WPF 用Clip属性实现蒙板特效

上一篇，已简单介绍Clip属性的用法，这一篇用它来实现简单蒙板功能，很简单，直接上代码

<Window x:Class="擦除效果.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="537" Width="866" MouseMove="canvas_MouseMove" MouseDown="Window_MouseDown" MouseUp="Window_MouseUp">
    <Grid>


        <Rectangle Height="100" HorizontalAlignment="Left" Margin="164,92,0,0" Name="rectangle1" Stroke="Black" VerticalAlignment="Top" Width="200" Fill="Lime" />
        <Button Content="Button" Height="83" HorizontalAlignment="Left" Margin="526,109,0,0" Name="button1" VerticalAlignment="Top" Width="115" Click="button1_Click" />
        <Grid x:Name="grid"  Background="#88FFFFFF" ></Grid>
    </Grid>


    <Window.Background>
        <ImageBrush ImageSource="/擦除效果;component/Images/s01.jpg" />
    </Window.Background>
</Window>

后台：

    public partial class MainWindow : Window
    {
        private bool isDown = false;
        public MainWindow()
        {
            InitializeComponent();
            RectangleGeometry rg = new RectangleGeometry();
            rg.Rect = new Rect(0, 0, this.Width, this.Height);
            gridGeometry = Geometry.Combine(gridGeometry, rg, GeometryCombineMode.Union, null);
            grid.Clip = gridGeometry;
        }
        PathGeometry gridGeometry = new PathGeometry();
        private void canvas_MouseMove(object sender, MouseEventArgs e)
        {
            if (isDown)
            {
                EllipseGeometry rg = new EllipseGeometry();
                rg.Center = e.GetPosition(this);
                rg.RadiusX = 50;
                rg.RadiusY = 50;
                //排除几何图形
                gridGeometry = Geometry.Combine(gridGeometry, rg, GeometryCombineMode.Exclude, null);
                grid.Clip = gridGeometry;
            }
        }


        private void button1_Click(object sender, RoutedEventArgs e)
        {
            MessageBox.Show("OK!");
        }


        private void Window_MouseDown(object sender, MouseButtonEventArgs e)
        {
            isDown = true;
        }


        private void Window_MouseUp(object sender, MouseButtonEventArgs e)
        {
            isDown = false;
        }
    }

效果如下：

源码