March 93 - PRINT TIPS
PRINT TIPS
LOOKING AHEAD TO QUICKDRAW GX
PETE ("LUKE" ALEXANDER
With the release of QuickDraw GX later this year, there are a few changes in store for
print land. In this column, I'm going to talk about two of these changes -- the
disappearance of the PDEF 10 resource from the QuickDraw GX LaserWriter driver,
and the disappearance of the 'STR ' (-8192) and 'PAPA' (-8192) resources from a
system running QuickDraw GX.
Like most changes, the fact that these resources are going away is both good news and
bad news. The good news is that printing is going to work much better in the GX world
than it does today. For one thing, the new printer driver architecture provides
functionality that used to be unavailable through the Printing Manager, which is why
people got involved in directly grabbing resources in the first place. The bad news is
that if youare currently grabbing these resources, you're going to have some problems
running under QuickDraw GX, and you need to decide now how you're going to deal with
this.
Before we get into solutions, however, let's back up a bit, and answer the question,
What's a PDEF, anyway? A PDEF is just a code resource for printer drivers. All
printer drivers contain multiple PDEFs, each of which implements a piece of the
driver's functionality, like displaying dialog boxes or alerts. PDEF 10 contains the
printer access protocol (PAP) code that enables a LaserWriter driver to communicate
with a network printer. (For details about the interface to PAP, see Chapter 10,
"Printer Access Protocol," inInside AppleTalk.) Some applications that need the PAP
code have acquired it by sucking PDEF 10 out of the LaserWriter driver. Before Apple
put together its PAP software licensing package, grabbing PDEF 10 like this was a
quick and easy way to get what you needed. But it's an approach that's unsupported by
Apple and that has always carried the seeds of compatibility problems.
So what should you do if you're currently grabbing PDEF 10 out of the LaserWriter
driver? You've got the following possible solutions:
• Continue to grab PDEF 10, but make sure you're prepared to handle
failure gracefully when you can't get it. Basically, you'll need to let the user
know that your application isn't compatible with the version of system
software being used -- that is, the QuickDraw GX-based system. Not a very
user-friendly solution, but that might be OK for your application.
• If all you need to do is download a PostScriptTM file to the LaserWriter,
use the PostScriptHandle PicComment and a basic print loop. Most applications
need to do a lot more than send a bunch of PostScript code down the pipe -- for
instance, they need to set the characteristics of the PostScript printer -- but
if your application's needs are really this limited, it can be happy in the GX
world. If you're interested in this approach, take a look at the Technical Notes
"A Printing Loop That Cares . . ." and "PicComments -- The Real Deal." You can
also look at the PostScriptHandleDemo snippet in the Snippets folder on
theDeveloper CD Seriesdisc.
• Write your own PAP interface files. This is a relatively time-consuming
operation, but it gives you total ownership of the code, and your application is
unlikely to break with future system software releases. Quite a few developers
have had success with this approach.
• License Apple's PAP library code -- the same library that's used within
the LaserWriter Font Utility. The latest version (v. 1.5) of the library
improves on the last version and has more complete documentation. If you're
interested in licensing this library, please contact
Software Licensing
Apple Computer, Inc.
20525 Mariani Avenue, M/S 38-I
Cupertino, CA 95014
AppleLink: SW.LICENSE
Phone: (408)974-4667
• Use Apple's LaserWriter Font Utility and add your custom features to it.
In System 7, the LaserWriter Font Utility can handle drop-in enhancements
called UTILs. UTILs take care of all the communication issues for you, and they
give you quite a bit of power and flexibility. If you're interested in this
approach, take a look at "PostScript Enhancements for the LaserWriter Font
Utility" in Issue 10 ofdevelop.
At this point, you're probably wondering which solution is the best for you. It all
depends on your requirements. From my point of view, any solution besides the first is
acceptable if it will keep your users happy and keep you compatible with future
system software releases.
Now let's turn to the disappearance of the 'STR ' (-8192) and 'PAPA' (-8192)
resources. On a non-QuickDraw GX system, the 'STR ' resource contains the name of
the currently chosen printer driver, while the 'PAPA' resource contains the name and
network address of the current PAP printer. Because QuickDraw GX will allow more
than one active printer at a time, these resources will become obsolete.
Why is this a problem? Only because some applications currently grab the 'STR ' and
'PAPA' resources to automatically select a printer without going through the Chooser.
Under QuickDraw GX, it will be possible to redirect a print job to another printer via
the Printing Manager's public API. So new applications and applications revised to
work under QuickDraw GX will be able to programmatically redirect print jobs on the
fly in a clean, supported manner.
If your application isn't GX-smart, the simplest way to deal with the disappearance of
the 'STR ' and 'PAPA' resources is probably just to remove your application's feature
of circumventing the Chooser. If your application absolutely requires this
functionality, however, make sure that when these resources aren't available, you tell
the user to go use the Chooser. This way your application will print on a QuickDraw GX
system without any problems.
This column has looked at a couple of compatibility problems that can emerge when
non- QuickDraw GX applications run under QuickDraw GX, and also at some of the ways
that you can avoid these problems. As long as you're prepared to implement one of the
solutions recommended here, your application will run just fine under QuickDraw GX.
And on the bright side, QuickDraw GX is going to allow your application to access and
control a vast amount of information at print time. QuickDraw GX will provide the API
your application requires to take care of all the user's printing needs without having
to cruise through printer driver or system resources. You asked for it, and soon you'll
have it!
REFERENCES
• Inside AppleTalk (Addison-Wesley, 1990), Chapter 10, "Printer Access
Protocol.
• Macintosh Technical Notes "PicComments -- The Real Deal" (formerly
#91), "A Printing Loop That Cares . . . " (formerly #161), and "Printer
Access Protocol Q&As" under "Using PAP & code for finding printer driver
under System 7.
• "PostScript Enhancements for the LaserWriter Font Utility" by Bryan K.
Ressler, develop Issue 10.
PETE ("LUKE") ALEXANDER In the winter, Luke likes to hit the cross-country ski
tracks. There you'll find him striding across meadows and down hills on long strips of
fiberglass. One day he agreed to a "small" uphill ski at a friend's urging, only to
discover halfway into it a virtually vertical two-mile climb! Weighing the risks of
descending uncontrollably from there versus continuing on, Luke forged ahead,
arriving at the summit an hour (and a lot of side stepping) later. Since then, he's been
problem."*
Grabbing the PAP driver from PDEF 10 is described both in the Macintosh
Technical Note "Printer Access Protocol Q&As" under "Using PAP & code for finding
printer driver under System 7" and in the article by Mike Schuster called "Laser
Print DA for PostScript" in MacTutor Volume 2, Number 2.*
To find out whether the QuickDraw GX Printing Manager is installed, call the
Gestalt function with the 'pmgr' selector. *
Thanks to Hugo Ayala, Tom Dowdy, Dave Hersey, Jim Luther, and Scott ("Zz")
Zimmerman for reviewing this column. *