WPF InkCanvas draw even on space beyond bounds of Clip. Override Hit Test

Question

I am using InkCanvas.Clip property to clip my InkCanvas to the shape I need (I am using PathGeometry for that). I can only start drawing in this area, but I want to be able to start drawing outside of it. Of course, stoke parts beyond this area would not be displayed. How can I do that? I thought about overriding HitTestCore of InkCanvas, perhaps by default HitTest fails outside of my allowed drawing area

Answer 1

Maybe OpacityMask can achieve what you want:

1. Stroke to be clipped outside
2. To start drawing outside and come inside.

---

<Grid Background="LightSalmon">
    <InkCanvas Background="LightBlue">
        <InkCanvas.OpacityMask>
            <DrawingBrush>
                <DrawingBrush.Drawing>
                    <GeometryDrawing>
                        <GeometryDrawing.Brush>
                            <SolidColorBrush Color="Black"/>
                        </GeometryDrawing.Brush>
                        <GeometryDrawing.Geometry>
                            <PathGeometry>
                                <PathGeometry.Figures>
                                    <PathFigure StartPoint="0,0">
                                        <PathFigure.Segments>
                                            <PolyLineSegment Points="100,0 100,100 0,100 0,0"/>
                                            <PolyLineSegment Points="100,0 100,100 0,100 0,0"/>
                                            <PolyLineSegment Points="30,30 70,30 70,70 30,70 30,30"/>
                                        </PathFigure.Segments>
                                    </PathFigure>
                                </PathGeometry.Figures>
                            </PathGeometry>
                        </GeometryDrawing.Geometry>
                    </GeometryDrawing>
                </DrawingBrush.Drawing>
            </DrawingBrush>
        </InkCanvas.OpacityMask>
    </InkCanvas>
</Grid>

Appended:

To avoid the shifting as @SaintMSent mentioned, we should enable the ClipToBounds property of the InkCanvas's AdornerDecorator:

<InkCanvas x:Name="MyInkCanvas" Background="LightBlue" Loaded="MyInkCanvas_OnLoaded">
    ......
</InkCanvas>

Code-behind:

private void MyInkCanvas_OnLoaded(object sender, RoutedEventArgs e)
{
    var adornerDecorator = VisualTreeHelper.GetChild(MyInkCanvas, 0) as AdornerDecorator;
    if (adornerDecorator != null)
    {
        adornerDecorator.ClipToBounds = true;
    }
}