WPF clipping even when no clipping is desired - how to turn it off?

Question

I need to float out some content out of the ListBox as specified in a DataTemplate for an ListBox.ItemTemplate. I am using Rende

Answer 1

I stumbled upon a solution to this problem by accident while working around it. If you change the ScrollViewer's HorizontalScrollMode and VerticalScrollMode to "Disabled" within the style template, it will stop clipping in each direction respectively.

Edit: May not work for WPF. I tested with a UWP app. The fields in question are:

ScrollViewer.HorizontalScrollMode="Disabled"

ScrollViewer.VerticalScrollMode="Disabled"

Answer 2

The ListBoxItem's are getting clipped by the ScrollViewer in the ListBox Template. To work around this I think you'll need to remove the ScrollViewer from the Template and if you need scrolling you can wrap the ListBox in a ScrollViewer

<ScrollViewer HorizontalScrollBarVisibility="Auto"
              VerticalScrollBarVisibility="Auto">
    <ListBox Margin="100,10,0,0">
        <ListBox.Template>
            <ControlTemplate TargetType="{x:Type ListBox}">
                <Border x:Name="Bd" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Background="{TemplateBinding Background}" Padding="1" SnapsToDevicePixels="true">
                    <ItemsPresenter SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"/>
                </Border>
                <ControlTemplate.Triggers>
                    <Trigger Property="IsEnabled" Value="false">
                        <Setter Property="Background" TargetName="Bd" Value="{DynamicResource {x:Static SystemColors.ControlBrushKey}}"/>
                    </Trigger>
                </ControlTemplate.Triggers>
            </ControlTemplate>
        </ListBox.Template>
        <ListBox.ItemTemplate>
            <DataTemplate>
                <Rectangle Fill="Red" Stroke="Green" StrokeThickness="4" Width="100" Height="50">
                    <Rectangle.RenderTransform>
                        <TranslateTransform X="-50" />
                    </Rectangle.RenderTransform>
                </Rectangle>
            </DataTemplate>
        </ListBox.ItemTemplate> 42
    </ListBox>
</ScrollViewer>

Update

The ScrollViewer in the Template will generate a ScrollContentPresenter which in turn has the following GetLayoutClip

protected override Geometry GetLayoutClip(Size layoutSlotSize)
{
    return new RectangleGeometry(new Rect(base.RenderSize));
}

This class is Sealed so you can't derive from it to override this method. You would have to implement your own ScrollContentPresenter (e.g MyScrollContentPresenter) and probably your own ScrollViewer that uses MyScrollContentPresenter as well to make this work (and if you return null in this method I think that some items below the bounds of the ListBox could become visible as well)