIGS) group in Developer Technical Support at Apple. He's been whiling away his days (and many of his evenings) coming to grips with the Display Manager and other QuickDraw-related esoterica. When not indulging in his hobby, which also happens to be playing around with the Toolbox and programming his Macintosh, Mike spends his time exploring the San Francisco Bay Area in his trusty Subaru. Mike's from Seattle and misses the rain.*

Thanks to Eric Anderson, David Hayward, and Ian Hendry for reviewing this column.*

 
AAPL
$99.18
Apple Inc.
-1.57
MSFT
$45.90
Microsoft Corpora
-0.46
GOOG
$568.27
Google Inc.
-9.09

MacTech Search:
Community Search:

Software Updates via MacUpdate

Cocktail Family License (5 Macs) 7.6.1 -...
Cocktail is a general purpose utility for OS X that lets you clean, repair and optimize your Mac. It is a powerful digital toolset that helps hundreds of thousands of Mac users around the world get... Read more
Cocktail 8.0 Beta 2 - General maintenanc...
Cocktail is a general purpose utility for OS X that lets you clean, repair and optimize your Mac. It is a powerful digital toolset that helps hundreds of thousands of Mac users around the world get... Read more
QuickBooks 2015 16.0.0.1352 R1 - Financi...
QuickBooks 2015 helps you manage your business easily and efficiently. Organize your finances all in one place, track money going in and out of your business, and spot areas where you can save.... Read more
Mac DVDRipper Pro 5.0.1 - Copy, backup,...
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
Apple OS X bash Update 1.0 - Fix for sec...
The OS X bash Update fixes a security flaw in the bash UNIX shell on OS X 10.9.5 (also on OS X 10.8 and 10.7 [see Related Links below]). OS X 10.9.5 or later Downloads for OS X 10.8 and OS X 10.7 in... Read more
SyncTwoFolders 2.0.5 - Syncs two user-sp...
SyncTwoFolders simply synchronizes two folders. It supports synchronization across mounted network drives and it is a possibility to run a simulation showing in a log what will be done. Please visit... Read more
FinderPop 2.5.7 - Classic Mac utility, n...
FinderPop is a Universal preference pane that extends OS X's contextual menus using a FinderPop Items folder much as the Apple Menu Items folder used to do for the Apple menu. It has other features... Read more
VueScan 9.4.45 - 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
LibreOffice 4.3.2.2 - 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
calibre 2.4 - Complete e-library managem...
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... Read more

Latest Forum Discussions

See All

iKeywi - Customizable 5-Row Keyboard (U...
iKeywi - Customizable 5-Row Keyboard 1.0 Device: iOS Universal Category: Utilities Price: $.99, Version: 1.0 (iTunes) Description: Want to add an extra row to your iPhone/iPad? One of the most popular keyboard extension in iOS... | Read more »
Manage Your Cloud – Wunderlist Now Suppo...
Manage Your Cloud – Wunderlist Now Supports Dropbox Posted by Jessica Fisher on October 1st, 2014 [ permalink ] Universal App - Designed for iPhone and iPad | Read more »
Nexticy Review
Nexticy Review By Jennifer Allen on October 1st, 2014 Our Rating: :: IDEAL FORM CREATIONiPad Only App - Designed for the iPad Nexticy allows you to make your own forms for research purposes or to organize your business better. It’s... | Read more »
Tiny Troopers: Alliance Marches onto the...
Tiny Troopers: Alliance Marches onto the App Store Tomorrow Posted by Jessica Fisher on October 1st, 2014 [ permalink ] Tiny Troopers: Alliance, by Kukouri, is a | Read more »
HeroCraft Introduces Unlimited Sequel to...
HeroCraft Introduces Unlimited Sequel to WW2: Sandbox. Strategy & Tactics Posted by Jessica Fisher on October 1st, 2014 [ permalink ] | Read more »
RGB Express Review
RGB Express Review By Jennifer Allen on October 1st, 2014 Our Rating: :: DELIGHTFUL PUZZLINGUniversal App - Designed for iPhone and iPad Guide trucks along their delivery routes in RGB Express, a testing but charming puzzle game... | Read more »
The Sagas of Fire*Wolf (Games)
The Sagas of Fire*Wolf 1.0 Device: iOS Universal Category: Games Price: $9.99, Version: 1.0 (iTunes) Description: | Read more »
BuggyFun Review
BuggyFun Review By Amy Solomon on October 1st, 2014 Our Rating: iPad Only App - Designed for the iPad BuggyFun allows children to create their own tracks for bugs to interact with for a unique open-ended experience.   | Read more »
Fold the Adventure Review
Fold the Adventure Review By Jennifer Allen on October 1st, 2014 Our Rating: :: AWKWARD FOLDSUniversal App - Designed for iPhone and iPad Fold pieces of paper to create platforms for a princely rabbit in this puzzle game; something... | Read more »
WW2: Sandbox. Strategy & Tactics (G...
WW2: Sandbox. Strategy & Tactics 1.0.0 Device: iOS Universal Category: Games Price: $9.99, Version: 1.0.0 (iTunes) Description: ***NOTE: Compatible with iPhone 4s and up, iPad 2 and up - may not work properly on earlier devices... | Read more »

