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

Tor Browser 12.5.5 - Anonymize Web brows...
Using Tor Browser you can protect yourself against tracking, surveillance, and censorship. Tor was originally designed, implemented, and deployed as a third-generation onion-routing project of the U.... Read more
Malwarebytes 4.21.9.5141 - Adware remova...
Malwarebytes (was AdwareMedic) helps you get your Mac experience back. Malwarebytes scans for and removes code that degrades system performance or attacks your system. Making your Mac once again your... Read more
TinkerTool 9.5 - Expanded preference set...
TinkerTool is an application that gives you access to additional preference settings Apple has built into Mac OS X. This allows to activate hidden features in the operating system and in some of the... Read more
Paragon NTFS 15.11.839 - Provides full r...
Paragon NTFS breaks down the barriers between Windows and macOS. Paragon NTFS effectively solves the communication problems between the Mac system and NTFS. Write, edit, copy, move, delete files on... Read more
Apple Safari 17 - Apple's Web brows...
Apple Safari is Apple's web browser that comes bundled with the most recent macOS. Safari is faster and more energy efficient than other browsers, so sites are more responsive and your notebook... Read more
Firefox 118.0 - Fast, safe Web browser.
Firefox offers a fast, safe Web browsing experience. Browse quickly, securely, and effortlessly. With its industry-leading features, Firefox is the choice of Web development professionals and casual... Read more
ClamXAV 3.6.1 - Virus checker based on C...
ClamXAV is a popular virus checker for OS X. Time to take control ClamXAV keeps threats at bay and puts you firmly in charge of your Mac’s security. Scan a specific file or your entire hard drive.... Read more
SuperDuper! 3.8 - Advanced disk cloning/...
SuperDuper! is an advanced, yet easy to use disk copying program. It can, of course, make a straight copy, or "clone" - useful when you want to move all your data from one machine to another, or do a... Read more
Alfred 5.1.3 - Quick launcher for apps a...
Alfred is an award-winning productivity application for OS X. Alfred saves you time when you search for files online or on your Mac. Be more productive with hotkeys, keywords, and file actions at... Read more
Sketch 98.3 - Design app for UX/UI for i...
Sketch is an innovative and fresh look at vector drawing. Its intentionally minimalist design is based upon a drawing space of unlimited size and layers, free of palettes, panels, menus, windows, and... Read more

Latest Forum Discussions

See All

Listener Emails and the iPhone 15! – The...
In this week’s episode of The TouchArcade Show we finally get to a backlog of emails that have been hanging out in our inbox for, oh, about a month or so. We love getting emails as they always lead to interesting discussion about a variety of topics... | Read more »
TouchArcade Game of the Week: ‘Cypher 00...
This doesn’t happen too often, but occasionally there will be an Apple Arcade game that I adore so much I just have to pick it as the Game of the Week. Well, here we are, and Cypher 007 is one of those games. The big key point here is that Cypher... | Read more »
SwitchArcade Round-Up: ‘EA Sports FC 24’...
Hello gentle readers, and welcome to the SwitchArcade Round-Up for September 29th, 2023. In today’s article, we’ve got a ton of news to go over. Just a lot going on today, I suppose. After that, there are quite a few new releases to look at... | Read more »
‘Storyteller’ Mobile Review – Perfect fo...
I first played Daniel Benmergui’s Storyteller (Free) through its Nintendo Switch and Steam releases. Read my original review of it here. Since then, a lot of friends who played the game enjoyed it, but thought it was overpriced given the short... | Read more »
An Interview with the Legendary Yu Suzuk...
One of the cool things about my job is that every once in a while, I get to talk to the people behind the games. It’s always a pleasure. Well, today we have a really special one for you, dear friends. Mr. Yu Suzuki of Ys Net, the force behind such... | Read more »
New ‘Marvel Snap’ Update Has Balance Adj...
As we wait for the information on the new season to drop, we shall have to content ourselves with looking at the latest update to Marvel Snap (Free). It’s just a balance update, but it makes some very big changes that combined with the arrival of... | Read more »
‘Honkai Star Rail’ Version 1.4 Update Re...
At Sony’s recently-aired presentation, HoYoverse announced the Honkai Star Rail (Free) PS5 release date. Most people speculated that the next major update would arrive alongside the PS5 release. | Read more »
‘Omniheroes’ Major Update “Tide’s Cadenc...
What secrets do the depths of the sea hold? Omniheroes is revealing the mysteries of the deep with its latest “Tide’s Cadence" update, where you can look forward to scoring a free Valkyrie and limited skin among other login rewards like the 2nd... | Read more »
Recruit yourself some run-and-gun royalt...
It is always nice to see the return of a series that has lost a bit of its global staying power, and thanks to Lilith Games' latest collaboration, Warpath will be playing host the the run-and-gun legend that is Metal Slug 3. [Read more] | Read more »
‘The Elder Scrolls: Castles’ Is Availabl...
Back when Fallout Shelter (Free) released on mobile, and eventually hit consoles and PC, I didn’t think it would lead to something similar for The Elder Scrolls, but here we are. The Elder Scrolls: Castles is a new simulation game from Bethesda... | Read more »

