TweetFollow Us on Twitter

Hertzfeld
Volume Number:4
Issue Number:6
Column Tag:Programmer's Spotlight

Andy Hertzfeld on QuickerDraw

By Chester Peterson Jr., Reporter-At-Large, Lindsborg, Kansas

The Story of QuickerDraw

QuickDraw, the imaging program used on the Mac, doesn’t always live up to its name when used on the Mac II.

Incredibly fast and wonderfully crisp at one bit per pixel, it bogs down to something that could be more aptly described as SlowDraw at eight bits per pixel. The normal subtle responsiveness of the Mac II suffers.

“Actually, in the eight bit per pixel mode it almost feels like you’re using your Mac II under water,” is how Andy Hertzfeld describes the action--or lack thereof.

Hertzfeld is, of course famous in Mac circles as the man responsible for much of the Mac’s Operating System and design of the Toolbox.

So, in late December he decided to satisfy his curiosity about the QuickDraw graphics routines and how they were coded. This is really easy to do, he says.

Just get the Mac II to do the graphics operation in which you’re interested, and then randomly hit the interrupt button. This will interrupt it statistically in the place it’s executing the most--the inner loop.

What Hertzfeld discovered was that the inner loops weren’t optimally coded. His initial strategy was to move the entire QuickDraw into RAM. He wrote an INIT that moved 60k of the ROM out into RAM where he could patch it.

And, although there were some problems with that, Hertzfeld got it working. But, as he progressed, disassembling to the bottom of the system, he saw this wasn’t really necessary.

The reason: Apple had the foresight to have this low-level jump table that all the inner loops are bottle-necked through. All he had to do was replace addresses in the little memory jump table to take over the inner loops in a clean way.

“So, once I saw that, I thought, ‘Hey, this could be a project worth looking into’,” Hertzfeld recalls.

“And, the more I got into it, the more I was able to find ways to increase the speed of QuickDraw. I ended up improving the speed of some important operations by a factor of three or so, ending up with QuickerDraw.”, or as Apple has called it in release 6.0 of the operating system, QuickerGraf.

Something that confuses people and which he thinks is important is that the performance increases are anything but flat. Instead it’s a spiky curve, with some things speeding up a whole lot and others not at all.

The explanation is that the speed-ups are both case dependent and also data dependent. Depending on exactly what you’re doing, you’ll get different responses.

“My point is that the speed-ups aren’t uniform,” Hertzfeld points out. “Apple has some of the code, such as when you say either EraseRect or PaintRect with black, that are already fairly well optimized. I wasn’t able to improve them only because they’re already about as good as they can be.

“But, if you take PaintRect with a color that isn’t black or white, then it goes to a different loop that wasn’t well done. Here’s where I was able to improve speed by that factor of three.

Hertzfeld believes that the most important item in the graphical programmer’s bag of tricks is special casing. In other words, certain instances of a particular problem are easier to handle than are other instances.

So, he thinks that when speed isn’t important that a programmer should try to fold his cases to write as little code as possible to handle the entire situation.

But, when speed is essential, as it is in the QuickDraw routines, the opposite approach must be used, he says. This involves picking off all the different cases and seeing if you can handle each case a little faster.

A compromise Apple made on its standard graphics card was that it has to support one bit, two bits, four bits, and eight bits per pixel.

A lot of the QuickDraw routines were coded in such a way that they were common for four different screen formats, according to Hertzfeld.

“I was able to special case the eight bit per pixel case , because that’s the only one that’s really important from a performance point of view,” he says.

“While Apple used rather slow bit-field instructions, I used special cache code to take advantage of the faster addressing modes in the 68020 to do things faster.”

“I also saved some registers doing that, registers that the Apple code uses just for maintaining which bits per pixel are to be used. Freeing up these for other things allowed me to go faster.”

Hertzfeld also took advantage of the “principal of locality”. He defines this as meaning whatever you’re doing, it’s pretty likely you just did the same thing a short time ago.

He exploited this in producing QuickerDraw through the use of caches. In the computationally intensive parts of QuickDraw like the arithmetic transfer modes, he put in caches that say, “Hey, this is just the same as what I saw before--I don’t have to do all the work again, because I’ve already figured out the answer.”

Hertzfeld used this technique in the instance of copy bits to two different pix maps that have different color look-up tables, a common thing on the Mac II with digitized images.

Each digitized image would have its own color look-up table that wouldn’t be identical to the one on the screen.

When you do a copy bits, it has to do a mapping operation, taking each pixel and looking it up in a table to find the correct pixel in destination bit map.

