MACINTOSH Q & A

MACINTOSH DEVELOPER TECHNICAL SUPPORT

QHow can I set the Protect bit of a file?

AThe Protect bit is neither documented nor supported. PBSetCatInfo and PBSetFInfo cannot set this bit. Additionally, attempting to change the Lock bit also fails with either of these calls. SetFLock trap must be used to set the Lock bit of the file's attribute. The Protect bit was an early method of copy protection. If the Finder sees this bit set, it will not allow the user to copy, move, delete, or rename the file. It is important to note that ONLY the Finder pays any attention to this bit. So, it would be possible to use any file utility to copy the file even if it is "protected".

QSystem 6's "About Finder" memory info for my 16 MB Macintosh IIfx is incorrect.

ASystem 6 does not run in 32-bit address mode so it cannot support more than 8 MB of RAM. What you are seeing in the "About" box is the Finder trying to understand what has happened to the other 8 MB of RAM. It assumes the system is using it, but in reality the RAM is not being used by anything. A/UX and System 7 both support up to 1 GB of RAM for 68030 Macintoshes since the IIci. System 7's "Memory" cdev must be set for 32-bit addressing in order to take advantage of RAM beyond 8 MB. This also requires "32-bit clean" ROMs (Macintosh IIci or later).

QIs there a way to determine if a machine has a PMMU installed?

AThe Gestault Manager's gestaultMMUType selector (available since System 6.0.4) will tell you if, and which type of, MMU is installed. For preliminary Gestault documentation and interface files, check AppleLink and developer CDs.

QHow do I set the cursor at interrupt time, for instance in a VBL task?

AChanging the cursor at interrupt time is permissible as long as the cursor handle is locked in memory and the cursor routines are not busy. A test needs to be performed before you change the cursor. If you want to call SetCursor (with a cursor handle locked in memory), you nmust check CrsrBusy, a low-global defined in the Macintosh Programmer's Workshop (MPW) SysEqu. If CrsrBusy is true, then you cannot call SetCursor. Changing the cursor while CrsrBusy is true causes it to leave mouse bits, or trails, on the screen.

CrsrBusy    EQU     $8CD    ; Cursor locked out? [byte]

QHow do penguins know when it’s safe to go in the water?

APenguins in the Antarctic face many perils, not the least of which are several species of sea mammals waiting at the edge of icebergs to nibble on their little penguin bods when they go in the water. So, penguins will just wander around on the edge of an ice floe until one of them accidentally falls in the ocean. When that happens all the penguins will stand by and watch to see if the fallen penguin gets eaten. If the penguin comes to harm it’s back to business as usual on the iceberg. If the penguin is safe (apparently for a period of time known only to the other penguins) then the entire dissimulation leaps in, hunting for food.

QIs the maximum size of a resource still 32K?

ANo. There used to be a bug in the 64K ROMs that didn’t allow you to write even multiples of 32K (that is, 32K-64K, 128K-192K). This was fixed in 128K ROMs. As of 128K ROMs, the resource size is limited to “maxlongint” bytes.

QHow do I write a background-only application for MultiFinder?

AA background-only application is similar to a standard MultiFinder-aware application except that it performs a task in the background with no user interface such as windows or menus. A background-only application must not initialize any Toolbox managers; for example, it must not call InitWindows or InitMenus. If a dialog needs to be displayed by a background application, the Notification Manager should be used.

QI am writing a Chooser PACK resource. When I change the flags that control which messages I will be sent, nothing seems to change. Why?

AChooser caches the flags from your Chooser PACK the first time it sees the file. From then on, changes are ignored until the PACK's name is changed, or until the Chooser's cache is flushed. To flush the cache, simply hold down the Command and Option keys when selecting Chooser from the Apple menu. When the cache is flushed, the system will beep.

QWhat can I do and not do while executing in interrupt code?

AInterrupt code is most commonly used for I/O completion routines, VBLs, Time Manager tasks, and deferred tasks. Contrary to popular belief, the Deferred Task Manager will run your task at interrupt level. All code that runs at interrupt level must follow very strict rules. The most important rule is that the code cannot allocate, move, or purge memory, reference memory manager structures (that is, HUnlock), or call a Toolbox routine that would. This eliminates nearly, if not all, QuickDraw operations. For a more complete list of these Toolbox routines, refer to the Inside Macintosh X-Ref .

