TweetFollow Us on Twitter

Print Hints

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?

WHY NOT USE POSTSCRIPTHANDLE?

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.

THE RIGHT WAY(S)

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?")

    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 sw.license@apple.com for more details. It's really not that expensive, and you don't want to write it all yourself. Trust me.*

THE OPEN TRANSPORT CODE

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.

WRAPPING UP

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.


    RECOMMENDED READING

    • Inside Macintosh: Open Transport and Open Transport Client Developer Note (Apple Computer, Inc., 1996), available on the Open Transport Web site, http://www.devworld.apple.com/dev/opentransport/.
    • 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 http://web.xplain.com/mactech.com/magazine/features/articlearchives.html.
    • 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 (davep@best.com, http://www.best.com/~davep/) 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

Duet 1.6.9.3 - Use your iPad as an exter...
Duet is the first app that allows you to use your iDevice as an extra display for your Mac using the Lightning or 30-pin cable. Note: This app requires a $14.99 iOS companion app. Version 1.6.9.3:... Read more
Duet 1.6.9.3 - Use your iPad as an exter...
Duet is the first app that allows you to use your iDevice as an extra display for your Mac using the Lightning or 30-pin cable. Note: This app requires a $14.99 iOS companion app. Version 1.6.9.3:... Read more
iExplorer 4.1.10 - View and transfer fil...
iExplorer is an iPhone browser for Mac lets you view the files on your iOS device. By using a drag and drop interface, you can quickly copy files and folders between your Mac and your iPhone or... Read more
iExplorer 4.1.10 - View and transfer fil...
iExplorer is an iPhone browser for Mac lets you view the files on your iOS device. By using a drag and drop interface, you can quickly copy files and folders between your Mac and your iPhone or... Read more
Adobe InCopy CC 2018 13.0.1.207 - Create...
InCopy 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 InCopy customer). Adobe InCopy CC 2018, ideal for large team projects... Read more
Microsoft Office 2016 15.40 - 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 InDesign CC 2018 13.0.1.207 - Prof...
InDesign 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 InDesign customer). Adobe InDesign CC 2018 is part of Creative Cloud.... Read more
Apple iOS 11.1.2 - The latest version of...
iOS 11 sets a new standard for what is already the world’s most advanced mobile operating system. It makes iPhone better than before. It makes iPad more capable than ever. And now it opens up both to... Read more
Slack 2.9.0 - Collaborative communicatio...
Slack is a collaborative communication app that simplifies real-time messaging, archiving, and search for modern working teams. Version 2.9.0: Slack now officially, and fully, supports Japanese.... Read more
iExplorer 4.1.9 - View and transfer file...
iExplorer is an iPhone browser for Mac lets you view the files on your iOS device. By using a drag and drop interface, you can quickly copy files and folders between your Mac and your iPhone or... Read more

Latest Forum Discussions

See All

Mighty Battles guide - how to build a so...
Mighty Battles, the latest title from Hothead Games, is set to take the App Store by storm. The game puts a welcome twist on lane battlers, adding FPS elements to spice things up a bit. You'll collect cards to put your own military unit to gether,... | Read more »
Rules of Survival guide - how to be the...
The PUBG craze makes its way to mobile, with more and more battle royale games debuting on iOS and Android. Rules of Survival joins the ranks of mobile PUBG-likes, offering a classic battle royale experiences that doesn't vary too much from its... | Read more »
The best new games we played this week -...
The weekend is upon us friends, and it's time to take a look back and reflect on all of the wonderful games we've played over the past few days. This week was jam packed with new releases. There were some big, long awaited launches, some fun... | Read more »
Lineage II: Revolution guide - tips and...
At long last, Lineage II: Revolution has now come to western shores, bring Netmarble's sweeping MMORPG to mobile devices. It's an addictive, epic experience, but some of the systems in the game can be a bit overwhelming. Here are a few tips to help... | Read more »
A Boy and His Blob (Games)
A Boy and His Blob 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: | Read more »
Fight terrible monsters and collect epic...
Released on Western markets early last month, Dragon Project, created by Japanese developer COLOPL, brings epic monster hunting action to mobile for the very first time. Collect a huge array of weapons and armor, and join up with friends to fight... | Read more »
I Am The Hero (Games)
I Am The Hero 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: I Am The Hero is a pixel art, beat 'em up, fighting game that tells the story of a "Hero" with a glorious but mysterious past.... | Read more »
Kauldron (Music)
Kauldron 1.0 Device: iOS Universal Category: Music Price: $3.99, Version: 1.0 (iTunes) Description: Kauldron is our warmest sounding, punchiest synth yet! A completely new modeling technology, combined with carefully designed... | Read more »
Lineage II: Revolution is mobile’s bigge...
NCSoft’s hit fantasy MMORPG series has just made the leap to mobile with the help of Netmarble in Lineage II: Revolution. With over 1.5 million players having already pre-registered ahead of the game’s launch, Revolution hit the app stores... | Read more »
Swing skilfully in new physics-based pla...
Sometimes it’s the most difficult of obstacles that can be the most rewarding. One game hoping to prove this is OCMO, the new tough but fair platformer from developers Team Ocmo. Primed to set every speedrunner’s pulse racing, as an otherworldly... | Read more »