Hertzfeld changed this so that long word maps are remembered, short- circuiting the memory references involved in doing the look-up. He used similar techniques in many places to gain significant speed-ups.

“You want to hit memory as little as possible,” he advises. “A lot of the Apple loops were doing essentially one memory reference per pixel.

“My routines always do one memory reference per long word. Why? Because the 68020 is capable of pulling in 32 bits just as quickly as it can pull in eight bits at a time.”

The Apple routines makes it a little easier to code just accessing memory eight bits at a time, while Hertzfeld accesses memory 32 bits at a time, spinning it around in the registers and mailing it faster.

“You just attempt to be as clever as possible when you’re trying to code,” he says. “This is interesting code to write, because it has an unusual sort of design criterium.”

With most code in normal circumstances you’re always balancing the twin trade-offs between speed and space, or as Hertzfeld puts it, trying to serve two masters while producing the nicest code possible.

But, the interesting thing about the QuickerDraw code he wrote is that space isn’t a consideration. He says the system spends so much time in the QuickDraw inner loops that he did everything to make them go faster. He used a different coding style that also made it a little more interesting and fun.

“Like, for example, I did everything possible to avoid a subroutine call in the inner loops,” Hertzfeld explains. “You copy 50 in-line instructions, because it’s worth it in the context of the inner loop.”

Hertzfeld also devised another creative and interesting technique to speed up QuickDraw, something he calls region counting.

“As I was speeding up QuickDraw, I was just a little bit disappointed that I wasn’t getting as much speed-up as I would have liked when I was clipping to regions,” he says.

“What I then realized is that the region mask doesn’t change much from scan line to scan line.”

“The other thing to notice is an eight bit per pixel region mask is eight times as long as it would be in one bit per pixel, or eight times as likely to be homogeneous,” Hertzfeld observes.

If you pick up a long word of the region mask it’s extremely likely that it will be all ones or all zeros. Hertzfeld started special casing the region mask.

He found that normally when masking you have to do something like a seven-instruction sequence that involves three memory references to plot a long word with a mask. But, if it turns out the mask is all zeros you don’t have to do anything, because it’s all going to be masked out.

You don’t even have to hit memory at all, just skip over it. If the mask is all ones, you can just use one store instead of having to read it back and do the coding in order to accomplish the masking.

So, he began special casing that way. And, even though the tests cost him a little, he still won enough to make it worthwhile, because the region mask does tend to be homogeneous. The result: A 40 percent speed increase from that special casing of the region mask.

Then as Hertzfeld was looking at the region mask as it went by, he began counting up runs in it so it could remember how many successive long words in a row were all zeros or how many successive long words in a row were all ones.

“If the region mask doesn’t change from scan line to scan line, which it doesn’t more than 90 percent of the time, I don’t have to fetch it. As a matter of fact, if it’s all masked out at the beginning I can just skip over it,” he observes.

Where the Apple routines were pulling a long word from memory, then sticking the same long word back, Hertzfeld just skipped over all that.

He’s proud of this original technique of region counting for obtaining a tremendous speed increase when things are heavily clipped.

Contrary to a misconception about its size, the QuickerDraw memory resident code is only approximately 10k. And, half of that is devoted to the arithmetic transfer modes that aren’t used too often.

The QuickerDraw file is 27k, but that includes logo resources. The nice colored picture that it comes up with is 12k alone.

Incidentally, the arithmetic transfer modes were introduced with the Mac II and are only relevant to color. Most applications don’t use them yet.

Hertzfeld accomplished his QuickerDraw core work in a two-week period between this last December 22 and January 7. It then became apparent that Apple was interested in his acceleration of QuickDraw.

Hertzfeld realized that if he was truly producing a speed-up, then he’d also have to address the arithmetic transfer modes. A second two-week burst of work got these speed-ups implemented, too.

The bottom line: QuickerDraw involves no change in the architecture of QuickDraw. Instead, view it as implementing a high performance tune-up of Apple’s standard.

Hertzfeld signed a non-exclusive contract with Apple for QuickerDraw in February, accepting less money so he could upload it to CompuServe and distribute it on his own.

Apple will incorporate QuickerDraw in its next release file 6.0, due out at the end of May.

“Although there are a few cases that I didn’t handle, I do think I’m pretty close to the optimal plotting speed of QuickDraw,” Hertzfeld comments. “I basically just re-implemented the inner loops so they were more efficient.”

There will be no need to further refine QuickerDraw for the 68030. This is because it has an instruction set identical to the 68020’s.

