/// 计算三点之间的角度
    ///
    /// - Parameters:
    ///   - p1: 点1
    ///   - p2: 点2（也是角度所在点）
    ///   - p3: 点3
    /// - Returns: 角度（180度制）
    func getAnglesWithThreePoints(p1:CGPoint,p2:CGPoint,p3:CGPoint) -> Double {
        //排除特殊情况，三个点一条线
        if (p1.x == p2.x && p2.x == p3.x) || ( p1.y == p2.x && p2.x == p3.x){
            return 0
        }
        
        let a = fabs(p1.x - p2.x)
        let b = fabs(p1.y - p2.y)
        let c = fabs(p3.x - p2.x)
        let d = fabs(p3.y - p2.y)
        
        if (a < 1.0 && b < 1.0) || (c < 1.0 && d < 1.0){
            return 0
        }
        let e = a*c+b*d
        let f = sqrt(a*a+b*b)
        let g = sqrt(c*c+d*d)
        let r = Double(acos(e/(f*g)))
        return r        //弧度值
        
//        return (180*r/Double.pi)      //角度值

    }