ios - Swift:有没有一种简单的方法来绘制形状并检测它们是否相交？

Question

<分区>

Answer 1

如果这由一系列线段组成，则可以采用 Martin R 对 UIBezierPath intersect 的回答不仅要检测交叉点，还要识别交叉点的位置:

func intersectionBetweenSegments(_ p0: CGPoint, _ p1: CGPoint, _ p2: CGPoint, _ p3: CGPoint) -> CGPoint? {
    var denominator = (p3.y - p2.y) * (p1.x - p0.x) - (p3.x - p2.x) * (p1.y - p0.y)
    var ua = (p3.x - p2.x) * (p0.y - p2.y) - (p3.y - p2.y) * (p0.x - p2.x)
    var ub = (p1.x - p0.x) * (p0.y - p2.y) - (p1.y - p0.y) * (p0.x - p2.x)
    if (denominator < 0) {
        ua = -ua; ub = -ub; denominator = -denominator
    }
    
    guard ua >= 0 && ua <= denominator && ub >= 0 && ub <= denominator && denominator != 0 else {
        return nil
    }

    return CGPoint(x: p0.x + ua / denominator * (p1.x - p0.x), y: p0.y + ua / denominator * (p1.y - p0.y))
}

因此，如果您有一个 CGPoint 值数组并且您想要识别所有交叉点，您可以这样做:

let n = points.count - 1

for i in 1 ..< n {
    for j in 0 ..< i-1 {
        if let intersection = intersectionBetweenSegments(points[i], points[i+1], points[j], points[j+1]) {
            // do whatever you want with `intersection`
        }
    }
}

例如，您可以在屏幕的线段相交处添加一个点:

但是，如果您的曲线由三次贝塞尔曲线组成，则情况会更加复杂。不过，您可能会考虑 Checking if two cubic Bézier curves intersect .