Question

I am making a drawing app and I want to increment my brush size depending on the touches velocity.

How would I accomplish this?

Answer 1

Yes. See the methods on UIView named touches*, specifically:

- (void)touchesMoved:(NSSet*)touches withEvent:(UIEvent*)event

It gets called when a move (“slide”?) is detected, and doesn’t suffer from being “fooled” by multiple quick touches. You can get the coordinate of the current finger position in the view and the time the event ocurred:

UITouch *touch = [touches anyObject];
CGPoint inFrameCoordinate = [touch locationInView:self];
NSTimeInterval timestamp = [touch timestamp]

Get the distance and time between two coordinates to calculate the velocity.