C#GDI绘制矩形框，用鼠标移动、放大缩小矩形框

先大概介绍一下原因，GDI画矩形框就不说了，很简单的。这里面最主要的就是滚轮放大和左键移动两个事件，要计算矩形框的坐标位置。下面将代码贴出如下：    先是定义需要的变量，就四个变量。        //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;然后编写鼠标事件        private void this_MouseWheel(object sender, MouseEventArgs e)             {                      if (e.Delta > 0)                    {                              if (zoom < 80)// 最大放大80倍                                      zoom++;                        }                      else                   {                              if (zoom > 0)                                      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                     DrawRect.Height = this.Height - zoom * 2;                    //按比例计算宽度              DrawRect.Width = (int)(Convert.ToSingle(DrawRect.Height) * (Convert.ToSingle(this.Width) / Convert.ToSingle(this.Height)));                  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.X = DrawRect.X - (DrawRect.Right - this.Width) - 1;                            DrawRect.X = DrawRect.X > 1 ? DrawRect.X : 1;                 }                 //如果Bottom超过控件高度                if (DrawRect.Bottom > this.Height)               {                             DrawRect.Y = DrawRect.Y - (DrawRect.Bottom - this.Height) - 1;                        DrawRect.Y = DrawRect.Y > 1 ? DrawRect.Y : 1;                     }                      DrawImg();            }        private void this_MouseMove(object sender, MouseEventArgs e)             {                      if (e.Button == MouseButtons.Left)                      {                         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;                    
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         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++;                            }                  }         }        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
                g.FillRectangle(new SolidBrush(Color.LightGray), 0, 0, this.Width, this.Height);
                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.DrawRectangle(new Pen(Color.Red), DrawRect);
            }
        }      主要就是这么几个事件。有需要的可以参考参考。


原文转载自：https://www.cnblogs.com/caigege/p/5505897.html