Additionally, interrupt code should avoid accessing a low-memory global or calling a trap that would access one. While MultiFinder is running, the applications' low-memory globals are being swapped in and out. Because of this, the interrupt code cannot rely on which application's globals are currently available. Even if CurApName is correct, the interrupt routine may be called while MultiFinder is in the process of swapping the applications' globals. This restriction is difficult to deal with because there is no documention as to which low-memory globals are swapped by MultiFinder, nor which globals are accessed by traps.

A typical example of this problem is interrupt routines that attempt to restore A5 by examining CurrentA5. This low-memory global is valid only while the current application is running at non-interrupt time. Thus, the Macintosh Programmer's Workshop (MPW) routine SetCurrentA5 (or the obsoleteSetupA5) cannot be used at interrupt level. It is necessary to place the application's A5 value somewhere it can be located while in the interrupt routine. This is documented in Technical Notes #180 and #208. In fact, the exact code you need is in #180.

Also, there are interrupt limitations while System 7 is running under Virtual Memory. Therefore, it is best to avoid interrupt code if at all possible. Move the functionality of the interrupt code into the application. For example, if you do require a VBL, limit the code to an absolute minimum. Also, set a global flag for the application to check in its event loop.

QIs the maximum size for global and local data still 32K?

AStarting with MPW 3.0, the maximum size for global data in MPW became larger than 32K, using compiler and linker options -m and -srt. Local data is tougher, because local data is allocated by using the LINK instruction, for example, LINK A6,#$-380. With this relative addressing mode, you're constrained to the negative side of a 16-bit value for local space, which translates to 32K. That is, this limit is basically due to the Motorola processor architecture. If you are allocating more than 32K either globally or locally, you might want to rearchitect your system to use dynamic (and theoretically unbounded, especially on virtual architectures) storage space.

QIs it possible to get PAL (Phased Alternate Lines) timing from the new 4*8 and 8*24 cards?

AThe 4*8 and 8*24 cards currently support NTSC (National Television Standards Committee) output and will support PAL output as well when the next ROM revision is put into production early this year. (The 8*24 GC card currently supports PAL.)

QWhat is a System Error 29? It's not in any of the documentation I have available. One of my applications has been reported to crash with this error occasionally.

AWhen the Package Manager can't load in a PACK resource for any reason, it calls SysErr. There is a range of system error codes reserved for the situation in which the PACK resource couldn't be loaded. That range is 17 through 24. So if it couldn't load the List Manager package, which is PACK 0, the Package Manager adds 0 to 17 and calls SysErr with a code of 17. If it couldn't load the Standard File package, which is PACK 3, the Package Manager adds 3 to 17 and calls SysErr with a code of 20.

The problem is, we overflowed our PACK SysErr range. The Color Picker is PACK 12. If the Package Manager couldn't load in PACK 12, it adds 12 to 17 and calls SysErr with a code of ... 29. And there you have it.

PACKs are loaded into the system heap. If there's not enough room in the system heap for a PACK, the system heap is expanded and the PACK is loaded in. If you set your application to take over the entire application memory space, the system heap can't grow anymore. The GetResource('PACK',12) call that the Package Manager makes fails: It adds 12 to 17, and calls SysErr with a code of 29. This could be what's causing the crashes in your case.

QHow can we increase the stack space allocated by the DA Handler?

AThere is no simple, supported way to increase the stack space available to a DA. DAs were designed to provide easy access to simple tools from the user's desktop. As such, the environment of a DA is relatively limited. Now, with MultiFinder and especially with System 7.0, applications can provide all the functionality of a DA with none of the limitations. Under MultiFinder the DA Handler actually reduces the stack space available to a DA by about 25 percent. This limitation is not a problem for applications. If you need stack space beyond the bounds of the DA's environment, we encourage you to convert your DA to a full application.

QDoes 32-Bit QuickDraw support packed PICTs? What's the technique for saving packed PICT formats? What compression schemes are supported?

