The touch pressure for paper is done with a new touch Radius property. The radius property on touches was available as a private API, but only made available publicly in iOS 8.
The Ink and Adonit touch pixel point, which are basically the same (We manufacture the Ink and Slide for adobe) use a pressure sensitive tip in the pen itself, and communicate that pressure over Bluetooth. This gives you a much higher resolution on the pressure, with the trade off of the BT stack latency.
The Ink and Adonit touch pixel point, which are basically the same (We manufacture the Ink and Slide for adobe) use a pressure sensitive tip in the pen itself, and communicate that pressure over Bluetooth. This gives you a much higher resolution on the pressure, with the trade off of the BT stack latency.