computed costumes

Folks,
	I'm building a math demo.  It is a complex diagram that 
changes as the user moves a slider.  I'm using the turtle Pen to draw 
the diagram.  It needs to be "double-buffered" so that the user does 
not see the area get cleared to white and does not see the drawing 
being made.  That is, no flashing.
	Here's the plan.  Make a drawing (SketchMorph).  Make another 
drawing that is the same size and hide it.  Each sketch will be a 
costume for a player of the first sketch.
	Whenever the slider moves, get the Form of the sketch that is 
not currently showing.  Draw into it with the Pen.  Switch it to be 
the costume that shows.
	Is there a simpler way to do this in Etoys?
	If not, maybe we can extend Etoys to allow this, so an author 
does not need to know Squeak to make it happen.

--Ted.

-- 
Ted Kaehler
If you're not hungry enough to eat an apple, then you're not hungry. 
If you are that hungry, then do eat an apple.  -- paraphrasing 
Michael Pollan.
http://www.vpri.org/html/team_bios/kaehler.html