CGPoint 到线段的最短距离

Question

我一直在尝试实现 Douglas-Peucker algorithm into my code and I'm able to translate pseudocode into Swift, except for the shortestDistanceToSegment function. Only Swift version I could find was answered here，但我不明白它的实际作用。

我需要一个函数，它获取三个点作为参数（点和线的两端）和 returns CGPoint 和线段之间的最短距离。关于代码做什么（以及为什么）的一些解释会很好但不是必需的。

Answer 1

来自的答案，其中变量重命名并添加了一些注释：

/* Distance from a point (p1) to line l1 l2 */
func distanceFromPoint(p: CGPoint, toLineSegment v: CGPoint, and w: CGPoint) -> CGFloat {
    let pv_dx = p.x - v.x
    let pv_dy = p.y - v.y
    let wv_dx = w.x - v.x
    let wv_dy = w.y - v.y

    let dot = pv_dx * wv_dx + pv_dy * wv_dy
    let len_sq = wv_dx * wv_dx + wv_dy * wv_dy
    let param = dot / len_sq

    var int_x, int_y: CGFloat /* intersection of normal to vw that goes through p */

    if param < 0 || (v.x == w.x && v.y == w.y) {
        int_x = v.x
        int_y = v.y
    } else if param > 1 {
        int_x = w.x
        int_y = w.y
    } else {
        int_x = v.x + param * wv_dx
        int_y = v.y + param * wv_dy
    }

    /* Components of normal */
    let dx = p.x - int_x
    let dy = p.y - int_y

    return sqrt(dx * dx + dy * dy)
}

CGPoint 到线段的最短距离

Shortest distance from CGPoint to segment

line

cgpoint

swift