def __init__(self, canvas=None, ns=None):
args = canvas is not None and [canvas] or []
CanvasContext.__init__(self, *args)
if ns is None:
ns = {}
self._ns = ns
# todo: better way to handle mouse events
self._ns["MOUSEX"] = 0
self._ns["MOUSEY"] = 0
self._ns["mousedown"] = False
