d:DataContext="{d:DesignInstance Contents:OverlayDesignerViewModel}">

<Contents:DrawingCanvasCustom
                Background="#00000000"
                Name="_drawingCanvas"
                Width="650"
                Height="450">

        <i:Interaction.Triggers>
            <i:EventTrigger EventName="CanvasMouseDown">
                <i:InvokeCommandAction Command="{Binding Path=DataContext.CanvasMouseDownCommand, RelativeSource={RelativeSource AncestorType={x:Type Window}}}"
                                   CommandParameter="{Binding ElementName=CanvasOverlayView}"/>
            </i:EventTrigger>