It was a sunny friday afternoon, I was trying to fix a glitch in my animation path. To my own happy surprise I discovered that it was fairly simple to plug this hole. All I needed was a special case when a parameter reached angle 0.00000, so of I went with some duck tape and glue (pronounced if-statements) looking something like:
if(curveAmplitude == 0.0f){
//dragon-code
}


To my total surprise the if-statement never turned out to be true. After using my favorite method for discovering how stuff works, trial-and-error, I remembered something about floats & doubles not being reliable. I started reading over the IEEE standard and David Goldberg’s paper “What Every Computer Scientist Should Know About Floating-Point Arithmetic”. As Mr. Goldberg states it all boils down to this:

“Squeezing infinitely many real numbers into a finite number of bits requires an approximate representation. [...] the results of a floating-point calculation must often be rounded in order to fit back into its finite representation. The rounding error is the characteristic feature of floating-point computation.”

Thank you Mr. Goldberg for that! Now that the problem is identified it is time for a solution.

Solution:
Add two minimal macros to your source, these macros compares your number to epsilon which is the smallest float available to the system.

#define fEqual(a,b) (fabs((a) - (b)) < FLT_EPSILON)
#define fEqualToZero(a) (fabs(a) < FLT_EPSILON)

Note that if you are into precision this will not get you all the way. There rounding problem is still there, but in most simple cases this is a good-enough-solution.

Recently I have submerged myself in the world of Core Animation. Apple has done a great job with this framework. For someone who is graphically challenged this has been a steep uphill battle. One mine I stepped on, was that all the core C math functions really prefer radians over degrees. I wrote the following two helper methods to do this conversion:

- (CGFloat)_degreesToRadians:(CGFloat)degrees{
return degrees * (M_PI / 180);
}
- (CGFloat)_radiansToDegrees:(CGFloat)radians{
return radians * (180 / M_PI);
}

The first talk I attended was performed by a User Experience Evangelist at Apple, Mr. Eric Hope.

All the talks at Tech Talk were very focused and intensive (compressing the subject of interaction design on the iPhone to one hour naturally leads to this). Mr. Hope immediately started of by presenting the 10 essentials of interface design, so here it goes:

1. Elegant solution – Your application needs to solve a specific problem or a set of problems for the user. Start of by pinpointing a problem and then move on the implementation and what features it will contain. Many developers move in the other direction — starting of with an idea about what cool features they want to include in their app. The users are not going to come back to your app for a cool animation.
2. Essential style – Finding which style your application belongs to can help you in making the right design decisions. Your application can probably be quartered into one of these groups:
   • Serious – Use minimal graphics, metaphors and keep the alignment clean. These apps are focused on the data so you don’t want to irritate the user with a lot of animations. E.g. Mail app.
   • Fun - These kind of apps focus on productivity and being graphically rich though still utilizing a simple information hierarchy.
   • Fun entertainment – This category is mainly populated by games; graphically intensive, no boring tables and full screen. Remember to let the user get to the game in as few taps as possible.
   • Serious entertainment - Moderately graphical, not excessively hierarchical with a focus on content consumption. E.g. Classics.
   • Utilities - A utility is also characterized by being graphically rich and focused on the main function. The UI should be readable from ~1.5m away, also try to use the “flip for settings” metaphor. E.g. Weather.
3. Great usability – Your application needs to be built on a solid hierarchy, a linear flow is usually what is best suited. Build it by the “one door to one room”-principle, this states that there should only be one way to enter a view. If the flow of the application is to complex the user won’t feel she has the ability to mentally map it out. In addition one thing many developers forget is to build their UI with finger sized targets, this translates to ~44×44 pixels for buttons, links and such.
4. Gorgeous app icon – Mr. Hope really stressed the importance of having an attractive icon. The icon is the first and last visual impression of your application (because of the shrinking animation being shown when an app quits). It is also the primary attractor in App Store, apps are made and broken from their icon. The human mind parses shapes first, so use a silhouette  without any text. The icon should be so rich in detail it can be printed as a poster and put on your wall. =)
5. High fidelity UI – Apple has been so kind to compress all their knowledge about UIs to a single document called the HIG (Human Interface Guidelines), both and Eric warmly recommend it. By conforming to iPhone-like behavior and looks you meet a level of standard. As a developer you can stand on the shoulders of others while the user will be able to feel at home using your interface. This is of course a trade-of when wanting to build something unique.Mr. Hope also emphasized how much there is to gain by involving the client/end user in the beginning of the design process. Creating a paper prototype for every screen will help you to avoid those costly cavities later on. There is also a cheap way of increasing the perceived value of your application; use rich materials like wood, leather and glass. Employing tactile design by using real things ad a model for your graphical objects you can enrich the user experience. E.g. The compass app.

