C# 图片缩放，拖拽后保存成图片的功能

窗体界面部分如下：

鼠标的缩放功能需要手动在 OpertaionImg.Designer.cs 文件里面添加一句代码，具体代码如下：

//picturePhoto显示图片的控件

this.picturePhoto.MouseWheel += new System.Windows.Forms.MouseEventHandler(this.picturePhoto_MouseWheel);

下面是窗体的后台代码：

 public partial class OpertaionImg : Form
     {
         Bitmap myBmp;
         Point mouseDownPoint = new Point(); //记录拖拽过程鼠标位置
         bool isMove = false;    //判断鼠标在picturebox上移动时，是否处于拖拽过程(鼠标左键是否按下)
         int zoomStep = ;      //缩放步长
         public OpertaionImg()
         {
             InitializeComponent();
         }

         private void btnChoise_Click(object sender, EventArgs e)
         {
             string filename = "";
             OpenFileDialog dlg = new OpenFileDialog();
             dlg.Filter = "Tiff文件|*.tif|Bmp文件|*.bmp|Erdas img文件|*.img|EVNI文件|*.hdr|jpeg文件|*.jpg|raw文件|*.raw|vrt文件|*.vrt|所有文件|*.*";
             dlg.FilterIndex = ;
             if (dlg.ShowDialog() == DialogResult.OK)
             {
                 filename = dlg.FileName;
             }
             if (filename == "")
             {
                 return;
             }
             myBmp = new Bitmap(filename);
             if (myBmp == null)
             {
                 MessageBox.Show("读取失败");
                 return;
             }
           //  textBox1.Text = filename;
             picturePhoto.Image = myBmp;
             picturePhoto.SizeMode = PictureBoxSizeMode.Zoom; //设置picturebox为缩放模式
             picturePhoto.Width = myBmp.Width;
             picturePhoto.Height = myBmp.Height;
         }

         private void picturePhoto_MouseDown(object sender, MouseEventArgs e)
         {
             if (e.Button == MouseButtons.Left)
             {
                 mouseDownPoint.X = Cursor.Position.X;
                 mouseDownPoint.Y = Cursor.Position.Y;
                 isMove = true;
                 picturePhoto.Focus();
             }
         }

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

         private void picturePhoto_MouseMove(object sender, MouseEventArgs e)
         {
             picturePhoto.Focus();
             if (isMove)
             {
                 int x, y;
                 int moveX, moveY;
                 moveX = Cursor.Position.X - mouseDownPoint.X;
                 moveY = Cursor.Position.Y - mouseDownPoint.Y;
                 x = picturePhoto.Location.X + moveX;
                 y = picturePhoto.Location.Y + moveY;
                 picturePhoto.Location = new Point(x, y);
                 mouseDownPoint.X = Cursor.Position.X;
                 mouseDownPoint.Y = Cursor.Position.Y;
             }
         }
         private void picturePhoto_MouseWheel(object sender, MouseEventArgs e)
         {
             int x = e.Location.X;
             int y = e.Location.Y;
             int ow = picturePhoto.Width;
             int oh = picturePhoto.Height;
             int VX, VY;
             if (e.Delta > )
             {
                 picturePhoto.Width += zoomStep;
                 picturePhoto.Height += zoomStep;

                 PropertyInfo pInfo = picturePhoto.GetType().GetProperty("ImageRectangle", BindingFlags.Instance |BindingFlags.NonPublic);
                 Rectangle rect = (Rectangle)pInfo.GetValue(picturePhoto, null);

                 picturePhoto.Width = rect.Width;
                 picturePhoto.Height = rect.Height;
             }
             if (e.Delta < )
             {
                 if (picturePhoto.Width < myBmp.Width / )
                     return;
                 picturePhoto.Width -= zoomStep;
                 picturePhoto.Height -= zoomStep;
                 PropertyInfo pInfo = picturePhoto.GetType().GetProperty("ImageRectangle", BindingFlags.Instance |BindingFlags.NonPublic);
                 Rectangle rect = (Rectangle)pInfo.GetValue(picturePhoto, null);
                 picturePhoto.Width = rect.Width;
                 picturePhoto.Height = rect.Height;
             }

             VX = (int)((double)x * (ow - picturePhoto.Width) / ow);
             VY = (int)((double)y * (oh - picturePhoto.Height) / oh);
             picturePhoto.Location = new Point(picturePhoto.Location.X + VX, picturePhoto.Location.Y + VY);
         }

         private void btnSave_Click(object sender, EventArgs e)
         {
             SaveFileDialog sa = new SaveFileDialog();
             //设置文件类型
             sa.Filter = "图片文件（*.png）|*.png";
             //设置默认文件类型显示顺序
             sa.FilterIndex = ;
             if (sa.ShowDialog() == DialogResult.OK)
             {
                 Bitmap bit = new Bitmap(picturePhoto.Width, picturePhoto.Height);//实例化一个和窗体一样大的bitmap
                 Graphics g = Graphics.FromImage(bit);
                 g.CompositingQuality = CompositingQuality.HighQuality;//质量设为最高
                 // g.CopyFromScreen(this.Left, this.Top, 0, 0, new Size(panel2.Width, panel2.Height));//保存整个窗体为图片
                 g.CopyFromScreen(picturePhoto.PointToScreen(Point.Empty), Point.Empty, picturePhoto.Size);//只保存某个控件（这里是panel游戏区）
                 bit.Save(sa.FileName);//默认保存格式为PNG，保存成jpg格式质量不是很好
             }
         }
     }