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

Direct Mail 4.3.9 - Create and send grea...
Direct Mail is an easy-to-use, fully-featured email marketing app purpose-built for OS X. It lets you create and send great looking email campaigns. Start your newsletter by selecting from a gallery... Read more
FotoMagico 5.4 - Powerful slideshow crea...
FotoMagico lets you create professional slideshows from your photos and music with just a few, simple mouse clicks. It sports a very clean and intuitive yet powerful user interface. High image... Read more
beaTunes 4.6.12 - Organize your music co...
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
Spotify 1.0.49.125. - 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
Eye Candy 7.2.0.50 - 30 professional Pho...
Eye Candy renders realistic effects that are difficult or impossible to achieve in Photoshop alone, such as Fire, Chrome, and the new Lightning. Effects like Animal Fur, Smoke, and Reptile Skin are... Read more
Safari Technology Preview 10.2 - The new...
Safari Technology Preview contains the most recent additions and improvements to WebKit and the latest advances in Safari web technologies. And once installed, you will receive notifications of... Read more
Microsoft Office 2016 15.31 - Popular pr...
Microsoft Office 2016 - Unmistakably Office, designed for Mac. The new versions of Word, Excel, PowerPoint, Outlook and OneNote provide the best of both worlds for Mac users - the familiar Office... Read more
QuickBooks 16.1.12.1564 R13 - Financial...
QuickBooks 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. Built for... Read more
1Password 6.6.1 - Powerful password mana...
1Password is a password manager that uniquely brings you both security and convenience. It is the only program that provides anti-phishing protection and goes beyond password management by adding Web... Read more
1Password 6.6.1 - Powerful password mana...
1Password is a password manager that uniquely brings you both security and convenience. It is the only program that provides anti-phishing protection and goes beyond password management by adding Web... Read more

Tavern Guardians (Games)
Tavern Guardians 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: Tavern Guardians is a Hack-and-Slash action game played in the style of a match-three. You can experience high pace action... | Read more »
Slay your way to glory in idle RPG Endle...
It’s a golden age for idle games on the mobile market, and those addictive little clickers have a new best friend. South Korean developer Ekkorr released Endless Frontier last year, and players have been idling away the hours in the company of its... | Read more »
Tiny Striker: World Football Guide - How...
| Read more »
Good news everyone! Futurama: Worlds of...
Futurama is finding a new home on mobile in TinyCo and Fox Interactive's new game, Futurama: Worlds of Tomorrow. They're really doing it up, bringing on board Futurama creator Matt Groening along with the original cast and writers. TinyCo wants... | Read more »
MUL.MASH.TAB.BA.GAL.GAL (Games)
MUL.MASH.TAB.BA.GAL.GAL 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: ENDLESS UPGRADES. CONSTANT DANGER. ANCIENT WISDOM. BOUNCY BALLS. Launch Sale, 40% OFF for a very limited time!!! MUL.... | Read more »
Dungeon Rushers (Games)
Dungeon Rushers 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: Dungeon Rushers is a 2D tactical RPG combining dungeon crawler’s gameplay and turn based fights. Manage your team, loot dusty... | Read more »
Blasty Bubs is a colorful Pinball and Br...
QuickByte Games has another arcade treat in the works -- this time it's a mishmash of brick breaking and Pinball mechanics. It's called Blasty Bubs, and it's a top down brickbreaker that has you slinging balls around a board. [Read more] | Read more »
Corsola and Heracross are the new region...
Generation 2 finally launched in Pokémon GO, unleashing a brand new batch of Pokémon into the wild. Even before the update went live people were speculating on how to catch elusive Pokémon like the legendary "dogs", Unknown, and whether or not... | Read more »
The Warlock of Firetop Mountain (Games)
The Warlock of Firetop Mountain 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: An epic adventure through a mysterious mountain filled with monsters, magic and mayhem! “...it looks downright... | Read more »
Fantasy MMORPG MU Origin’s receives a hu...
Developer Webzen are looking to take their highly popular fantasy battler MU Origin to the next level this month, with its most ambitious overhaul yet. The latest update introduces the long sought after Server Arena, new treasure dungeons, and much... | Read more »

Price Scanner via MacPrices.net

15-inch Touch Bar MacBook Pros on sale for up...
B&H Photo has the new 2016 15″ Apple Touch Bar MacBook Pros in stock today and on sale for up to $150 off MSRP. Shipping is free, and B&H charges NY sales tax only: - 15″ 2.7GHz Touch Bar... Read more
12-inch Retina MacBooks on sale for $1150, $1...
B&H has 12″ 1.1GHz Retina MacBooks on sale for $150 off MSRP. Shipping is free, and B&H charges NY sales tax only: - 12″ 1.1GHz Space Gray Retina MacBook: $1149 $150 off MSRP - 12″ 1.1GHz... Read more
Apple restocks refurbished 11-inch MacBook Ai...
Apple has Certified Refurbished 11″ MacBook Airs (the latest models recently discontinued by Apple), available for up to $170 off original MSRP. An Apple one-year warranty is included with each... Read more
Apple Park Opens to Employees in April With T...
Apple has announced that Apple Park, the company’s new 175-acre campus, will be ready for employees to begin occupying in April. The process of moving more than 12,000 people will take over six... Read more
Manhattan Neighbors for Safer Telecommunicati...
A new education and advocacy group focused on cell phone and wireless risks, Manhattan Neighbors for Safer Telecommunications, launched today at http://www.ManhattanNeighbors.org. Manhattan... Read more
Portable Dual DisplayPort Monitor Dock Enable...
IOGEAR has announced the launch of its USB-C Dual DisplayPort Monitor Portable Dock (GUC3CMST). The dock enables users to easily connect two DisplayPort monitors to a USB-C or Thunderbolt 3 laptop to... Read more
13-inch 2.7GHz Retina MacBook Pro on sale for...
Amazon.com has restocked the 13″ 2.7GHz/128GB Retina MacBook Pro (MF839LL/A) for $200 off MSRP including free shipping: - 13″ 2.7GHz/128GB Retina MacBook Pro: $1099 $200 off MSRP This model tends to... Read more
Apple’s New iPad Ads Don’t Address Pro Users’...
Apple launched a new tranche of iPad Pro TV ads last week addressing actual queries and challenges from the Twitterverse, albeit using actors for the visuals. That’s great. As an iPad fan and heavy... Read more
Free Verbum Catholic Bible Study App For iOS
The Verbum mobile app runs on Logos’ powerful Bible software and is an advanced resource for mobile Catholic study. The Verbum app surrounds the Bible with the Tradition. Verbum comes with 15 free... Read more
27-inch Apple iMacs on sale for up to $200 of...
B&H Photo has 27″ Apple iMacs on sale for up to $200 off MSRP, each including free shipping plus NY sales tax only: - 27″ 3.3GHz iMac 5K: $2099.99 $200 off MSRP - 27″ 3.2GHz/1TB Fusion iMac 5K: $... Read more

Jobs Board

Manager *Apple* Systems Administration - Pu...
Req ID 3315BR Position Title Manager, Apple Systems Administration Job Description The Manager of Apple Systems Administration oversees the administration and 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
Manager *Apple* Systems Administration - Pu...
Req ID 3315BR Position Title Manager, Apple Systems Administration Job Description The Manager of Apple Systems Administration oversees the administration and 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
Manager *Apple* Systems Administration - Pu...
Req ID 3315BR Position Title Manager, Apple Systems Administration Job Description The Manager of Apple Systems Administration oversees the administration and Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.