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.*

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Merlin Project 4.2.0 - Project managemen...
Merlin Project is the leading professional project management software for OS X. If you plan complex projects on your Mac, you won’t get far with a simple list of tasks. Good planning raises... Read more
Skim 1.4.28 - PDF reader and note-taker...
Skim is a PDF reader and note-taker for OS X. It is designed to help you read and annotate scientific papers in PDF, but is also great for viewing any PDF file. Skim includes many features and has a... Read more
RapidWeaver 7.3.2 - Create template-base...
RapidWeaver is a next-generation Web design application to help you easily create professional-looking Web sites in minutes. No knowledge of complex code is required, RapidWeaver will take care of... Read more
Together 3.8.1 - Store and organize all...
Together helps you organize your Mac, giving you the ability to store, edit and preview your files in a single clean, uncluttered interface. Features Smart storage. With simple drag-and-drop... Read more
Apple MainStage 3.3 - Live performance t...
Apple MainStage makes it easy to bring to the stage all the same instruments and effects that you love in your recording. Everything from the Sound Library and Smart Controls you're familiar with... Read more
Apple iOS 10.3 - The latest version of A...
iOS 10 is the biggest release of iOS ever. A massive update to Messages brings the power of the App Store to your conversations and makes messaging more personal than ever. Find your route with... Read more
Postbox 5.0.12 - Powerful and flexible e...
Postbox is a new email application that helps you organize your work life and get stuff done. It has all the elegance and simplicity of Apple Mail, but with more power and flexibility to manage even... Read more
Apple Keynote 7.1 - Apple's present...
Easily create gorgeous presentations with the all-new Keynote, featuring powerful yet easy-to-use tools and dazzling effects that will make you a very hard act to follow. The Theme Chooser lets you... Read more
Apple Pages 6.1 - Apple's word proc...
Apple Pages is a powerful word processor that gives you everything you need to create documents that look beautiful. And read beautifully. It lets you work seamlessly between Mac and iOS devices, and... Read more
Apple Numbers 4.1 - Apple's spreads...
With Apple Numbers, sophisticated spreadsheets are just the start. The whole sheet is your canvas. Just add dramatic interactive charts, tables, and images that paint a revealing picture of your data... Read more

4 smart and stylish puzzle games like Ty...
TypeShift launched a little over a week ago, offering some puzzling new challenges for word nerds equipped with an iOS device. Created by Zach Gage, the mind behind Spelltower, TypeShift boasts, like its predecessor, a sleak design and some very... | Read more »
The best deals on the App Store this wee...
Deals, deals, deals. We're all about a good bargain here on 148Apps, and luckily this was another fine week in App Store discounts. There's a big board game sale happening right now, and a few fine indies are still discounted through the weekend.... | Read more »
The best new games we played this week
It's been quite the week, but now that all of that business is out of the way, it's time to hunker down with some of the excellent games that were released over the past few days. There's a fair few to help you relax in your down time or if you're... | Read more »
Orphan Black: The Game (Games)
Orphan Black: The Game 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: Dive into a dark and twisted puzzle-adventure that retells the pivotal events of Orphan Black. | Read more »
The Elder Scrolls: Legends is now availa...
| Read more »
Ticket to Earth beginner's guide: H...
Robot Circus launched Ticket to Earth as part of the App Store's indie games event last week. If you're not quite digging the space operatics Mass Effect: Andromeda is serving up, you'll be pleased to know that there's a surprising alternative on... | Read more »
Leap to victory in Nexx Studios new plat...
You’re always a hop, skip, and a jump away from a fiery death in Temple Jump, a new platformer-cum-endless runner from Nexx Studio. It’s out now on both iOS and Android if you’re an adventurer seeking treasure in a crumbling, pixel-laden temple. | Read more »
Failbetter Games details changes coming...
Sunless Sea, Failbetter Games' dark and gloomy sea explorer, sets sail for the iPad tomorrow. Ahead of the game's launch, Failbetter took to Twitter to discuss what will be different in the mobile version of the game. Many of the changes make... | Read more »
Splish, splash! The Pokémon GO Water Fes...
Niantic is back with a new festival for dedicated Pokémon GO collectors. The Water Festival officially kicks off today at 1 P.M. PDT and runs through March 29. Magikarp, Squirtle, Totodile, and their assorted evolved forms will be appearing at... | Read more »
Death Road to Canada (Games)
Death Road to Canada 1.0 Device: iOS Universal Category: Games Price: $7.99, Version: 1.0 (iTunes) Description: Get it now at the low launch price! Price will go up a dollar every major update. Update news at the bottom of this... | Read more »

