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.)

 
AAPL
$528.49
Apple Inc.
+3.55
MSFT
$40.07
Microsoft Corpora
+0.06
GOOG
$529.11
Google Inc.
-6.99

MacTech Search:
Community Search:

Software Updates via MacUpdate

Lens Blur 1.3.0 - True out-of-focus boke...
Let Lens Blur transform your existing photo into true SLR-quality out-of-focus bokeh effect! Everyone needs a gorgeous personalized background for a social profile, blog, Web/UI design, presentation... Read more
VMware Fusion 6.0.3 - Run Windows apps a...
VMware Fusion allows you to create a Virtual Machine on your Mac and run Windows (including Windows 8.1) and Windows software on your Mac. Run your favorite Windows applications alongside Mac... Read more
Tweetbot 1.5.1 - Popular iOS twitter cli...
Tweetbot is a full-featured OS X Twitter client with a lot of personality. Whether it's the meticulously-crafted interface, sounds and animation, or features like multiple timelines and column views... Read more
Mac DVDRipper Pro 4.1.7 - Copy, backup,...
Mac DVDRipper Pro is the DVD backup solution that lets you protect your DVDs from scratches, save your batteries by reading your movies from your hard disk, manage your collection with just a few... Read more
PDFpenPro 6.2 - Advanced PDF toolkit for...
PDFpenPro allows users to edit PDF's easily. Add text, images and signatures. Fill out PDF forms. Merge or split PDF documents. Reorder and delete pages. Even correct text and edit graphics! Create... Read more
PDFpen 6.2 - Edit and annotate PDFs with...
PDFpen allows users to easily edit PDF's. Add text, images and signatures. Fill out PDF forms. Merge or split PDF documents. Reorder and delete pages. Even correct text and edit graphics! Features... Read more
Monolingual 1.5.9 - Remove unwanted OS X...
Monolingual is a program for removing unnecesary language resources from OS X, in order to reclaim several hundred megabytes of disk space. It requires a 64-bit capable Intel-based Mac and at least... Read more
Maya 2015 - Professional 3D modeling and...
Maya is an award-winning software and powerful, integrated 3D modeling, animation, visual effects, and rendering solution. Because Maya is based on an open architecture, all your work can be scripted... Read more
Starcraft II: Wings of Liberty 1.1.1.180...
Download the patch by launching the Starcraft II game and downloading it through the Battle.net connection within the app. Starcraft II: Wings of Liberty is a strategy game played in real-time. You... Read more
Sibelius 7.5.0 - Music notation solution...
Sibelius is the world's best-selling music notation software for Mac. It is as intuitive to use as a pen, yet so powerful that it does most things in less than the blink of an eye. The demo includes... Read more

Latest Forum Discussions

See All

Hearthstone: Heroes of Warcraft Review
Hearthstone: Heroes of Warcraft Review By Rob Thomas on April 21st, 2014 Our Rating: :: PERFECTLY (WAR)CRAFTEDiPad Only App - Designed for the iPad This World of Warcraft CCG spin-off is easy to pick up, almost impossible to put... | Read more »
Hearthstone: Tips and Tricks for Becomin...
Hearthstone: Heroes of Warcraft is a deceptive game because it can be so easy to get into, but doing well winds up being a bit of a challenge. Well, for those just jumping into the game with its iPad release, here are a few general tips on how to... | Read more »
Puzzle Breaker Review
Puzzle Breaker Review By Jordan Minor on April 21st, 2014 Our Rating: :: PUZZLES AND DRAGONSUniversal App - Designed for iPhone and iPad Puzzle Breaker combines simple match-3 gameplay with a surprisingly strong RPG feel.   | Read more »
Createrria Gets an Update that Adds Lead...
Createrria Gets an Update that Adds Leaderboards, Parental Controls, and More Posted by Tre Lawrence on April 21st, 2014 [ permalink ] | Read more »
The Amazing Spider-Man 2 Review
The Amazing Spider-Man 2 Review By Lee Hamlet on April 21st, 2014 Our Rating: :: SPIDER-SENSE TINGLING. IN A GOOD WAYUniversal App - Designed for iPhone and iPad With great power comes… Ah who cares? I just want to swing!   | Read more »
This Week at 148Apps: April 14-18, 2014
Spring Into Our App Reviews   | Read more »
Have a Special Dead Trigger 2 Easter Bas...
Have a Special Dead Trigger 2 Easter Basket Full of Goodies, Courtesy of Madfinger Games Posted by Rob Rich on April 18th, 2014 [ permalink ] Dead Trigger 2 | Read more »
Almost All of Playdek’s Library is on Sa...
Almost All of Playdek’s Library is on Sale Right Now, and You Should Check it Out Posted by Rob Rich on April 18th, 2014 [ permalink ] Playdek has released quite a few great iOS ports of board and card games over the years, and now most of them... | Read more »
Zynga Launches Brand New Farmville Exper...
Zynga Launches Brand New Farmville Experience with Farmville 2: Country Escape Posted by Tre Lawrence on April 18th, 2014 [ permalink ] | Read more »
David. Review
David. Review By Cata Modorcea on April 18th, 2014 Our Rating: :: MINIMALISTIC IN A DIFFERENT WAYUniversal App - Designed for iPhone and iPad David is a minimalistic game wrapped inside of a soothing atmosphere in which the hero... | Read more »

