/// <summary>
/// 以中心点旋转Angle角度
/// </summary>
/// <param name="center">中心点</param>
/// <param name="p1">待旋转的点</param>
/// <param name="angle">旋转角度（弧度）</param>
private void PointRotate(Point center, ref Point p1, double angle)
{
double x1 = (p1.X - center.X) * Math.Cos(angle) + (p1.Y - center.Y) * Math.Sin(angle) + center.X;
double y1 = -(p1.X - center.X) * Math.Sin(angle) + (p1.Y - center.Y) * Math.Cos(angle) + center.Y;
p1.X = (int)x1;
p1.Y = (int)y1;
}