Example project from blog post.
If you want to grab the quad tree you can get it from my GitHub
or just install using cocoapods
pod 'TBQuadTree', '~> 0.0'
Added a Swift version of the code as an attempt at playing with Swift and figuring out Objective-C code. Note: this is not an exemplary Swift code, I'm still trying to figure out the best way past all this explict casting hell and might missed some memory management problems.