TweetFollow Us on Twitter

September 94 - DESIGNING APPLICATIONS FOR THE POWER MACINTOSH

DESIGNING APPLICATIONS FOR THE POWER MACINTOSH

GREG ROBBINS AND RON AVITZUR

[IMAGE 020-023_Designing_for_PP1.GIF]

The Power Macintosh offers surprises both for users and for developers. Users notice that it's a fully compatible Macintosh and that native applications run blazingly fast. Developers, upon learning how the Power Macintosh differs from a 680x0-based Macintosh, discover that it's still basically a Macintosh. But the Power Macintosh can offer a much richer experience than was possible with previous computers if developers break free of their old assumptions and harness the power of the machine to make software not just faster, but easier and more enjoyable to use.

The Graphing Calculator desk accessory that ships with the Power Macintosh was designed to take advantage of the machine's power to make some challenging mathematical tasks easily accessible -- in particular, algebraic manipulation and 2-D and 3-D graphing. In this column we'll share some lessons we learned when writing the Graphing Calculator. We'll speak about software design rather than programming details because we frequently discovered that our intuition and the standard approaches to many aspects of the application design were no longer appropriate.

In general, we learned that it's time to break free of the idioms developed for the machines of 1984 and begin designing a new generation of software. We're not in Kansas anymore . The lowest common denominator of hardware -- where developers usually aim in order to maintain consistency across all Macintosh models -- has changed. The target has typically been an 8 MHz 68000 processor or, for color applications, perhaps a machine twice as fast. The lowest common denominator for Apple's RISC-based line of machines is a 60 MHz PowerPC 601 processor. This change represents an enormous jump: on some floating-point operations, for example, the Power Macintosh is as much as 20,000 times faster.

In our tests, calculations using the PowerPC processor's single-precision floating-point multiply-add instruction were 20,000 times faster. This means that if we had started a lengthy floating-point calculation in 1984 at the release of the Macintosh, and that calculation were still being worked on by the computer, it would take a Power Macintosh starting now just four hours to catch up.*

Even for developers targeting 680x0-based machines, a new approach to software design can dramatically improve users' experiences. The goal is to maximize use of whatever processing power is available in the design of the user interface.

Here's a summary of the tips we'd like to pass on; we'll look at each one in more detail below.

  1. Tackle expensive computations when they can improve the interface.
  2. Eliminate dialogs and command lines in favor of direct manipulation.
  3. Drop old assumptions and idioms. Use the processing power to explore new interfaces.
  4. Provide a starting point for exploration.
  5. Avoid programming cleverness. Instead, assume a good compiler and write readable code.
  6. Invest development time in user-centered design.
  7. Learn the new rules for performance.
  8. Design tiered functionality: take advantage of whatever hardware you're running on.
  9. Test on real users.

THE TIPS IN DETAIL

1. Tackle expensive computations when they can improve the interface.

We took a fresh look at how to implement the visual feedback for dragging, scrolling, and zooming. Traditionally, the Macintosh has represented these with XOR animation, which gives the impression of the action without really recalculating the window contents. This is how we first implemented them in the Graphing Calculator as well; redrawing an algebraic equation or 2-D curve, not to mention a 3-D rendered surface, is computationally expensive.

But to try to stress the processor, we tested the direct approach, and we found that the PowerPC processor could easily keep up. So now in the Calculator, when the user drags the axes, not only is the image dragged live but the exposed parts of the function are calculated and drawn as the mouse is moved. When the zoom buttons are clicked, the entire function is recomputed and redrawn several times to animate the zoom. In this way, applications can take advantage of the PowerPC processor to dramatically improve the quality of interaction in ways that are not possible on slower machines.

2. Eliminate dialogs and command lines in favor of direct manipulation.

Since there's processing power to burn in the PowerPC 601, we simplified the user interface by replacing many dialogs with direct manipulation. The Graphing Calculator doesn't have the dialogs typical of graphing programs for specifying the range and precision of a graph (xmin, xmax, ymin, ymax, number of points, and so on). Instead, the user controls the view of a graph through direct manipulation.

