TweetFollow Us on Twitter

December 96 - Print Hints: Safe Travel Through the Printing Jungle

Print Hints:
Safe Travel Through the Printing Jungle

Dave Polaschek

Implementing printing in a Macintosh application should be pretty straightforward, right? There are currently 18 high-level printing calls (listed on pages 9-92 and 9-93 of Inside Macintosh: Imaging With QuickDraw), which is only three more than were listed in Inside Macintosh Volume II. Calling them in the right order gives you a printing port that you can treat just like a graphics port -- and every Macintosh application knows (or at least ought to know) how to draw into a graphics port.

But in spite of this apparent simplicity, there are an astounding number of Macintosh applications that have problems printing. (Even products from Apple make the list once in a while.) I think one of the reasons for this is that, while basic QuickDraw printing is simple, printing is something that can be -- and has been -- made more complex by various "extensions" to the original printing architecture. These extensions offer greater control of the printing process, allowing you to take advantage of special features available on some printers and to draw in more sophisticated ways than QuickDraw allows. But they also introduce complexities that can get you in trouble if you're not careful. In this column I'll give a few examples of places where control comes only at the price of complexity, and therefore places where you need to tread very carefully, if at all.


Picture comments are, on the face of it, wonderful things. They let you embed commands in your output that can take advantage of particular printer features if they're available, and they're automatically ignored by printer drivers that don't support them. But there's a flip side: for every picture comment you use, you have to provide an alternative for those printers that don't support it. There are also a number of picture comments that should be avoided, as listed on page B-40 of Inside Macintosh: Imaging With QuickDraw. As with any complex and powerful tool, the potential for getting things wrong with picture comments is ever-present.

The SetLineWidth picture comment is a perfect example: not only is it supported by only a few printer drivers, but it's implemented slightly differently in each of them. On some printers the value you pass for the line width is used to modify the current line width (for instance, passing 1/2 will halve the current line width), and on others it's used as an "absolute" value (passing 1/2 will set the line width to 1/2 point, regardless of the previous width). To obtain the desired results, you have to write your code very carefully, and even then the SetLineWidth picture comment may not work on the printer driver that the user happens to be using -- and there's no QuickDraw alternative. The territory here is treacherous. Unless you really need fractional line widths, it may be better to take the nice safe QuickDraw path.


The PrGeneral call added complexity to the Printing Manager -- and even more complexity could be added by driver developers, often without accompanying documentation. After all, since supporting the various PrGeneral opcodes (in fact, supporting PrGeneral itself) is optional, printer drivers can define their own new opcodes and nobody need be the wiser -- nobody, that is, except for the one developer who needs the new opcode and the functionality it provides. Things get even more confusing when the same added functionality is available via a different mechanism in a different printer driver, so the application has to start using special-case code for each printer driver it knows about. If you find yourself writing special-case code for particular printer drivers, stop! Back up and look for another solution.

One commonly used PrGeneral capability, provided by the getRslOp and setRslOp opcodes, is finding the resolution(s) supported by the printer you're using and setting the resolution you want to print with. There's clearly a need for this sort of capability. An application that shows graphs of curves or of raw data gathered from some source wants the graphs to look good. Plotting individual pixels at 72 dpi doesn't make for smooth-looking curves, so an application might be justified in asking to print at the highest resolution the printer is capable of. But is PrGeneral the right approach?

A potential problem with using PrGeneral to get and set resolutions is that you're depending on the printer driver to keep up with the times. The LaserWriter driver, for example, is used for printers from the original LaserWriter all the way up to high-end typesetters. The driver reports that the maximum physical resolution of the printer is 300 dpi, even if you're printing to a typesetter that's capable of 1270 or even 2540 dpi. The reason for this is that reporting a higher resolution could cause applications that create bitmaps at the printer's resolution to run into QuickDraw's limitations, such as the limit on rowBytes and the 32K maximum region size. This is something that we plan to address in future versions of LaserWriter 8, but currently an application that wants to know a PostScript(TM) printer's real maximum resolution has to either parse the PostScript Printer Description file (PPD) associated with it or query the printer directly, both of which are functions that the driver should have to worry about, not the application.

In this case, there's an alternative to PrGeneral: If you're going to be generating your data in a GWorld, just make sure the GWorld's resolution is whatever you need for best results. Then take that same GWorld and use CopyBits to copy the PixMap in it to the printer. If you provide appropriate source and destination rectangles, the implementation of CopyBits in the printer driver will scale the PixMap, and you'll be taking advantage of the resolution of the printer without having to worry about new coordinate systems.

