Thanks! GUI and animations are all custom. I wanted very specific multitouch capabilities that would not be practical by using standard gesture recognizers. So a lot of work went into imitating the rubber banding and momentum scrolling of the all-familiar scroll view. It was definitely worth it in my view. Said gestures manipulate two base values; origin, and scale (1D scroll and zoom.) Values on each side are defined as a multiple and an offset of the base (linear function.) All numbers on screen are basically entities of a particle system and are spawned, positioned, and destroyed according to their relation to origin and scale.