Today's computers are fast enough to allow you to implement direct interaction for complex tasks. Certain time constants play crucial roles in human factors analysis. Recognizing these thresholds can help create a smoother interface. If a task like interacting with an equation takes under one-tenth of a second, users won't be bothered by the delay; if it takes under one-fourth of a second, it's fast enough not to be annoying. Longer delays, however, make users realize that they're waiting. With fast response times, users can ignore the computer and have fun exploring the subject at hand.

By emphasizing direct manipulation, we reduced even algebraic simplification, a task that might seem to require a command-line interface, to the paradigm of MacDraw. Math is traditionally intimidating, and math programs even more so, but we wanted to make mathematics fun. This was really a user-interface challenge, and it required rethinking many fundamental assumptions. Usability was our primary design goal; functionality was second. We were pleased to discover that with direct manipulation, we could simplify the interface without giving up powerful functionality.

Since direct manipulation doesn't require users to learn any new commands or concepts, the manipulations immediately become part of a user's arsenal of tools. A powerful example of this is the drag algebra facility, which strikes many people as the most intriguing feature of the Calculator. The user can select a term of an equation and drag it elsewhere in the equation, just like dragging an object in a drawing program. The Calculator performs the algebraic manipulations necessary to keep the equation consistent. This feature immediately boosts users into a realm where they can confidently and easily manipulate an equation. Just as simple calculators did with multiplication and division, it allows users who understand the essential concepts to immediately move on to more interesting problems.

3. Drop old assumptions and idioms. Use the processing power to explore new interfaces.

On a Power Macintosh, you can handle hundreds or thousands of times more information than before interactively. This might allow rendered 3-D objects to become user-interface components, for example. While the Graphing Calculator flashes its buttons for the usual 8 ticks to indicate that they've been clicked, in that time it could compute and render a 3-D surface with 1000 polygons. Imagine what controls might look like if they really taxed the processing power of the machine.

Because functions are rendered so quickly on a Power Macintosh, we made 3-D surfaces spin by default. This gives users more information about the functions right away. Furthermore, there are no menus or dialogs to control the view of surfaces; just as it does for 2-D graphs, the Calculator lets users change the 3-D view by grabbing the surface with the mouse.

4. Provide a starting point for exploration.

Applications should avoid batch setup operations, such as requiring users to set a lot of dialog options before performing an operation. Instead, provide a starting point for exploration, with reasonable defaults for whatever's necessary to get users to that point.

Perhaps the most unusual aspect of the Graphing Calculator is what it doesn't ask of users. They don't have to set up any graphing options before viewing a curve or a surface; there are no preliminary dialogs or required commands for users to do this. For any equation that can be graphed, the user simply clicks a Graph button to draw it.

We've all had the bewildering experience of trying to use a program only to discover that we don't even know how to begin. One of the toughest problems is to create an interface that makes functionality available and enjoyable for first-time users. But clearly this is where the design effort offers the greatest payoff.

5. Avoid programming cleverness. Instead, assume a good compiler and write readable code.

Cycle-counting and compiler-specific optimizations are favorite pastimes of hackers, and sometimes they're important. But we could never have completed the Graphing Calculator in under six months had we worried about optimizing each routine. Rather, we dealt with speed problems only when they were perceptible to users.

We made no attempt to look at performance bottlenecks or at the compiled code of the Calculator until after running execution profiles. We were surprised where the time was being spent. Most of the time that the Calculator is compute-bound it's either in the math libraries or in QuickDraw. So little time is spent in our code that even compiling it unoptimized didn't slow it down perceptibly. Improving our code's performance meant calling the math libraries less often.

