override protected function updateDisplayList(unscaledWidth:Number, unscaledHeight:Number):void {
 
super.updateDisplayList(unscaledWidth, unscaledHeight);
 
// Set the clipping of the 3D scene to make sure only the visible elements are rendered,
// this is great improvement for the performance
var clipping:RectangleClipping = new RectangleClipping(-this.width/2, -this.width/2, this.width/2, this.width/2);
 
// Asign the clipping to the _view3D, in this case a private variable within my class
_view3D.clip = clipping;
 
// Remove the old mask if there is one
if (_mask != null) {
this.removeChild(_mask);
}
 
// Create a new mask
_mask = new Sprite();
_mask.x = this.x;
_mask.y = this.y;
_mask.graphics.beginFill(0xFF0000,1);
_mask.graphics.drawRect(0, 0, this.width, this.height);
_mask.graphics.endFill();
 
// Add it to the displayList
this.addChild(_mask);
// And assign the mask to the view3D
_view3D.mask = _mask;
 
// And center the view3D in the available space
_view3D.x = this.width / 2;
_view3D.y = this.height / 2;
}