射线法：实现检测绘制是否在指定不规则区域内(函数)

• 场景：绘制元素的指定区域检测

isPointInPolygon=(vertices, P)=> {
        let count = 0;
        const n = vertices.length;
        for (let i = 0; i < n; i++) {
            const A = vertices[i];
            const B = vertices[(i + 1) % n];
            // 如果A和B在射线的同一侧，跳过
            if (A.y === B.y) continue;
            if (P.y >= Math.max(A.y, B.y) || P.y < Math.min(A.y, B.y)) continue;
            // 计算交点的x坐标
            const x_intersect = A.x + (P.y - A.y) * (B.x - A.x) / (B.y - A.y);
            // 如果交点在射线的右侧，计数加一
            if (x_intersect >= P.x) count++;
        }
        // 如果交点数为奇数，点在内部
        return count % 2 === 1;
    }