问题情境：
上司对自己的关怀，称现有的画圈圈区域不太理想，需要有：
可拖拽移动圆的位置，
滚轮可以控制大小，
边界也可以通过拖拽调整圆的长轴短轴调整大小。
原理描述：
1.画形状容易实现；
2.调整大小通过整个窗体的鼠标move事件。来进行实时刷新显示；
3.拖拽移动位置用mousedown事件和MouseMove事件，可以实时监控光标位置；
4.滚轮控制用MouseWheel事件，MouseEventArgs的Delta属性可控制上下滚；
自己做了个简单demo实例：
public Form1() { InitializeComponent(); this.MouseWheel += new System.Windows.Forms.MouseEventHandler(this_MouseWheel); this.MouseMove += new System.Windows.Forms.MouseEventHandler(this_MouseMove); this.MouseDown += new System.Windows.Forms.MouseEventHandler(this_MouseDown); DrawRect.X = (this.Width - DrawRect.Width) / 2; DrawRect.Y = (this.Height - DrawRect.Height) / 2; log("zoom width height"); } //矩形框坐标 private Rectangle DrawRect = new Rectangle(0, 0, 100, 100); //鼠标按下时坐标 private Point MouseDownP = new Point(); //放大倍数 private int zoom = 0; //鼠标移动矩形框次数，如果移动过矩形框则不从中心放大，以移动后的位置放大缩小，缩小为原大小，缩放数为0时，重置此数 private int MoveCount = 0; private void this_MouseWheel(object sender, MouseEventArgs e) { Rectangle tmpRec = DrawRect; int zmTemp = zoom; int incTemp = 0; if (e.Delta > 0)//上滚放大 { if (zoom < 80)// 最大放大80倍 zoom++; incTemp = -zoom; } else//下滚缩小 { if (zoom > 0) incTemp = zoom--; if (zoom == 0) //放大倍数＝0,不放大，鼠标拖动标记归0 MoveCount = 0; } //放大原理 //1、先获取放大倍数 //2、根据放大倍数，计算矩形框高度，高度＝控件高度－倍数×2； //3、根据高度，提取矩形宽度，宽度＝高度×（控件宽度/控件高度），为保证矩形和原控件纵横比例，所以要乘以比例 //4、根据矩形框大小，和控件大小，计算矩形框在控件中的位置，即X,Y坐标 //1）如果没有拖动过矩形，则按默认中间位置取值，X＝（控件宽度－矩形宽度)/2,Y＝（控件高度－矩形高度）/2 //2）如果拖动过矩形框，则原X，Y坐标不变化 //5、根据得到的新矩形框的坐标和范围，判断是否超界，判断XY坐标 //滚轮放大事件 //矩形区域高度=控件高度-放大缩小倍数*2 double ratio = Math.Round(DrawRect.Width / (DrawRect.Height * 1.0) , 2); DrawRect.Height = DrawRect.Height - incTemp * 2; //按比例计算宽度 DrawRect.Width = (int)(Convert.ToSingle(DrawRect.Height) * ratio); //if (MoveCount == 0)//没有拖动过，滚动滚轮才按中间放大缩小 //{ // DrawRect.X = (this.Width - DrawRect.Width) / 2; // DrawRect.Y = (this.Height - DrawRect.Height) / 2; //} //===============判断是否超界＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝ //如果Right超过控件宽度 if (DrawRect.Right > this.Width) { DrawRect = tmpRec; zoom = zmTemp; return; } //如果Bottom超过控件高度 if (DrawRect.Bottom > this.Height - 20) { DrawRect = tmpRec; zoom = zmTemp; return; } DrawImg(); } int cursorFlag = 0; private void this_MouseMove(object sender, MouseEventArgs e) { if (e.Button == MouseButtons.Left) { int limitRadius = 5; if (cursorFlag != 0) { switch (cursorFlag) { case 1://left if (DrawRect.Width + DrawRect.X - e.X < limitRadius) { return; } DrawRect.Width += DrawRect.X - e.X; DrawRect.X = e.X; break; case 2://right if (e.X - DrawRect.X < limitRadius) { return; } DrawRect.Width = e.X - DrawRect.X; break; case 3://top if (DrawRect.Height + DrawRect.Y - e.Y < limitRadius) { return; } DrawRect.Height += DrawRect.Y - e.Y; DrawRect.Y = e.Y; break; case 4://bottom if (e.Y - DrawRect.Y < limitRadius) { return; } DrawRect.Height = e.Y - DrawRect.Y; break; } DrawImg(); } else { if (DrawRect.Contains(MouseDownP))//判断鼠标按下的坐标是否在红框中，确定是否拖动的红框 { //拖动鼠标位置，矩形框新X＝矩形框原X＋（当前鼠标X－按下时X），原X＋偏移量 //Y轴一样变化 DrawRect.X = DrawRect.X + (e.X - MouseDownP.X); //.Location = ClienP; DrawRect.Y = DrawRect.Y + (e.Y - MouseDownP.Y); // ClienP.Y; //判断是否超过左上角 if (DrawRect.X < 0) DrawRect.X = 0; if (DrawRect.Y < 0) DrawRect.Y = 0; //判断是否超过右下角 if (DrawRect.X > (this.Width - DrawRect.Width - 1)) DrawRect.X = this.Width - DrawRect.Width - 1; if (DrawRect.Y > (this.Height - DrawRect.Height - 1)) DrawRect.Y = this.Height - DrawRect.Height - 1; //画图 DrawImg(); //计算完坐标系，鼠标按下坐标转换成当前鼠标坐标，以重新计算偏移 MouseDownP.X = e.X; MouseDownP.Y = e.Y; //拖动过鼠标，鼠标拖动标记累加 MoveCount++; } } } else { //如果光标在边界上，显示对应的光标形状 int boundary = 3; if ((e.X <= DrawRect.X - 1 && e.X >= DrawRect.X - boundary) && e.Y >= DrawRect.Y && e.Y <= DrawRect.Y + DrawRect.Height)//left { cursorFlag = 1; this.Cursor = Cursors.SizeWE; } else if ((e.X >= DrawRect.X + DrawRect.Width + 1 && e.X <= DrawRect.X + DrawRect.Width + boundary) && e.Y >= DrawRect.Y && e.Y <= DrawRect.Y + DrawRect.Height)//right { cursorFlag = 2; this.Cursor = Cursors.SizeWE; } else if ((e.Y <= DrawRect.Y - 1 && e.Y >= DrawRect.Y - boundary) && e.X > DrawRect.X && e.X < DrawRect.X + DrawRect.Width)//top { cursorFlag = 3; this.Cursor = Cursors.SizeNS; } else if ((e.Y >= DrawRect.Y + DrawRect.Height + 1 && e.Y <= DrawRect.Y + DrawRect.Height + boundary) && e.X > DrawRect.X && e.X < DrawRect.X + DrawRect.Width)//bottom { cursorFlag = 4; this.Cursor = Cursors.SizeNS; } else { cursorFlag = 0; this.Cursor = Cursors.Default; } } } private void this_MouseDown(object sender, MouseEventArgs e) { if (e.Button == MouseButtons.Left) MouseDownP = new Point(e.X, e.Y); } void DrawImg() { using (Graphics g = this.CreateGraphics()) { //重绘背景 Ellipse Rectangle g.FillRectangle(new SolidBrush(Color.LightGray), 0, 0, this.Width, this.Height);//达到去重效果 g.DrawString("滚轮放大，左键拖动矩形框" + zoom, new Font("黑体", 12f), new SolidBrush(Color.Green), 5, 5); g.DrawString("放大" + zoom, new Font("黑体", 12f), new SolidBrush(Color.Red), 5, 20); //重绘矩形 g.DrawEllipse(new Pen(Color.Red), DrawRect); g.DrawRectangle(new Pen(Color.Red), DrawRect); //日志 log(zoom.ToString("00") + " " + DrawRect.Width + " " + DrawRect.Height); } } private void log(string text) { string path = Application.StartupPath + "\" + DateTime.Now.ToString("yyyy-MM-dd") + ".log"; StreamWriter sw = File.AppendText(path); sw.WriteLine(text); sw.Flush(); sw.Close(); } private void Form1_Paint(object sender, PaintEventArgs e) { Graphics g = this.CreateGraphics(); //重绘背景 Ellipse Rectangle g.FillRectangle(new SolidBrush(Color.LightGray), 0, 0, this.Width, this.Height);//达到去重效果 g.DrawString("滚轮放大，左键拖动矩形框" + zoom, new Font("黑体", 12f), new SolidBrush(Color.Green), 5, 5); g.DrawString("放大" + zoom, new Font("黑体", 12f), new SolidBrush(Color.Red), 5, 20); //重绘矩形 DrawRect.X = (this.Width - DrawRect.Width) / 2; DrawRect.Y = (this.Height - DrawRect.Height) / 2; g.DrawEllipse(new Pen(Color.Red), DrawRect); g.DrawRectangle(new Pen(Color.Red), DrawRect); }