C#开发实例-订制屏幕截图工具（四）基本截图功能实现代码

实现原理

基本截图的功能主要靠响应主窗体的鼠标按下、鼠标移动、鼠标抬起几个事件的功能来实现的。截取的图片区域使用“Label”组件来显示，需要重新实现“Label”组件的“Paint”方法。

左键单击开始截图，右键单击取消截图，双击鼠标左键完成截图，将截取的图片保存到Windows剪贴板中。

添加“Label”组件

工具箱》公共组件》双击“Label”组件，修改组件属性：

Name=lbl_CutImage，

AutoSize=False，

BackColor=Transparent，

Text = “”

“Form1_Load”事件添加代码：

this.lbl_CutImage.Hide();

定义截图功能依赖的基本变量

        #region 截图基本变量
        /// <summary>
        /// 用于判断是否已经开始截图，控制信息框是否显示。
        /// </summary>
        private bool isCuting;
        /// <summary>
        /// 鼠标按下的点
        /// </summary>
        private Point beginPoint;
        /// <summary>
        /// 最终确定的绘图基点
        /// </summary>
        private Point endPoint;
        /// <summary>
        /// 用于记录截图显示区域的大小（包括调整块的区域，调整区域边框宽度2px）
        /// </summary>
        private Rectangle cutImageRect = new Rectangle(0, 0, 5, 5);
        #endregion

定义枚举类型：更新UI的模式

        /// <summary>
        /// 更新UI的模式，用于标记哪些需要显示，哪些需要隐藏；
        /// </summary>
        [FlagsAttribute]
        public enum UpdateUIMode : uint
        {
            //值得注意的是，如果要使用组合值，那么就不能用连接的数字表示，必须是几何级增长！
            None = 0,
            ShowTextPro = 1,
            ShowPenStyle = 2,
            ShowToolBox = 4,
            ShowInfoBox = 8,
            ShowZoomBox = 16,
            ShowCutImage = 32,
            HideTextPro = 64,
            HidePenStyle = 128,
            HideToolBox = 256,
            HideInfoBox = 512
        }

添加方法：计算并保存截图的区域框的大小

        /// <summary>
        /// 计算并保存截图的区域框的大小
        /// </summary>
        private void SaveCutImageSize(Point beginPoint, Point endPoint)
        {
            // 保存最终的绘图基点，用于截取选中的区域
            this.endPoint = beginPoint;

            // 计算截取图片的大小
            int imgWidth = Math.Abs(endPoint.X - beginPoint.X) + 1;
            int imgHeight = Math.Abs(endPoint.Y - beginPoint.Y) + 1;
            int lblWidth = imgWidth + 4;
            int lblHeight = imgHeight + 4;

            // 设置截图区域的位置和大小
            this.cutImageRect = new Rectangle(beginPoint.X - 2, beginPoint.Y - 2, lblWidth, lblHeight);
        }

添加方法：执行截图,将选定区域的图片保存到剪贴板

        /// <summary>
        /// 执行截图,将选定区域的图片保存到剪贴板
        /// </summary>
        /// <param name="saveToDisk">
        /// 是否将图片保存到磁盘
        /// </param>
        private void ExecCutImage(bool saveToDisk, bool uploadImage) //bool saveToDisk = false, bool uploadImage = false
        {
            // 如果图片获取区域不可见,则退出保存图片过程
            if (!this.lbl_CutImage.Visible) { return; }
            Rectangle srcRect = new Rectangle();
            srcRect.X = this.lbl_CutImage.Location.X + 2;
            srcRect.Y = this.lbl_CutImage.Location.Y + 2;
            srcRect.Width = this.lbl_CutImage.Width - 4;
            srcRect.Height = this.lbl_CutImage.Height - 4;
            Rectangle destRect = new Rectangle(0, 0, srcRect.Width, srcRect.Height);
            Bitmap bmp = new Bitmap(srcRect.Width, srcRect.Height);
            Graphics g = Graphics.FromImage(bmp);
            g.DrawImage(this.screenImage, destRect, srcRect, GraphicsUnit.Pixel);

            Clipboard.SetImage(bmp);

            ExitCutImage(true);
        }

添加方法：退出截图过程

       /// <summary>
        /// 退出截图过程
        /// </summary>
        private void ExitCutImage(bool hideWindow) //  = true
        {
            this.lbl_CutImage.Visible = false;
            this.isCuting = false;

            if (hideWindow)
            {
                this.screenImage.Dispose();
                this.Hide();
            }
        }