Price Scanner via MacPrices.net

Updated Price Trackers
We’ve updated our Mac Price Trackers with the latest information on prices, bundles, and availability on systems from Apple’s authorized internet/catalog resellers: - 15″ MacBook Pros - 13″ MacBook... Read more
Apple refurbished MacBook Airs available for...
The Apple Store has Apple Certified Refurbished 2013 MacBook Airs available for up to $200 off the cost of new models. An Apple one-year warranty is included with each MacBook, and shipping is free... Read more
Android Leads in Operating System Share Andro...
Consumer Intelligence Research Partners, LLC (CIRP) has released its latest results of its research on mobile phone operating systems for the calendar quarter that ended March 31, 2014. This analysis... Read more
Pelican Products, Inc. Introduces New Lineup...
Pelican Products, Inc., the global leader in the design and manufacture of high-performance protective cases, today announced the launch of a new line of rugged phone cases for both the Apple iPhone... Read more
SaveDrives – Car Dashboard Video Camera &...
Drivers who want to help reduce potential damage to their health and finances in the event of an accident can download the innovative new no-cost app SaveDrives – Car Dashboard Video Camera &... Read more
Deal Alert! 13-inch MacBook Pro on sale for $...
Best Buy has the 13″ 2.5GHz MacBook Pro on sale for $999.99 on their online store. Choose free shipping or free instant local store pickup (if available). Their price is $200 off MSRP. Price is valid... Read more
Free HopTo 2.2 Helps Enhance Your Productivit...
The HopTo app helps you do more on your iPad by providing more and easier adaccess to files and documents. Version 2.2 adds Egnyte and HopTo’s Mac OSX File Connector. If you already have the hopTo... Read more
National Distracted Driving Awareness Month:...
As the country recognizes National Distracted Driving Awareness Month, Sprint is reminding wireless consumers to focus on driving while behind the wheel, to not text or email while driving, and to... Read more
13-inch 2.4GHz Retina MacBook Pro available f...
Abt has the 13″ 2.4GHz 128GB Retina MacBook Pro available for $1229 including free shipping. Their price is $70 off MSRP. Read more
iMacs on sale for up to $160 off MSRP this we...
Best Buy has iMacs on sale for up to $160 off MSRP for a limited time. Choose free home shipping or free instant local store pickup (if available). Prices are valid for online orders only, in-store... Read more

Jobs Board

*Apple* Solutions Consultant (ASC) - Apple (...
**Job Summary** The ASC is an Apple employee who serves as an Apple brand ambassador and influencer in a Reseller's store. The ASC's role is to grow Apple Read more
Position Opening at *Apple* - Apple (United...
…customers purchase our products, you're the one who helps them get more out of their new Apple technology. Your day in the Apple Store is filled with a range of Read more
*Apple* Solutions Consultant (ASC) - Apple (...
**Job Summary** The ASC is an Apple employee who serves as an Apple brand ambassador and influencer in a Reseller's store. The ASC's role is to grow Apple Read more
*Apple* Inc. Research Data Specialist - Appl...
…of Worldwide Market Research & Intelligence. The team is responsible for conducting Apple branded consumer market research. It is also responsible for analyzing data Read more
*Apple* Automotive Parts Department position...
Apple Automotive is one of the fastest growing dealer…and it shows. Consider making the switch to the Apple Automotive Group today! At Apple Automotive, we Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.