IOS多边形 画法

//let sx = sRadius * cos(Double.pi/2.0 + (Double(i) - 1.0) * (2.0 * Double.pi)/count)

//CGPoint point = CGPointMake(x+radius*cos(2*M_PI*i/num), y+radius*sin(2*M_PI*i/num));

point.x = CGFloat(Double(_center.x) + Double(radius) * cos(2.0*Double.pi*Double(item)/Double(_numberOfItems) - Double.pi /2))

point.y = CGFloat(Double(_center.y) + Double(radius) * sin(2.0*Double.pi*Double(item)/Double(_numberOfItems) - Double.pi /2))