Determining just what resolution you need is, however, still a tricky issue. For example, if you're printing a color image to a LaserWriter that can print only black-and-white images and only at 300 dpi, the color image you're displaying onscreen already has more detail than the printer can reproduce, so you don't need to worry about sending a higher-resolution image at all. The way to tell for sure if you have enough data is that your pixel density (in dpi) should be between one and two times the "screen frequency" (in lpi) for the printer. The default screen frequency for PostScript printers is listed in the PPD file for the printer, and in the future we'll be providing access to the PPD file parsing code that's contained in LaserWriter 8's PrintingLib, but for now you may just want to ask the user rather than parse it out yourself.

If you're generating line art or other data that needs to have "hard edges" in a GWorld that's going to be sent to the printer, you've got a different problem: unless you specify the data at the printer's resolution (or higher), it will need to be scaled up to the printer's resolution, producing large, blocky pixels. Your users will think you're a bozo, unless of course your product is supposed to make large, blocky pixels. The right solution is to avoid sending data that needs to have hard edges as bitmapped images, if at all possible. This is the sort of data that really should be maintained as objects. If you want to draw the letter A, for instance, ask QuickDraw to draw it to the printer for you if possible, rather than image it into a bitmap first. If you really need to generate bitmaps of hard-edged data, be aware that you'd better have your machete sharpened and ready, since you're heading into the brush. On the other hand, this may be a great opportunity to generate your own PostScript code.


Generating your own PostScript code is another powerful technique that can get your application into trouble. In many cases, it's the right answer to a thorny dilemma; for instance, if you need drawing primitives that QuickDraw doesn't supply, this may be the only way to get them. After all, cubic Bézier curves are neat and powerful. The problem arises when the application developer either doesn't understand how to write compatible PostScript code or takes shortcuts in the PostScript code.

An excellent example is an old version of a certain very popular graphics program that saved its pictures with an EPS version of the graphic embedded in the PICT data. Unfortunately, the PostScript code in the EPS version depended on the md dictionary, a private dictionary used by the LaserWriter driver. After warning developers for years that the md dictionary was private, Apple Engineering felt justified in changing it. When the new version of the LaserWriter driver shipped, suddenly many graphics quit printing. The problem was made even worse by the fact that many of these graphics had been shipped as clip art, and they still occasionally pop up to bedevil us today.

The solution isn't to avoid PostScript code entirely. Just make sure that if you do generate it, the code is compatible and portable. Obviously, it shouldn't use any of the LaserWriter driver's private PostScript operators. If you make graphics with PostScript code embedded in them, be sure that the PostScript code they contain conforms to the EPS specification that's described by Adobe(TM) in the PostScript Language Reference Manual, Second Edition, Appendix H. Also, be sure to send the PostScript code with the PostScriptBegin, PostScriptHandle, and PostScriptEnd picture comments, as described beginning on page B-38 of Inside Macintosh: Imaging With QuickDraw.

Another thing application developers have tried over the years (with mixed success) is to do their own PostScript font management by talking directly to the printer. This is something applications really need to avoid. The LaserWriter driver knows how to handle the PostScript fonts needed to print a page (or series of pages). Applications that attempt to manage the fonts themselves are more likely to get poor font management for their efforts, since the LaserWriter driver (or the LaserWriter GX driver) will have a much harder time recognizing which fonts are needed on which page. When this happens, the drivers err on the side of safety: if there's any doubt about when a font is used, it will be included for the whole job, which is usually exactly what the developer was trying to avoid. Let the driver handle font management.


I've given a few of the more common examples of how printing has grown in complexity over the years, and how application developers can sometimes get in trouble by trying to take advantage of it. Printing doesn't need to be much harder than drawing to the screen if you stick to the rules, and even when you want to take advantage of particular printer capabilities, you can usually do so in safe, compatible ways. As tempting as it sometimes is to wander off the known path and plunge headlong into the uncharted jungle of possibilities, doing so usually just results in trouble -- for you and for your users. In printing, as in all programming, remember: keep it simple.


    • Technote PR 10, "A Printing Loop That Cares."

    • Writing Solid Code by Steve Maguire (Microsoft Press, 1993).

    • The History of the English-Speaking Peoples (4 volumes), by Sir Winston S. Churchill (Dodd, Mead, & Co., 1958 & 1959).

