WPF C#截图功能 仿qq截图

先上效果图

源码下载地址：http://download.youkuaiyun.com/detail/candyvoice/9788099

描述：启动程序，点击窗口button，开始截图，鼠标左键按下拖动，选中任意区域，拖动过程中，左上角实时显示选中区域大小，拖动结束，鼠标左键抬起，出现右下角保存、取消、ok三个button。右键点击，取消当前选中，可以继续拖动鼠标左键进行截图。双击右键，退出截图功能。按键盘ESC键，可退出截图。

原理：说的通俗一些，就是在原有的界面上盖上一层Canvas，就是画布，然后在这个画布上画矩形，也就是填充矩形的四周，空出来的地方就变成矩形了，如下图。边框线，线上可拖动的小方框、顶角可拖动的小圆球，都是自定义的样式，可在代码的generic.xaml文件中看到具体的设计。

参考资料：http://www.cnblogs.com/zhouyinhui/archive/2010/08/20/1804762.html

这个楼主原理的细节方面已经说的很详细，大家可以仔细看看。

根据上述楼主的代码，主要修改了以下两个类。

MaskCanvas.cs就是操作画布的类，MaskWindow.cs就是截图窗口的类。左上角大小显示框，是一label；右下角的三个按钮是一个自定义的toolbar。

1 MaskCanvas.cs

using System;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Input;
using System.Windows.Media;

namespace RisCaptureLib
{

    internal class MaskCanvas : Canvas
    {
        public delegate void FrameDrawEventHander(Rect rect);
        public event FrameDrawEventHander OnMove;
        public MaskCanvas()
        {
            Loaded += OnLoaded;
        }

        private void OnLoaded(object sender, RoutedEventArgs e)
        {
            //make the render effect same as SnapsToDevicePixels
            //"SnapsToDevicePixels = true;" doesn't work on "OnRender"
            //however, this maybe make some offset form the render target's origin location
            //SetValue(RenderOptions.EdgeModeProperty, EdgeMode.Aliased);

            //ini this
            Cursor = BitmapCursor.CreateCrossCursor();
            Background = Brushes.Transparent;



            //ini mask rect
            maskRectLeft.Fill = maskRectRight.Fill = maskRectTop.Fill = maskRectBottom.Fill = Config.MaskWindowBackground;

            //these propeties(x, y...) will not changed
            SetLeft(maskRectLeft, 0);
            SetTop(maskRectLeft, 0);
            SetRight(maskRectRight, 0);
            SetTop(maskRectRight, 0);
            SetTop(maskRectTop, 0);
            SetBottom(maskRectBottom, 0);
            maskRectLeft.Height = ActualHeight;


            Children.Add(maskRectLeft);
            Children.Add(maskRectRight);
            Children.Add(maskRectTop);
            Children.Add(maskRectBottom);

            //ini selection border
            selectionBorder.Stroke = Config.SelectionBorderBrush;
            selectionBorder.StrokeThickness = Config.SelectionBorderThickness.Left;
            Children.Add(selectionBorder);

            //ini indicator
            indicator = new IndicatorObject(this);
            Children.Add(indicator);

            CompositionTarget.Rendering += OnCompositionTargetRendering;
        }

        private void UpdateSelectionBorderLayout()
        {
            if (!selectionRegion.IsEmpty)
            {
                SetLeft(selectionBorder, selectionRegion.Left);
                SetTop(selectionBorder, selectionRegion.Top);
                selectionBorder.Width = selectionRegion.Width;
                selectionBorder.Height = selectionRegion.Height;
            }
        }

        private void UpdateMaskRectanglesLayout()
        {
            var actualHeight = ActualHeight;
            var actualWidth = ActualWidth;

            if (selectionRegion.IsEmpty)
            {
                SetLeft(maskRectLeft, 0);
                SetTop(maskRectLeft, 0);
                maskRectLeft.Width = actualWidth;
                maskRectLeft.Height = actualHeight;

                maskRectRight.Width = maskRectRight.Height = maskRectTop.Width = maskRectTop.Height = maskRectBottom.Width = maskRectBottom.Height = 0;
            }
            else
            {
                var temp = selectionRegion.Left;
                if (maskRectLeft.Width != temp)
                {
                    maskRectLeft.Width = temp < 0 ? 0 : temp; //Math.Max(0, selectionRegion.Left);
                }

                temp = ActualWidth - selectionRegion.Right;
                if (maskRectRight.Width != temp)
                {
                    maskRectRight.Width = temp < 0 ? 0 : temp; //Math.Max(0, ActualWidth - selectionRegion.Right);
                }

                if (maskRectRight.Height != actualHeight)
                {
                    maskRectRight.Height = actualH