Price Scanner via MacPrices.net

Amazon offers 13-inch MacBook Air for $899, $...
Amazon.com has the 13″ 1.4GHz 128GB MacBook Air on sale for $100 off MSRP including free shipping: - 13″ 1.4GHz 128GB MacBook Air: $899.99 Read more
Apple resting On Its iPhone Laurels? – The ‘B...
Apple calls its new iPhone 6 and 6 Plus “The Biggest Advancements in iPhone History,” but does reality live up to the hype? “Seldom have so many waited so breathlessly for so little,” tweeted veteran... Read more
Roundup of Apple Mac and iPad Education disco...
Purchase a new Mac or iPad at The Apple Store for Education and take up to $300 off MSRP. All teachers, students, and staff of any educational institution qualify for the discount. Shipping is free,... Read more
Apple Boycotts German Magazine Computer Bild...
Apple has revoked its PR accreditation of Germany’s Computer Bild, Europe’s best-selling PC magazine, in reaction to Bild’s posting of a “#Bentgate” YouTube video. Axel Telzerow, editor in chief of... Read more
iPhone 6 & iPhone 6 Plus Available in Chi...
Apple has announced that iPhone 6 and iPhone 6 Plus will be available in China beginning Friday, October 17 from the Apple Online Store (http://www.apple.com), Apple’s retail stores, and an expansive... Read more
MacBook Airs on sale for $100 off MSRP, start...
Best Buy has the new 2014 MacBook Airs on sale for $100 off MSRP on their online store. Choose free home shipping or free local store pickup (if available). Prices valid for online orders only, in-... Read more
Apple Releases OS X Mavericks bash Update 1.0...
Apple has released a patch update for OS X Mavericks users to address the recently-detected “Shellshock” security bug in BSD UNIX’s bash shell. Apple says only a few Mac users who had manually... Read more
Pivotal Payments Ready for Apple Pay – FlexPo...
Pivotal Payments, a provider of merchant services and global payment processing solutions, has announced its proprietary FlexPoint platform will support credit and debit transactions through Apple’s... Read more
iStabilizer Announces Tabarm — First Friction...
iStabilizer, a specialist in universal lightweight compact tripods, steady cams, dollies, mounts, and remotes for smartphones, tablets, and cameras, announced today the iStabilizer tabArm, the first... Read more
IStabilizer Flex Smartphone Tripod Wins Usa T...
iStabilizer, a specialist in universal lightweight compact tripods, steady cams, and other products for smartphones, tablets, and cameras, has announced today that its iStabilizer Flex smartphone... 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...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, 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
*Apple* Solutions Consultant (ASC) - Apple (...
**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
Project Manager / Business Analyst, WW *Appl...
…a senior project manager / business analyst to work within our Worldwide Apple Fulfillment Operations and the Business Process Re-engineering team. This role will work Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.