Price Scanner via MacPrices.net

Clearance M1 Max Mac Studio available today a...
Apple has clearance M1 Max Mac Studios available in their Certified Refurbished store for $270 off original MSRP. Each Mac Studio comes with Apple’s one-year warranty, and shipping is free: – Mac... Read more
Apple continues to offer 24-inch iMacs for up...
Apple has a full range of 24-inch M1 iMacs available today in their Certified Refurbished store. Models are available starting at only $1099 and range up to $260 off original MSRP. Each iMac is in... Read more
Final weekend for Apple’s 2023 Back to School...
This is the final weekend for Apple’s Back to School Promotion 2023. It remains active until Monday, October 2nd. Education customers receive a free $150 Apple Gift Card with the purchase of a new... Read more
Apple drops prices on refurbished 13-inch M2...
Apple has dropped prices on standard-configuration 13″ M2 MacBook Pros, Certified Refurbished, to as low as $1099 and ranging up to $230 off MSRP. These are the cheapest 13″ M2 MacBook Pros for sale... Read more
14-inch M2 Max MacBook Pro on sale for $300 o...
B&H Photo has the Space Gray 14″ 30-Core GPU M2 Max MacBook Pro in stock and on sale today for $2799 including free 1-2 day shipping. Their price is $300 off Apple’s MSRP, and it’s the lowest... Read more
Apple is now selling Certified Refurbished M2...
Apple has added a full line of standard-configuration M2 Max and M2 Ultra Mac Studios available in their Certified Refurbished section starting at only $1699 and ranging up to $600 off MSRP. Each Mac... Read more
New sale: 13-inch M2 MacBook Airs starting at...
B&H Photo has 13″ MacBook Airs with M2 CPUs in stock today and on sale for $200 off Apple’s MSRP with prices available starting at only $899. Free 1-2 day delivery is available to most US... Read more
Apple has all 15-inch M2 MacBook Airs in stoc...
Apple has Certified Refurbished 15″ M2 MacBook Airs in stock today starting at only $1099 and ranging up to $230 off MSRP. These are the cheapest M2-powered 15″ MacBook Airs for sale today at Apple.... Read more
In stock: Clearance M1 Ultra Mac Studios for...
Apple has clearance M1 Ultra Mac Studios available in their Certified Refurbished store for $540 off original MSRP. Each Mac Studio comes with Apple’s one-year warranty, and shipping is free: – Mac... Read more
Back on sale: Apple’s M2 Mac minis for $100 o...
B&H Photo has Apple’s M2-powered Mac minis back in stock and on sale today for $100 off MSRP. Free 1-2 day shipping is available for most US addresses: – Mac mini M2/256GB SSD: $499, save $100 –... Read more

Jobs Board

Licensed Dental Hygienist - *Apple* River -...
Park Dental Apple River in Somerset, WI is seeking a compassionate, professional Dental Hygienist to join our team-oriented practice. COMPETITIVE PAY AND SIGN-ON Read more
Sublease Associate Optometrist- *Apple* Val...
Sublease Associate Optometrist- Apple Valley, CA- Target Optical Date: Sep 30, 2023 Brand: Target Optical Location: Apple Valley, CA, US, 92307 **Requisition Read more
*Apple* / Mac Administrator - JAMF - Amentum...
Amentum is seeking an ** Apple / Mac Administrator - JAMF** to provide support with the Apple Ecosystem to include hardware and software to join our team and Read more
Child Care Teacher - Glenda Drive/ *Apple* V...
Child Care Teacher - Glenda Drive/ Apple ValleyTeacher Share by Email Share on LinkedIn Share on Twitter Read more
Cashier - *Apple* Blossom Mall - JCPenney (...
Cashier - Apple Blossom Mall Location:Winchester, VA, United States (https://jobs.jcp.com/jobs/location/191170/winchester-va-united-states) - Apple Blossom Mall Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.