TweetFollow Us on Twitter

Aug 00 Online Volume Number: 16 (2000)
Issue Number: 8
Column Tag: MacTech Online

Quartz and PDF

by Jeff Clites <online@mactech.com>

As you've probably heard, Apple's new graphics system, Quartz, is based on PDF. You've seen screen shots of Quartz, and undoubtedly you've encountered PDF documents before, but that's probably where your knowledge of PDF ends. While you really don't need to know anything about PDF in order to develop applications for Mac OS X, it always helps to know a little bit more about the technologies you are working with, so that you can fully leverage them in developing your products. This month we are going to take a closer look at Adobe's PDF and its role in Apple's new imaging system.

So what is PDF exactly? The acronym stands for "Portable Document Format", as you probably know, and it is fundamentally a file format. In fact, Adobe's description, stated at the beginning of their PDF Reference Manual is, "PDF is a file format used to represent a document in a manner independent of the application software, hardware, and operating system used to create it. A PDF file contains a PDF document and other supporting data." This is in stark contrast to PostScript, which is a full-fledged programming language. So at first blush it may seem a bit strange to base a graphics and windowing system on a file format-Apple refers to PDF as a superset of PostScript, but now this seems somewhat like calling Photoshop a superset of C++. So what's the deal? Things begin to make a little more sense when you learn that PDF (and specifically, a PDF file) has four conceptual parts: a set of basic data types, a file structure, a document structure, and a page description. It is this last part, the page description, which is the core of PDF-as-a-graphics-model.

The Adobe Imaging Model

PostScript and PDF are based on the same conceptual imaging model, sometimes called the Adobe imaging model. At the most basic level, this model is no different from that of QuickDraw or most other 2D graphics systems: you create an image using operators which move a virtual pen to place marks on a canvas. In PostScript, you have primitive marking operators and in addition you have programming constructs such as loops and variables. In PDF, you retain these basic marking operators (and add others), but without the additional programmatic infrastructure, so a PDF document ends up being a description rather than a program. As a simple example, a page with 30 circles on it might be created in PostScript by placing the circle-drawing instructions in a loop which iterates 30 times; in a PDF file, this would be represented by 30 separate circle descriptions. As a consequence, a PDF document is potentially larger than a PostScript document, but it doesn't require the overhead of an interpreter to draw a page, it can render faster because the primitive marking operators are implemented directly in machine code, and it is easier to manipulate because strings and other components can be reliably located within a document (in PostScript you really have to "execute" the entire page first). You can think of this aspect of PDF as a RISC version of PostScript.

So, basing Quartz on the Adobe imaging model really means basing its primitive marking operators on those of PDF (and consequently of PostScript). These operators live in the part of Quartz called Core Graphics Rendering. (I'll call this "CG" for short, as Apple seems to have not officially named their new graphics model. I'll avoid just calling it "Quartz", as this includes Core Graphics Services, which is essentially the window server.) As I mentioned above, there isn't a huge conceptual leap from QuickDraw, but that doesn't mean that there aren't huge advantages. For one, distances in CG are given as floating-point numbers rather then integers, and can be in real-world units such as inches and centimeters. This difference is profound, as it largely divorces the drawing process from explicit concerns of screen or printer page size or resolution, and reduces such things to primarily a scaling issue. It's also fundamentally vector-based, so you're not tempted to draw a single "pixel", although even in QuickDraw one tends to do this by drawing a 1 x 1 square. Also importantly, CG has a sophisticated set of text layout and graphics transformation operators, so finally it will be easy for a Macintosh programmer to rotate text and images on the screen. And on top of PDF's core, Apple has added features such as composition and translucency. It wouldn't be surprising if these were to migrate back into a future version of the PDF specification. (Also note that CG is based on PDF 1.2, rather than the current version 1.3, but Apple plans keep pace with the Adobe's specification as it evolves.)

Core Graphics Rendering at the Center

Core Graphics Rendering serves as the hub of drawing activity, accepting instructions using its native C-based API (which you'll likely access through a higher-level framework), QuickDraw commands, PDF files, or possibly other input sources. From here it can render them to the screen, create raster data for a printer, or record them in a format such as PDF or PostScript. (It's fairly trivial to record a sequence of CG drawing operations to a PDF document, much as a PICT could store a recording of QuickDraw commands. It's easy to forget that PICT is actually a vector format, isn't it?) Note that this doesn't mean that all graphics, before displaying to the screen, exist as actual PDF documents.

There are several key advantages to this arrangement. First, it brings the conceptual simplicity that Display PostScript brought to NeXT's operating systems, namely a single graphics model for both screen and printer. This makes things such as print preview and print-to-file trivial, since PDF is the default spool-file format. This also means that you can get perfect output from cheaper, non-PostScript laser printers, and it opens the door for a new generation of "dumb" printers with minimal computational power, because the operating system fundamentally understands how to render documents all the way to raster data at printer resolutions. (This is a tactic used by the first generation of laser printers produced by NeXT, which were cheaper and operated at a higher resolution than other printers available at the time, and which I'm excited to see finally make it to the Macintosh. It always seemed like a waste to pay for a slow processor which sits mostly idle in a printer when there is a much more powerful processor available in your computer.) Core Graphics has many technological improvements over Display PostScript, but it also has the very clever advantage of freeing Apple from Adobe's licensing fees and restrictions while maintaining a very similar API which allows long-time OpenStep developers to leverage their past experience.

