' Determine if a geometry within the visual was hit.
Public Shared Sub HitTestGeometryInVisual(ByVal visual As Visual, ByVal pt As Point)
    ' Retrieve the group of drawings for the visual.
    Dim drawingGroup As DrawingGroup = VisualTreeHelper.GetDrawing(visual)
    EnumDrawingGroup(drawingGroup, pt)
End Sub

' Enumerate the drawings in the DrawingGroup.
Public Shared Sub EnumDrawingGroup(ByVal drawingGroup As DrawingGroup, ByVal pt As Point)
    Dim drawingCollection As DrawingCollection = drawingGroup.Children

    ' Enumerate the drawings in the DrawingCollection.
    For Each drawing As Drawing In drawingCollection
        ' If the drawing is a DrawingGroup, call the function recursively.
        If drawing.GetType() Is GetType(DrawingGroup) Then
            EnumDrawingGroup(CType(drawing, DrawingGroup), pt)
        ElseIf drawing.GetType() Is GetType(GeometryDrawing) Then
            ' Determine whether the hit test point falls within the geometry.
            If (CType(drawing, GeometryDrawing)).Geometry.FillContains(pt) Then
                ' Perform action based on hit test on geometry.
            End If
        End If

    Next drawing
End Sub