Programmers are often tempted to spend time saving a few bytes or cycles or to fine-tune an algorithm. If the change isn't visible to users, however, the benefits may not extend beyond the programmer's satisfaction. When most of the code in an application is straightforward and readable, maintenance and improvements are easier to make. Those are changes that userswill notice.

To maximize drawing speed without sacrificing compatibility, the Calculator renders its graphs offscreen in GWorlds and uses CopyBits to transfer them to the screen. See "Drawing in GWorlds for Speed and Versatility" in develop Issue 10 for a discussion of this technique.*

6. Invest development time in user-centered design.

Complex algorithms should be used not for their own sake but to improve the user experience. For example, as the user drags the pane divider in the Calculator window, the application redraws most of the window (offscreen in a GWorld) rather than recalculating exposed areas. The Power Macintosh is fast enough that it wasn't worth spending coding and debugging time to save on runtime calculation, because the savings wouldn't be perceived by the user.

In contrast, when users click on a 2-D curve to read an (x,y) coordinate, some quite sophisticated processing happens. As the user moves the mouse, a numeric root-finding algorithm looks for interesting points such as maxima, minima, and zero-crossings to solve equations numerically. Furthermore, because numerical methods to find maxima and minima are imprecise, we also compute symbolic derivatives of the functions and then look for where the derivative is 0, which locates maxima and minima much more accurately. All this work goes completely unnoticed by the user. But the user does notice the result: simply clicking on the curve tells with great precision what's interesting at that point.

7. Learn the new rules for performance.

You may discover that thereare places where performance tuning would be worthwhile in your application. The rules for performance have changed, and knowing the new rules is essential. Some programming techniques that traditionally improve performance can be counterproductive. In particular, on PowerPC-based systems, avoiding instruction cache misses is far more important than saving instructions.

Getting good performance out of a fast machine doesn't always come without effort. To be able to exploit modern hardware to improve an application, you must have some understanding of the hardware and what allows it to be fast. It's extremely important to understand the processor and memory architecture of your target platform.

The memory system in the Power Macintosh is much faster than the memory system of other Macintosh models. The 64-bit bus allows for substantially improved data transfer. However, the processor is much, much faster than the memory system. An uncached memory reference may take 20 times as long as a cached memory reference. Performance will actually be slowed down dramatically by a speedoptimization that saves floating-point multiply instructions (expensive on some processors, but not on the PowerPC) at the expense of extra memory usage that forces instructions or data out of the cache.

Understanding patterns of memory reference is very important in analyzing algorithms for performance. Stepping through an array across cache lines can quickly flush all lines out of the cache. (Cache lines are discussed in the Balance of Power column in this issue.) This can cripple attempts to walk the data structures typically maintained by interface-intensive applications. The PowerPC 601 has an eight-way set associative cache, which is fairly resilient to degradation from flushing of cache lines. However, the 603 processor has just a two-way set associative cache. Any processor-intensive calculations must avoid cache thrashing if they are to avoid degrading below an acceptable level of user responsiveness.

For additional architecture insights and tuning strategies, see the Balance of Power column in develop Issue 18 and in this issue.*

Because no two platforms will run at the same speed, it's important to design software to work well on a variety of machines. In principle, this means that the same application could run on any Macintosh, while being far more powerful -- and more pleasant to use -- on a Power Macintosh.

8. Design tiered functionality: take advantage of whatever hardware you're running on.

Just as it's frustrating for users of entry-level machines to be unable to run software, it's equally frustrating for users of fast, high-end hardware with plenty of memory to have features execute unnecessarily slowly, or to be constrained by programs that expect and only take advantage of minimal resources.

The Graphing Calculator does assume a Power Macintosh as its base platform; otherwise its expectations are modest. However, its appetite is unbounded. It does all drawing using offscreen buffers in temporary memory when adequate RAM is available, but will scale back to onscreen, QuickDraw-based rendering when temporary memory is limited. System 7 makes this easy with purgeable GWorlds; once LockPixels fails, the Calculator knows that it must work within tighter constraints. Later, when it can reallocate the offscreen buffer, it does so and resumes the fast, smooth graphing effects. When memory is abundant, the Calculator uses many temporary GWorlds to buffer frames of 2-D inequality graphs calculated for varying values ofn , such as the animation of cosn x < 0.

