c# 图片截图

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Drawing.Imaging;
using System.Reflection;

namespace WindowsFormsApplication3
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {

        }

        private void button1_Click(object sender, EventArgs e)
        {
            string strFilename = "";
            OpenFileDialog dlgOpen = null;
            try
            {
                dlgOpen = new OpenFileDialog();
                dlgOpen.Filter = "All Image Files(*.*)|*.*";
                if (dlgOpen.ShowDialog() == DialogResult.OK)
                {
                    if (dlgOpen.FileName == "") return;
                    strFilename = dlgOpen.FileName;
                    pictureBox1.Image = Image.FromFile(strFilename);
                    this.SetImageSizeMode(pictureBox1);
                }
            }
            catch (Exception ex)
            {
                MessageBox.Show("无法识别的图片格式(" + strFilename + ")\r\n" + ex.Message, "错误", MessageBoxButtons.OK, MessageBoxIcon.Error);
            }
            finally
            {
                if (dlgOpen != null)
                    dlgOpen.Dispose();
                dlgOpen = null;
            }
        }
/********************************************************************************************************/
        private void SetImageSizeMode(PictureBox pImage)
        {
            if (pImage == null) return;
            Image imgResult = pImage.Image;
            if (imgResult != null)
            {
                //控制图片显示方式
                if (imgResult.Width > pImage.Width || imgResult.Height > pImage.Height)
                {
                    pImage.SizeMode = PictureBoxSizeMode.Zoom;
                }
                else
                {
                    pImage.SizeMode = PictureBoxSizeMode.CenterImage;
                }
            }
        }
/*****************************************************************************************************/
        #region 绘制及剪切
        Point fPtStart;                     //开始位置矩形的位置
        bool fHaveImage = false;            //是否有图片
        Point fPtFirst;                     //鼠标按下去的位置
        Point fPtSecond;                    //鼠标当前位置

        private void pictureBox1_MouseDown(object sender, MouseEventArgs e)
        {
            this.Cursor = Cursors.Cross;
            fPtFirst = new Point(e.X, e.Y);
            fPtStart = new Point(e.X, e.Y);
            if ((sender as PictureBox).Image != null)
            {
                this.fHaveImage = true;
            }
            else
            {
                this.fHaveImage = false;
            }
        }

        private void pictureBox1_MouseMove(object sender, MouseEventArgs e)
        {
            if (this.Cursor == Cursors.Cross)
            {
                fPtSecond = new Point(e.X, e.Y);


                if ((fPtSecond.X - fPtFirst.X) > 0 && (fPtSecond.Y - fPtFirst.Y) > 0)
                {
                    //鼠标当前位置在，按下去位置的右下角
                    fPtStart = new Point(fPtFirst.X, fPtFirst.Y);
                }
                else if ((fPtSecond.X - fPtFirst.X) > 0 && (fPtSecond.Y - fPtFirst.Y) < 0)
                {
                    //鼠标当前位置在，按下去位置的右上角
                    fPtStart = new Point(fPtFirst.X, fPtSecond.Y);
                }
                else if ((fPtSecond.X - fPtFirst.X) < 0 && (fPtSecond.Y - fPtFirst.Y) > 0)
                {
                    //鼠标当前位置在，按下去位置的左下角
                    fPtStart = new Point(fPtSecond.X, fPtFirst.Y);
                }
                else
                {
                    //鼠标当前位置在，按下去位置的左上角
                    fPtStart = new Point(fPtSecond.X, fPtSecond.Y);
                }
                pictureBox1.Invalidate();
            }
        }

