On 2012-01-05, at 1:49 PM, Eric E. Dolecki wrote:
> I'd like to calculate the angle from a center point of a view to a touch
> point.
>
> 0º behind top of screen, 180º being bottom of screen.
>
> Calculating from touchesMoved.
I think you can just retrieve the arctangent between the x axis and the vector
formed by the origin and location of the touch (reversing the y coordinate).
For example:
- (void) touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
CGPoint center = self.center;
CGPoint location = [[touches anyObject] locationInView:self];
CGPoint vectorOfInterest = CGPointMake(location.x - center.x, center.y -
location.y);
NSLog(@"Vector: %@, Angle: %.2fº",
NSStringFromCGPoint(vectorOfInterest),
atan2(vectorOfInterest.x, vectorOfInterest.y) * 57.29);
}
The resulting angle will be [0, π) clockwise starting from the top, and [-π, 0)
from the bottom (or something like that—my trig is horribly rusty).
HTH,
—Mt._______________________________________________
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