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Object Overlay on Video

We always welcome guest bloggers on This edition was prepared by Tejas Jasani and covers how to overlay objects on live video using Brad Larson’s GPUImage project.
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E-Mail Validation

For the ProductLayer sign-up form I wanted to make sure that the user can only send a sign up if the email address is valid. If you google for ways to validate an email address you most often solutions involving regular expressions. But since I don’t trust a RegEx unless I know it by heart, I implemented the validation with Apple’s own NSDataDetector for links.

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Forward Geocoding

There are two kinds of Geocoding which you might encounter: forward and reverse. The class doing that for you in iOS is CLGeocoder. It is both capable of doing it forward (from address to lat/long) and reverse (from geo coordinates to placemarks). For this tutorial we will build an app that lets you search for addresses and display the results individually on a map view.

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You know the story: you have an app laid out as storyboard, want to show a modal view controller and when the user is done with it it you want to dismiss it, … or un-present it, or whatever you need to get rid of the modal VC and return. Now what about a view controller that can be both presented modally or via push onto a navigation controller?

Then it starts to get complicated. Unless you know about how to unwind. It’s actually quite awesome, but you have to use it several times because it is a little bit counter-intuitive how to implement unwinding. I’m writing this tutorial so that I myself can remember how to do it in the future.

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M7 Pedometer

Apple’s iPhone 5S features a dedicated motion coprocessor, dubbed the “M7”. Probably because the M stands for Movement/Motion similar to the A in “A7” standing for … um, Apple. This coprocessor collects and analyzes data from multiple iPhone sensors and determines two interesting pieces of information:

  • the motion activity state of its user (car, walking, running, standing still) ad hoc and history
  • the number of steps taken ad hoc and history

Let’s build a functional pedometer app so that we can learn about and explore the latter.

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Assuring Documentation Completeness

For your open source projects you want to make sure that pull requests you merge don’t destabilise the project. Having a large number of unit tests in combination with a Continuos Integration platform like Travis-CI helps greatly. With this setup each pull request or new branch sent to your repo triggers a build and Travis-CI will let you know if all tests pass or not.

If you annotate your headers with appledoc then you can build nice class documentation viewable that integrates with the Xcode documentation viewer or can be put on a web server as HTML.

Now what about pull requests which add new functionality but which are lacking some documentation annotations? This blog post looks into using Travis-CI for making sure documentation is also complete on pull requests.

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Can you Smell the iBeacon?


iBeacons are one of the hot new topics introduced with iOS 7, though I have not seen any actual real life use case for it.

Last week I received my Developer Preview Kit from Estimote and also I have begun to research iBeacons for inclusion in the book I am currently working on. Here are my findings.

There are two words that you should know to understand the difference between the two modes of operation:

  • Monitoring – this refers to a low-power region-monitoring, you get didEnterRegion: and didExitRegion: delegate messages
  • Ranging – this means a higher-power activity where you get the signal strength from individual iBeacons and can estimate distance to them from this

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Wrapping a Dynamic C-Array

For version 0.2.0 of DTMarkdownParser I needed an array that would allow me to look up the string range for individual lines of a string. My initial approach was to simple use the provided method of NSValue to wrap an NSRange in it. The problem with this approach is that as the number of ranges in the array grows so does the time needed to find a range at a higher index.

Jan Weiß of Geheimwerk suggested to replace this approach with one based on C memory allocation and searching functions. This required me to brush up on my dynamic C-array allocation skills which had become somewhat rusty from only using Objective-C objects for everything. The techniques I’ll be discussing in this blog might be of great value to you, too, if you ever find yourself needing to quickly find a scalar value (i.e. a number or struct) in a dynamically sizing array.

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Blurring Views on Mac

“Frosted Glass” abounds on iOS 7 and this new look is the new “Corinthian Leather”. Apple has often used design ideas from their mobile OS and let them inform UI design on OS X. This begs the question: where is frosted glass on Mac?

Mac developer Raffael Hannemann offered to do a guest tutorial for demonstrating how to achieve the same view blurring effect on Mac, where you are much less constrained by the GPU performance. On Mac the necessary ingredients for view blurring are readily available.

On iOS Apple kept the necessary APIs for blurring private for the time being because of a severe performance problem that goes hand in hand with live Gaussian blurring. Raffel’s blog post after the break.

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Xcode Coverage

Code Coverage is described on Wikipedia as:

… a measure used to describe the degree to which the source code of a program is tested by a particular test suite. A program with high code coverage has been more thoroughly tested and has a lower chance of containing software bugs than a program with low code coverage.

Less bugs? Yes, please!

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