MouseCameraControllerEventsSourceElementName Property

public string EventsSourceElementName { get; set; }

Property Value

Note that if EventsSourceElement property is set to Viewport3D (manually or automatically) the mouse events occur only on the area of Viewport3D that actually shows a content. So mouse events do not happen on the empty area of the Viewport3D. To enable mouse events on the whole area of Viewport3D, add a Grid or Border as a parent of a Viewport3D, set its Background to any Brush - for example White or Transparent and than set the EventsSourceElement or EventsSourceElementName to the added control.

Reference