Price Scanner via MacPrices.net

Black Friday pricing on Macs and iPads now av...
B&H Photo has lowered prices on many Macs, iPads, and iPad Pros as part of their Black Friday week sale. Save up to $200 on MacBooks and iMacs and up to $150 on iPads. B&H charges sales tax... Read more
Best Apple iPad deals this weekend, up to $80...
Apple resellers are offering 9.7″ iPads and 10.5″ iPad Pros for up to $80 off MSRP this weekend as part of their early Holiday and Black Friday sales: Adorama is offering new 2017 9.7″ 32GB WiFi... Read more
Early Black Friday sale: Apple iMacs for up t...
B&H Photo has 27-inch iMacs in stock and on sale for up $130-$150 off MSRP including free shipping. B&H charges sales tax in NY & NJ only: – 27″ 3.8GHz iMac (MNED2LL/A): $2149 $150 off... Read more
Apple restocks refurbished Mac minis starting...
Apple has restocked Certified Refurbished Mac minis starting at $419. Apple’s one-year warranty is included with each mini, and shipping is free: – 1.4GHz Mac mini: $419 $80 off MSRP – 2.6GHz Mac... Read more
Save on 12″ MacBooks, Apple refurbished model...
Apple has Certified Refurbished 2017 12″ Retina MacBooks available for $200-$240 off the cost of new models. Apple will include a standard one-year warranty with each MacBook, and shipping is free.... Read more
Early Holiday sale: 12″ iPad Pros for up to $...
B&H Photo has 12″ iPad Pros on sale today for up to $130 off MSRP. Shipping is free, and B&H collects no sales tax outside NY & NJ: – 12″ 64GB WiFi iPad Pro: $749, save $50 – 12″ 256GB... Read more
Holiday sale prices on Apple 13″ MacBook Pros...
B&H Photo has 2017 13″ MacBook Pros in stock today and on sale for $100-$150 off MSRP, each including free shipping plus NY & NJ sales tax only: – 13-inch 2.3GHz/128GB Space Gray MacBook Pro... Read more
Sale: 13″ MacBook Airs starting at $899, $100...
B&H Photo has 2017 13″ MacBook Airs on sale today for $100 off MSRP including free shipping. B&H charges NY & NJ sales tax only: – 13″ 1.8GHz/128GB MacBook Air (MQD32LL/A): $899, $100 off... Read more
Week’s Best Deal on 13″ MacBook Pros: Apple r...
Apple has a full line of Apple Certified Refurbished 2017 13″ MacBook Pros available for $200-$300 off MSRP. A standard Apple one-year warranty is included with each MacBook, and shipping is free.... Read more
Deal: 15″ 2.6GHz MacBook Pro for $1799 w/free...
B&H Photo has clearance 2016 15″ 2.6GHz Touch Bar MacBook Pros in stock today and available for $600 off original MSRP. Shipping is free, and B&H charges NY & NJ sales tax only: – 15″ 2.... Read more

Jobs Board

Product Manager - *Apple* Pay on the *Appl...
Job Summary Apple is looking for a talented product manager to drive the expansion of Apple Pay on the Apple Online Store. This position includes a unique Read more
*Apple* Pro/Consumer Apps Support Engineer -...
…exemplify AppleCare's expert technical support paired with exceptional customer service for Apple 's software apps. This person is a problem solver, who understands Read more
Partner Marketing Manager, *Apple* Pay - Ap...
Job Summary The Apple Pay partner marketing team is looking for a Marketing Manager to develop and drive US programs. The right candidate will be passionate about Read more
*Apple* Solution Consultant - Apple (United...
# Apple Solution Consultant - Rochester, MN Job Number: 113037950 Rochester, MN, Minnesota, United States Posted: 19-Sep-2017 Weekly Hours: 40.00 **Job Summary** Are Read more
Sr. Experience Producer, Today at *Apple* -...
# Sr. Experience Producer, Today at Apple Job Number: 56495251 Santa Clara Valley, California, United States Posted: 23-Jun-2017 Weekly Hours: 40.00 **Job Summary** Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.