private void pictureBox1_MouseDown(object sender, MouseEventArgs e)
        {
            if (e.Button == MouseButtons.Left)
            {
                mouseDownPoint.X = Cursor.Position.X;   //记录鼠标左键按下时位置
                mouseDownPoint.Y = Cursor.Position.Y;                
                isMove = true;
                pictureBox1.Focus();    //鼠标滚轮事件(缩放时)需要picturebox有焦点
            }
        }

        private void pictureBox1_MouseUp(object sender, MouseEventArgs e)
        {
            if (e.Button == MouseButtons.Left)
            {
                isMove = false;                
            }
        }

        private void pictureBox1_MouseMove(object sender, MouseEventArgs e)
        {
            pictureBox1.Focus();    //鼠标在picturebox上时才有焦点，此时可以缩放
            if (isMove)
            {
                int x, y;           //新的pictureBox1.Location(x,y)
                int moveX, moveY;   //X方向，Y方向移动大小。
                moveX = Cursor.Position.X - mouseDownPoint.X;
                moveY = Cursor.Position.Y - mouseDownPoint.Y;
                x = pictureBox1.Location.X + moveX;
                y = pictureBox1.Location.Y + moveY;                
                pictureBox1.Location = new Point(x, y);
                mouseDownPoint.X = Cursor.Position.X;
                mouseDownPoint.Y = Cursor.Position.Y;                
            }
        }
        
        private void panel2_MouseDown(object sender, MouseEventArgs e)
        {
            if (e.Button == MouseButtons.Left)
            {
                mouseDownPoint.X = Cursor.Position.X;   //记录鼠标左键按下时位置
                mouseDownPoint.Y = Cursor.Position.Y;
                isMove = true;
            }
        }

        private void panel2_MouseUp(object sender, MouseEventArgs e)
        {
            if (e.Button == MouseButtons.Left)
            {
                isMove = false;
            }
        }

        private void panel2_MouseMove(object sender, MouseEventArgs e)
        {
            panel2.Focus();  //鼠标不在picturebox上时焦点给别的控件，此时无法缩放            
            if (isMove)
            {
                int x, y;           //新的pictureBox1.Location(x,y)
                int moveX, moveY;   //X方向，Y方向移动大小。
                moveX = Cursor.Position.X - mouseDownPoint.X;
                moveY = Cursor.Position.Y - mouseDownPoint.Y;
                x = pictureBox1.Location.X + moveX;
                y = pictureBox1.Location.Y + moveY;
                pictureBox1.Location = new Point(x, y);
                mouseDownPoint.X = Cursor.Position.X;
                mouseDownPoint.Y = Cursor.Position.Y;
            }
        }

//实现锚点缩放(以鼠标所指位置为中心缩放)；
        //步骤：
        //①先改picturebox长宽，长宽改变量一样；
        //②获取缩放后picturebox中实际显示图像的长宽，这里长宽是不一样的；
        //③将picturebox的长宽设置为显示图像的长宽；
        //④补偿picturebox因缩放产生的位移，实现锚点缩放。
        //  注释：为啥要②③步？由于zoom模式的机制，把picturebox背景设为黑就知道为啥了。
        //这里需要获取zoom模式下picturebox所显示图像的大小信息，添加 using System.Reflection；
        //pictureBox1_MouseWheel事件没找到。。。手动添加，别忘在Form1.Designer.cs的“Windows 窗体设计器生成的代码”里加入：        
        //this.pictureBox1.MouseWheel += new System.Windows.Forms.MouseEventHandler(this.pictureBox1_MouseWheel)。
        private void pictureBox1_MouseWheel(object sender, MouseEventArgs e)
        {
            int x = e.Location.X;
            int y = e.Location.Y;
            int ow = pictureBox1.Width;
            int oh = pictureBox1.Height;            
            int VX, VY;     //因缩放产生的位移矢量
            if (e.Delta > 0)    //放大
            {
                //第①步
                pictureBox1.Width += zoomStep;
                pictureBox1.Height += zoomStep;
                //第②步
                PropertyInfo pInfo = pictureBox1.GetType().GetProperty("ImageRectangle", BindingFlags.Instance |
                    BindingFlags.NonPublic);
                Rectangle rect = (Rectangle)pInfo.GetValue(pictureBox1, null);
                //第③步
                pictureBox1.Width = rect.Width;
                pictureBox1.Height = rect.Height;
            }
            if (e.Delta < 0)    //缩小
            {
                //防止一直缩成负值
                if (pictureBox1.Width < myBmp.Width / 10)
                    return;
                
                pictureBox1.Width -= zoomStep;
                pictureBox1.Height -= zoomStep;
                PropertyInfo pInfo = pictureBox1.GetType().GetProperty("ImageRectangle", BindingFlags.Instance |
                    BindingFlags.NonPublic);
                Rectangle rect = (Rectangle)pInfo.GetValue(pictureBox1, null);
                pictureBox1.Width = rect.Width;
                pictureBox1.Height = rect.Height;
            }
            //第④步，求因缩放产生的位移，进行补偿，实现锚点缩放的效果
            VX = (int)((double)x * (ow - pictureBox1.Width) / ow);
            VY = (int)((double)y * (oh - pictureBox1.Height) / oh);
            pictureBox1.Location = new Point(pictureBox1.Location.X + VX, pictureBox1.Location.Y + VY);
        }