xna.Input.Mouse.GetState().X, 
xna.Input.Mouse.GetState().Y, 

 // Perform picking if in edit mode and the mouse has been pressed while the window has focus
if (inEditMode && hasMouseFocus &&
    mouseState.RightButton == xna.Input.ButtonState.Pressed &&
    _cachedMouseState.RightButton == xna.Input.ButtonState.Released &&
    Device != null)
{
    CameraEntity activeCamera = update.ActiveCamera;

    xna.Vector3 cameraPos = activeCamera.World.Translation;
    xna.Vector3 mousePos = Device.Viewport.Unproject(new xna.Vector3(xna.Input.Mouse.GetState().X, xna.Input.Mouse.GetState().Y, 1),
    activeCamera.ProjectionMatrix, activeCamera.ViewMatrix, xna.Matrix.Identity);

    xna.Ray r = new xna.Ray(
          cameraPos,
          xna.Vector3.Normalize(mousePos - cameraPos)); // Xna is peculiar and rays need normalized directions for bounding spheres

    // Picking has trouble with the following types
    Type[] typesNotToPick = new Type[] { typeof(SkyEntity), typeof(TerrainEntity), typeof(HeightFieldEntity), typeof(SkyDomeEntity) };

    List<TriangleIntersectionRecord> intersectionRecords = SimulationEngine.GlobalInstance.IntersectRayWithoutTypes(r, SimulationEngine.IntersectInvisFlags.SkipDisabledRendering, typesNotToPick);

    if (intersectionRecords.Count > 0)
           SimulationEngine.SimUI.SelectSingleEntity(intersectionRecords[0].OwnerEntity);
    else
           SimulationEngine.SimUI.SelectSingleEntity(null);
}