点在多边形内

[xinglie]

var EPSILON = 1e-8;
function isAroundEqual(a, b) {
    return Math.abs(a - b) < EPSILON;
}
function contain(points, x, y) {
    var w = 0;
    var p = points[0];
    if (!p) {
        return false;
    }
    for (var i = 1; i < points.length; i++) {
        var p2 = points[i];
        w += windingLine(p[0], p[1], p2[0], p2[1], x, y);
        p = p2;
    }
    // Close polygon
    var p0 = points[0];
    if (!isAroundEqual(p[0], p0[0]) || !isAroundEqual(p[1], p0[1])) {
        w += windingLine(p[0], p[1], p0[0], p0[1], x, y);
    }
    return w !== 0;
}
function windingLine(x0, y0, x1, y1, x, y) {
    if ((y > y0 && y > y1) || (y < y0 && y < y1)) {
        return 0;
    }
    // Ignore horizontal line
    if (y1 === y0) {
        return 0;
    }
    var t = (y - y0) / (y1 - y0);
    var dir = y1 < y0 ? 1 : -1;
    // Avoid winding error when intersection point is the connect point of two line of polygon
    if (t === 1 || t === 0) {
        dir = y1 < y0 ? 0.5 : -0.5;
    }
    var x_ = t * (x1 - x0) + x0;
    // If (x, y) on the line, considered as "contain".
    return x_ === x ? Infinity : x_ > x ? dir : 0;
}

[xinglie]

function isPointInPolygon(point, polygon) {
    let x = point.x, y = point.y;
    let inside = false;
    for (let i = 0, j = polygon.length - 1; i < polygon.length; j = i++) {
        let xi = polygon[i].x, yi = polygon[i].y;
        let xj = polygon[j].x, yj = polygon[j].y;

        let intersect = ((yi > y) != (yj > y))
            && (x < (xj - xi) * (y - yi) / (yj - yi) + xi);
        if (intersect) inside = !inside;
    }
    return inside;
}

// Example usage:
const point = {x: 3, y: 4};
const polygon = [{x: 1, y: 1}, {x: 5, y: 1}, {x: 5, y: 5}, {x: 1, y: 5}];
console.log(isPointInPolygon(point, polygon)); // O