一个坐标点围绕任意中心点旋转--C#实现

    假设对图片上任意点(x,y)，绕一个坐标点(rx0,ry0)逆时针旋转RotaryAngle角度后的新的坐标设为(x', y')，有公式：
    x'= (x - rx0)*cos(RotaryAngle) + (y - ry0)*sin(RotaryAngle) + rx0 ;
    y'=-(x - rx0)*sin(RotaryAngle) + (y - ry0)*cos(RotaryAngle) + ry0 ;
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/// <summary>  
        /// 对一个坐标点按照一个中心进行旋转  
        /// </summary>  
        /// <param name="center">中心点</param>  
        /// <param name="p1">要旋转的点</param>  
        /// <param name="angle">旋转角度，笛卡尔直角坐标</param>  
        /// <returns></returns>  
        private  Point PointRotate(Point center, Point p1, double angle)  
        {  
            Point tmp = new Point();  
            double angleHude = angle * Math.PI / 180;/*角度变成弧度*/  
            double x1 = (p1.X - center.X) * Math.Cos(angleHude) + (p1.Y - center.Y ) * Math.Sin(angleHude) + center .X;  
            double y1 = -(p1.X - center.X) * Math.Sin(angleHude) + (p1.Y - center.Y) * Math.Cos(angleHude) + center.Y;  
            tmp.X = (int)x1;  
            tmp.Y = (int)y1;  
            return tmp;  
        }  

另一种旋转的方法：

  private void Form1_Paint(object sender, PaintEventArgs e)
        {

            Graphics graphics = e.Graphics;
            var picRect = new RectangleF(200, 200, 100, 50);
            PointF[] points = new PointF[] {  // 将原来四边形的4个顶点坐标放入数组
                                     picRect.Location,
                                     new PointF(picRect.Right, picRect.Top),
                                     new PointF(picRect.Right, picRect.Bottom),
                                     new PointF(picRect.Left, picRect.Bottom)
                                    };
            graphics.DrawPolygon(new Pen(Color.Red), points);
            Matrix matrix=new Matrix();

            //更改坐标系
            graphics.TranslateTransform(100, 100);
            //旋转角度
            graphics.RotateTransform(10);
            //恢复坐标系
            graphics.TranslateTransform(-100, -100);

            //获取旋转后的坐标
            graphics.Transform.TransformPoints(points);

            graphics.DrawPolygon(new Pen(Color.Red), points);
          

        }

//获取旋转中心

               
                //var center = new PointF(rectBorder.Width/2, rectBorder.Height/2);

                ////矩形左上坐标
                //float offsetX = 0;
                //float offsetY = 0;
                //offsetX = center.X - rectBorder.Width/2;
                //offsetY = center.Y - rectBorder.Height/2;

                ////要画的图
                //var picRect = new RectangleF(offsetX, offsetY, rectBorder.Width, rectBorder.Height);
                //var Pcenter = new PointF(picRect.X + picRect.Width/2, picRect.Y + picRect.Height/2);

                ////让图片绕中心旋转一周
                ////for (int i = 0; i < 361; i += 10)
                ////{
                //var changeRect = new Rectangle((int) picRect.X, (int) picRect.Y, (int) picRect.Width,
                //                               (int) picRect.Height);
              
                ////绘图平面以图片的中心点旋转
                //graphics.TranslateTransform(Pcenter.X, Pcenter.Y);
                //graphics.RotateTransform(_ShapeExAngle);
                ////恢复绘图平面在水平和垂直方向的平移
                //graphics.TranslateTransform(-Pcenter.X, -Pcenter.Y);
                
                ////绘制图片并延时
                //graphics.DrawRectangle(borderPen, changeRect);
                ////重置绘图平面的所有变换
                //graphics.ResetTransform();