DAVE POLASCHEK (, formerly of Apple's Developer Technical Support group, got so confused by the lack of weather in California that he moved back to Minnesota. This probably won't seem like such a smart move when Celsius and Fahrenheit show the same temperature and Dave starts singing that verse from Jimmy Buffett's "Boat Drinks" that goes, "This morning, I shot six holes in my freezer. I think I've got cabin fever. Somebody sound the alarm."*

Thanks to Rich Blanchard, Paul Danbold, Dan Lipton, and Steve Simon for reviewing this column.*


Community Search:
MacTech Search:

Software Updates via MacUpdate

Microsoft Office 2016 16.11 - 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
Adobe Photoshop CC 2018 19.1.2 - Profess...
Photoshop CC 2018 is available as part of Adobe Creative Cloud for as little as $19.99/month (or $9.99/month if you're a previous Photoshop customer). Adobe Photoshop CC 2018, the industry standard... Read more
Adobe Dreamweaver CC 2018 -...
Dreamweaver CC 2018 is available as part of Adobe Creative Cloud for as little as $19.99/month (or $9.99/month if you're a previous Dreamweaver customer). Adobe Dreamweaver CC 2018 allows you to... Read more
Adobe Flash Player - Plug-in...
Adobe Flash Player is a cross-platform, browser-based application runtime that provides uncompromised viewing of expressive applications, content, and videos across browsers and operating systems.... Read more
Drive Genius 5.2.0 - $79.00
Drive Genius features a comprehensive Malware Scan. Automate your malware protection. Protect your investment from any threat. The Malware Scan is part of the automated DrivePulse utility. DrivePulse... Read more
MegaSeg 6.0.6 - Professional DJ and radi...
MegaSeg is a complete solution for pro audio/video DJ mixing, radio automation, and music scheduling with rock-solid performance and an easy-to-use design. Mix with visual waveforms and Magic... Read more
ffWorks 1.0.7 - Convert multimedia files...
ffWorks (was iFFmpeg), focused on simplicity, brings a fresh approach to the use of FFmpeg, allowing you to create ultra-high-quality movies without the need to write a single line of code on the... Read more
Dash 4.1.5 - Instant search and offline...
Dash is an API documentation browser and code snippet manager. Dash helps you store snippets of code, as well as instantly search and browse documentation for almost any API you might use (for a full... Read more
Evernote 7.0.3 - Create searchable notes...
Evernote allows you to easily capture information in any environment using whatever device or platform you find most convenient, and makes this information accessible and searchable at anytime, from... Read more
jAlbum Pro 15.3 - Organize your digital...
jAlbum Pro has all the features you love in jAlbum, but comes with a commercial license. You can create gorgeous custom photo galleries for the Web without writing a line of code! Beginner-friendly... Read more

Latest Forum Discussions

See All

Around the Empire: What have you missed...
Oh hi nice reader, and thanks for popping in to check out our weekly round-up of all the stuff that you might have missed across the Steel Media network. Yeah, that's right, it's a big ol' network. Obviously 148Apps is the best, but there are some... | Read more »
All the best games on sale for iPhone an...
It might not have been the greatest week for new releases on the App Store, but don't let that get you down, because there are some truly incredible games on sale for iPhone and iPad right now. Seriously, you could buy anything on this list and I... | Read more »
Everything You Need to Know About The Fo...
In just over a week, Epic Games has made a flurry of announcements. First, they revealed that Fortnite—their ultra-popular PUBG competitor—is coming to mobile. This was followed by brief sign-up period for interested beta testers before sending out... | Read more »
The best games that came out for iPhone...
It's not been the best week for games on the App Store. There are a few decent ones here and there, but nothing that's really going to make you throw down what you're doing and run to the nearest WiFi hotspot in order to download it. That's not to... | Read more »
Death Coming (Games)
Death Coming Device: iOS Universal Category: Games Price: $1.99, Version: (iTunes) Description: --- Background Story ---You Died. Pure and simple, but death was not the end. You have become an agent of Death: a... | Read more »
Hints, tips, and tricks for Empires and...
Empires and Puzzles is a slick match-stuff RPG that mixes in a bunch of city-building aspects to keep things fresh. And it's currently the Game of the Day over on the App Store. So, if you're picking it up for the first time today, we thought it'd... | Read more »
What You Need to Know About Sam Barlow’s...
Sam Barlow’s follow up to Her Story is #WarGames, an interactive video series that reimagines the 1983 film WarGames in a more present day context. It’s not exactly a game, but it’s definitely still interesting. Here are the top things you should... | Read more »
Pixel Plex Guide - How to Build Better T...
Pixel Plex is the latest city builder that has come to the App Store, and it takes a pretty different tact than the ones that came before it. Instead of being in charge of your own city by yourself, you have to work together with other players to... | Read more »
Fortnite Will Be Better Than PUBG on Mob...
Before last week, if you asked me which game I prefer between Fortnite Battle Royale and PlayerUnknown’s Battlegrounds (PUBG), I’d choose the latter just about 100% of the time. Now that we know that both games are primed to hit our mobile screens... | Read more »
Siege of Dragonspear (Games)
Siege of Dragonspear 2.5.12 Device: iOS Universal Category: Games Price: $9.99, Version: 2.5.12 (iTunes) Description: Experience the Siege of Dragonspear, an epic Baldur’s Gate tale, filled with with intrigue, magic, and monsters.... | Read more »