Reading Assignment

In the coming months I hope to cover additional aspects of Mac OS X's new graphics environment. Until then, you have some reading to do. First and foremost, you should read Apple's Inside Mac OS X: System Overview. In fact, you should read the whole thing, from cover to cover, and then read it again, because it's all important information that you'll need to know as we move forward with Mac OS X. There are also several articles on the Ars Technica web site which augment this same material, including an article specifically on Quartz and Aqua. Second, take a look at Adobe's PDF specification - it's large but fairly readable. You won't have to know this information directly in order to use Core Graphics, but it helps to know a little bit about PDFs in greater depth, since you'll be working with a lot of them. This reference also spells out the connection between PDF and PostScript more fully. If you're interested, you might also do a little light reading on PostScript, mostly for perspective rather than for the details. Adobe's PostScript Language Reference has a great deal of explanatory material, and you can also download the electronic version of Glenn Reid's Thinking in PostScript book, which is much shorter. (Somewhat ironically, even the PostScript references come in PDF form.)

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Airmail 3.3.2 - Powerful, minimal email...
Airmail is an mail client with fast performance and intuitive interaction. Support for iCloud, MS Exchange, Gmail, Google Apps, IMAP, POP3, Yahoo!, AOL, Outlook.com, Live.com. Airmail was designed... Read more
Numi 3.15.1 - Menu-bar calculator suppor...
Numi is a calculator that magically combines calculations with text, and allows you to freely share your computations. Numi combines text editor and calculator Support plain English. For example, '5... Read more
TextSoap 8.4.1 - Automate tedious text d...
TextSoap can automatically remove unwanted characters, fix up messed up carriage returns, and do pretty much anything else that we can think of to text. Save time and effort. Be more productive. Stop... Read more
TextSoap 8.4.1 - Automate tedious text d...
TextSoap can automatically remove unwanted characters, fix up messed up carriage returns, and do pretty much anything else that we can think of to text. Save time and effort. Be more productive. Stop... Read more
Backblaze 4.3.0.44 - Online backup servi...
Backblaze is an online backup service designed from the ground-up for the Mac. With unlimited storage available for $5 per month, as well as a free 15-day trial, peace of mind is within reach with... Read more
Numi 3.15 - Menu-bar calculator supports...
Numi is a calculator that magically combines calculations with text, and allows you to freely share your computations. Numi combines text editor and calculator Support plain English. For example, '5... Read more
EtreCheck 3.3.3 - For troubleshooting yo...
EtreCheck is an app that displays the important details of your system configuration and allow you to copy that information to the Clipboard. It is meant to be used with Apple Support Communities to... Read more
BusyContacts 1.1.8 - Fast, efficient con...
BusyContacts is a contact manager for OS X that makes creating, finding, and managing contacts faster and more efficient. It brings to contact management the same power, flexibility, and sharing... Read more
TunnelBear 3.0.14 - Subscription-based p...
TunnelBear is a subscription-based virtual private network (VPN) service and companion app, enabling you to browse the internet privately and securely. Features Browse privately - Secure your data... Read more
Apple Final Cut Pro X 10.3.4 - Professio...
Apple Final Cut Pro X is a professional video editing solution.Completely redesigned from the ground up, Final Cut Pro adds extraordinary speed, quality, and flexibility to every part of the post-... Read more

Latest Forum Discussions

See All

The best new games we played this week
We were quite busy this week. A bunch of big mobile games launched over the past few days, alongside a few teeny surprises. There're lots of quality games to load your phone with. We've gone and picked out five of our favorites for the week. [... | Read more »
Magikarp Jump beginner's guide
Magikarp Jump is a mystifying little game. Part Tamagotchi, part idle clicker, there's not a whole lot of video game there, per se, but for some reason we can't help coming back to it again and again. Your goal is to train up a little Magikarp to... | Read more »
Goat Simulator PAYDAY (Games)
Goat Simulator PAYDAY 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: ** IMPORTANT - SUPPORTED DEVICES **iPhone 4S, iPad 2, iPod Touch 5 or better Goat Simulator: Payday is the most... | Read more »
GRID Autosport delayed until autumn
Sorry mobile racing fans -- GRID Autosport has been delayed a few months. The game is now expected to launch this fall on iOS. Feral Interactive announced that they wanted more time to work on the game's UI and overall performance before launching... | Read more »
Zombie Gunship Survival Beginner's...
The much anticipated Zombie Gunship Survival is here. In this latest entry in the Zombie Gunship franchise, you're tasked with supporting ground troops and protecting your base from the zombie horde. There's a lot of rich base building fun, and... | Read more »
Mordheim: Warband Skirmish (Games)
Mordheim: Warband Skirmish 1.2.2 Device: iOS Universal Category: Games Price: $3.99, Version: 1.2.2 (iTunes) Description: Explore the ruins of the City of Mordheim, clash with other scavenging warbands and collect Wyrdstone -... | Read more »
Mordheim: Warband Skirmish brings tablet...
Legendary Games has just launched Mordheim: Warband Skirmish, a new turn-based action game for iOS and Android. | Read more »
Magikarp Jump splashes onto Android worl...
If you're tired ofPokémon GObut still want something to satisfy your mobilePokémon fix,Magikarp Jumpmay just do the trick. It's out now on Android devices the world over. While it looks like a simple arcade jumper, there's quite a bit more to it... | Read more »
Purrfectly charming open-world RPG Cat Q...
Cat Quest, an expansive open-world RPG from former Koei-Tecmo developers, got a new gameplay trailer today. The video showcases the combat and exploration features of this feline-themed RPG. Cat puns abound as you travel across a large map in a... | Read more »
Jaipur: A Card Game of Duels (Games)
Jaipur: A Card Game of Duels 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: ** WARNING: iPad 2, iPad Mini 1 & iPhone 4S are NOT compatible. ** *** Special Launch Price for a limited... | Read more »

