JS判断坐标点是否在给定的多边形内

1(function (window) {
2        "use strict";
3        /**
4         * 判断给出的坐标点是否在多边形内
5         * */
6        function pointInPolygon(targetPoint, targetPoints) {
7            var leftPointCount = 0;
8            var rightPointCount = 0;//左右点的个数
9            var _points = [];
10            //第一步：取出所有的点，并计算交点坐标
11            for (var i = 0, _length = targetPoints.length - 1; i < _length; i++) {
12                var p1 = targetPoints[i], p2 = targetPoints[i + 1];//取出当前点和当前点的下一个点
13                var point = _calcCrossoverPoint(targetPoint, p1, p2);
14                //如果交点有效，则保存
15                if (point) {
16                    _points.push(point);
17                }
18            }
19//            第二步：计算给定的坐标点，左右两边的交点个数，奇数在范围内，偶数则不在
20            for (var j = 0, length = _points.length; j < length; j++) {
21                var x = _points[j];
22                if (x === targetPoint.x) {
23                    return false;//在线上，直接返回不在范围内
24                } else {
25                    (targetPoint.x !== x && targetPoint.x > x) ? leftPointCount++ : rightPointCount++;
26                }
27            }
28            //判断交点个数
29            return (leftPointCount % 2 !== 0 && rightPointCount % 2 !== 0);
30        }
31
32        /**
33         * 算交点坐标，坐标点在扫描行上或者上方时，交点无效
34         * @param targetPoint
35         * @param startPoint
36         * @param endPoint
37         * @returns {*}
38         */
39        function _calcCrossoverPoint(targetPoint, startPoint, endPoint) {
40            var crossoverPointX = startPoint.x - ((startPoint.y - targetPoint.y) * (startPoint.x - endPoint.x) / (startPoint.y - endPoint.y));
41//            判断交点坐标是否有效，即交点在startPoint，endPoint构成的线段范围内
42            if ((startPoint.y < targetPoint.y && endPoint.y >= targetPoint.y) || (endPoint.y < targetPoint.y && startPoint.y >= targetPoint.y)) {
43                if ((crossoverPointX >= startPoint.x && crossoverPointX <= endPoint.x) || (crossoverPointX <= startPoint.x && crossoverPointX >= endPoint.x)) {
44                    return crossoverPointX;
45                } else {
46                    return false;
47                }
48            } else {
49                return false;
50            }
51
52        }
53
54        var isIn = pointInPolygon({x: 4, y: 4}, [{x: 2, y: 1}, {x: 1, y: 3}, {x: 3, y: 5}, {x: 5, y: 4}, {
55            x: 4,
56            y: 1
57        }, {x: 3, y: 2}, {
58            x: 2,
59            y: 1
60        }]);
61        console.log(isIn);
62    })(window);