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 = 20;      //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 = 8;
            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 > 0)
            {
                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 < 0)
            {
                if (picturePhoto.Width < myBmp.Width / 10)
                    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 = 1;
            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
            }
        }
    }