TweetFollow Us on Twitter

Multiple Monitors
Volume Number:10
Issue Number:7
Column Tag:There’s a right way...

Related Info: Window Manager Dialog Manager Standard File
Quickdraw

Multiple Monitors vs. Your Application

Assume one monitor, go to jail...

By Eric Shapiro, Rock Ridge Enterprises

Note: Source code files accompanying article are located on MacTech CD-ROM or source code disks.

About the author

Eric earned fame with his big-hit, glam-hack VideoBeep, first shown at MacHack as a prize-winning entry in the MacHax™ Best Hack contest. When he’s not busy writing his next hack for MacHack, Eric is president of Rock Ridge Enterprises, a Macintosh consulting firm. His other smash hits include Spectator, EzTape, Business Simulator, and (the now illegal) The Grouch.

Eric is currently working on course materials for Apple Developer University’s OpenDoc seminar. He has taught Macintosh Programming Fundamentals and Macintosh Device Drivers seminars for Apple as well. Eric has degrees in both Computer and Electrical Engineering from the University of Michigan and is a past president of MacTechnics Users Group.

You can reach Eric at Shapiro@aol.com

[Eric, otherwise way-too-busy-to-write-an-article, found a reason to sound off. The result? A stream-of-consciousness gripe piece with some useful information. If you’d like to see more of these kinds of articles, please let us know. Better yet, pick your favorite gripe about software done the wrong way, and write up your own “There’s a right way ” article. - Ed stb]

I am writing this article because I’ve recently come across 5 new Mac programs in the last few weeks that don’t support multiple monitors correctly. I’m getting sick of rebooting, and of explaining the various problems to the companies involved, so I’m going to send them a copy of this article instead.

Like many programmers, my main screen is a 2-page b&w display while my second screen is a 13” color display. Several of the programs I’ve been running have problems with all 2 monitor systems. Other programs run properly on some 2 monitor setups, but get confused when the main device has a lower depth than the second one.

Here’s a checklist for writing well-behaved Macintosh software:

Open windows on the proper screen

New document windows should be opened on the same screen as the parent window. If there is no parent window, use the main screen (or, if you want to be really cool, use whichever screen was most recently used for a document).

It is easiest to create windows invisibly, add controls and other items to the window, position and resize it, and then make it visible. A new version of one popular developer tool creates the window visibly first, and then quickly snaps it to its new size/location. This is very disconcerting (and somewhat reminiscent of HyperCard).

The Window Manager in System 7 makes it easy to properly place new windows, as long as they don’t need to be resized dynamically. Simply set the Auto-Position field in a WIND or DLOG resource to Parent window or Parent window’s screen.. If your application contains floating palette windows, you’ll have to hide them before calling GetNewWindow or GetNewDialog for this scheme to work.

The standard file box is a particularly nasty dialog, because it’s difficult to center on the proper monitor. The problem is that the size stored in the DLOG resource is unreliable, especially when using utilities like Norton’s “Directory Assistance”. Generally, though, everything works fine if you assume the standard size and place the dialog on the top portion of the designated screen. You will have to use the CustomGetFile call instead of the easier StandardGetFile call to position the dialog on an arbitrary device.

The color picker also needs to be special cased, because it should probably be placed on the deepest device (although this might not be true for all programs). Under recent System versions, this can be accomplished by passing (-1, -1) for the dialog location. Programs like PhotoShop have their own moveable color pickers that the user can drag to any screen.

Default document size

Don’t assume that new document windows should completely fill the main screen. This is very annoying to owners of large displays. Let the user specify a default document size or write a little code to make sure that the default document isn’t oversized.

Dragging

There are still some programs that don’t allow windows to be dragged to second monitors. While holding down the Cmd/Option keys often overrides this problem, the programs really should be updated. Many programs pass screenBits.bounds to DragWindow as the limit rectangle. This works on multiple monitor systems only because Apple put a kludge in the Window Manager to support old software [It may be a kludge, but Apple would be crazy to change it - Ed stb]. Don’t inset it, just pass screenBits.bounds to DragWindow or use the following “morally correct” code:


/* 1 */
 if ( gHasColorQuickDraw )
 limitR = (**GetGrayRgn()).rgnBBox;
 else
 limitR = screenBits.bounds;

 DragWindow( myWindow, theEvent->where, &limitR );

Reference screenBits.bounds as qd.screenBits.bounds when using either MPW or the universal header files.

