zoom_in = function(x,y)
	-- precondition: Zoomed_out
	-- precondition: Viewport == Global_viewport
	-- precondition: Save_viewport exists
	-- center Viewport on x,y at zoom level Saved_viewport.zoom
	snapshot_canvas()
	Animating = {
		{
			x=sx(x)-App.screen.width/Save_viewport.zoom/2,
			y=sy(y)-App.screen.height/Save_viewport.zoom/2,
			w=App.screen.width/Save_viewport.zoom,
			h=App.screen.height/Save_viewport.zoom,
			zoom=Save_viewport.zoom,
		},
	}
	Zoomed_out = nil
	Save_viewport = nil	
end