iphone - 寻找离CGPoint最近的物体

Question

我在 UIScrollView 上有四个 UIView(屏幕分为四分位数)

在四分位数上，每个四分位数上都有一些对象(UIImageViews)。

当用户点击屏幕时，我想找到距离给定CGPoint最近的对象？

有什么想法吗？

我有每个四分位数内对象的 CGPoint 和框架 (CGRect)。

更新:

_{(来源:skitch.com)}

红色图钉是 UIImageView。

    // UIScrollView
    NSLog(@" UIScrollView: %@", self);

    // Here's the tap on the Window in UIScrollView's coordinates
    NSLog(@"TapPoint: %3.2f, %3.2f", tapLocation.x, tapLocation.y);

    // Find Distance between tap and objects
    NSArray *arrayOfCGRrectObjects = [self subviews];
    NSEnumerator *enumerator = [arrayOfCGRrectObjects objectEnumerator];

    for (UIView *tilesOnScrollView in enumerator) {

        // each tile may have 0 or more images
        for ( UIView *subview in tilesOnScrollView.subviews ) {

            // Is this an UIImageView?
            if ( [NSStringFromClass([subview class]) isEqualToString:@"UIImageView"]) {

                // Yes, here are the UIImageView details (subView)
                NSLog(@"%@", subview);

                // Convert CGPoint of UIImageView to CGPoint of UIScrollView for comparison...
                // First, Convert CGPoint from UIScrollView to UIImageView's coordinate system for reference
                CGPoint found =  [subview convertPoint:tapLocation fromView:self];
                NSLog(@"Converted Point from ScrollView: %3.2f, %3.2f", found.x, found.y);

                // Second, Convert CGPoint from UIScrollView to Window's coordinate system for reference
                found =  [subview convertPoint:subview.frame.origin toView:nil];
                NSLog(@"Converted Point in Window: %3.2f, %3.2f", found.x, found.y);

                // Finally, use the object's CGPoint in UIScrollView's coordinates for comparison
                found =  [subview convertPoint:subview.frame.origin toView:self]; // self is UIScrollView (see above)
                NSLog(@"Converted Point: %3.2f, %3.2f", found.x, found.y);

                // Determine tap CGPoint in UIImageView's coordinate system
                CGPoint localPoint = [touch locationInView:subview];
                NSLog(@"LocateInView: %3.2f, %3.2f",localPoint.x, localPoint.y );

               //Kalle's code
                    CGRect newRect = CGRectMake(found.x, found.y, 32, 39);
                    NSLog(@"Kalle's Distance: %3.2f",[self distanceBetweenRect:newRect andPoint:tapLocation]);

            }

调试控制台

问题就在这里。每个图 block 的尺寸为 256x256。第一个UIImageView的CGPoint转换为UIScrollView 的坐标系 (53.25, 399.36) 应该与 tapPoint (30,331) 完全一致。为什么有区别？？点击点右侧的另一个点正在计算较近(距离方面)？？

<CALayer: 0x706a690>>
[207] TapPoint: 30.00, 331.00
[207] <UIImageView: 0x7073db0; frame = (26.624 71.68; 32 39); opaque = NO; userInteractionEnabled = NO; tag = 55; layer = <CALayer: 0x70747d0>>
[207] Converted Point from ScrollView: 3.38, 3.32
[207] Converted Point in Window: 53.25, 463.36
[207] Converted Point: 53.25, 399.36 *** Looks way off!
[207] LocateInView: 3.38, 3.32
[207] Kalle's Distance: 72.20 **** THIS IS THE TAPPED POINT
[207] <UIImageView: 0x7074fb0; frame = (41.984 43.008; 32 39); opaque = NO; userInteractionEnabled = NO; tag = 55; layer = <CALayer: 0x7074fe0>>
[207] Converted Point from ScrollView: -11.98, 31.99
[207] Converted Point in Window: 83.97, 406.02
[207] Converted Point: 83.97, 342.02
[207] LocateInView: -11.98, 31.99
207] Kalle's Distance: 55.08 ***** BUT THIS ONE's CLOSER??????

Answer 1

下面的方法应该可以解决问题。如果您发现其中有任何奇怪的地方，请随时指出。

- (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);
}

示例输出:

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

可能有更优化的版本，因此可能值得深入挖掘。

以下方法确定两个 CGPoint 之间的距离。

- (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)
}

更新:删除了 fabsf()； -x^2 与 x^2 相同，因此不需要。

更新 2:为了完整性，还添加了 distanceBetweenPoint:andPoint: 方法。