移动图像，部分重写，解决闪屏问题

privatevoid pictureBox1_MouseMove(object sender, MouseEventArgs e)
        {
            
            if (e.Button == MouseButtons.Left)
            {
                //移动处理
                if (!isLeftCtrlKeyDown)
                {
                     offset.Width += e.X - mousePressPoint.X;
                     offset.Height += e.Y - mousePressPoint.Y;
                     mousePressPoint = e.Location;
                     Bitmap newbmp =new Bitmap(this.ClientSize.Width, this.ClientSize.Height);
                     Graphics g = Graphics.FromImage(newbmp);
                    //重绘一小段图片
                     g.DrawImage(bmp, new Rectangle(0, 0, this.ClientSize.Width, this.ClientSize.Height),
                        -offset.Width, -offset.Height, this.ClientSize.Width, this.ClientSize.Height, GraphicsUnit.Pixel);
                     pictureBox1.Image = newbmp;
                     pictureBox1.Refresh();                   
                 }
                else
                {
                    //放大缩小处理
                    int width = bmp.Width + pictureBox1.Location.X + e.X - mousePressPoint.X;
                    int height = bmp.Height + pictureBox1.Location.Y + e.Y - mousePressPoint.Y;
                    if (width >0&& height >0)
                    {
                         bmp =new Bitmap(bmp, new Size(width, height));
                         pictureBox1.Image = bmp;
                         pictureBox1.Refresh();
                     }
                 }
                
             }
         }