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June 95 - Macintosh Q & A

Macintosh Q & A

Q I'm using the TPopup class in MacApp 3.0.1 in my window and I want to underline the title string of a pop-up menu programmatically. The title text style is stored in a field in the class but is used only when the pop-up menu is first created. How can I change the text style of a pop-up menu title after it has been created?

AMacApp's TPopup class is basically just a wrapper around System 7's Popup CDEF (with its own CDEF for pre-System 7) and so is subject to the same limitations as normal System 7 pop-up menus. You're correct that the title style is stored in the TPopup class and referenced only once, when the pop-up control is created. What happens is that when a pop-up menu is created with NewControl, the Popup CDEF interprets the value parameter to NewControl to be the title style of the pop-up menu control. Thereafter, the value of the control is equal to the currently selected menu item. TPopup::CreateCMgrControl calls NewControl as follows:

ControlHandle aCMgrControl = NewControl(itsPort, qdArea, itsTitle,
      FALSE, (short) this->GetPopupTitleStyle(), fMenuID,
      fItemOffset, this->GetProcID(), fUseAddResMenuResType);
The important setting is the title style: notice the TPopup::GetPopupTitleStyle call, which returns a short integer corresponding to the text style settings. The problem is that there's no way of defining this title style after the control has been created, so you have to recreate the control when you want to change the title style. This may seem a bit much, but it takes only a few lines of code. The important thing to remember is that most of the information you need is already part of TPopup; all you're doing is recreating the control.

Dispose of the old control, set the fTitleStyle field to the title style you want, and then call CreateCMgrControl to create a new control with this title style, using all the characteristics already set in your TPopup object. Here's the code to do this:

CStr255   itsLabel;
short      itsVal;

/* First free the old control. */
myPopup->fCMgrControl = NULL;
/* Now set the pop-up title style to underline. */
myPopup->fTitleStyle = myPopup->fTitleStyle + underline;
/* Get title and current value to send to CreateCMgrControl. */
itsVal = myPopUp->GetCurrentItem();
/* Now create a new control with the desired text style. */
myPopup->CreateCMgrControl(itsLabel, itsVal, 0, 0, 0);
Q I'm having a problem with Balloon Help, getting HMCompareItem to work properly. I've got several menu items that can change dynamically, and while HMCompareItem successfully finds the first item, all other items have no balloons. What's the problem here?

AThe problem is that the match string isn't exact. HMCompareItem only finds exact matches for the actual menu items. (A common case to look out for is ellipsis (...) versus three periods (...): always use an ellipsis in menus.)

If you can't determine the exact match ahead of time, we suggest that you use a different technique: modify the help string on the fly. A method that other developers have used is to store the current menu state in their preferences file along with the current menu help string; then, as the application changes menu items, they modify the 'STR ' resource that the help item refers to on the fly.

Q I'm writing a QuickDraw GX printer driver and need to get the text size of a shape. I've tried GXGetStylePenSize and GXGetShapePenSize, but these continuously send back 12 no matter what the real size is. I've looked through the shapes in GraphicsBug, and 12 is there for the text size. What can I do to get the correct size?

AQuickDraw GX has three different shapes to handle typography -- text, glyph, and layout -- and each one stores the typographic style objects (which are what you need) differently. (There's a good discussion of the three types of typographic shapes in QuickDraw GX: Programmer's Overview on pages 97 through 115.)

The important thing to remember is that simple text shapes can have only one type style (attached to the style attribute of the object), so they're fairly easy to work with. However, glyph and layout shapes can have one or more runs of type styles (attached to the style list attribute of the object's geometry), so they can be more complex to work with. Only if a glyph or layout shape doesn't have a style list attached to its geometry is the style attribute of the object itself used. For shapes with multiple style runs, there's no simple answer to the question "What is the text size of this object?"

For glyph and layout shapes, you'll need to write a "GetSizes" function that's capable of returning one or more sizes. This routine should get the style list by calling GXGetGlyphShapeParts or GXGetLayoutShapeParts. If the style list is nil, return the default size in the style attribute of the object itself; otherwise, return an array of each size in the list of styles, or whatever is appropriate for your application.

Q I'm writing a QuickDraw GX application, and the glyphs that are drawn on the screen sometimes don't match the character codes in the shape. Any idea what's going on?

