Vista - using UIAutmation to

Is it possible to retrieve the AutomationElement of a control that is
contained inside a VisualBrush? Or can controls that are rendered inside a
VisualBrush not participate in UIAutomation ?

Basically I have a ViewPort3D that contains a ModelVisual3D wich again has a
GeometryModel3D with a DiffuseMaterial that has Brush of Type VisualBrush.
This VisualBrush contains Controls such as a Button. I use UIAutomation to
get the Button like this: (no success)

PropertyCondition findWindow
= new PropertyCondition(AutomationElement.NameProperty, "MyWindowTitle");
AutomationElement window
= AutomationElement.RootElement.FindFirst(TreeScope.Descendants,
findWindow);
PropertyCondition findButton
= new PropertyCondition(AutomationElement.ControlTypeProperty,
ControlType.Button);
// unfortunately the following returns null allthough there actually is a
button (inside the VisualBrush)
AutomationElement button
= window.FindFirst(TreeScope.Descendants, findButton);
InvokePattern pattern = button.GetCurrentPattern(InvokePattern.Pattern) as
InvokePattern;
pattern.Invoke(); // click that button !

any hints ?

The basic goal behind all this is to enable Interactivity on a VisualBrush.
I sucessfully used RayMeshGeometry3DHitTestResult to get the
Texturecoordinates that where hit by the mouse. And I converted those to
real PositionCoordinates of the Grid that contains the Buttons inside the
VisualBrush. All I need to do now is simulate a mouseclick on the grid at
that position. I wanted to do that using UIAutomation.