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因为截图时可能须要精确截取某一部分，所以须要放大镜的功能，这样截取的时候才更easy定位截图的位置。

加入PictureBox，name属性设置为“pictureBox_zoom”；

在“Form1_Load”事件处理函数中加入下面代码：

//设置放大镜的大小

            this.pictureBox_zoom.Width = this.ZoomBoxWidth;

            this.pictureBox_zoom.Height = this.ZoomBoxHeight;

在“ExitCutImage”方法中加入代码：

在“Form1_MouseUp”事件处理函数中加入代码：

在“ShowForm”方法的else条件最后加入代码：

if (this.ZoomBoxVisible)

                {

                    UpdateCutInfoLabel(UpdateUIMode.ShowZoomBox);

                    this.pictureBox_zoom.Show();

                }

在“UpdateCutInfoLabel”函数最后加入下面代码：

if (this.pictureBox_zoom.Visible || (updateUIMode & UpdateUIMode.ShowZoomBox) != UpdateUIMode.None)

            {

                Point zoomLocation = new Point(MousePosition.X + 15, MousePosition.Y + 22);

                if (zoomLocation.Y + this.pictureBox_zoom.Height > this.Height)

                {

                    if (zoomLocation.X + this.pictureBox_zoom.Width > this.Width)

                    {

                        zoomLocation = new Point(MousePosition.X - this.pictureBox_zoom.Width - 10, MousePosition.Y - this.pictureBox_zoom.Height - 10);

                    }

                    else

                    {

                        zoomLocation = new Point(MousePosition.X + 15, MousePosition.Y - this.pictureBox_zoom.Height - 15);

                    }

                }

                else

                {

                    if (zoomLocation.X + this.pictureBox_zoom.Width > this.Width)

                    {

                        zoomLocation = new Point(MousePosition.X - this.pictureBox_zoom.Width - 15, MousePosition.Y);

                    }

                }

                this.pictureBox_zoom.Location = zoomLocation;

                if (!this.pictureBox_zoom.Visible)

                {

                    this.pictureBox_zoom.Show();

                }

            }

在“Form1_KeyUp”事件处理函数中加入下面代码：

为“pictureBox_zoom”加入“Paint”事件处理程序，代码例如以下：

        /// <summary>

        /// 放大镜组件重绘事件处理程序

        /// 实时显示鼠标指针位置放大后的图像

        /// </summary>

        /// <param name="sender"></param>

        /// <param name="e"></param>

        private void pictureBox_zoom_Paint(object sender, PaintEventArgs e)

        {

            Bitmap bmp_lbl = new Bitmap(e.ClipRectangle.Width, e.ClipRectangle.Height);

            int srcWidth = (int)(this.ZoomBoxWidth / 10);

            int srcHeight = (int)(this.ZoomBoxHeight / 10);

            Bitmap bmp = new Bitmap(srcWidth, srcHeight);

            Rectangle srcRect = new Rectangle(MousePosition.X - 5, MousePosition.Y - 4, srcWidth, srcHeight);

            if (!isCuting)

            {

                srcRect = new Rectangle(MousePosition.X - 6, MousePosition.Y - 5, srcWidth, srcHeight);

            }

            Graphics g = Graphics.FromImage(bmp);

            g.DrawImage(screenImage, 0, 0, srcRect, GraphicsUnit.Pixel);

            g.Dispose();

            //Zoom

            int x, y;

            for (int row = 0; row < bmp.Height; row++)

            {

                for (int col = 0; col < bmp.Width; col++)

                {

                    Color pc = bmp.GetPixel(col, row);

                    for (int h = 0; h < 10; h++)

                    {

                        for (int w = 0; w < 10; w++)

                        {

                            x = col * 10 + w;

                            y = row * 10 + h;

                            if (x < bmp_lbl.Width && y < bmp_lbl.Height)

                            {

                                bmp_lbl.SetPixel(x, y, pc);

                            }

                        }

                    }

                }

            }

            e.Graphics.DrawImage(bmp_lbl, 0, 0);

            int blockX = e.ClipRectangle.Width / 2;

            int blockY = e.ClipRectangle.Height / 2;

            SolidBrush brush = new SolidBrush(Color.FromArgb(10, 124, 202));

            Pen pen = new Pen(brush, 2.0F);

            e.Graphics.DrawLine(pen, new Point(0, blockY), new Point(e.ClipRectangle.Width, blockY));

            e.Graphics.DrawLine(pen, new Point(blockX, 0), new Point(blockX, e.ClipRectangle.Height));

            g.Dispose();

            bmp_lbl.Dispose();

        }

编译，执行，截图看看效果吧！

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