Zooming

See develop Magazine #17 for a good article on proper zooming. Windows should zoom out to their current monitor and not the main monitor.

Remember window positions

Window positions should be stored within the document file for document windows or within the application’s “Preferences” file for non-document windows. When a document is opened, return the window to the saved location. Be sure to check that the window and its title bar still overlap the grayRgn, because the monitor setup may have changed. I’ve seen several programs (including some best sellers) that will open a window positioned completely off all monitors. Other programs will open windows with their title bars underneath the menu bar. The window’s size should never be larger than the device, because it may be impossible for the user to reach the growBox. Forcing the entire window onscreen is not unreasonable. Lastly, make sure your calculations don’t choke on negative window coordinates - this will be the case for monitors positioned to the left or above the main device.


/* 2 */
/*
 IsPositionOK
 
 Description:
 Checks to make sure the passed global rectangle is completely contained 
within the gray region. Pass the window’s portRect in global coordinates.

 Notes:
Depends on two regions, gSpareRgn1 and gSpareRgn2, having been allocated 
globally (using NewRgn).
  
 Your application might want to allow partially offscreen windows. 
 
Document windows are assumed to have title heights of 20 pixels. There 
are moredynamic ways of handling this, such as positioning the window 
way offscreen and checking its structure region. 
*/
Boolean IsPositionOK( Rect *globalR, Boolean isDocWindow )
{
 BooleanisOK = false;
 Rect   fullWindowR;
  
 #define kDocWindowHeight 20// pixels
 
 // put the window rect into gSpareRgn1
 fullWindowR = *globalR;
 if ( isDocWindow )
 fullWindowR.top -= kDocWindowHeight;
 RectRgn( gSpareRgn1, &fullWindowR );
 
 // see if the window completely intersects the grayRgn
 SectRgn( GetGrayRgn(), gSpareRgn1, gSpareRgn2 );
 if ( EqualRgn( gSpareRgn1, gSpareRgn2 ) )
 isOK = true;
 
 return( isOK );
}

Games

Games are notorious for not running properly on multiple monitor systems. With my particular setup (a b&w main screen and a color 2nd screen), many games look at the main device and put up an error message complaining about the screen depth.

A little extra checking solves this problem. Let’s say your game requires an 8-bit monitor. (Apple says that programs shouldn’t require specific screen depths, but they don’t write games, either [although there was an entire session and a show of support for games at WWDC this year - Ed stb]). If the main screen supports 8-bits, use it. Apple says you shouldn’t force the monitor to a particular depth, but for games it is probably ok. [You can always ask the user whether that’s ok - Ed stb] Use the HasDepth and SetDepth calls to do this and do not call the video drivers directly. If the main screen doesn’t support 8-bit graphics, scan the device list for a device that does. Using the first device you find that supports 8-bit graphics is reasonable, because very few users have 3 monitor systems. If you want to be really cool, though, let the user choose which monitor to play the game on (or play it across several monitors!).

Many games (and other programs a well) use screenBits.bounds to find the size of the monitor. On systems with Color QuickDraw, use the gdRect field of a GDevice instead.


/* 3 */
/*
 FindDeviceThatSupportsDepth
 
 Returns:
 The GDHandle for a device that supports the passed depth.
 Returns nil if no device found or no color quickdraw.
 
 Notes:
 Requires System 6.05 or later.
*/
GDHandle FindDeviceThatSupportsDepth( short theDepth )
{
 GDHandle aScreen;
 
 if ( !gHasColorQuickDraw )
 return( nil );

 // first check the main screen - it takes precedence
 aScreen = GetMainDevice();
 if ( DoesDeviceSupportDepth( aScreen, theDepth ) )
 return( aScreen );
 
 // step through all the screens
 aScreen = GetDeviceList();
 
 while ( aScreen )
 {
 if ( DoesDeviceSupportDepth( aScreen, theDepth ) )
 return( aScreen );
 aScreen = GetNextDevice( aScreen );
 }

 return( nil );
}

Boolean DoesDeviceSupportDepth( GDHandle theDevice, short theDepth )
{
 if (   IsDeviceActive( theDevice ) && 
 HasDepth( theDevice, theDepth, 0/*whichFlags*/, 0 ) )
 return( true );
 else 
 return( false );
}