“The things that will make Apple change QuickDraw next are the architectural issues such as scaleable fonts and resolution independent display routines--basically catching up with Display Postscript,” Hertzfeld thinks.

He’d like to see Apple offer both an enhanced QuickDraw and Postscript so applications programmers could select their choice for both screens and printers.

“The Macintosh would be better off if it could have both. And, I also think it would be a little less risky for Apple than to continue trying to develop on their own all the things that Postscript does so well”, Hertzfeld says.

“In the meantime, my QuickerDraw ‘tune-up’ will make graphics production easier and faster on the Mac II.”

Hertzfeld on Creativity

Is computer programming creative, creative in the sense as producing a masterpiece painting or writing a best-seller?

“Absolutely!” Hertzfeld states.

“There are two different types of programming creativity, though,” he advises, “and both are equally important in a good programmer.”

The first sort of creativity is involved in initially picking the right area and then the right problem on which to work. This involves thinking about what the users really need that will help them the most.

Then there’s the actual writing of code and choosing instructions which can be as individualistic as any painting or writing style, he says.

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

DiskCatalogMaker 7.1.3 - Catalog your di...
DiskCatalogMaker is a simple disk management tool which catalogs disks. Simple, light-weight, and fast Finder-like intuitive look and feel Super-fast search algorithm Can compress catalog data for... Read more
Together 3.8.7 - Store and organize all...
Together helps you organize your Mac, giving you the ability to store, edit and preview your files in a single clean, uncluttered interface. Together Features Smart storage. With simple drag-and-... Read more
Little Snitch 4.0.1 - Alerts you about o...
Little Snitch gives you control over your private outgoing data. Track background activity As soon as your computer connects to the Internet, applications often have permission to send any... Read more
Sparkle Pro 2.2.1 - $79.99
Sparkle Pro will change your mind if you thought building websites wasn't for you. Sparkle is the intuitive site builder that lets you create sites for your online portfolio, team or band pages, or... Read more
iWatermark Pro 2.0.0fc4 - Easily add wat...
iWatermark Pro is the essential watermarking app for professional, business, and personal use. Easily secure and protect your photos with text, a graphic, a signature, or a QR watermark. Once added... Read more
Amadeus Pro 2.4 - Multitrack sound recor...
Amadeus Pro lets you use your Mac for any audio-related task, such as live audio recording, digitizing tapes and records, converting between a variety of sound formats, etc. Thanks to its outstanding... Read more
iFFmpeg 6.4.2 - Convert multimedia files...
iFFmpeg is a comprehensive media tool to convert movie, audio and media files between formats. The FFmpeg command line instructions can be very hard to master/understand, so iFFmpeg does all the hard... Read more
EtreCheck 3.4.2 - 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
Carbon Copy Cloner 4.1.17 - Easy-to-use...
Carbon Copy Cloner backups are better than ordinary backups. Suppose the unthinkable happens while you're under deadline to finish a project: your Mac is unresponsive and all you hear is an ominous,... Read more
VueScan 9.5.81 - Scanner software with a...
VueScan is a scanning program that works with most high-quality flatbed and film scanners to produce scans that have excellent color fidelity and color balance. VueScan is easy to use, and has... Read more

Latest Forum Discussions

See All

Eden: Renaissance (Games)
Eden: Renaissance 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: Eden: Renaissance is a thrilling turn-based puzzle adventure set in a luxurious world, offering a deep and moving... | Read more »
Glyph Quest Chronicles guide - how to ma...
Glyph Quest returns with a new free-to-play game, Glyph Quest Chronicles. Chronicles offers up more of the light-hearted, good humored fantasy fun that previous games featured, but with a few more refined tricks up its sleeve. It's a clever mix of... | Read more »
Catch yourself a Lugia and Articuno in P...
Pokémon Go Fest may have been a bit of a disaster, with Niantic offering fans full refunds and $100 worth of in-game curency to apologize for the failed event, but that hasn't ruined trainers' chances of catching new legendary Pokémon. Lugia nad... | Read more »
The best deals on the App Store this wee...
There are quite a few truly superb games on sale on the App Store this week. If you haven't played some of these, many of which are true classics, now's the time to jump on the bandwagon. Here are the deals you need to know about. [Read more] | Read more »
Realpolitiks Mobile (Games)
Realpolitiks Mobile 1.0 Device: iOS Universal Category: Games Price: $5.99, Version: 1.0 (iTunes) Description: PLEASE NOTE: The game might not work properly on discontinued 1GB of RAM devices (iPhone 5s, iPhone 6, iPhone 6 Plus, iPad... | Read more »
Layton’s Mystery Journey (Games)
Layton’s Mystery Journey 1.0.0 Device: iOS Universal Category: Games Price: $15.99, Version: 1.0.0 (iTunes) Description: THE MUCH-LOVED LAYTON SERIES IS BACK WITH A 10TH ANNIVERSARY INSTALLMENT! Developed by LEVEL-5, LAYTON’S... | Read more »
Full Throttle Remastered (Games)
Full Throttle Remastered 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: Originally released by LucasArts in 1995, Full Throttle is a classic graphic adventure game from industry legend Tim... | Read more »
Stunning shooter Morphite gets a new tra...
Morphite is officially landing on iOS in September. The game looks like the space shooter we've been needing on mobile, and we're going to see if it fits the bill quite shortly. The game's a collaborative effort between Blowfish Studios, We're Five... | Read more »
Layton's Mystery Journey arrives to...
As you might recall, Layton's Mystery Journey is headed to iOS and Android -- tomorrow! To celebrate the impending launch, Level-5's released a new trailer, complete with an adorable hamster. [Read more] | Read more »
Sidewords (Games)
Sidewords 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: Grab a cup of coffee and relax with Sidewords. Sidewords is part logic puzzle, part word game, all original. No timers. No... | Read more »