AColor QuickDraw has always supported packed PICTs. See Inside Macintosh , volume V, for details on how CLUT PixMaps are packed. Under 32-Bit QuickDraw, to pack direct RGB PixMaps in PICTs, call CopyBits with the packType field in the source PixMap set to one of the following constants that apply to direct RGB PixMaps: 0default packing (pixelSize 16 defaults to packType 3 and pixelSize 32 defaults to packType 4) 1no packing 2remove pad byte (32-bit pixels only) 3run-length encoding by pixel size chunks (16-bit pixels only) 4run-length encoding, all of one component at the time, one scan line at a time (24-bit pixels only) Scheme 4 will store the alpha channel also if cmpCount is set to to four. PackSize is not used and should be set to zero for compatibility reasons. See Inside Macintosh, Volume 6, for complete details.

QIs there any way to stop the Dialog Manager from playing with the txSize and txFace fields of a dialog's grafPort so that I can draw Geneva 9-point text from within a userItem proc?

AUnfortunately, because the Dialog Manager forgets about your previous calls to TextFont and TextSize when you put up your dialog again, you will need to call TextFont and TextSize every time your userItem proc is called.

QWhen should the Color Manager be used and when should the Palette Manager be used?

AThe Palette Manager is by far the friendlier and more versatile of the two. It provides all the functionality you need to customize and animate the colors in your application. You shouldn't ever need to use the Color Manager unless you require custom color search and complement functions. Unless you really understand the Color Manager in detail, you are likely to have problems getting the Color Manager to work in a clean fashion.

When using the Palette Manager, applications following the rules will maintain their respective color environments safely as windows move back and forth from foreground to background, and from one screen to another. Accomplishing this with the Color Manager calls is not worth the effort. For additional information, see the Palette Manager article in this issue.

QI would like to make my fills print better. Currently, they come out as 72 dpi patterns. Is there a way that I can make them print at a higher resolution, but have my patterns still print as patterns?

ATo make your patterns print at the printer's resolution, you need to use Printing Manager PrGeneral's GetRslData and SetRsl opcodes to get and set the resolution, and you must scale the pattern to match. Let me explain.

If we do not scale our patterns up to the printer's resolution before print time, we would get "big chunky" patterns because the printer driver would need to scale the patterns on the fly from 72 dpi to its resolution. Therefore, we use the "cookie cutter" approach to "place" the pattern into the object that is being filled. The size of the "cookie cutter" (the destination Rect) depends on the "scaleFactor." For example, a "scaleFactor" of 2 will have a destination rect of 16 x 16. We will then CopyBits the pattern one square at a time into the object that is being filled.

You might find the article "Meet PrGeneral" from the July 1990 issue of develop useful for describing the functionality of PrGeneral in greater detail.

QWhat versions of Apple Color Printer software work with what system software versions? Can Apple Color Printer software distributed with System 6.0.7 work with System 6.0.5 and earlier versions? I am distributing LaserWriter ® drivers with modified pgsz resources. I would like to cut back on the number of files I need to distribute.

AThe software sent with version 6.0.7 will work with all other 6.0.x systems. This should be the rule with most other LaserWriter printer software as well. Color has been supported since LaserWriter driver 6.0, for color depths of 8 bits or less. Depths greater than 8 bits must be converted before printing.

There really isn't any simple way to match up the version of released printer software with what version of the system it is compatible. LaserWriter 7.x is compatible with both System 7 and System 6. It's still prerelease software, however. Do not ship the preliminary LaserWriter 7.x driver with your application. You'll be able to ship the final LaserWriter 7 driver with your product as soon as System 7 is final.

QHow can I use SndPlay to function asynchronously? It seems to ignore the async parameter.

