<Window x:Class="Drawing.OpacityMask"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="OpacityMask" Height="313.6" Width="317.6"
    >
  <Window.Background>
    <ImageBrush ImageSource="grandpiano.jpg"></ImageBrush>
  </Window.Background>
    <Grid Margin="10,50">
      <Button Background="Purple" FontSize="14" FontWeight="Bold">
        <Button.OpacityMask>
          <LinearGradientBrush StartPoint="0,0" EndPoint="1,0">
            <GradientStop Offset="0" Color="Black"></GradientStop>
            <GradientStop Offset="1" Color="Transparent"></GradientStop>
          </LinearGradientBrush>
        </Button.OpacityMask>
        <Button.Content>A Partially Transparent Button</Button.Content>
      </Button>
    </Grid>
</Window>
