BitmapCacheBrush 和 VisualBrush 之间的区别（WPF4）

“BitmapCacheBrush总是从一个目标元素的缓存或者通过BitmapCache属性定义的缓存来渲染并且BitmapCacheBrush类忽略以下位于根Visual的属性：VisualOffset，VisualTransform，VisualClip，VisualEffect，VisualOpacity，VisualOpacity。这种行为有别于VisualBrush类。”

－－http://social.msdn.microsoft.com/Forums/zh-CN/wpfzhchs/thread/96a254b8-ab18-4096-9c9e-255822decd2f

测试代码（部分取自MSDN）

<Window
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="Window1"  
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
        Height="300" Width="300" >
    <Window.Resources>
        <RichTextBox x:Key="cachedRichTextBox"  >
          <RichTextBox.CacheMode>
                <BitmapCache EnableClearType="True" RenderAtScale="1" SnapsToDevicePixels="True" />
            </RichTextBox.CacheMode>
            <FlowDocument>
              <Paragraph>
                <Run FontSize="16" Text="0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ" />
              </Paragraph>
            </FlowDocument>
        </RichTextBox>
        <BitmapCacheBrush x:Key="cachedRichTextBoxBrush" Target="{StaticResource cachedRichTextBox}">
           <BitmapCacheBrush.BitmapCache>
                <BitmapCache EnableClearType="False" RenderAtScale="0.4" SnapsToDevicePixels="False" />
            </BitmapCacheBrush.BitmapCache>
        </BitmapCacheBrush>        
        
        <BitmapCacheBrush x:Key="cachedr1" Target="{Binding ElementName=r1}">
           <BitmapCacheBrush.BitmapCache>
                <BitmapCache EnableClearType="False" RenderAtScale="0.4" SnapsToDevicePixels="False" />
            </BitmapCacheBrush.BitmapCache>
        </BitmapCacheBrush>       
        
        <VisualBrush x:Key="visualr1" Visual="{Binding ElementName=r1}"></VisualBrush>
    </Window.Resources>
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="*" />
            <RowDefinition Height="*" />
            <RowDefinition Height="*" />
            <RowDefinition Height="*" />
            <RowDefinition Height="*" />
        </Grid.RowDefinitions>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="*" />
            <ColumnDefinition Width="*" />
            <ColumnDefinition Width="*" />
            <ColumnDefinition Width="*" />
            <ColumnDefinition Width="*" />
        </Grid.ColumnDefinitions>
        <Button Background="{StaticResource cachedRichTextBoxBrush}" Content="Button" Name="button1" FontWeight="Bold" />
        <Button Background="{StaticResource cachedRichTextBoxBrush}" Content="Button" Name="button2" Grid.Column="1" FontWeight="Bold" />
        <Button Background="{StaticResource cachedr1}" Content="Button" Name="button3" Grid.Column="2" FontWeight="Bold" />
        <Button Background="{StaticResource cachedr1}" Content="Button" Name="button4" Grid.Column="3" FontWeight="Bold" />
        <Button Background="{StaticResource cachedRichTextBoxBrush}" Content="Button" Name="button5" Grid.Column="4" FontWeight="Bold" />
        <Button Background="{StaticResource cachedRichTextBoxBrush}" Content="Button" Name="button6" Grid.Row="1" FontWeight="Bold" />
        <Button Background="{StaticResource cachedr1}" Content="Button" Grid.Column="1" Name="button7" Grid.Row="1" FontWeight="Bold" />
        <Button Background="{StaticResource cachedr1}" Content="Button" Grid.Column="2" Name="button8" Grid.Row="1" FontWeight="Bold" />
        <Button Background="{StaticResource cachedRichTextBoxBrush}" Content="Button" Grid.Column="3" Name="button9" Grid.Row="1" FontWeight="Bold" />
        <Button Background="{StaticResource cachedRichTextBoxBrush}" Content="Button" Grid.Column="4" Name="button10" Grid.Row="1" FontWeight="Bold" />
        <Button Background="{StaticResource cachedr1}" Content="Button" Name="button11" Grid.Row="2" FontWeight="Bold" />
        <Button Background="{StaticResource cachedr1}" Content="Button" Grid.Column="1" Name="button12" Grid.Row="2" FontWeight="Bold" />
        <Button Background="{StaticResource cachedRichTextBoxBrush}" Content="Button" Grid.Column="2" Name="button13" Grid.Row="2" FontWeight="Bold" />
        <Button Background="{StaticResource cachedRichTextBoxBrush}" Content="Button" Grid.Column="3" Name="button14" Grid.Row="2" FontWeight="Bold" />
        <Button Background="{StaticResource visualr1}" Content="Button" Grid.Column="4" Name="button15" Grid.Row="2" FontWeight="Bold" />
        <Button Background="{StaticResource visualr1}" Content="Button" Name="button16" Grid.Row="3" FontWeight="Bold" />
        <Button Background="{StaticResource cachedRichTextBoxBrush}" Content="Button" Grid.Column="1" Name="button17" Grid.Row="3" FontWeight="Bold" />
        <Button Background="{StaticResource cachedRichTextBoxBrush}" Content="Button" Grid.Column="2" Name="button18" Grid.Row="3" FontWeight="Bold" />
        <Button Background="{StaticResource visualr1}" Content="Button" Grid.Column="3" Name="button19" Grid.Row="3" FontWeight="Bold" />
        <Button Background="{StaticResource visualr1}" Content="Button" Grid.Column="4" Name="button20" Grid.Row="3" FontWeight="Bold" />
        <Button Background="{StaticResource cachedRichTextBoxBrush}" Content="Button" Name="button21" Grid.Row="4" FontWeight="Bold" />
        <Button Background="{StaticResource cachedRichTextBoxBrush}" Content="Button" Grid.Column="1" Name="button22" Grid.Row="4" FontWeight="Bold" />
        <Button Background="{StaticResource visualr1}" Content="Button" Grid.Column="2" Name="button23" Grid.Row="4" FontWeight="Bold" />
        <Button Background="{StaticResource visualr1}" Content="Button" Grid.Column="3" Name="button24" Grid.Row="4" FontWeight="Bold" />
        <Button Background="{StaticResource cachedRichTextBoxBrush}" Content="Button" Grid.Column="4" Name="button25" Grid.Row="4" FontWeight="Bold" />
        <RichTextBox Name="r1">
            <RichTextBox.CacheMode>
                <BitmapCache EnableClearType="True" RenderAtScale="1" SnapsToDevicePixels="True" />
            </RichTextBox.CacheMode>
            <FlowDocument>
              <Paragraph>
                <Run Foreground="Red" FontSize="16" Text="0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ" />
              </Paragraph>
            </FlowDocument>
        </RichTextBox>
    </Grid>
</Window>

效果图：