The Graphing Calculator does all 2-D graph computation in 15-tick chunks. For simple curves, this typically renders the entire curve at once. But 2-D inequalities are drawn piece by piece. Once Power Macintosh computers are fast enough that an entire, complex inequality graph can be drawn in a single 15-tick time slice, users will be able to explore inequalities as fluidly as they can now play with simple functions.

To take advantage of faster machines, always base computational units on real time rather than on more arbitrary measures. If the Calculator had recomputed a fixed number of points and then called WaitNextEvent, too much time would have been yielded to other processes, even on graphs simple enough to be recomputed and drawn all at once. Instead, the Calculator calls TickCount and lets that dictate when it needs to yield time. This approach allows for a smooth user interface and cooperative execution regardless of the processor's speed.

Designing tiered functionality means abandoning assumptions about what is and is not practical on the target hardware. For addressing resources, such as available hardware and memory, or when execution can be threaded or time-sliced, the options are usually clear. For matters of raw speed, the proper approach may not be so obvious. It may come down to measuring the execution speed of a particular procedure at run time and basing a decision on that. For example, an animation effect might be suitable if it takes under 8 ticks, or a routine that bypasses QuickDraw for drawing in a GWorld may be worthwhile if it really is faster than its QuickDraw alternative.

For an example of timing graphics speed, see the article "Exploiting Graphics Speed on the Power Macintosh" in develop Issue 18.*

9. Test on real users.

The Graphing Calculator reflects our vision of a new kind of calculator. But user testing was essential for showing us the holes in our vision. For example, elements that were directly manipulable in our eyes were overlooked by users. So we redesigned them to make their functions clearer, and then added a demo mode to point out important controls explicitly.

In tests, the users who looked at the help pages invariably turned first to the page at the end offering "tips." This surprised us, but also made clear where to put the most important information for using the Calculator.

Toward the end of the development of the Graphing Calculator, as the final user tests were being conducted, we saw students using the Calculator effectively within minutes, without instruction. Watching a high school student say "Wow!" as an equation came to life on the screen was probably the most satisfying moment for us as programmers. It was also the one that offered us the greatest hope about the future of personal computing. The Power Macintosh offers us the chance to reach more people while making the experience more enjoyable and easier for users than ever possible on earlier generations of computers. As developers, we have a new world to explore.


GREG ROBBINS began writing educational software on the Apple II as a high school student. Since then, he's picked up computer engineering degrees from U.C. San Diego and the University of Pennsylvania, bagged wild boar in Fiji, and evaded sharks off Australia. When he's not consulting on Macintosh development, Greg gets way off the beaten track as a member of the Bay Area Mountain Rescue Unit. *

RON AVITZUR considered working on the Graphing Calculator to be an exercise in single-minded obsessive behavior -- good training for graduate school in physics. Ron has been writing educational math software since the dawn of the Macintosh. You haven't really seen the Graphing Calculator until Ron has shown it to you; in fact, Stewart Alsop's PC Letter names Ron one of the first Demo Gods. *

Thanks to Arnaud Gourdol, Mike Neil, Don Norman, and Alex Rosenberg for reviewing this column. *