       
/*******************************************************************************************************/
         private void pictureBox1_MouseUp(object sender, MouseEventArgs e)
        {
            if (this.fHaveImage == false) return;
            try
            {
                fPtSecond = new Point(e.X, e.Y);
                if ((fPtSecond.X - fPtFirst.X) > 0 && (fPtSecond.Y - fPtFirst.Y) > 0)
                {
                    //鼠标当前位置在，按下去位置的右下角
                    fPtStart = new Point(fPtFirst.X, fPtFirst.Y);
                }
                else if ((fPtSecond.X - fPtFirst.X) > 0 && (fPtSecond.Y - fPtFirst.Y) < 0)
                {
                    //鼠标当前位置在，按下去位置的右上角
                    fPtStart = new Point(fPtFirst.X, fPtSecond.Y);
                }
                else if ((fPtSecond.X - fPtFirst.X) < 0 && (fPtSecond.Y - fPtFirst.Y) > 0)
                {
                    //鼠标当前位置在，按下去位置的左下角
                    fPtStart = new Point(fPtSecond.X, fPtFirst.Y);
                }
                else
                {
                    //鼠标当前位置在，按下去位置的左上角
                    fPtStart = new Point(fPtSecond.X, fPtSecond.Y);
                }

                Rectangle rectDisplay = this.GetPictureDisplaySize(pictureBox1);        //图片实际显示的大小


                int Width = Math.Abs((fPtSecond.X - fPtFirst.X));
                int Height = Math.Abs((fPtSecond.Y - fPtFirst.Y));

                double dWRate = pictureBox1.Image.Width / (double)rectDisplay.Width;    //缩放比例：宽
                double dHRate = pictureBox1.Image.Height / (double)rectDisplay.Height;  //缩放比例：高

                int intRealWidth = (int)(dWRate * Width);           //实际需要截取的图片宽度
                int intRealHeight = (int)(dHRate * Height);         //实际需要截取的图片高度

                int intRealX = (int)((fPtStart.X - rectDisplay.X) * dWRate); //实际的X坐标
                int intRealY = (int)((fPtStart.Y - rectDisplay.Y) * dHRate); //实际的Y坐标

                Bitmap bmpDest = new Bitmap(intRealWidth, intRealHeight, PixelFormat.Format32bppRgb);       //目标图片大小

                Graphics g = Graphics.FromImage(bmpDest);               //创建GDI

                Rectangle rectDest = new Rectangle(0, 0, intRealWidth, intRealHeight);
                Rectangle rectSource = new Rectangle(intRealX, intRealY, intRealWidth, intRealHeight);

                g.DrawImage(pictureBox1.Image, rectDest, rectSource, GraphicsUnit.Pixel);               //绘图

                pictureBox2.Image = (Image)bmpDest;

                g.Dispose();

                SetImageSizeMode(pictureBox2);
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message, "错误", MessageBoxButtons.OK, MessageBoxIcon.Error);
            }
            finally
            { this.Cursor = Cursors.Default; }
        }

         private Rectangle GetPictureDisplaySize(PictureBox pbxImage)
         {
             if (pbxImage != null)
             {
                 PropertyInfo ppiImageRect = pbxImage.GetType().GetProperty("ImageRectangle", BindingFlags.Instance | BindingFlags.NonPublic);
                 return (Rectangle)ppiImageRect.GetValue(pbxImage, null);
             }
             return new Rectangle(0, 0, 1, 1);
         }
/***********************************************************************************/
         private void pictureBox1_Paint(object sender, PaintEventArgs e)
         {
             int intWidth = 0;
             int intHeight = 0;
             if (this.fHaveImage == true)
             {
                 Pen p = new Pen(Color.Black, 1);
                 p.DashStyle = System.Drawing.Drawing2D.DashStyle.Dash;

                 intWidth = Math.Abs(fPtFirst.X - fPtSecond.X);
                 intHeight = Math.Abs(fPtFirst.Y - fPtSecond.Y);

                 Rectangle rectDraw = new Rectangle(fPtStart, new Size(intWidth, intHeight));
                 e.Graphics.DrawRectangle(p, rectDraw);
             }
         }

         
/***************************************************************************************************/
        #endregion
        /// <summary>
        /// 保存剪切后的图片
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void button2_Click(object sender, EventArgs e)
         {
             SaveFileDialog dlgSave = new SaveFileDialog();

             if (dlgSave.ShowDialog() == DialogResult.OK)
             {
                 pictureBox2.Image.Save(dlgSave.FileName);
             }
         }

        private void pictureBox2_Click(object sender, EventArgs e)
        {

        }


    }
}