AIt's very important to pass the correct script system, language, and platform when your application creates a layout shape or a style used within a layout shape. The following code fragment will do the trick:

long   script;
long   language;
// Set myStyle's encoding correctly for this machine.
if ((script = GetEnvirons(smKeyScript)) != 0 &&
    (language = GetScript(script, smScriptLang)) != 0)
   GXSetStyleEncoding(myStyle, gxMacintoshPlatform, 
      (gxFontScript) (script + 1), (gxFontLanguage) (language + 1));
   GXSetStyleEncoding(myLayoutStyle, gxMacintoshPlatform,
      gxRomanScript, gxNoLanguage);
In the case of a shape, the code is similar but calls GXSetShapeEncoding instead of GXSetStyleEncoding. Note the "(script + 1)" and "(language + 1)": this synchronizes the information returned by the Script Manager with QuickDraw GX's representation of the same data.

Q When displaying JPEG-compressed PICTs with DrawPicture, I call QDError and get the error code -8976, which isn't documented anywhere I've looked. What's going on?

AThis is the codecNothingToBlitErr error. It means that the picture was drawn into an entirely clipped-out bitmap. You can safely ignore this error. This is fixed in Apple's Multimedia Tuner (and will be fixed in future versions of QuickTime), so that the error won't be reported. Better, of course, would be to avoid drawing into clipped-out bitmaps at all.

Q I'd like to add the capability to turn the Macintosh on and off automatically in my application. Is there an API for scheduled startup and shutdown?

AYes and no: there's an API for auto-startup, but not for timed shutdown. The auto-startup feature is built into the Time Manager. The Power Manager features flag has been updated so that it can easily be tested. Timed shutdown will have to be done manually: we recommend creating a background-only application that simply waits for the appropriate time and then issues the Finder event to shut the system down.

Auto-startup can be used if the PMFeatures routine returns a long word with bit 10 set. The name of the enum in the new headers is hasStartupTimer. If this flag is present, these routines are also supported:

void SetStartupTimer(StartupTime *theTime);
OSErr GetStartupTimer(StartupTime *theTime);

SetStartupTimer sets the time that the Macintosh will start up from a power-off state, and enables or disables the startup timer. On a Macintosh that doesn't support the startup timer, SetStartupTimer does nothing. The time and enable flags are passed in the following structure:

typedef struct WakeupTime WakeupTime, StartupTime;
struct WakeupTime {
  unsigned  long wakeTime; 
                     /* startup time (same format as current time) */
  Boolean   wakeEnabled;  /* 1 = enable startup timer, 0 = disable */
  SInt8     filler;
GetStartupTimer returns the startup time and the state of the startup timer. If a particular Macintosh doesn't support the startup timer, GetStartupTimer returns 0.

Q We'd like to open a (usually color) dialog with GetNewDialog such that, if indicated by the user, it ignores the 'dctb' resource and opens in black and white instead. This is a feature request from our users. The best solution we've got so far is to check to see whether we want a dialog to appear in color before calling GetNewDialog. If we want to suppress color, we patch GetResource with code that will look for any call to fetch a 'dctb' resource with the same ID as our dialog. If the patch detects such a call, it returns a nil handle; otherwise, it calls the original GetResource trap and returns its return value. When the GetNewDialog call is complete, we unpatch GetResource if we had patched it. Is this a good solution?

AThe method you describe -- patching GetResource -- will probably work, but is a needlessly complex solution to the problem. In general, patching should be considered a last resort solution, suitable only when there are no other options.

Why not just have two duplicate DLOG resources (both referencing the same DITL), one with a corresponding 'dctb' and one without? (DLOG resources are small, on the order of 30 bytes, so there shouldn't be a size problem.) You can then pass the appropriate ID to GetNewDialog to get either a color or a noncolor dialog. If you want to make this "automatic," make the DLOG resource without a corresponding 'dctb' have an ID that's, say, 1000 more than the one that has a 'dctb'; then keep a global variable that contains either 0 (if the user wants color) or 1000 (for black and white). When you call GetNewDialog, add the global to the (color) dialog ID and pass the result to GetNewDialog. Voilà! You get color if the global is 0, black and white if it's 1000. This is far cleaner and safer than patching could ever be -- and easier, too.

Q I have a question about the MailTime structure and setting the postIt.coreData.sendTime field based on the contents of GetDateTime. The messages I'm reading have the time and date in them, so I can retrieve the time the message was received. I convert this to a DateTimeRec and then call Date2Secs. What's the real way to handle this? I've written a routine that seems to be the right approach, but the time in the mailbox is always wrong, though my location is correct in the Date & Time control panel.

AHere's a snippet that does what you need:

void MacToMailTime(unsigned long macTime, MailTime& mailTime)
   long               internalGmtDelta;
   long               dlsDelta = 0;
   MachineLocation   aLocation;

   internalGmtDelta = aLocation.gmtFlags.gmtDelta & 0x00ffffff;
   if (BitTst(&internalGmtDelta, 23))
      internalGmtDelta = internalGmtDelta | 0xff000000;
   mailTime.time = macTime;
   mailTime.offset = internalGmtDelta;
Q I'm trying to get unread mail messages from the PowerTalk mailbox, but the SMPGetNextLetter routine is returning an error of -903. That's a PPC Toolbox error noPortErr! What's going on?