Price Scanner via

Sunday Sales: $200 off 13″ Touch Bar MacBook...
Amazon has new 2017 13″ 3.1GHz Touch Bar MacBook Pros on sale this weekend for $200 off MSRP, each including free shipping: – 13″ 3.1GHz/256GB Space Gray MacBook Pro (MPXV2LL/A): $1599.99 $200 off... Read more
B&H drops prices on 15″ MacBook Pros up t...
B&H Photo has dropped prices on new 2017 15″ MacBook Pros, now up to $300 off MSRP and matching Adorama’s price drop yesterday. Shipping is free, and B&H charges sales tax for NY & NJ... Read more
Apple restocks Certified Refurbished 2017 13″...
Apple has restocked Certified Refurbished 2017 13″ 2.3GHz MacBook Pros for $200-$230 off MSRP. A standard Apple one-year warranty is included with each MacBook, models receive new outer cases, and... Read more
13″ Space Gray Touch Bar MacBook Pros on sale...
Adorama has new 2017 13″ Space Gray Touch Bar MacBook Pros on sale for $150 off MSRP. Shipping is free, and Adorama charges sales tax in NY & NJ only: – 13″ 3.1GHz/256GB Space Gray MacBook Pro (... Read more
Best deal of the year on 15″ Apple MacBook Pr...
Adorama has New 2017 15″ MacBook Pros on sale for up to $300 off MSRP. Shipping is free, and Adorama charges sales tax in NJ and NY only: – 15″ 2.8GHz Touch Bar MacBook Pro Space Gray (MPTR2LL/A): $... Read more
Save $100-$150+ on 13″ Touch Bar MacBook Pros...
B&H Photo has 13″ Touch Bar MacBook Pros on sale for $100-$150 off MSRP. Shipping is free, and B&H charges sales tax for NY & NJ residents only: – 13″ 3.1GHz/256GB Space Gray MacBook Pro... Read more
Current deals on 27″ Apple iMacs, models up t...
B&H Photo has 27″ iMacs on sale for up to $150 off MSRP. Shipping is free, and B&H charges sales tax for NY & NJ residents only: – 27″ 3.8GHz iMac (MNED2LL/A): $2149 $150 off MSRP – 27″ 3... Read more
Thursday Deal: 13″ 2.3GHz MacBook Pro for $11...
B&H Photo has the 13″ 2.3GHz/128GB Space Gray MacBook Pro on sale for $100 off MSRP. Shipping is free, and B&H charges sales tax for NY & NJ residents only: – 13-inch 2.3GHz/128GB Space... Read more
How to save $100-$190 on 10″ & 12″ iPad P...
Apple is now offering Certified Refurbished 2017 10″ and 12″ iPad Pros for $100-$190 off MSRP, depending on the model. An Apple one-year warranty is included with each model, and shipping is free: –... Read more
Silver 12″ 1.3GHz MacBook on sale at B&H...
B&H Photo has the 2017 12″ 1.3GHz Silver MacBook on sale for $1399.99 including free shipping plus sales tax for NY & NJ residents only. Their price is $200 off MSRP, and it’s the lowest... Read more

Jobs Board

Firmware Engineer - *Apple* Accessories - A...
# Firmware Engineer - Apple Accessories Job Number: 113452350 Santa Clara Valley, California, United States Posted: 28-Feb-2018 Weekly Hours: 40.00 **Job Summary** Read more
Automation and Performance Engineer, *Apple*...
# Automation and Performance Engineer, Apple Pay Job Number: 113557967 Santa Clara Valley, California, United States Posted: 09-Mar-2018 Weekly Hours: 40.00 **Job Read more
Hardware Systems Architect - *Apple* Watch...
# Hardware Systems Architect - Apple Watch Job Number: 113565323 Santa Clara Valley, California, United States Posted: 05-Mar-2018 Weekly Hours: 40.00 **Job Read more
Lead *Apple* Solution Consultant - Apple (U...
# Lead Apple Solution Consultant Chicago IL Job Number: 113560644 Chicago, Illinois, United States Posted: 10-Mar-2018 Weekly Hours: 40.00 **Job Summary** As a Lead Read more
Art Director, *Apple* Music + Beats1 Market...
# Art Director, Apple Music + Beats1 Marketing Design Job Number: 113258081 Culver City, California, United States Posted: 07-Mar-2018 Weekly Hours: 40.00 **Job Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.