主窗口鼠标按下事件处理程序

        /// <summary>
        /// 截图窗口鼠标按下事件处理程序
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void Form1_MouseDown(object sender, MouseEventArgs e)
        {
            // 左键单击事件
            if (e.Button == MouseButtons.Left && e.Clicks == 1)
            {
                if (!this.lbl_CutImage.Visible)
                {
                    this.isCuting = true;
                    this.beginPoint = e.Location;
                    this.endPoint = e.Location;
                    SaveCutImageSize(e.Location, e.Location);

                    UpdateCutInfoLabel(UpdateUIMode.ShowCutImage | UpdateUIMode.ShowInfoBox);
                }
            }
            // 左键双击事件
            if (e.Button == MouseButtons.Left && e.Clicks == 2)
            {
                if (this.lbl_CutImage.Visible)
                {
                    ExecCutImage(false, false);
                }

            }
            // 右键单击事件
            if (e.Button == MouseButtons.Right)
            {
                ExitCutImage(!this.lbl_CutImage.Visible);
            }

        }

主窗口鼠标移动事件处理程序

        /// <summary>
        /// 截图窗口鼠标移动事件处理程序
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void Form1_MouseMove(object sender, MouseEventArgs e)
        {
            // 如果截取区域不可见,则退出处理过程
            if (!this.lbl_CutImage.Visible)
            {
                UpdateCutInfoLabel(UpdateUIMode.None);
                return;
            }

            Point pntBgn = this.beginPoint;
            Point pntEnd = e.Location;

            // 如果是反向拖动，重新设置起始点
            if (e.Location.X < this.beginPoint.X && e.Location.Y < this.beginPoint.Y)
            {
                pntBgn = e.Location;
                pntEnd = this.beginPoint;
            }
            else
            {
                if (e.Location.X < this.beginPoint.X)
                {
                    pntBgn = new Point(e.Location.X, this.beginPoint.Y);
                    pntEnd = new Point(this.beginPoint.X, e.Location.Y);
                }
                else
                {
                    if (e.Location.Y < this.beginPoint.Y)
                    {
                        pntBgn = new Point(this.beginPoint.X, e.Location.Y);
                        pntEnd = new Point(e.Location.X, this.beginPoint.Y);
                    }
                }
            }

            if (this.isCuting)
            {
                SaveCutImageSize(pntBgn, pntEnd);
            }

            UpdateCutInfoLabel(UpdateUIMode.None);
        }

主窗口鼠标抬起事件处理程序

        /// <summary>
        /// 截图窗口鼠标抬起事件处理程序
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void Form1_MouseUp(object sender, MouseEventArgs e)
        {
            if (e.Button == MouseButtons.Left)
            {
                if (this.isCuting)
                {
                    this.isCuting = false;

                    UpdateCutInfoLabel(UpdateUIMode.None);
                }
            }
        }

截取区域图片绘制

        /// <summary>
        /// 截取区域图片的绘制事件处理程序
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void lbl_CutImage_Paint(object sender, PaintEventArgs e)
        {
            int imgWidth = this.lbl_CutImage.Width - 4;
            int imgHeight = this.lbl_CutImage.Height - 4;
            if (imgWidth < 1) { imgWidth = 1; }
            if (imgHeight < 1) { imgHeight = 1; }

            // 创建缓存图像，先将要绘制的内容全部绘制到缓存中，最后再一次性绘制到 Label 上，
            // 这样可以提高性能，并且可以防止屏幕闪烁的问题
            Bitmap bmp_lbl = new Bitmap(this.lbl_CutImage.Width, this.lbl_CutImage.Height);
            Graphics g = Graphics.FromImage(bmp_lbl);

            // 将要截取的部分绘制到缓存
            Rectangle destRect = new Rectangle(2, 2, imgWidth, imgHeight);
            Point srcPoint = this.lbl_CutImage.Location;
            srcPoint.Offset(2, 2);
            Rectangle srcRect = new Rectangle(srcPoint, new System.Drawing.Size(imgWidth, imgHeight));
            g.DrawImage(this.screenImage, destRect, srcRect, GraphicsUnit.Pixel);

            SolidBrush brush = new SolidBrush(Color.FromArgb(10, 124, 202));
            Pen pen = new Pen(brush, 1.0F);

