TweetFollow Us on Twitter

Print Hints


Sending PostScript Files to a LaserWriter

Dave Polaschek

A question that popped up pretty often for me when I worked in Apple's Developer Technical Support group, and that continues to appear in the Mac programming newsgroups on the Internet, is "How do I send PostScript TM files to a LaserWriter?" The simplest answer appears to be to use the PostScriptHandle picture comment. Wrong! In the Print Hints column "The Top 10 Printing Crimes Revisited" in develop Issue 26, I said that this would be a misuse of the PostScriptHandle picture comment, but I didn't give a full explanation of just how to send files to a printer. This column will explain how to send complete PostScript files the correct way.

First, though, I'd like to backtrack a little and explain more thoroughly why you shouldn't use the picture comment to send complete PostScript files. After all, if you do implement code that uses this technique, the files get to the printer, pages come out, and things seem mostly to work. What's the problem?


The problem with using the PostScriptHandle picture comment to send files to a printer is that you're using the Printing Manager to do some of the work for you and then bypassing it unexpectedly. The problems that will show up when you do this may not be obvious, but when a user does notice them it can lead to confusion.

First, when you use the PostScriptHandle picture comment, the LaserWriter driver has already set up the PostScript state for QuickDraw imaging. It has changed the coordinate system and has sent down the md dictionary that it will need to draw pages. At best, this is extra baggage that your PostScript files don't need in the way. At worst, since the driver has changed the coordinate system, your PostScript file may not print correctly. There's also a chance that the extra memory used by the LaserWriter's PostScript dictionary may cause your job not to print at all.

Second, using PostScriptHandle is wasteful. If background printing is enabled, the complete PostScript file, plus the extra things you don't need, will be spooled to the user's hard drive. Since what you're interested in is just getting the file to the printer, this is wasteful. In some cases, the job won't even be able to print, since your user won't have enough free space on the hard drive to hold a second copy of the PostScript file.

Finally, there's an aesthetic problem. The Printing Manager counts the pages that are going to be sent by looking at how many times PrOpenPage is called during your print job. If you've got a multiple-page PostScript file, the page count displayed by the Printing Manager will be out of whack. While messages like "Printing Page 4 of 1" won't actually hurt the user, spreading confusion is bad.


There are actually two right ways to send PostScript files to the printer. They're essentially the same in that you open a connection directly to the printer and send it the file you want to print, but the implementations are very different. You can either use classic networking and the PAPWorkStation.o library, or you can use Open Transport, which contains support for the PAP protocol. (For more on PAP, see "PAP? What's That?")


    The Printer Access Protocol (PAP) is the protocol spoken by all LaserWriters (and third-party Macintosh-compatible PostScript printers). It's designed around a few simple ideas:

    • Only one computer can be talking to the printer at once, so there's a unique connection between the two.
    • When the printer is ready to receive some data, it will ask the computer for that data. Similarly, when the printer wants to send data back to the computer, the computer must have already asked for that data. In other words, a read must always be active.
    • There's a separate status channel for the printer to report things like "Printer On Fire" or "Paper Jam."

    This last point means that there are actually multiple connections open for the one connection to the printer. This is a major source of the complexity of the code in the classic networking case. Open Transport hides this complexity from you.

    You can find out more about PAP in Chapter 10 of Inside AppleTalk.

The classic networking solution has the advantage that it's available in all Macintosh computers, out of the box. But it's more difficult to implement. Since you're working at a lower level, there's more room for you to get things wrong -- but there's also less worry of having library code that doesn't do things the way you want. Note that your code (at least part of it) can't be PowerPC native, because the libraries are 680x0 only.

Open Transport is a much simpler way to implement sending PostScript files to your printer. You talk to the networking library at a higher level, and you get a PowerPC-native implementation of networking. But of course you lose compatibility with older Macintosh models.

We'll look at both these solutions; sample code for each one accompanies this column on this issue's CD and develop's Web site. The choice of which technique to use is up to you. Note also that there may be other, more attractive alternatives in the future. For now, however, these are the two best options.