Price Scanner via MacPrices.net

PHOOZY World’s First Thermal Capsules to Summ...
Summer days spent soaking up the sun can be tough on smartphones, causing higher battery consumption and overheating. To solve this problem, eXclaim IP, LLC has introduced the PHOOZY Thermal Capsule... Read more
2018 Honda Ridgeline with Android Auto and Ap...
The 2018 Honda Ridgeline is arriving in dealerships nationwide with a Manufacturer’s Suggested Retail Price (MSRP1) starting at $29,630. The 2017 Honda Ridgeline was named North American Truck of the... Read more
comScore Ranks Top 15 U.S. Smartphone Apps fo...
comScore, Inc. recently released data from comScore Mobile Metrix, reporting the top smartphone apps in the U.S. by audience reach for June 2017. * “Apple Music,” as it appears in comScore’s monthly... Read more
13-inch 3.1GHz MacBook Pros on sale for $100...
B&H Photo has the new 2017 13″ 3.1GHz Space Gray MacBook Pros in stock today and on sale for $100 off MSRP including free shipping. B&H charges sales tax in NY and NJ only: – 13″ 3.1GHz/256GB... Read more
Apple refurbished Mac minis available startin...
Apple has Certified Refurbished Mac minis available 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
Apple’s 2017 Back to School Promotion: Free B...
Purchase a new Mac using Apple’s Education discount, and take up to $300 off MSRP. All teachers, students, and staff of any educational institution qualify for the discount. Shipping is free. As part... Read more
Clearance 2016 13-inch MacBook Pros available...
B&H Photo has clearance 2016 13″ MacBook Pros in stock today for up to $220 off original MSRP. Shipping is free, and B&H charges NY & NJ sales tax only: – 13″ 2.9GHz/512GB Touch Bar... Read more
Apple Move Away from White Label Event Apps C...
DoubleDutch, Inc., a global provider of Live Engagement Marketing (LEM) solutions, has made a statement in the light of a game-changing announcement from Apple at this year’s WWDC conference.... Read more
70 Year Old Artist Creates Art Tools for the...
New Hampshire-based developer Pirate’s Moon has announced MyArtTools 1.1.3, the update to their precision drawing app, designed by artist Richard Hoeper exclusively for use with the 12.9-inch iPad... Read more
Sale! New 2017 13-inch 2.3GHz MacBook Pros fo...
Amazon has new 2017 13″ 2.3GHz/128GB MacBook Pros on sale today for $150 off MSRP including free shipping. Their prices are the lowest available for these models from any reseller: – 13″ 2.3GHz/128GB... Read more

Jobs Board

*Apple* Solutions Consultant (ASC) - Poole -...
Job Summary The people here at Apple don't just create products - they create the kind of wonder that's revolutionised entire industries. It's the diversity of those Read more
SW Engineer *Apple* TV - Apple Inc. (United...
Changing the world is all in a day's work at Apple . If you love innovation, here's your chance to make a career of it. You'll work hard. But the job comes with more Read more
Frameworks Engineering Manager, *Apple* Wat...
Frameworks Engineering Manager, Apple Watch Job Number: 41632321 Santa Clara Valley, California, United States Posted: Jun. 15, 2017 Weekly Hours: 40.00 Job Summary Read more
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* Retail - Multiple Positions - Apple...
SalesSpecialist - Retail Customer Service and SalesTransform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.