AThe problem is that you haven't set the isHighLevelEventAware flag in the SIZE resource for your application. This is necessary because the AOCE Standard Mail Package routines require your application to accept high-level events.

Q How can I count the number of unread messages in the PowerTalk mailbox?

AUsing the existing AOCE programming interfaces, this isn't possible. However, a new mailbox API will be available soon (if it isn't already) that will allow these types of operations.

Q I've been using the Standard Mail Package to add mail capability to my application. In some circumstances we generate text or PICT files and add them as attachments to the document we're mailing. The documentation states that the enclosure isn't actually added until well after SMPAddAttachment has returned. I'd like to delete the files as soon as possible after I've generated them. How do I know when the file has been completely copied so that I can delete the original?

AThe problem with SMPAddAttachment is that the process is nondeterministic. The file is added by an asynchronous background process that's controlled by sending Apple events between your application and the Finder. Apple events are returned to your application during the file copy (they'll be handled by the normal Apple event mechanism).

Generally, these are the indications that the copy is complete:

  • SMPMailerEvent returns with the kSMPDisposeCopyWindow bit set in the whatHappened field.

  • The Finder sends a kAEReply Apple event to your application.

  • The size of the enclosures field goes up by sizeof(FSSpec).
However, if you were to try to add another enclosure at this point, you might still end up getting the kSMPCopyInProgress error.

What you need to do is treat the kSMPCopyInProgress error as a "busy, try later" indication, and try the action again the next time through your event loop. This ensures that the Mailer (and the Finder) get a chance to move data between successive tries.

Q I'm trying to write a patch that gets called when a floppy disk is inserted. I tried a GNE filter patch that looks for the diskEvt message in the event queue. It works, but it's not really what I want; the patch also gets called when any volume, not just a floppy disk, is mounted. Also, when a floppy disk is inserted, the patch gets called after the disk's icon shows up on the desktop, and I'd like to trigger the action before that. Any ideas?

AThe Finder always gets events before your GNE patch, which is why your patch gets called after the icon shows up on the desktop. Instead you should patch MountVol inside the Finder.

Q I'm attempting to use the MenuHook routine called by MenuSelect to update a status bar with text as the user traverses menu items with the mouse. It seems that if I call TextEdit functions directly from within the function pointed to by MenuHook, problems occur: the mouse highlights the first item in a menu, but that item stays highlighted no matter where you move the mouse. In other words, it seems that MenuSelect stops working correctly or that the screen is no longer correctly updated. Can you tell me how to fix this?

A You need to save and restore the graphics port in your MenuHook routine. Even if you aren't explicitly changing the port yourself, the TextEdit routines will probably leave it set to the edit record's owning port, not what it was when you started.

Q I found the following declarations in Scripts.h:

extern PASCAL Boolean IsCmdChar(const EventRecord *eventRecord,
         short test)

    FOURWORDINLINE(0x2F3C, 0x8206, 0xFFD0, 0xA8B5);
But I can't seem to find any documentation for this call. Does such documentation exist? If this is what I think it is, it could be very useful.

A Whoops, thanks for pointing this out. That routine was introduced with System 7. We've updated the Macintosh Technical Note "International Canceling" (TE 23) accordingly. Here's a description of the routine:

FUNCTION IsCmdChar(keyEvent: EventRecord; testChar: CHAR): BOOLEAN;
This function tests whether the Command key is being pressed in conjunction with another key (or keys) that could generate testChar for some combination of Command up or down and Shift up or down. This accommodates European keyboards that may have testChar as a shifted character, and non-Roman keyboards that will only generate testChar if Command is down. It's most useful for testing for Command-period.

The caller passes in the event record, which is assumed by the function to be an event record for a key-down or auto-key event with the Command key down. The caller also passes in the character to be tested for (for example, '.'). The function returns TRUE if testChar is produced with the current modifier keys, or if it would be produced by changing the current modifier key bits in either or both of the following ways:

  • turning the Command bit off

  • toggling the Shift bit
Q Someone has to ask this: just what are the "Miscellaneous Traps" toward the end of Traps.h, and in particular _HFSPinaforeDispatch?

