Orphion is an iOS app that uses a "private API" that enables the application to sense how much of each finger is touching the screen. What is the API Bastus Trump used for Orphion in order to do this? Couldn't we all take advantage of this API for more robust touchscreen interactions? Orphion was previously given flack by Apple for using that API but now it is out on iPhone without any crippling. I'd love to make an app of my own that uses articulation.
In iOS 8.0, UITouch has a new property, majorRadius, the radius of the touch.
In prior iOS releases, UITouch had a private property, pathMajorRadius. You could access this property indirectly using the KVC valueForKey: method, which might have avoided App Store detection.
This question and its answers cover the undocumented pathMajorRadius property in more depth.