Question

I am trying to figure out the math for rotating a UIView a certain side is always “follows” a finger when moving on the screen.

I’m almost there but I haven’t had trigonometry in years and I can’t figure out exactly what to do. Here is what I’ve got:

-(void) touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
    UITouch *touch = [touches anyObject];
    CGPoint touchPoint = [touch locationInView:self.view];

    int dy = cannon.frame.origin.y - touchPoint.y;
    int dx = cannon.frame.origin.x - touchPoint.x;

    cannon.transform = CGAffineTransformMakeRotation(atan2(dy,dx) - 135);
}

Answer 1

First, thank you to everyone who took the time to answer!

I played around with it for a while, and it seems that the only problem was that I used ints for dy and dx instead of floats. I also found a nifty, quick “method” for converting degrees to radians. Here is the final, working code:

#define DEGREES_TO_RADIANS(angle) (angle / 180.0 * M_PI)

-(void) touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
    UITouch *touch = [touches anyObject];
    CGPoint touchPoint = [touch locationInView:self.view];

    float dy = cannon.frame.origin.y - touchPoint.y;
    float dx = cannon.frame.origin.x - touchPoint.x;

    cannon.transform = CGAffineTransformMakeRotation(atan2(dy,dx) - DEGREES_TO_RADIANS(90));
}