            //以下部分（边框和调整块）的绘制放在（编辑内容）的后面，是解决绘制编辑内容会覆盖（边框和调整块）的问题

            // 绘制边框外的区域，解决会被编辑内容覆盖的问题
            // 上边
            destRect = new Rectangle(0, 0, this.lbl_CutImage.Width, 2);
            srcPoint = this.lbl_CutImage.Location;
            //srcPoint.Offset(2, 2);
            srcRect = new Rectangle(srcPoint, new System.Drawing.Size(this.lbl_CutImage.Width, 2));
            g.DrawImage(this.BackgroundImage, destRect, srcRect, GraphicsUnit.Pixel);

            // 下边
            destRect = new Rectangle(0, this.lbl_CutImage.Height - 2, this.lbl_CutImage.Width, 2);
            srcPoint = this.lbl_CutImage.Location;
            srcPoint.Offset(0, this.lbl_CutImage.Height - 2);
            srcRect = new Rectangle(srcPoint, new System.Drawing.Size(this.lbl_CutImage.Width, 2));
            g.DrawImage(this.BackgroundImage, destRect, srcRect, GraphicsUnit.Pixel);

            // 左边
            destRect = new Rectangle(0, 2, 2, this.lbl_CutImage.Height - 4);
            srcPoint = this.lbl_CutImage.Location;
            srcPoint.Offset(0, 2);
            srcRect = new Rectangle(srcPoint, new System.Drawing.Size(2, this.lbl_CutImage.Height - 4));
            g.DrawImage(this.BackgroundImage, destRect, srcRect, GraphicsUnit.Pixel);

            // 右边
            destRect = new Rectangle(this.lbl_CutImage.Width - 2, 2, 2, this.lbl_CutImage.Height - 4);
            srcPoint = this.lbl_CutImage.Location;
            srcPoint.Offset(this.lbl_CutImage.Width - 2, 2);
            srcRect = new Rectangle(srcPoint, new System.Drawing.Size(2, this.lbl_CutImage.Height - 4));
            g.DrawImage(this.BackgroundImage, destRect, srcRect, GraphicsUnit.Pixel);

            // 绘制边框
            g.DrawLine(pen, 2, 2, this.lbl_CutImage.Width - 3, 2);
            g.DrawLine(pen, 2, 2, 2, this.lbl_CutImage.Height - 3);
            g.DrawLine(pen, this.lbl_CutImage.Width - 3, 2, this.lbl_CutImage.Width - 3, this.lbl_CutImage.Height - 3);
            g.DrawLine(pen, 2, this.lbl_CutImage.Height - 3, this.lbl_CutImage.Width - 3, this.lbl_CutImage.Height - 3);

            // 绘制四个角的调整块
            g.FillRectangle(brush, 0, 0, 4, 5);
            g.FillRectangle(brush, this.lbl_CutImage.Width - 4, 0, 4, 5);
            g.FillRectangle(brush, 0, this.lbl_CutImage.Height - 5, 4, 5);
            g.FillRectangle(brush, this.lbl_CutImage.Width - 4, this.lbl_CutImage.Height - 5, 4, 5);

            // 绘制中间的四个调整块
            int blockX = this.lbl_CutImage.Width / 2 - 2;
            int blockY = this.lbl_CutImage.Height / 2 - 2;
            g.FillRectangle(brush, blockX, 0, 4, 5);
            g.FillRectangle(brush, 0, blockY, 4, 5);
            g.FillRectangle(brush, blockX, this.lbl_CutImage.Height - 5, 4, 5);
            g.FillRectangle(brush, this.lbl_CutImage.Width - 4, blockY, 4, 5);

            // 绘制到 Label 上
            e.Graphics.DrawImage(bmp_lbl, 0, 0);
            bmp_lbl.Dispose();
        }

双击鼠标左键完成截图功能

        /// <summary>
        /// 截取区域图片的鼠标按下事件处理程序
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void lbl_CutImage_MouseDown(object sender, MouseEventArgs e)
        {
            // 左键双击事件
            if (e.Button == MouseButtons.Left && e.Clicks == 2)
            {
                if (this.lbl_CutImage.Visible)
                {
                    ExecCutImage(false, false);
                }
            }
        }

注意：代码都贴完了，别忘了为窗体或组件绑定事件处理程序；

例如：截取区域图片的鼠标按下事件处理程序“lbl_CutImage_MouseDown”，就是“lbl_CutImage”组件的“MouseDown”事件的处理程序，绑定方法参考下图：

到此，基本截图的功能实现已经实现，赶快去截取一张图片，粘贴到QQ的聊天窗口看看吧。

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