Boolean IsDeviceActive( GDHandle theDevice )
{
 if ( !theDevice )
 return( false );

 /*
 sometimes newly installed video cards show the main device
 as inactive. we’ll make an extra check for this case.
 */
 if ( theDevice == GetMainDevice() )
 return( true ); // main device is always active
 
 if (   TestDeviceAttribute( theDevice, screenDevice ) &&
 TestDeviceAttribute( theDevice, screenActive ) )
 return( true );
 else
 return( false );
}

General drawing

Responding properly to update events on multiple monitor systems is a little tricky. The programs I’ve been using fall under one of the following categories:

1) Work properly on single monitor systems

2) Work properly on multiple monitor systems, as long as windows don’t span 2 screens of different depths

3) Work properly on all systems and window sizes

Your software should fall under category 3, or at least number 2.

Let’s say your program contains 2 versions of all its artwork - one for b&w monitors and one for color monitors (since dithering is so ugly, you don’t want to draw your color pictures on b&w devices). On a single device system, it is easy to choose which picture to display - just look at the main screen’s depth. On a multiple device system, the picture choice must be made by looking at the window’s size and position. If a window spans 2 monitors, you may have to load and draw both the b&w picture and the color picture in response to a single update event.

See develop #13 for an article on the DeviceLoop call and how it will help you handle this problem. For programmers supporting older System versions, it’s not too hard to write your own version of DeviceLoop.

As an example of improper drawing, look at these two screen dumps from America Online. The top one indicates how the b&w artwork should look. The bottom one shows what happens when the color artwork is displayed on a b&w screen.

Screen depth change

Except for games, programs should be able to run at any screen depth. Users can change the depth at will - you should check the monitor depth during update events to see if it has changed. If you keep offscreen buffers, you may have to change their size and depth as well. This can present a problem if the user increases the screen depth and you don’t have enough memory for your offscreen buffers. In that case, consider drawing the window contents without the buffers.

Even games shouldn’t crash if the user changes screen depths. I suggest pausing the game and opening a moveable error dialog explaining the situation.

Minimizing the amount of RAM required for update events is always a good idea. You can spool picture resources instead of loading them completely into RAM. Unfortunately, there’s no simple “DrawSpooledPictureResource” call, so you’ll have to write the spooling code yourself.

“This model’s so fast we had to put speedbumps on the hard drive!”

Use GWorlds and not offscreen CGrafPorts.

In order to draw properly offscreen, you should use either GWorlds or CGrafPort/GDevice combinations. Creating only a CGrafPort is not enough, because QuickDraw will use the current GDevice’s inverse table when drawing to the offscreen buffer. On my machine, the default GDevice is a 1-bit device, so its inverse table is pretty useless (it actually is filled with 0x01). If your graphics appear in a light yellow color on secondary screens, this is likely the cause.

Window PixMaps

Some sample code I recently looked at chose the depth of its offscreen buffers by looking at the portPixMap field within a CWindowRecord. This PixMap always represents the main device, even when a window is on another screen. Color QuickDraw “notices” this when drawing and special cases its drawing calls to work across multiple devices.

To find the desired depth and color table for an offscreen copy of a window’s contents, use a routine like:

 
/* 4 */
short FindWindowDepth( WindowPtr myWindow )
{
 Rect   r;
 GDHandle theDevice;
 short  theDepth;
 GrafPtroldPort;

 if ( !gHasColorQuickDraw )
 return( 1 );    // 1-bit if no color quickdraw

 GetPort( &oldPort );// save old port
 SetPort( myWindow );
 
 // get the window’s content rect in global coords
 r = myWindow->portRect;  
 LocalToGlobal( (Point*) &r );
 LocalToGlobal( 1 + (Point*) &r );

 // find the deepest device intersecting the window
 theDevice = GetMaxDevice( &r );
 theDepth = theDevice ? (**(**theDevice).gdPMap).pixelSize : 1;

 // color table is at: (**(**theDevice).gdPMap).pmTable

 SetPort( oldPort ); // restore port
 return( theDepth );
}

Hiding the menu bar

Most programs shouldn’t hide the menu bar, but it’s a necessary evil for games, slide shows, and multimedia demos. Be sure to hide the menu bar only if your presentation is running on the main device. Be sure to save/restore the menu bar area on switch events because it will be changed while you are in the background. Many programs incorrectly assume that users won’t be able to “switch out” of their applications because they create windows the same size as the screen. On multi-monitor systems, switching out is as easy as clicking on the desktop on the second monitor. (If you really must prevent switching out, your best bet is to never call GetNextEvent or WaitNextEvent).