Price Scanner via MacPrices.net

13-inch MacBook Airs, Apple refurbished, in s...
Apple has Certified Refurbished 2016 13″ MacBook Airs available starting at $849. An Apple one-year warranty is included with each MacBook, and shipping is free: - 13″ 1.6GHz/8GB/128GB MacBook Air: $... Read more
12-inch Retina MacBooks on sale for $1199, sa...
B&H has 12″ 1.1GHz Retina MacBooks on sale for $100 off MSRP. Shipping is free, and B&H charges NY sales tax only: - 12″ 1.1GHz Space Gray Retina MacBook: $1199 $100 off MSRP - 12″ 1.1GHz... Read more
Save up to $260 with Apple refurbished 12-inc...
Apple has Certified Refurbished 2016 12″ Retina MacBooks available for $200-$260 off MSRP. Apple will include a standard one-year warranty with each MacBook, and shipping is free. The following... Read more
13-inch 2.7GHz Retina MacBook Pro on sale for...
B&H Photo has the 2015 13″ 2.7GHz/128GB Retina Apple MacBook Pro on sale for $170 off MSRP. Shipping is free, and B&H charges NY tax only: - 13″ 2.7GHz/128GB Retina MacBook Pro (MF839LL/A): $... Read more
15-inch 2.2GHz Retina MacBook Pro on sale for...
B&H Photo has the 2015 15″ 2.2GHz Retina MacBook Pro (MJLQ2LL/A) on sale for $1799.99 including free shipping plus NY sales tax only. Their price is $200 off MSRP. Read more
Save up to $160 with Apple refurbished 9-inch...
Apple has Certified Refurbished 9″ and 12″ Apple iPad Pros available for up to $160 off the cost of new iPads. An Apple one-year warranty is included with each model, and shipping is free: - 32GB 9″... Read more
Apple Chip Foundry TSMC To Begin A11 System-o...
Digitimes’ Steve Shen is reporting today that according to the Chinese-language Economic Daily News (EDN), chipmaker and major Apple supplier foundery Taiwan Semiconductor Manufacturing Company (TSMC... Read more
MacX MediaTrans 3.5 iOS Data Transfer Spring...
MacXDVD Software has announced general availability of the latest MacX MedTrans 3.5, featuring a new user interface (UI). MacX MediaTrans is ann iPhone manager that enables free data transfer between... Read more
Regular Price $19.95 DupeZap 4 Finder For OS...
Hyperbolic Software has announced the release of DupeZap 4.0.2, their modern duplicate finder developed exclusively for macOS. DupeZap 4 is an utility for Mac owners seeking to reclaim disk space... Read more
B-Eng Releases SSD Health Check for MVNe for...
Fehraltorf, Switzerland based B-Eng has announced the release and immediate availability of SSD Health Check for MVNe for MacBook Pro, their app that delivers important data and insights for MVNe... Read more

Jobs Board

Fulltime aan de slag als shopmanager in een h...
Ben jij helemaal gek van Apple -producten en vind je het helemaal super om fulltime shopmanager te zijn in een jonge en hippe elektronicazaak? Wil jij werken in Read more
*Apple* Mobile Master - Best Buy (United Sta...
**492889BR** **Job Title:** Apple Mobile Master **Location Number:** 000886-Norwalk-Store **Job Description:** **What does a Best Buy Apple Mobile Master do?** Read more
*Apple* Mobile Master - Best Buy (United Sta...
**492472BR** **Job Title:** Apple Mobile Master **Location Number:** 000470-Seattle-Store **Job Description:** **What does a Best Buy Apple Mobile Master do?** Read more
*Apple* Mobile Master - Best Buy (United Sta...
**492562BR** **Job Title:** Apple Mobile Master **Location Number:** 000853-Jackson-Store **Job Description:** **What does a Best Buy Apple Mobile Master do?** 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
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.