如何获得到CGPath的距离以进行命中测试? [英] How to get the distance to a CGPath for hit-testing?

问题描述

我有一个开放的CGPath/UIBezierPath，我想为其检测用户是否触摸了它，即一个点是否在距路径一定距离之内.路径是开放的(即线/曲线，而不是形状).它可以同时包含&"和&"；弯曲的元素.我如何获得到路径的距离以进行命中测试?

I have an open CGPath/UIBezierPath for which I want to detect if the user touches it, i.e. whether a point is within a certain distance from the path. The path is open (i.e. a line/curve, not a shape). It can contain both straight & curved elements. How do I get the distance to the path to hit-test it?

推荐答案

似乎CGPath/UIBezierPath都没有执行此操作的功能.根据@nielsbot的建议，您可以使用 CGPathApply(…)编写自定义实现.但是，计算到弯曲部分的距离并不是一件容易的事.

It seems neither CGPath/UIBezierPath has a function to do this. As per @nielsbot's suggestion, you could write a custom implementation using CGPathApply(…). Computing the distance to the curved parts is not so trivial though.

但是，我找到了一种实现原始目标的巧妙方法，对路径进行了命中测试: CGPathCreateCopyByStrokingPath(...).

However I have found a neat way to achieve my original goal, hit-testing the path: CGPathCreateCopyByStrokingPath(…).

- (BOOL)isPoint:(CGPoint)p withinDistance:(CGFloat)distance ofPath:(CGPathRef)path
{
    CGPathRef hitPath = CGPathCreateCopyByStrokingPath(path, NULL, distance*2, kCGLineCapRound, kCGLineJoinRound, 0);
    BOOL isWithinDistance = CGPathContainsPoint(hitPath, NULL, p, false);
    CGPathRelease(hitPath);
    return isWithinDistance;
}

为了获得更好的性能，您可以缓存hitPath.通过使用 CGPathAddPath(...)

For better performance, you can cache hitPath. Could also be used for closed paths by adding the original path to hitPath using CGPathAddPath(…)

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