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前言

做桌面截屏功能时需要放大镜，显示鼠标所在位置的放大图像，在wpf中使用Bursh的ViewBox属性可以实现图像放大，桌面的画面则需要截屏了，总的来说还是比较容易实现的。

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一、如何实现？

1、制作无边框窗口

推荐使用WindowChrome

<Window Background="{x:Null}" ResizeMode="NoResize"  WindowStyle="None">

WindowChrome放在Window 标签内

<WindowChrome.WindowChrome><WindowChrome GlassFrameThickness="-1"   CaptionHeight="0"   />
</WindowChrome.WindowChrome>

2、Viewbox放大

定义一个Ellipse 控件作为放大镜，Viewbox默认为相对单位，即范围时0-1，值越小放大比例越大

<Ellipse Stroke="LightBlue"><Ellipse.Fill><ImageBrush x:Name="ib" Viewbox="0,0,0.5,0.5" /></Ellipse.Fill>
</Ellipse>

3、截屏显示

（1）、截屏

参考《C# wpf 使用GDI+实现截屏》里的简单截屏即完成。获取的数据类型为Bitmap。

（2）、转BitmapSource

参考《C# wpf Bitmap转换成WriteableBitmap（BitmapSource）的方法》将Bitmap转换为转换成wpf对象。

（3）、显示

获取到BitmapSource给控件赋值即可。

//显示到界面
ib.ImageSource = wb;

4、定时截屏

显示桌面必然需要实时的画面，所以需要定时截屏。

//启动定时器，截屏
var dispatcherTimer = new DispatcherTimer() { Interval = TimeSpan.FromMilliseconds(33), };
dispatcherTimer.Tick += (s, e) =>
{//截屏并显示
};
dispatcherTimer.Start();

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二、完整代码

完整代码依赖System.Drawing，添加引用方法可以参考《C# wpf 使用GDI+实现截屏》。

MainWindow.xaml

<Window x:Class="WpfMagnifier.MainWindow"xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"xmlns:d="http://schemas.microsoft.com/expression/blend/2008"xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"xmlns:local="clr-namespace:WpfMagnifier"mc:Ignorable="d"Background="{x:Null}"ResizeMode="NoResize"WindowStyle="None"ShowInTaskbar="False"Topmost="True"Title="MainWindow" Height="200" Width="200" MouseLeftButtonDown="Window_MouseDown"><WindowChrome.WindowChrome><WindowChrome GlassFrameThickness="-1"   CaptionHeight="0"   /></WindowChrome.WindowChrome><Ellipse Stroke="LightBlue"><Ellipse.Fill><ImageBrush x:Name="ib" Viewbox="0,0,0.5,0.5" /></Ellipse.Fill></Ellipse>
</Window>