   One fundamental point, that for some could come of as obvious, is that you WILL need a designer helping you build that app. His exact words were: “Hire, befriend or become a designer!”. I believe the last option will be the cheapest…

6. Dynamic content – This was THE single most important guideline of them all.
   iPhone users consume the data available in their apps then they throw them away. In order to get you user to regularly revisit you app it will need a “pulse”. Create a possibility for the users to share and/or generate new data. People love people, interconnectedness is the key. Facebook has a great API available for iPhone integration.

    

   People loves freshness and improvement! Don’t write “Bug fixes” in the update description of your app, take your time and try to “sell” your app again. By making available more content through in-app purchase there no need to release another app as you had to do before. But be detailed and transparent in your description about what the user will get. As the Swedish proverb says: “Ärlighet varar längst!” =)

7. Animation - Animation could help in increasing the perceived value, they could also (when done right) help to minimize graphical feedback to the user. E.g. instead of flashing an Alert in the face of the user when a podcast has been selected, the small icon flies to you Downloads-tab and the download begins.
8. Sound - Mr. Hope describes sound as the forgotten frontier. Unfortunately it is not present in many apps even though it could help in reducing visual noise and increase the value of the app. As with any feature it could be abused, always obey and respect the silent switch. Also remember that it needs to be symmetrical, if you play a sound when you expand a list you also need a sound when it contracts.
9. Polish – is not only a country in Europe! The details are as important as your main features. It only takes a small irritation to loose an otherwise happy user.Young iPhone are more likely to interact with their device using their thumbs, therefore implementing landscape mode could be wise if they are part of your expected population. There is no reason not to create a spotlight and settings icon, this should be 29×29 pixels and will take around 5 min of your time. The same argument holds true for Copy+Paste & Undo+Redo, even though it probably will take more than a few minutes to implement.
10. Application Definition Statement - As stated before, avoid developing from a long list of features. Try to find what is unique with your app.
    • What are your differentiators?
    • What problem are you trying to solve for the user?
    • Who are your audience? This really needs to be super focused, “laser precise!”.

    There is a mantra that could help you in finding your definition statement: “Pick the few features most frequently used, by the majority of your users, most appropriate for the mobile context.”

Remember to read through the HIG, it is loaded with tips for the interface designer as well as the developer.

Lastly I want to emphasize that any error expressed in this post most likely belongs to me, while any bit of knowledge can be credited to Eric Hope.

Stay tuned for part II; “In App Purchase by Mark Malone”.

The talks began with an introductory talk and some numbers. An exclude of these were:

• 2 billion+ apps downloded.
• 50 million+ devices sold (iPhone and iPod Touch).
• 100.000+ unique apps on the App Store.
• 125.000+ registered developers.

You can say what you want about Apple, but those are some impressive numbers. The talk went on with praising some really cool apps out there:

• Peaks – Which uses augmented reality to present information about a mountain peak.
• Zipcar – Let’s you locate and interact with rentable cars. Check out this vid.
• Snaptell – Which locates commercial products from a photo.
• These also deserve some attention: postage timetuner tweetie2 1112 ocarina roambi things.

There were loads of talk available during the conference, I decided to attend these:

• Interface Design by Eric Hope.
• In App Purchase by Mark Malone.
• Core Data by Michael Jurewitz.
• Optimizing Your App by Michael Jurewitz.
• Application Performance by Michael Jurewitz.

I will try to summarize my notes and post them on this blog within a few days. I did not expect the talks to go into as much detail as they did, this was a welcome surprise to me. Don’t get shocked if you stumble upon some code in the coming posts.

Any who, let’s get started!