AThose few defines in Traps.h are leftover baggage:

/* Miscellaneous Traps */
   _InitDogCow               = 0xA89F,
   _EnableDogCow             = 0xA89F,
   _DisableDogCow            = 0xA89F,
   _Moof                     = 0xA89F,
   _HFSPinaforeDispatch      = 0xAA52,
0xA89F is really _Unimplemented and 0xAA52 is really _HighLevelFSDispatch. They were possibly left there to keep system builds working -- or perhaps to keep the build engineers amused.

Q To get started writing a raster printer driver for QuickDraw GX, I wrote a "skeleton" driver (only 5K!) that overrides only two messages: RenderPage and RasterDataIn. The RenderPage override merely posts debug notices before and after forwarding the message. The RasterDataIn override also posts a debug message, then returns immediately. So no data is sent to the printer; this is, after all, only a demonstration driver.

A crash occurs after BuggyDriver forwards the RenderPage message but before control returns to the RenderPage override. RasterDataIn is called one or more times before the crash occurs. Since there's hardly any code, yet the driver still crashes, I'm guessing that incorrect driver resources are to blame (I don't pretend that I've figured out the 'rdip' resource yet).

AYou've stumbled onto a bug in QuickDraw GX: rendering into 32-bit-deep view devices at high resolutions causes the crash you're seeing. Since the problem is in several of the QuickDraw GX blitters, there's no workaround short of reducing the bit depth or the resolution, or both. This problem is fixed in version 1.1.

Q I'm patching NewControl so that I can replace the standard controls on AV and Power Macintosh machines. This seems to work fine everywhere except in alerts. When an alert is posted, NewControl doesn't get called until after the original control is drawn once. Any ideas?

AThe "proper" way to do this is to patch NewControl and GetNewControl to change the procID to your CDEF's procID. This is pretty clean: the Control Manager thinks your CDEF was the one that was always asked for. The only drawback is that you'll have to make sure your resource file is always available and in the search path. Be sure to set the system bit in your CDEF to avoid constant reloading.

Q I'm trying to call LMGetUnitTableEntryCount in my application, but when I compile for PowerPC I get a link error: the function isn't in the native libraries. Is this policy or an inadvertent omission? What can I do about it?

AThis is an oversight. You'll need to create an external function in a file (say, Extra.c) to access the low-memory global yourself (from native code only), as shown below. When an updated library is released, you'll only have to remove the Extra.c.o file from your link command and relink your application, not recompile it.

Your Extra.c file would be simple and look something like this:

// Compile with: PPCC -appleext on Extra.c -o Extra.c.o
// Add Extra.c.o to your PPCLink command line.
// Later, when a .xcoff file is provided by Apple, replace it with
// that, and delete your Extra.c.o file.
#if defined (powerc) || defined (__powerc)
   pascal short LMGetUnitTableEntryCount()
      return *(short *)0x01D2;
Of course, best of all would be to rewrite your application so that it doesn't depend on low memory at all.

Q The cursor flickers when it's over a playing QuickTime movie. Is there any way to stop this? I don't want to hide it completely because the user needs to access controls elsewhere on the screen, and the movie is large, so hiding it only over the movie is still disorienting.

AUnfortunately, there's no way to prevent the flickering cursor, short of hiding it completely. The Macintosh doesn't have a hardware cursor, so the cursor always has to be hidden during blits to the screen. QuickTime 2.0 improved this situation by shielding the cursor less of the time, but it still happens.

Q Is it OK for different nodes to run different versions of AppleTalk on a network?

AYou don't need to run the same version of AppleTalk for each node on the network. However, AppleTalk versions 53 and later support AppleTalk Phase 2, so if you're working on an application that depends on Phase 2 support (for instance, use of the NBP wildcard character "~"), you'll need to use AppleTalk version 53 or later for all nodes running that application.

Q When I use the LaunchApplication routine with the launchDontSwitch bit set in the launchControlFlags field for an application that doesn't have the canBackground size resource bit set, LaunchApplication returns 0 (noErr) but the application doesn't launch. What gives?

ALaunchApplication doesn't return an error in this case because the application actually is launched. But since it doesn't have the canBackground bit set and it was launched into the background, it never gets any processor time, which means that it doesn't initialize anything and isn't added to the Application menu. If the user double-clicks an application that has been launched like this, it will bounce forward and get processor time, initialize itself, and be added to the Application menu as usual.

Q A colleague of mine who is a Latin freak always calls me a "lens culinaris." What does it mean?

AYou are being called a "lentil."

These answers are supplied by the technical gurus in Apple's Developer Support Center. Special thanks to Pete "Luke" Alexander, Mark Baumwell, Mark "The Red" Harlan, David Hayward, Scott Kuechle, Larry Lai, Joseph Maurer, Jim Mensch, and Nick Thompson for the material in this Q & A column.



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