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
$99.76
Apple Inc.
+2.09
MSFT
$44.08
Microsoft Corpora
+0.45
GOOG
$520.84
Google Inc.
+9.67

MacTech Search:
Community Search:

Software Updates via MacUpdate

RestoreMeNot 2.0.3 - Disable window rest...
RestoreMeNot provides a simple way to disable the window restoration for individual applications so that you can fine-tune this behavior to suit your needs. Please note that RestoreMeNot is designed... Read more
Macgo Blu-ray Player 2.10.9.1750 - Blu-r...
Macgo Mac Blu-ray Player can bring you the most unforgettable Blu-ray experience on your Mac. Overview Macgo Mac Blu-ray Player can satisfy just about every need you could possibly have in a Blu-ray... Read more
Apple iOS 8.1 - The latest version of Ap...
The latest version of iOS can be downloaded through iTunes. Apple iOS 8 comes with big updates to apps you use every day, like Messages and Photos. A whole new way to share content with your family.... Read more
TechTool Pro 7.0.5 - Hard drive and syst...
TechTool Pro is now 7, and this is the most advanced version of the acclaimed Macintosh troubleshooting utility created in its 20-year history. Micromat has redeveloped TechTool Pro 7 to be fully 64... Read more
PDFKey Pro 4.0.2 - Edit and print passwo...
PDFKey Pro can unlock PDF documents protected for printing and copying when you've forgotten your password. It can now also protect your PDF files with a password to prevent unauthorized access and/... Read more
Yasu 2.9.1 - System maintenance app; per...
Yasu was originally created with System Administrators who service large groups of workstations in mind, Yasu (Yet Another System Utility) was made to do a specific group of maintenance tasks... Read more
Hazel 3.3 - Create rules for organizing...
Hazel is your personal housekeeper, organizing and cleaning folders based on rules you define. Hazel can also manage your trash and uninstall your applications. Organize your files using a... Read more
Autopano Giga 3.7 - Stitch multiple imag...
Autopano Giga allows you to stitch 2, 20, or 2,000 images. Version 3.0 integrates impressive new features that will definitely make you adopt Autopano Pro or Autopano Giga: Choose between 9... Read more
MenuMeters 1.8 - CPU, memory, disk, and...
MenuMeters is a set of CPU, memory, disk, and network monitoring tools for Mac OS X. Although there are numerous other programs which do the same thing, none had quite the feature set I was looking... Read more
Coda 2.5 - One-window Web development su...
Coda is a powerful Web editor that puts everything in one place. An editor. Terminal. CSS. Files. With Coda 2, we went beyond expectations. With loads of new, much-requested features, a few... Read more

Latest Forum Discussions

See All

This Week at 148Apps: October 13-17, 201...
Expert App Reviewers   So little time and so very many apps. What’s a poor iPhone/iPad lover to do? Fortunately, 148Apps is here to give you the rundown on the latest and greatest releases. And we even have a tremendous back catalog of reviews; just... | Read more »
Angry Birds Transformers Review
Angry Birds Transformers Review By Jennifer Allen on October 20th, 2014 Our Rating: :: TRANSFORMED BIRDSUniversal App - Designed for iPhone and iPad Transformed in a way you wouldn’t expect, Angry Birds Transformers is a quite... | Read more »
GAMEVIL Announces the Upcoming Launch of...
GAMEVIL Announces the Upcoming Launch of Mark of the Dragon Posted by Jessica Fisher on October 20th, 2014 [ permalink ] Mark of the Dragon, by GAMEVIL, put | Read more »
Interview With the Angry Birds Transform...
Angry Birds Transformers recently transformed and rolled out worldwide. This run-and-gun title is a hit with young Transformers fans, but the ample references to classic Transformers fandom has also earned it a place in the hearts of long-time... | Read more »
Find Free Food on Campus with Ypay
Find Free Food on Campus with Ypay Posted by Jessica Fisher on October 20th, 2014 [ permalink ] iPhone App - Designed for the iPhone, compatible with the iPad | Read more »
Strung Along Review
Strung Along Review By Jordan Minor on October 20th, 2014 Our Rating: :: GOT NO STRINGSUniversal App - Designed for iPhone and iPad A cool gimmick and a great art style keep Strung Along from completely falling apart.   | Read more »
P2P file transferring app Send Anywhere...
File sharing services like Dropbox have security issues. Email attachments can be problematic when it comes to sharing large files. USB dongles don’t fit into your phone. Send Anywhere, a peer-to-peer file transferring application, solves all of... | Read more »
Zero Age Review
Zero Age Review By Jordan Minor on October 20th, 2014 Our Rating: :: MORE THAN ZEROiPad Only App - Designed for the iPad With its mind-bending puzzles and spellbinding visuals, Zero Age has it all.   | Read more »
Hay Ewe Review
Hay Ewe Review By Campbell Bird on October 20th, 2014 Our Rating: :: SAVE YOUR SHEEPLEUniversal App - Designed for iPhone and iPad Pave the way for your flock in this line drawing puzzle game from the creators of Worms.   | Read more »
My Very Hungry Caterpillar (Education)
My Very Hungry Caterpillar 1.0.0 Device: iOS Universal Category: Education Price: $3.99, Version: 1.0.0 (iTunes) Description: Care for your very own Very Hungry Caterpillar! My Very Hungry Caterpillar will captivate you as he crawls... | Read more »

