WPF transparency changing, when elements are bound

Question

A VisualBrush is used to fill a Rectangle in a WPF window.

It fills by binding its Visual property to a non-transparent element in the window.

How can the Rectangle fill be made transparent, so that what is behind the window is visible through it, without making other elements transparent as well?

Roughly following the how-to on creating reflection effects on MSDN, and looking at SO questions about making specific elements opaque with a transparent window here and here, I've come up with the following in XAML. However, I cannot seem to make the Rectangle transparent, without also making the TextBlock it is bound to also transparent.

<!-- Window.AllowsTransparency is set to true,
    so WindowStyle must also be set to None.
    Background is set to Transparent so child
    elements have capability to be transparent
    to what is behind the window. -->

<Window x:Class="XAMLViewTests.TransparentTestWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="TransparentTestWindow"
        AllowsTransparency="True"
        WindowStyle="None" Background="Transparent">
    <StackPanel Orientation="Vertical">

        <!-- Two elements: TextBlock and Rectangle -->

        <TextBlock x:Name="textBlock" Background="White">This is some text.</TextBlock>

        <Rectangle Height="{Binding ElementName=textBlock, Path=ActualHeight}">
            <!-- Fill rectangle with a Visual element bound to TextBlock,
            so it shows exactly the same as TextBlock. Transforms, effects, etc
            can now be performed on the Visual. -->

            <Rectangle.Fill>
                <VisualBrush Stretch="None" Visual="{Binding ElementName=textBlock}">
                </VisualBrush>
            </Rectangle.Fill>
        </Rectangle>
    </StackPanel>
</Window>

What do you want to achieve here? If you set the Fill to an element, it will display that element as background. If you want a transparent rectangle, why dont you simply set it to transparent? — Domysee, May 12 '15 at 17:58
Rectangle background needs to be transparent, but what is inside needs to be opaque or at least only partially transparent. — Aaron Thomas, May 12 '15 at 18:03
What exactly should be transparent inside the rectangle? The background of the textblock? — Domysee, May 12 '15 at 18:05

score 0 · Accepted Answer · answered May 12 '15 at 18:20

0

You cannot set the textblock as background and make its background transparent just for the binding.

What you can do though is setting another textblock as background and bind all relevant values to the original textblock:

<Rectangle.Fill>
    <VisualBrush Stretch="None">
        <VisualBrush.Visual>
            <TextBlock Background="Transparent" 
                        Text="{Binding ElementName=textBlock, Path=Text}" 
                        Width="{Binding ElementName=textBlock, Path=ActualWidth}" />
        </VisualBrush.Visual>
    </VisualBrush>
</Rectangle.Fill>

answered May 12 '15 at 18:20

Domysee

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Using Transparent element as a Brush? This won't render anything, imho. – Liero May 12 '15 at 20:04
The element is not transparent, only the background – Domysee May 12 '15 at 21:08

WPF transparency changing, when elements are bound

1 Answers1