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Freeway Pro 7.0.3 - Drag-and-drop Web de...
Freeway Pro lets you build websites with speed and precision... without writing a line of code! With its user-oriented drag-and-drop interface, Freeway Pro helps you piece together the website of... Read more
Cloud 3.3.0 - File sharing from your men...
Cloud is simple file sharing for the Mac. Drag a file from your Mac to the CloudApp icon in the menubar and we take care of the rest. A link to the file will automatically be copied to your clipboard... Read more
Cyberduck 4.6.5 - FTP and SFTP browser....
Cyberduck is a robust FTP/FTP-TLS/SFTP browser for the Mac whose lack of visual clutter and cleverly intuitive features make it easy to use. Support for external editors and system technologies such... Read more
Firefox 36.0 - Fast, safe Web browser. (...
Firefox for Mac 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... Read more
Thunderbird 31.5.0 - Email client from M...
As of July 2012, Thunderbird has transitioned to a new governance model, with new features being developed by the broader free software and open source community, and security fixes and improvements... Read more
VOX 2.4 - Music player that supports man...
VoxIt just sounds better! The beauty is in its simplicity, yet behind the minimal exterior lies a powerful music player with a ton of features & support for all audio formats you should ever need... Read more
A Better Finder Rename 9.46 - File, phot...
A Better Finder Rename is the most complete renaming solution available on the market today. That's why, since 1996, tens of thousands of hobbyists, professionals and businesses depend on A Better... Read more
WALTR 1.0.9 - Drag-and-drop any media fi...
WALTR is designed to make it easy to upload and convert any music or video file to an iPad or iPhone format for native playback. It supports a huge variety of media file types, including MP3, MP4,... Read more
Default Folder X 4.6.14 - Enhances Open...
Default Folder X attaches a toolbar to the right side of the Open and Save dialogs in any OS X-native application. The toolbar gives you fast access to various folders and commands. You just click on... Read more
Boom 2 1.1 - System-wide pro audio app f...
Boom 2 is a system-wide volume booster and equalizer app that is designed especially for OS X 10.10 Yosemite. It comes with a smart interface, self-calibrates itself according to your Mac, offers... Read more

Check Out the Trailer for the Upcoming F...
Check Out the Trailer for the Upcoming FINAL FANTASY: Record Keeper Posted by Jessica Fisher on February 26th, 2015 [ permalink ] DeNA and Square Enix have announced that | Read more »
Legacy Quest is an Upcoming Rouge-like T...
Legacy Quest is an Upcoming Rouge-like That’ll Kill the Whole Family Posted by Jessica Fisher on February 26th, 2015 [ permalink ] Nexon Co. | Read more »
Grudgeball: Enter the Chaosphere Review
Grudgeball: Enter the Chaosphere Review By Jordan Minor on February 26th, 2015 Our Rating: :: MUSCLE MENUniversal App - Designed for iPhone and iPad Regular Show gets an above average game.   | Read more »
Action RPG League of Angels – Fire Raide...
Gaia is being invaded by the Devil Prince and the demonic Devil Army at his disposal, and it’s up to you and your avatar to defeat him in League of Angels – Fire Raiders. Raise a mighty army from hundreds of recruitable angel heroes and take the... | Read more »
Burn Rubber on the Ice With a New Cars:...
Burn Rubber on the Ice With a New Cars: Fast as Lightning Update Posted by Jessica Fisher on February 26th, 2015 [ permalink ] Universal App - Designed for iPhone and iPad | Read more »
AdVenture Capitalist Review
AdVenture Capitalist Review By Jordan Minor on February 26th, 2015 Our Rating: :: DAS KAPITALUniversal App - Designed for iPhone and iPad An inadvertent Marxist manifesto.   | Read more »
Monster vs Sheep Review
Monster vs Sheep Review By Jennifer Allen on February 25th, 2015 Our Rating: :: SAMEY FUNUniversal App - Designed for iPhone and iPad What Monster vs Sheep lacks in variety it makes up for with stress relieving fun. At least, for a... | Read more »
Is Your Face Ready for the New Outwitter...
Is Your Face Ready for the New Outwitters 2.0 Trailer? Posted by Jessica Fisher on February 25th, 2015 [ permalink ] One Man Left Studios has announced that their turn-based strategy game, | Read more »
HowToFormat Review
HowToFormat Review By Jennifer Allen on February 25th, 2015 Our Rating: :: USEFUL TIPSiPhone App - Designed for the iPhone, compatible with the iPad Making a presentation and want to get it just right? HowToFormat teaches you how... | Read more »
Thermo Diem Review
Thermo Diem Review By Jennifer Allen on February 25th, 2015 Our Rating: :: GETS TO THE POINTUniversal App - Designed for iPhone and iPad Want to know whether it’s warmer or colder tomorrow? That’s precisely what Thermo Diem will... | Read more »