Summary

If you follow these suggestions, your programs should be multi-monitor friendly. While it may not be trivial to support multiple monitors properly, annoying users is the only alternative. Remember that most PowerMacs have built-in support for 2 monitors, so this issue is more important now than ever.

Besides, this might just be the way to convince your boss to buy you a second screen.

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Minecraft 795 - Popular sandbox building...
Minecraft allows players to build constructions out of textured cubes in a 3D procedurally generated world. Other activities in the game include exploration, gathering resources, crafting, and combat... Read more
djay Pro 3.0.5 - Transform your Mac into...
djay Pro provides a complete toolkit for performing DJs. Its unique modern interface is built around a sophisticated integration with iTunes and Spotify, giving you instant access to millions of... Read more
Unicorn HTTPS 1.5.54 - Change DNS quickl...
Unicorn HTTPS can change DNS quickly and easily. Every function is served free of charge, no advertisement. Your personal information is never collected by us. Please use it with confidence. Faster... Read more
MarsEdit 4.4.11 - Quick and convenient b...
MarsEdit is a blog editor for OS X that makes editing your blog like writing email, with spell-checking, drafts, multiple windows, and even AppleScript support. It works with with most blog services... Read more
Printopia 3.0.16 - Share Mac printers wi...
Run Printopia on your Mac to share its printers to any capable iPhone, iPad, or iPod Touch. Printopia will also add virtual printers, allowing you to save print-outs to your Mac and send to apps.... Read more
beaTunes 5.2.19 - 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
Navicat Premium Essentials 15.0.25 - Pro...
Navicat Premium Essentials is a compact version of Navicat which provides basic and necessary features you will need to perform simple administration on a database. It supports the latest features... Read more
Apple Pages 10.3.9 - Apple's word p...
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
Numbers 10.3.9 - Apple's spreadshee...
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
Suitcase Fusion 21.2.2 - Font management...
Suitcase Fusion is the creative professional's font manager. Every professional font manager should deliver the basics: spectacular previews, powerful search tools, and efficient font organization.... Read more

Latest Forum Discussions

See All

Honkai Impact 3rd has revealed more deta...
Honkai Impact 3rd has now announced more details about its upcoming crossover with Neon Genesis Evangelion. This is set to arrive next week on January 22nd and will introduce an exclusive story, battlesuit and weapon to the popular action-RPG. [... | Read more »
Space Frog Intern, James Bolton's a...
James Bolton's arcade shooter Space Frog Intern is now available for Android devices following its release on iOS last year. It sees players taking control of the titular amphibian and blasting their way through various space beasties. [Read more... | Read more »
The 5 Best Mobile Ports
Ports or coversions of games from one platform to another can be quite tricky. This is especially true when porting games to phones and tablets, as these titles have to be designed with workable touch controls and account for smaller screen sizes... | Read more »
Erica, the PS4-exclusive FMV thriller, c...
London-based studio Flavourworks is bringing its FMV game Erica to iOS on Friday as a free trial, with a full release presumably following later. This is the second platform the game has launched on after its original release on PlayStation 4 two... | Read more »
Cute simulation game Dinosaur Park: Prim...
Dinosaur Park: Primeval Zoo is a cute zoo simulation game from upjers, and it sounds perfect for anyone who’s a dinosaur fan. It’s coming to Android in February, and is available right now for pre-registration. [Read more] | Read more »
Genshin Impact - Lost Riches Guide
| Read more »
Figment: Journey into the Mind, the surr...
Following its release on iOS devices last year, Bedtime Digital Games' surreal action-puzzler Figment: Journey into the mind will be heading for Android next Thursday, January 14th. If you're unfamiliar, it follows Dusty and his pal Piper as they... | Read more »
Skylanders Ring of Heroes' latest u...
Following the various game-changing updates made to Skylanders Ring of Heroes last year, the latest update to Activision and Com2uS' team-based RPG has introduced a new battle mode and they will celebrate its arrival with various in-game events... | Read more »
Distract Yourself With These Great Mobil...
There’s a lot going on right now, and I don’t really feel like trying to write some kind of pithy intro for it. All I’ll say is lots of people have been coming together and helping each other in small ways, and I’m choosing to focus on that as I... | Read more »
Genshin Impact - Combat Tips
Genshin Impact isn't a terribly difficult game, but its enemies get tougher the longer you play it and as your world level increases. This makes sense as a progression system, but it can also create gnarly difficulty spikes that are hard to... | Read more »