Price Scanner via MacPrices.net

Deals on 2011 13-inch MacBook Airs, from $649
Daily Steals has the Mid-2011 13″ 1.7GHz i5 MacBook Air (4GB/128GB) available for $699 with a 90 day warranty. The Mid-2011 13″ 1.7GHz i5 MacBook Air (4GB/128GB SSD) is available for $649 at Other... Read more
2013 15-inch 2.0GHz Retina MacBook Pro availa...
B&H Photo has leftover previous-generation 15″ 2.0GHz Retina MacBook Pros now available for $1599 including free shipping plus NY sales tax only. Their price is $400 off original MSRP. B&H... Read more
Updated iPad Prices
We’ve updated our iPad Air Price Tracker and our iPad mini Price Tracker with the latest information on prices and availability from Apple and other resellers, including the new iPad Air 2 and the... Read more
Apple Pay Available to Millions of Visa Cardh...
Visa Inc. brings secure, convenient payments to iPad Air 2 and iPad mini 3as well as iPhone 6 and 6 Plus. Starting October 20th, eligible Visa cardholders in the U.S. will be able to use Apple Pay,... Read more
Textkraft Pocket – the missing TextEdit for i...
infovole GmbH has announced the release and immediate availability of Textkraft Pocket 1.0, a professional text editor and note taking app for Apple’s iPhone. In March 2014 rumors were all about... Read more
C Spire to offer iPad Air 2 and iPad mini 3,...
C Spire on Friday announced that it will offer iPad Air 2 and iPad mini 3, both with Wi-Fi + Cellular, on its 4G+ LTE network in the coming weeks. C Spire will offer the new iPads with a range of... Read more
Belkin Announces Full Line of Keyboards and C...
Belkin International has unveiled a new lineup of keyboard cases and accessories for Apple’s newest iPads, featuring three QODE keyboards and a collection of thin, lightweight folios for both the... Read more
Verizon offers new iPad Air 2 preorders for $...
Verizon Wireless is accepting preorders for the new iPad Air 2, cellular models, for $100 off MSRP with a 2-year service agreement: - 16GB iPad Air 2 WiFi + Cellular: $529.99 - 64GB iPad Air 2 WiFi... Read more
Price drops on refurbished Mac minis, now ava...
The Apple Store has dropped prices on Apple Certified Refurbished previous-generation Mac minis, with models now available starting at $419. Apple’s one-year warranty is included with each mini, and... Read more
Apple refurbished 2014 MacBook Airs available...
The Apple Store has Apple Certified Refurbished 2014 MacBook Airs available for up to $180 off the cost of new models. An Apple one-year warranty is included with each MacBook, and shipping is free.... Read more

Jobs Board

Project Manager / Business Analyst, WW *Appl...
…a senior project manager / business analyst to work within our Worldwide Apple Fulfillment Operations and the Business Process Re-engineering team. This role will work Read more
*Apple* Retail - Multiple Positions (US) - A...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, 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
Position Opening at *Apple* - Apple (United...
**Job Summary** At the Apple Store, you connect business professionals and entrepreneurs with the tools they need in order to put Apple solutions to work in their Read more
Position Opening at *Apple* - Apple (United...
**Job Summary** The Apple Store is a retail environment like no other - uniquely focused on delivering amazing customer experiences. As an Expert, you introduce people Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.