The sample code for the classic networking solution is the SendPS tool -- an MPW tool rather than a full application, but still useful for demonstrating how things work. The process is also described in the MacTutor article "Laser Print DA for PostScript." If you're interested in the nitty-gritty details, consulting the code and that article is your best bet. Here I'm just going to give an overview of the code. In a few cases, I'll make suggestions for how you might enhance the code to make a real-world application.

The main thing you need to understand about the PAP library that Apple supplies for classic networking is that it reports the connection status to you via a few variables rather than by way of completion functions. It's not truly asynchronous code, so if you want to write a program that will run happily in the background, sending PostScript files to a printer, you've got some extra work to do. It's possible, but a little tricky.

When we're in the process of opening a connection (in the code near the call to PAPOpen in sendps.c), we look at the wstate variable to tell us what's happening. All these state variables have three basic states: a positive value means we're waiting for the printer; negative values are errors; and 0 means the operation we're watching has completed. We also call PAPStatus periodically to get the printer's status so that we can display it to the user.

Once the connection is opened, we issue a PAPRead call. This is necessary because when the printer wants to talk to us, it can't just tell us it's ready to talk, but rather we must have asked it for some data first. (Remember, PAP is a protocol where the parties have to ask for data.) We check the rstate variable periodically to see if the printer has said anything to us. When it does, we need to read the data it has sent us and issue another PAPRead call.

Now we're ready to start sending blocks of data. We issue a PAPWrite call, and for each call, we watch the wstate variable to see when the write is done. While we're waiting for the writes to complete, we need to remember to check the printer's status and display it to the user (our write might be "stuck" because the printer is out of paper and can't print a page, for example; the user should see this so that she can replenish the paper).

Once we've sent all our data, we send the end-of-file to the printer. We do this by sending a packet with no data, but with the eof flag set. If we've got another job to send, there's no need to close the connection and reopen it; we can just start sending it as soon as the printer acknowledges our end-of-file.

That's the quick overview of the SendPS tool. If you need more guidance, see the source code; I've tried to comment it so that everything will make sense.

    You're not allowed to redistribute the PAPWorkStation.o library included with the classic networking sample code without first licensing it from Apple. To license the code, contact for more details. It's really not that expensive, and you don't want to write it all yourself. Trust me.*


The main code for the Open Transport solution is considerably easier to follow than the classic networking code, primarily because you don't have to worry about multiple state variables in order to send. You simply create PAP and PAPStatus endpoints (connections), and the main loop calls the Snd and Rcv functions for the PAP endpoint. There's a callback function that gets notified when the state of the endpoint changes and then sets a single state variable to match the state of the endpoint. Exception handling can be localized to this callback, which makes the code easier to read, and the status reporting can be handled in one place as well.

Because we don't need to continually poll the state variables, it's much easier to fit this code into an application, and the application will cooperate better with other applications. Getting good performance is also quite a bit easier with the Open Transport-based code than with the classic networking code, since you don't have to worry about waiting in the wrong place, polling a state variable.


Implementing code to send PostScript files directly to a printer is more difficult than using the PostScriptHandle picture comment, but it offers a number of benefits to your users. The process is more straightforward, no extra print dialogs need to be shown, and no extra storage is required for spool files. You can provide as much or as little status information as you like (for example, you could add progress bars showing how much of the job is completed). And performance should improve in most cases, since you'll be talking directly to the printer, rather than through the layer of the Printing Manager. Convinced? I should hope so.


