FLICKERING!!!!
	- to avoid it, call layoutContainer()
	- any way to do this automatically?
	- should layoutContainer invalidate instead of doing stuff right away?
	

what do minimum, maxiumum, preferred layout size mean when displayobjects don't have preferred, min, max sizes?




make tree of layouts
on register or setConstraints, call invalidate: go up tree marking as invalid, invalidate stage, add render listener



	
LayoutRenderer
	setConstraints(obj:DisplayObject, constraints:LayoutRendererConstraints)		// for example, ease amount, etc.
	public function draw(layout):Layout												// does the actual layout painting


LayoutManager

	- should dispatch LAYED_OUT after every time it calls layoutContainer()

	final register(container:DisplayObjectContainer);                    // Automatically add all children, add ADDED listener to add children
	final unregister(container:DisplayObjectContainer);                  // Remove all children that were added
	final layoutContainer(container:DisplayObjectContainer);

	public function addLayoutDisplayObject(obj;DisplayObject):void
	public function removeLayoutDisplayObject(obj:DisplayObject):void
	
	final set renderer(renderer:LayoutRenderer):void

GridBagLayout extends LayoutManager
	setConstraints(child:DisplayObject, constraints:GridBagConstraints); 								- use weak keyed dictionary
	columnWidths = []
	rowHeights = []
	getConstraints(child:DisplayObject):GridBagConstraints
	? get layoutOrigin():Point
	
	override addLayoutDisplayObject
	override removeLayoutDisplayObject
	
	protected override calculateLayout(container:DisplayObjectContainer):Layout