MainWindow.xaml.cs

using System;
using System.Windows;
using System.Windows.Input;
using System.Windows.Media.Imaging;
using System.Windows.Threading;
namespace WpfMagnifier
{/// <summary>/// Interaction logic for MainWindow.xaml/// </summary>public partial class MainWindow : Window{public MainWindow(){InitializeComponent();//启动定时器，截屏var dispatcherTimer = new DispatcherTimer() { Interval = TimeSpan.FromMilliseconds(33), };dispatcherTimer.Tick += (s, e) =>{//gdi+截屏，截取窗口左边的区域（可根据具体使用场景调整截屏位置）,使用PointToScreen消除dpi影响var leftTop = PointToScreen(new Point(-Width, 0));var rightBottom = PointToScreen(new Point(0, Height));var bm = Snapshot((int)leftTop.X, (int)leftTop.Y, (int)(rightBottom.X - leftTop.X), (int)(rightBottom.Y - leftTop.Y));var wb = BitmapToWriteableBitmap(bm);//显示到界面ib.ImageSource = wb;};dispatcherTimer.Start();}private void Window_MouseDown(object sender, MouseButtonEventArgs e){DragMove();}/// <summary>/// 截取一帧图片/// </summary>/// <param name="x">x坐标</param>/// <param name="y">y坐标</param>/// <param name="width">宽</param>/// <param name="height">高</param>/// <returns>截屏后的位图对象，需要调用Dispose手动释放资源。</returns>public static System.Drawing.Bitmap Snapshot(int x, int y, int width, int height){System.Drawing.Bitmap bitmap = new System.Drawing.Bitmap(width, height, System.Drawing.Imaging.PixelFormat.Format32bppArgb);using (System.Drawing.Graphics graphics = System.Drawing.Graphics.FromImage(bitmap)){graphics.CopyFromScreen(x, y, 0, 0, new System.Drawing.Size(width, height), System.Drawing.CopyPixelOperation.SourceCopy);}return bitmap;}//将Bitmap 转换成WriteableBitmap public static WriteableBitmap BitmapToWriteableBitmap(System.Drawing.Bitmap src){var wb = CreateCompatibleWriteableBitmap(src);System.Drawing.Imaging.PixelFormat format = src.PixelFormat;if (wb == null){wb = new WriteableBitmap(src.Width, src.Height, 0, 0, System.Windows.Media.PixelFormats.Bgra32, null);format = System.Drawing.Imaging.PixelFormat.Format32bppArgb;}BitmapCopyToWriteableBitmap(src, wb, new System.Drawing.Rectangle(0, 0, src.Width, src.Height), 0, 0, format);return wb;}//创建尺寸和格式与Bitmap兼容的WriteableBitmappublic static WriteableBitmap CreateCompatibleWriteableBitmap(System.Drawing.Bitmap src){System.Windows.Media.PixelFormat format;switch (src.PixelFormat){case System.Drawing.Imaging.PixelFormat.Format16bppRgb555:format = System.Windows.Media.PixelFormats.Bgr555;break;case System.Drawing.Imaging.PixelFormat.Format16bppRgb565:format = System.Windows.Media.PixelFormats.Bgr565;break;case System.Drawing.Imaging.PixelFormat.Format24bppRgb:format = System.Windows.Media.PixelFormats.Bgr24;break;case System.Drawing.Imaging.PixelFormat.Format32bppRgb:format = System.Windows.Media.PixelFormats.Bgr32;break;case System.Drawing.Imaging.PixelFormat.Format32bppPArgb:format = System.Windows.Media.PixelFormats.Pbgra32;break;case System.Drawing.Imaging.PixelFormat.Format32bppArgb:format = System.Windows.Media.PixelFormats.Bgra32;break;default:return null;}return new WriteableBitmap(src.Width, src.Height, 0, 0, format, null);}//将Bitmap数据写入WriteableBitmap中public static void BitmapCopyToWriteableBitmap(System.Drawing.Bitmap src, WriteableBitmap dst, System.Drawing.Rectangle srcRect, int destinationX, int destinationY, System.Drawing.Imaging.PixelFormat srcPixelFormat){var data = src.LockBits(new System.Drawing.Rectangle(new System.Drawing.Point(0, 0), src.Size), System.Drawing.Imaging.ImageLockMode.ReadOnly, srcPixelFormat);dst.WritePixels(new Int32Rect(srcRect.X, srcRect.Y, srcRect.Width, srcRect.Height), data.Scan0, data.Height * data.Stride, data.Stride, destinationX, destinationY);src.UnlockBits(data);}}
}

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三、效果预览

显示的是窗口（放大镜）左边的画面

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总结

以上就是今天要讲的内容，本文仅仅简单介绍了实现桌面放大镜的方法，关键在于使用Viewbox，截屏的功能因为有现成的所以比较简单，当然本文的方法是简单实现，其实还是可以优化的，尤其是截屏是可以复用Bitmap对象的。总的来说，wpf实现桌面放大镜还是比较容易的，而且效果也很不错。