    • Inside Macintosh: Open Transport and Open Transport Client Developer Note (Apple Computer, Inc., 1996), available on the Open Transport Web site,
    • Inside Macintosh: Networking by Apple Computer, Inc. (Addison-Wesley, 1994) and Inside AppleTalk, 2nd ed., by Apple Computer, Inc. (Addison-Wesley, 1990).
    • Macintosh Technical Q&A QD 35, "Determining the Selected Printer's Address."
    • "Laser Print DA for PostScript" by Mike Schuster, MacTutor Vol. 2, No. 2 (February 1986). Articles from MacTutor, since renamed MacTech Magazine, can be found at
    • Lost Beauties of the English Language, by Charles Mackay, LL.D. (London: Bibliophile Books, 1987). Originally published by Chatto & Windus in 1874.
    • The UNIX-Haters Handbook by Simson Garfinkel, Daniel Weise, and Steven Strassman (IDG Books, 1994).

DAVE POLASCHEK (, now works for LaserMaster Corp., where he does "Mac things" that confuse the people who actually build printers, since Dave seems to spend most of his time designing spiffy icons and then dragging them around his screen. In his spare time, Dave scrapes ice off his windshield, jump-starts cars, and de-ices locks. Earlier this year he cut a hole in a lake and spent hours sitting on the ice waiting for fish to find his hook (while he consumed a judicious amount of antifreeze). Who said life in Minnesota isn't exciting?*

Thanks to Rich Kubota, Quinn "The Eskimo!", Steve Simon, and Tony Wingo for reviewing this column.*


Community Search:
MacTech Search:

Software Updates via MacUpdate

World of Tanks Generals guide - Tips and...
World of Tanks Generals is a brand new card game by the developer behind the World of Tanks shooter franchise. It plays like a cross between chess and your typical card game. You have to keep in consideration where you place your tanks on the board... | Read more »
TruckSimulation 16 guide: How to succeed...
Remember those strangely enjoyable truck missions in Grand Theft Auto V whereit was a disturbing amount of fun to deliver cargo? TruckSimulation 16 is reminiscent of that, and has you play the role of a truck driver who has to deliver various... | Read more »
The best GIF making apps
Animated GIFs have exploded in popularity recently which is likely thanks to a combination of Tumblr, our shorter attention spans, and the simple fact they’re a lot of fun. [Read more] | Read more »
The best remote desktop apps for iOS
We've been sifting through the App Store to find the best ways to do computer tasks on a tablet. That gave us a thought - what if we could just do computer tasks from our tablets? Here's a list of the best remote desktop apps to help you use your... | Read more »
Warhammer 40,000: Freeblade guide - How...
Warhammer 40,000: Freebladejust launched in the App Store and it lets you live your childhood dream of blowing up and slashing a bunch of enemies as a massive, hulking Space Marine. It's not easy being a Space Marine though - and particularly if... | Read more »
Gopogo guide - How to bounce like the be...
Nitrome just launched a new game and, as to be expected, it's a lot of addictive fun. It's called Gopogo, and it challenges you to hoparound a bunch of platforms, avoiding enemies and picking up shiny stuff. It's not easy though - just like the... | Read more »
Sago Mini Superhero (Education)
Sago Mini Superhero 1.0 Device: iOS Universal Category: Education Price: $2.99, Version: 1.0 (iTunes) Description: KAPOW! Jack the rabbit bursts into the sky as the Sago Mini Superhero! Fly with Jack as he lifts impossible weights,... | Read more »
Star Wars: Galaxy of Heroes guide - How...
Star Wars: Galaxy of Heroes is all about collecting heroes, powering them up, and using them together to defeat your foes. It's pretty straightforward stuff for the most part, but increasing your characters' stats can be a bit confusing because it... | Read more »
The best cooking apps (just in time for...
It’s that time of year again, where you’ll be gathering around the dinner table with your family and a huge feast in front of you. [Read more] | Read more »
Square Rave guide - How to grab those te...
Square Rave is an awesome little music-oriented puzzle game that smacks of games like Lumines, but with its own unique sense of gameplay. To help wrap your head around the game, keep the following tips and tricks in mind. [Read more] | Read more »