ATo use SndPlay asynchronously, you must have allocated a sound channel without passing NIL as the chan parameter. There is one thing to be aware of in doing this, which often confuses developers. If the 'snd' resource being used with SndPlay specifies a 'snth' resource, then you cannot create the sound channel with a synth. Because of a Sound Manager bug that has been present in all releases through System 6.0.7, SndPlay has not worked correctly for a 'snd' resource specifying a 'snth', with a user channel initialized with a 'snth'. For example, the following code will fail:

SndNewChannel(myChan,  sampledSound, init, @myCallBack);

SndPlay(myChan, sndHdl,  async); 
    {sndHdle is a sampled sound}

The Sound Manager attempts to link this 'snth' to the channel with every call to SndPlay. If the synthesizer has already been installed, the Sound Manager attempts to install it again, only this time as a modifier. The same 'snth' code ends up being installed more than once in the channel. If the 'snd' contains 'snth' information, then SndPlay can be used once and only once on a channel. A format 2 'snd' resource is assumed to be a sampled sound. For format 1, check the number of snths specified in the 'snd' and then check each one. The latest version of SoundApp has source code that does these tests.

This limitation has been fixed in System 7. In System 7, SndPlay can be called any number of times on a channel. For older system releases you need to create and dispose of the channel each time after calling SndPlay, as in the following code:

#include   <Resources.h>
#include   <Sound.h>

#define   TRUE  0xFF
#define   FALSE 0

main()
{
    Handle          Sound;
    SndChannelPtr   chan;
    int             i;
    OSErr           err;
    
    Sound = GetResource('snd', 100);
    if (ResError() != noErr || Sound == nil)
    Debugger();
    
    for (i = 0; i < 3; ++i) 
    {
        chan = nil;
        err = SndNewChannel(
            &chan, 0, 0, nil);
        if (err != noErr)
            Debugger();
    
        err = SndPlay (chan,
            Sound, FALSE);
        if (err != noErr)
            Debugger();
    }
}

A good method for playing sampled sound asynchronously on any Macintosh is to create a sound channel and use the bufferCmd. Find the sound header from the 'snd ' resource and pass the pointer to this in the bufferCmd. Use this with SndDoCommand or SndDoImmediate. To determine when the sound has completed so that you can know when to dispose of the channel, send a bufferCmd with SndDoCommand (in order to queue it) after the bufferCmd. Once your callback procedure is called, set a global signalling that the sound has finished. The new Sound Manager (System 6.0.7 and beyond) supports a new call, SndChannelStatus, which will tell you if the channel is playing a sound or not. Instead of the callback procedure, you can poll the channel’s status to determine when to dispose of the channel. Example code using the callback procedure can be found in the DTS sample code SoundApp.

Q What is the difference between North and West?

A North is an absolute direction on the globe. Once you are on the North Pole it is impossible to go any "further North." West, on the other hand, is a relative position. No matter where you are on the surface of the Earth, it’s always possible to go further West.

Q I have found that sounds recorded at good or better quality will not play with system software prior to 6.0.7. That’s expected, but the fact that SndPlay does not return an error message is not. How can I check to see if a sound is compressed when running older system software?

A There is a byte in the SoundHeader data structure (and thus in a 'snd' resource), called "encode." If the sound is compressed, the value of this byte will be $FE, which is defined as the constant cmpSH in the headers for the Sound Manager.

Q Why do golf balls have pocks?

A As counter intuitive as it may seem at first, the pocks on golf balls actually make them fly farther. A golf ball builds turbulence in front of it as it flies through the air. If the ball is pocked, the turbulence “fills” the pockets as the ball spins, resulting in less resistance and more flight. 747s have pocks on their wings for the same reason. Dolphins presumably have these pocks on their fins for this purpose as well, but to date none of them have come out publicly and said so.

Q We generate sounds using the Sound Driver’s four-tone synthesizer. Our application must run on all Macintosh computers and all system software versions starting with System 6.0.

According to an early version of Inside Macintosh, Volume VI, the new Sound Manager's wave-table synthesizer, which replaces the Sound Driver's four-tone synthesizer, does not perform as expected on some Macintosh systems. When should we use the Sound Manager and when should we use the Sound Driver?

AThe Sound Driver is no longer supported, as of System 6.0.7. The wave-form synthesizer in the Sound Manager released with 6.0.7 does not work correctly for non-Apple Sound Chip machines (Macintosh Plus, SE, Classic, and LC), but this will be fixed in System 7. If you need to use the wave-form synthesizer for non-ASC machines running 6.0.7, you could try the Sound Driver with 6.0.7 on the chance it'll work for your purpose. Use the Sound Driver for non-ASC machines running System 6.0.5 and earlier.