Price Scanner via MacPrices.net

Memorial Day savings: 13-inch Touch Bar MacBo...
B&H Photo has the 2016 Apple 13″ Touch Bar MacBook Pros in stock today and on sale for up to $150 off MSRP. Shipping is free, and B&H charges NY & NJ sales tax only: - 13″ 2.9GHz/512GB... Read more
Apple refurbished 13-inch MacBook Airs availa...
Apple has Certified Refurbished 2016 13″ MacBook Airs available starting at $849. An Apple one-year warranty is included with each MacBook, and shipping is free: - 13″ 1.6GHz/8GB/128GB MacBook Air: $... Read more
Apple restocks refurbished 11-inch MacBook Ai...
Apple has Certified Refurbished 11″ MacBook Airs (the latest models recently discontinued by Apple), available for up to $170 off original MSRP. An Apple one-year warranty is included with each... Read more
12-inch 1.2GHz Retina MacBooks on sale for up...
B&H has 12″ 1.2GHz Retina MacBooks on sale for up to $150 off MSRP. Shipping is free, and B&H charges NY & NJ sales tax only: - 12″ 1.2GHz Space Gray Retina MacBook: $1449.99 $150 off... Read more
15-inch 2.7GHz Silver Touch Bar MacBook Pro o...
MacMall has the 15-inch 2.7GHz Silver Touch Bar MacBook Pro (MLW82LL/A) on sale for $2569 as part of their Memorial Day sale. Shipping is free. Their price is $230 off MSRP. Read more
Free Tread Wisely Mobile App Endorsed By Fath...
Just in time for the summer driving season, Cooper Tire & Rubber Company has announced the launch of a new Tread Wisely mobile app. Designed to promote tire and vehicle safety among teens and... Read more
Commercial Notebooks And Detachable Tablets W...
Worldwide shipments of personal computing devices (PCDs), comprised of traditional PCs (a combination of desktop, notebook, and workstations) and tablets (slates and detachables), are forecast to... Read more
Best value this Memorial Day weekend: Touch B...
Apple has Certified Refurbished 2016 15″ and 13″ MacBook Pros available for $230 to $420 off original MSRP. An Apple one-year warranty is included with each model, and shipping is free: - 15″ 2.6GHz... Read more
13-inch MacBook Airs on sale for up to $130 o...
Overstock.com has 13″ MacBook Airs on sale for up to $130 off MSRP including free shipping: - 13″ 1.6GHz/128GB MacBook Air (sku MMGF2LL/A): $869.99 $130 off MSRP - 13″ 1.6GHz/256GB MacBook Air (sku... Read more
2.8GHz Mac mini available for $973 with free...
Adorama has the 2.8GHz Mac mini available for $973, $16 off MSRP, including a free copy of Apple’s 3-Year AppleCare Protection Plan. Shipping is free, and Adorama charges sales tax in NY & NJ... Read more

Jobs Board

*Apple* Retail - Multiple Positions - Apple,...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
*Apple* Media Products - Commerce Engineerin...
Apple Media Products - Commerce Engineering Manager Job Number: 57037480 Santa Clara Valley, California, United States Posted: Apr. 18, 2017 Weekly Hours: 40.00 Job Read more
*Apple* Media Products - Commerce Engineerin...
Apple Media Products - Commerce Engineering Manager Job Number: 57037480 Santa Clara Valley, California, United States Posted: Apr. 18, 2017 Weekly Hours: 40.00 Job Read more
Best Buy *Apple* Computing Master - Best Bu...
**509643BR** **Job Title:** Best Buy Apple Computing Master **Location Number:** 001482- Apple Valley-Store **Job Description:** **What does a Best Buy Apple Read more
*Apple* Media Products - Commerce Engineerin...
Apple Media Products - Commerce Engineering Manager Job Number: 57037480 Santa Clara Valley, California, United States Posted: Apr. 18, 2017 Weekly Hours: 40.00 Job Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.