Price Scanner via MacPrices.net

At only $809, these are the cheapest MacBooks...
Apple has restocked at full line of Certified Refurbished 2020 13″ Intel-based MacBook Airs available starting at only $809 and up to $280 off original MSRP. Each MacBook features a new outer case,... Read more
Find the best price on an Apple iPhone MagSaf...
Looking for an Apple MagSafe Charger for your new iPhone 12, or perhaps an Apple MagSafe Duo Charger for your new iPhone and Apple Watch? Check out our new MagSafe Charger Price Tracker. We scan the... Read more
Save $67 on 13″ M1 MacBook Pros at Expercom,...
Apple reseller Expercom has 2020 13″ M1 MacBook Pros on sale for $67 off Apple’s MSRP with prices starting at $1232. In addition to their MacBook Pro sale prices, take $40 off AppleCare+ when... Read more
Back in stock! 16″ MacBook Pros starting at o...
After a long absence, Apple has restocked a full line of Certified Refurbished 16″ MacBook Pros for up to $420 off the cost of new models, starting at $2039. Each model features a new outer case,... Read more
Saturday Steal! Clearance 2020 Mac mini for o...
Other World Computing has clearance 2020 Intel-based 4-core Mac minis on sale for only $549 this weekend, $250 off Apple’s original MSRP. These are new, unopened, factory-sealed models: – 3.6GHz 4-... Read more
Save up to $112 on 13″ Intel-based MacBook Pr...
Apple reseller Expercom has 2020 13″ 2.0GHz Intel-based MacBook Pros on sale for $100-$112 off Apple’s MSRP with prices starting at $1699. In addition to their MacBook Pro sale prices, take $70 off... Read more
New sale at B&H: Apple’s hot new 13″ M1 M...
Apple’s new 2020 13″ MacBook Pros with M1 Apple Silicon CPUs are on sale at B&H Photo today for $50-$100 off MSRP, starting at $1239. Free expedited shipping is available for most addresses in... Read more
New at US Cellular: Your choice of free iPhon...
US Cellular has the 64GB Apple iPhone 12, 64GB iPhone 12 mini, and 64GB iPhone SE each available for free for new customers signing up for an Unlimited data plan. Cost of the phone is spread over a... Read more
Verizon offers $30 discount on Apple AirPods...
Verizon has Apple AirPods Pro on sale for $219.99 on their online store through January 22, 2021. Their price is $30 off Apple’s MSRP, and it’s among the lowest prices currently available for AirPods... Read more
Apple has clearance 2020 13″ 1.4GHz Intel-bas...
Apple has clearance, Certified Refurbished, 2020 13″ 1.4GHz 4-Core Intel-based MacBook Pros available starting at $1059 and up to $270 off original MSRP. These are the cheapest MacBook Pros for sale... Read more

Jobs Board

*Apple* Administrator - Freedom Mortgage (Un...
Apple Administrator + Job ID:8595 + Functional Area:Information Technology + Employment Type:Full Time + Location:Moorestown, NJ + Department:IT Conferencing & AV + Read more
Systems Architect, *Apple* Production Engin...
…package beginning on your first day? If so, we hope you'll keep reading! The Apple Sales Engineering and account team is looking for a stellar presales engineer with Read more
*Apple* /Mac Support Engineer - BRMi (United...
**Overview** BRMi Technology is currently seeking an Apple /Mac Support Engineer for a large client. The support engineer will research, evaluate, design, implement, Read more
Security Officer - Temporary - *Apple* Stor...
**Security Officer \- Temporary \- Apple Store** **Description** Summary The Security Officer provides services for a variety of large and small business clients Read more
Transition Into Practice (TIP) - April 2021-R...
…Academy-Transition into Practice (TIP) Residency program at **St Mary Medical Center in Apple Valley, CA.** **We are seeking Registered Nurses who are:** + New Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.