QDoes stereo work? I was hoping to init the left and right channels separately (using initChanLeft and initChanRight) and send different sampled sounds out both channels. But the Sound Manager documentation says stereo is not supported. I figured this would be a "cheap" way of playing two sounds at the same time, sending them out the left and right channels and letting the Macintosh mix them together (or telling the user to flip the MONO switch on their stereo).

AStereo and mixing multiple channels are new features of the Sound Manager released with System 6.0.7. If you create a mono channel, the sounds come out both speakers. If you create a left channel, it is a mono sound coming from only the left channel. Alternatively, creating a right channel will only come from the right. If you create a stereo channel, then the sound's left or right position is determined by the sound header you use (with the bufferCmd). A stereo sound is only supported by a compressed or extended sound header. You cannot control the left or right panning of a stereo sound. This is only determined by the sound header and its interleaved data. The left or right init params will have no affect on a stereo channel. True stereo sounds can only occur by using a stereo sound header. Two mono channels, one for the left speaker and one for the right, could be opened for the affect that most developers want.

Only the Macintosh SE/30 and the Macintosh IIsi have both the left and right sources mixed to the internal speaker. A stereo sound on all other Macintosh systems have the left source only sent to the internal speaker. The right source is only sent to the external port, and it isn't possible to determine if the external port is in use or not.

QIs it necessary to lock a 'snd' resource that is to be played asynchronously with SndPlay?

AYes, if you are playing a sound resource asynchronously with SndPlay, then you have to lock the sound. SndPlay will restore the handle's state as soon as the trap returns to the caller. If the call is asynchronous, the handle's state is restored immediately after calling SndPlay, before the sound finishes playing.

QWhen converting stacks from HyperCard 1.2.5 to 2.0, the default "fixed line height" setting for text fields sometimes enlarges the space required by text and destroys the layout of the screen. For example,text tends to disappear outside the edges of the field, or be misaligned. Deselecting "fixed line height" corrects the problem in most instances, but there can still be a slight discrepancy in the amount of space taken up by identical fonts in identical fields between 1.2.5 and 2.0, such that layouts are disrupted even if "fixed line height" is not selected.

AInherent in the design of HyperCard 2.0, the way a field is displayed may be different in HyperCard 2.0 than in HyperCard 1.2.5. Converting a stack to HyperCard 2.0 from HyperCard 1.2.5 may require that fields be tweaked to appear properly. Therefore, developers may want to provide special versions of their stacks for use with HyperCard 2.0, regardless of whether features specific to HyperCard 2.0 are incorporated.

QSince I have received HyperCard 2.0 I have converted several stacks for 1.x to 2.0 and have experienced several problems with scripts that worked fine in 1.x. I have recently learned that HyperCard 1.x will NOT run on System 6.0.7 and later versions. For HyperCard 1.x users this results in stacks that cannot be used in HyperCard 2.0. For HyperCard stack developers this presents a nightmare in converting old 1.x stacks for users into 2.0 stacks. Since encountering these problems I have changed my scripts in 1.x so that when converted they work. What is Apple's position on "seamless conversion" of HyperCard 1.x stacks to HyperCard 2.0?

AMost functioning 1.x scripts will work without modification under HyperCard 2.0. However, HyperCard 2.0 is a bit more strict in enforcing some of the grammar of HyperTalk. For example, keywords can no longer be used as variable names under 2.0. Under 1.x, keywords could be used as variable names, but the documentation specifically warned against doing this.

Kudos to our readers who care enough to ask us terrific and well-thought-out questions. The answers to these puzzles have been supplied courtesy of our teams of technical gurus; our thanks to all. Special thanks to Pete "Luke Skywalker" Alexander, Mark Baumwell, Jeremy Bornstein, Rich Collyer, Dennis Hescox, Jim Luther, Guillermo Ortiz, Jim Reekes, Bryan Stearns, Robert Stobel,Forrest Tanaka,Vince Tapia, Jon Zap, and Scott "Zz" Zimmerman for the material in this Q & A column. *

Have more questions? Need more answers? Take a look at the new developer technical library on AppleLink (updated weekly) or the Q & A stack on each Developer CD Series disc. *