Restrict the area that a WPF shader effect gets applied to

Question

How can I restrict the area that a WPF shader effect gets applied to, in a similar manner to the way the obsolete BitmapEffectInput.AreaToApplyEffect used to work for BitmapEffects? Is there an equivalent property for shader effects, or do I have to add it myself within each and every shader effect that I'm writing?

Answer 1

Draw a layout (Grid, Canvas etc.), so that one or more cells contain the restricted area. Then draw a Rectangle or Border control on that particular area to get the desired effect you are looking for. Remember to add the Rectangle first, or play with ZIndex as I show below so that your code does not hide any controls.

<Grid>
    <Grid.RowDefinitions>
        <RowDefinition/>
        <RowDefinition/>
    </Grid.RowDefinitions>
    <Grid.ColumnDefinitions>
        <ColumnDefinition/>
        <ColumnDefinition/>
    </Grid.ColumnDefinitions>
    <Rectangle Grid.Column="0" Grid.Row="1" Panel.ZIndex="0" >
        <Rectangle.Style>
            <Style TargetType="{x:Type Rectangle}">
                <Setter Property="Fill" Value="Blue"/>
            </Style>
        </Rectangle.Style>
    </Rectangle >
    <TextBox Grid.Column="0" Grid.Row="1" Height="25" Margin="10" Text="Test 123" Panel.ZIndex="1" />
</Grid>