Price Scanner via MacPrices.net

New Travel Health App “My Travel Health” iOS...
Rochester, Minnesota based Travel Health and Wellness LLC has announced that its new iOS app help safeguard the user’s health when traveling abroad — “My Travel Health” is now available on the Apple... Read more
Sale! MacBook Airs for up to $115 off MSRP
B&H Photo has MacBook Airs on sale for up to $100 off MSRP. Shipping is free, and B&H charges NY sales tax only: - 11″ 128GB MacBook Air: $799 100 off MSRP - 11″ 256GB MacBook Air: $999 $100... Read more
15-inch 2.0GHz Retina MacBook Pro (refurbishe...
The Apple Store has Apple Certified Refurbished previous-generation 15″ 2.0GHz Retina MacBook Pros available for $1489 including free shipping plus Apple’s standard one-year warranty. Their price is... Read more
Wither The iPad mini? End Of The Road Imminen...
AppleDailyReport’s Dennis Sellers predicts that the iPad mini is going to be left to wither on the vine, as it were, and then just allowed to fade away — a casualty of the IPhone 6 Plus and other... Read more
Android and iOS Duopoly Owns 96.3% of Smartph...
IDC reports that Android and iOS inched closer to total domination of the worldwide smartphone market in both the fourth quarter (4Q14) and the calendar year 2014 (CY14). According to data from the... Read more
13-inch 2.4GHz Retina MacBook Pro available f...
MacMall has the 2013 13″ 2.4GHz/128GB Retina MacBook Pro available for $999.99 for a limited time. Shipping is free. Their price is $300 off original MSRP, and it’s the only sub-$1000 new Retina... Read more
Save up to $300 on a new Mac, $30 on an iPad,...
Purchase a new Mac or iPad at The Apple Store for Education and take up to $300 off MSRP. All teachers, students, and staff of any educational institution qualify for the discount. Shipping is free,... Read more
Mac minis available for up to $75 off MSRP
MacMall has Mac minis on sale for up to $75 off MSRP including free shipping. Their prices are the lowest available for these models from any reseller: - 1.4GHz Mac mini: $459.99 $40 off - 2.6GHz Mac... Read more
WaterField Unveils Versatile Padded Gear Pouc...
San Francisco manufacturer WaterField Design’s new Padded Gear Pouch is a light and handy-sized, yet protective, organizer for every kind of take-along gear: technology, travel, toiletries,... Read more
College Student Deals: Additional $50 off Mac...
Take an additional $50 off all MacBooks and iMacs at Best Buy Online with their College Students Deals Savings, valid through April 11, 2015. Anyone with a valid .EDU email address can take advantage... Read more

Jobs Board

*Apple* Solutions Consultant - Retail Sales...
**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* Solutions Consultant - Retail Sales...
**Job Summary** As an Apple Solutions Consultant (ASC) you are the link between our customers and our products. Your role is to drive the Apple business in a retail Read more
*Apple* Solutions Consultant (ASC)- Retail S...
**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* Solutions Consultant - Retail Sales...
**Job Summary** As an Apple Solutions Consultant (ASC) you are the link between our customers and our products. Your role is to drive the Apple business in a retail Read more
Sr. Technical Services Consultant, *Apple*...
**Job Summary** Apple Professional Services (APS) has an opening for a senior technical position that contributes to Apple 's efforts for strategic and transactional Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.