Finding closest object to CGPoint
If you're using Swift, here's how you can calculate the distance between a CGPoint and a CGRect (e.g. an UIView's frame)
private func distanceToRect(rect: CGRect, fromPoint point: CGPoint) -> CGFloat {
// if it's on the left then (rect.minX - point.x) > 0 and (point.x - rect.maxX) < 0
// if it's on the right then (rect.minX - point.x) < 0 and (point.x - rect.maxX) > 0
// if it's inside the rect then both of them < 0.
let dx = max(rect.minX - point.x, point.x - rect.maxX, 0)
// same as dx
let dy = max(rect.minY - point.y, point.y - rect.maxY, 0)
// if one of them == 0 then the distance is the other one.
if dx * dy == 0 {
return max(dx, dy)
} else {
// both are > 0 then the distance is the hypotenuse
return hypot(dx, dy)
}
}
The following method should do the trick. If you spot anything weird in it feel free to point it out.
- (CGFloat)distanceBetweenRect:(CGRect)rect andPoint:(CGPoint)point
{
// first of all, we check if point is inside rect. If it is, distance is zero
if (CGRectContainsPoint(rect, point)) return 0.f;
// next we see which point in rect is closest to point
CGPoint closest = rect.origin;
if (rect.origin.x + rect.size.width < point.x)
closest.x += rect.size.width; // point is far right of us
else if (point.x > rect.origin.x)
closest.x = point.x; // point above or below us
if (rect.origin.y + rect.size.height < point.y)
closest.y += rect.size.height; // point is far below us
else if (point.y > rect.origin.y)
closest.y = point.y; // point is straight left or right
// we've got a closest point; now pythagorean theorem
// distance^2 = [closest.x,y - closest.x,point.y]^2 + [closest.x,point.y - point.x,y]^2
// i.e. [closest.y-point.y]^2 + [closest.x-point.x]^2
CGFloat a = powf(closest.y-point.y, 2.f);
CGFloat b = powf(closest.x-point.x, 2.f);
return sqrtf(a + b);
}
Example output:
CGPoint p = CGPointMake(12,12);
CGRect a = CGRectMake(5,5,10,10);
CGRect b = CGRectMake(13,11,10,10);
CGRect c = CGRectMake(50,1,10,10);
NSLog(@"distance p->a: %f", [self distanceBetweenRect:a andPoint:p]);
// 2010-08-24 13:36:39.506 app[4388:207] distance p->a: 0.000000
NSLog(@"distance p->b: %f", [self distanceBetweenRect:b andPoint:p]);
// 2010-08-24 13:38:03.149 app[4388:207] distance p->b: 1.000000
NSLog(@"distance p->c: %f", [self distanceBetweenRect:c andPoint:p]);
// 2010-08-24 13:39:52.148 app[4388:207] distance p->c: 38.013157
There might be more optimized versions out there, so might be worth digging more.
The following method determines the distance between two CGPoints.
- (CGFloat)distanceBetweenPoint:(CGPoint)a andPoint:(CGPoint)b
{
CGFloat a2 = powf(a.x-b.x, 2.f);
CGFloat b2 = powf(a.y-b.y, 2.f);
return sqrtf(a2 + b2)
}
Update: removed fabsf(); -x^2 is the same as x^2, so it's unnecessary.
Update 2: added distanceBetweenPoint:andPoint:
method too, for completeness.
Thanks @cristian,
Here's Objective-C version of your answer
- (CGFloat)distanceToRect:(CGRect)rect fromPoint:(CGPoint)point
{
CGFloat dx = MAX(0, MAX(CGRectGetMinX(rect) - point.x, point.x - CGRectGetMaxX(rect)));
CGFloat dy = MAX(0, MAX(CGRectGetMinY(rect) - point.y, point.y - CGRectGetMaxY(rect)));
if (dx * dy == 0)
{
return MAX(dx, dy);
}
else
{
return hypot(dx, dy);
}
}