Price Scanner via

Cyber Monday: Apple MacBooks on sale for up t...
Apple resellers have MacBook Pros, MacBook Airs, and MacBooks on sale for up to $250 off MSRP for Cyber Monday 2015. The following is a roundup of the lowest prices available for new models from any... Read more
Cyber Monday: 15% off Apple products, and sto...
Use code CYBER15 on Cyber Monday only to take 15% on Apple products at Target, and store-wide. Choose free shipping or free local store pickup (if available). Sale prices for online orders only, in-... Read more
iPad Air 2 And iPad mini Among Top Five Black...
Adobe has released its 2015 online shopping data for Black Friday and Thanksgiving Day. The five best selling electronic products on Black Friday were Samsung 4K TVs, Apple iPad Air 2, Microsoft Xbox... Read more
All-in-one PC Shipments Projected To Drop Ove...
Digitimes’ Aaron Lee and Joseph Tsai report that all-in-one (AIO) PC shipments may drop a double-digit percentage on-year in 2015 due to weaker-than-expected demand, although second-largest AIO make... Read more
Sprint Offers iPad Pro
Sprint now offers Apple’s new iPad Pro with Wi-Fi + Cellular, featuring a 12.9-inch Retina display with 5.6 million pixels. Customers can pick up iPad Pro at select Sprint retail locations. It can... Read more
Cyber Monday: Target offers 15% discount on A...
Target has discounted Apple Watches by 15% for Cyber Monday. Choose free shipping or free local store pickup (if available). Sale prices for online orders only, in-store prices may vary: - Apple... Read more
Sunday roundup of Holiday weekend Mac sales:...
Take up to $500 off MSRP on the price of a new Mac at B&H Photo today as part of their Black Friday/Holiday weekend sale. Shipping is free, and B&H charges NY tax only. These prices are... Read more
Holiday weekend: Apple Watch on sale for $50-...
B&H Photo has the Apple Watch on sale today for $50-$100 off MSRP. Shipping is free, and B&H charges NY sales tax only: - Apple Watch Sport: $50 off - Apple Watch: $50-$100 off Read more
Holiday weekend: iPad Air 2s on sale for up t...
B&H Photo has iPad Air 2s on sale for up to $80 off MSRP including free shipping plus NY sales tax only: - 16GB iPad Air 2 WiFi: $459 $40 off - 64GB iPad Air 2 WiFi: $569 $30 off - 128GB iPad Air... Read more
Holiday weekend Mac sales roundup: B&H Ph...
B&H Photo continues to have all new Macs on sale for up to $500 off MSRP as part of their Black Friday/Holiday weekend sale. Shipping is free, and B&H charges NY tax only: - 15″ 2.2GHz Retina... Read more

Jobs Board

Technical Program Manager, Strategic Merchant...
# Technical Program Manager, Strategic Merchants - Apple Pay Job Number: 44001177 Santa Clara Valley, Califo ia, United States Posted: Oct. 30, 2015 Weekly Hours: 40.00 Read more
Frameworks Engineer, *Apple* Watch - Apple...
# Frameworks Engineer, Apple Watch Job Number: 41403122 Santa Clara Valley, Califo ia, United States Posted: Jul. 1, 2015 Weekly Hours: 40.00 **Job Summary** Join the Read more
Software Engineer - *Apple* Pay - Apple (Un...
# Software Engineer - Apple Pay Job Number: 44003246 Santa Clara Valley, Califo ia, United States Posted: Nov. 16, 2015 Weekly Hours: 40.00 **Job Summary** Apple Pay Read more
Merchant Operations Manager: *Apple* Pay -...
# Merchant Operations Manager: Apple Pay Job Number: 43593822 Santa Clara Valley, Califo ia, United States Posted: Nov. 10, 2015 Weekly Hours: 40.00 **Job Summary** The Read more
Product Design Engineer - *Apple* Watch - A...
# Product Design Engineer - Apple Watch Job Number: 41727161 Santa Clara Valley, Califo ia, United States Posted: Jul. 22, 2015 Weekly Hours: 40.00 **Job Summary** Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.