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

Victorious Knight (Games)
Victorious Knight 1.3 Device: iOS Universal Category: Games Price: $1.99, Version: 1.3 (iTunes) Description: New challenges awaits you! Experience fresh RPG experience with a unique combat mechanic, packed with high quality 3D... | Read more »
Agent Gumball - Roguelike Spy Game (Gam...
Agent Gumball - Roguelike Spy Game 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: Someone’s been spying on Gumball. What the what?! Two can play at that game! GO UNDERCOVERSneak past enemy... | Read more »
Runaway Toad (Games)
Runaway Toad 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: It ain’t easy bein’ green! Tap, hold, and swipe to help Toad hop to safety in this gorgeous new action game from the creators of... | Read more »
PsyCard (Games)
PsyCard 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: From the makers och Card City Nights, Progress To 100 and Ittle Dew PSYCARD is a minesweeper-like game set in a cozy cyberpunk... | Read more »
Sago Mini Robot Party (Education)
Sago Mini Robot Party 1.0 Device: iOS Universal Category: Education Price: $2.99, Version: 1.0 (iTunes) Description: -- Children's Technology Review Editor's Choice -- | Read more »
How to get a high score in every level o...
Sky Charms is an adorable match three puzzler that provides a decent challenge thanks to its creative level design. It regularly presents something new, forcing you to think on your feet. [Read more] | Read more »
Apestorm: Full Bananas (Games)
Apestorm: Full Bananas 1.0 Device: iOS Universal Category: Games Price: $.99, Version: 1.0 (iTunes) Description: ***Launch sale – limited time only!*** Fugitive Apes have taken to the skies in search of revenge after humans have... | Read more »
How to create bigger words in Spellspire
Words have power. At least they do in Spellspire,a game about blasting out magical attacks by making words out of a jumble of letters. And it's a lot of fun. But if you want to be the best, you're going to have to think tactically when you start... | Read more »
Steel Media and DeePoon have partnered f...
Virtual reality is the next big thing, and 148Apps's publisher,Steel Media, wants to know what the hottest upcoming games are. [Read more] | Read more »
Airline Director 2 - Tycoon Game (Games...
Airline Director 2 - Tycoon Game 1.2.1 Device: iOS Universal Category: Games Price: $2.99, Version: 1.2.1 (iTunes) Description: Airline Director 2 is a management game set in the challenging field of commercial aviation. As the... | Read more »

Price Scanner via MacPrices.net

Aleratec Releases Mac Software Upgrade for 1...
California based Aleratec Inc., designer, developer and manufacturer of Portable Device Management (PDM) charge/sync products for mobile devices and professional-grade duplicators for hard disk... Read more
Sale! Amazon offers 27-inch iMac, 13-inch 2.9...
Amazon has the 27″ 3.2GHz 5K iMac and the 13″ 3.9GHz Retina MacBook Pro on sale for $300 off MSRP, each including free shipping, for a limited time: - 27″ 3.2GHz/1TB HD 5K iMac (model MK462LL/A): $... Read more
Apple refurbished 13-inch Retina MacBook Pros...
Apple has Certified Refurbished 13″ Retina MacBook Pros available for up to $270 off the cost of new models. An Apple one-year warranty is included with each model, and shipping is free: - 13″ 2.7GHz... Read more
13-inch 2.7GHz/128GB Retina MacBook Pro on sa...
Take $200 off MSRP on the price of a new 13″ 2.7GHz/128GB Retina MacBook Pro (model MF839LL/A) at Amazon. Shipping is free: - 13″ 2.7GHz/128GB Retina MacBook Pro: $1099.99 $200 off MSRP Act now if... Read more
Apple refurbished clearance 15-inch Retina Ma...
Apple has Certified Refurbished 2014 15″ 2.2GHz Retina MacBook Pros available for $1609, $390 off original MSRP. Apple’s one-year warranty is included, and shipping is free. They have refurbished 15... Read more
27-inch 5K iMacs on sale for up to $150 off M...
B&H Photo has 27″ 5K iMacs on sale for up to $150 off MSRP including free shipping plus NY sales tax only: - 27″ 3.3GHz iMac 5K: $2199 $100 off MSRP - 27″ 3.2GHz/1TB Fusion iMac 5K: $1849.99 $150... Read more
What Does The Refreshed 12-Inch MacBook Tell...
A lot of commentators are complaining that Apple’s update of the 12-Inch MacBook last week is a bit of a damp squib. I don’t know what they were expecting, since it would be very unlike Apple to do a... Read more
Free Wittify Keyboard Now Available On The Ap...
A team of Harvard Business School students have announced that the Wittify Keyboard, a new app utility for iOS devices, is now available on the Apple App Store. The Wittify keyboard and application... Read more
Apple Reports First Year-Over-Year Quarterly...
Apple on TUesday announced financial results for its fiscal 2016 second quarter ending March 26, 2016. The Company posted quarterly revenue of $50.6 billion and quarterly net income of $10.5 billion... Read more
13-inch 2.7GHz Retina MacBook Pros on sale fo...
Take $130-$150 off MSRP on the price of a new 13″ 2.7GHz Retina MacBook Pro at Amazon. Shipping is free: - 13″ 2.7GHz/128GB Retina MacBook Pro: $1169 $130 off MSRP - 13″ 2.7GHz/256GB Retina MacBook... Read more

Jobs Board

Simply Mac *Apple* Specialist- Service Repa...
Simply Mac is the largest premier retailer of Apple products in the nation. In order to support our growing customer base, we are currently looking for a driven Read more
*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
Restaurant Manager (Neighborhood Captain) - A...
…in every aspect of daily operation. WHY YOU'LL LIKE IT: You'll be the Big Apple . You'll solve problems. You'll get to show your ability to handle the stress and Read more
*Apple* Solutions Consultant - … (United Sta...
Job Summary As an Apple Solutions Consultant, you'll be the link between our future customers and our products. You'll showcase your entrepreneurial spirit as you Read more
Restaurant Manager (Neighborhood Captain) - A...
…in every aspect of daily operation. WHY YOU'LL LIKE IT: You'll be the Big Apple . You'll solve problems. You'll get to show your ability to handle the stress and Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.