Before you create the gesture recognizer, you need to choose a gesture and determine how to detect it. Since it returns the iPad app to a known state, you can use a small letter r. The first challenge is determining how to recognize the character.
The easiest way to recognize a stroke is by breaking it down into components separated by transitions in
y movement. As part of the events, you get both the current and previous touch points, allowing detection of changes in movement. The
x value increases from left to right of the screen, and
y increases from top to bottom. You can use comparisons between previous and current positions to determine changes in direction. If you needed other information ...