animate_to = function(v)
	local global_viewport, globalw, globalh = initialize_global_viewport()
	local canvas = snapshot_canvas(global_viewport, globalw, globalh)
	v = v or global_viewport
	local initial = copy_viewport(Viewport)
	local final = v
	local step, frame_time = 0, 0
	while true do
		love.event.pump()
		for name, a,b,c,d,e,f in love.event.poll() do
			if name == "quit" then
				os.exit(0)
			end
			-- ignore other events
		end
		-- update
		dt = love.timer.step()
		frame_time = frame_time + dt
		if frame_time > 0.01 then
			frame_time = frame_time - 0.01
			step = step + 1
			if step > Num_animation_frames then
				break
			end
			interpolate_viewport(initial, final, step)
--? 			print('animation frame: Viewport is now', Viewport.x, Viewport.y, Viewport.zoom)
			B()
		end
		-- draw
		love.graphics.origin()
		love.graphics.clear(love.graphics.getBackgroundColor())
		local q = love.graphics.newQuad(
			(Viewport.x-global_viewport.x)*Viewport.zoom,
			(Viewport.y-global_viewport.y)*Viewport.zoom,
			App.screen.width,
			App.screen.height,
			globalw*Viewport.zoom,
			globalh*Viewport.zoom)
		App.color{r=1,g=1,b=1}
		love.graphics.draw(canvas, q, 0,0)
		love.graphics.present()
		love.timer.sleep(0.001)
	end
end
	A()

	local zoom, globalw, globalh
		globalw = maxx-minx
		globalh = globalw*App.screen.height/App.screen.width
		globalh = maxy-miny
		globalw = globalh*App.screen.width/App.screen.height
	local global_viewport = {x=minx, y=miny, zoom=zoom}
	return global_viewport, globalw, globalh
end
	end
	else
		zoom = zoomy
	if zoomx < zoomy then
		zoom = zoomx

	local initial_viewport = copy_viewport(Viewport)
	animate_to(--[[global viewport]] nil)
	animate_to(initial_viewport)
	print('Viewport at end of survey animation', Viewport.x, Viewport.y, Viewport.zoom)

	animate_to(Save_viewport)
	print('Viewport at end of undo zoom out animation', Viewport.x, Viewport.y, Viewport.zoom)
	Save_viewport = nil
end

	-- precondition: Viewport == global_viewport
	animate_to{
		x=sx(x)-App.screen.width/Save_viewport.zoom/2,
		y=sy(y)-App.screen.height/Save_viewport.zoom/2,
		zoom=Save_viewport.zoom,
	}
	print('Viewport at end of zoom in animation', Viewport.x, Viewport.y, Viewport.zoom)
	-- precondition: Save_viewport exists
	-- center Viewport on x,y at zoom level Saved_viewport.zoom

snapshot_canvas = function(global_viewport, globalw, globalh)
	App.screen.width, App.screen.height = globalw, globalh
	Viewport = copy_viewport(global_viewport)
	local canvas = love.graphics.newCanvas(w, h)
	love.graphics.setCanvas(canvas)
	return canvas
end
	on.draw()
	Viewport.zoom = 1.0
	A()
	local saved_viewport = Viewport
	-- Render the canvas at pixel perfect resolution.

	animate_to(--[[global viewport]] nil)
	print('Viewport at end of zoom out animation', Viewport.x, Viewport.y, Viewport.zoom)

	return {x=v.x, y=v.y, zoom=v.zoom}
end

	for _, k in ipairs{'x', 'y', 'zoom'} do
		Viewport[k] = (initial[k]*(Num_animation_frames - step) + final[k]*step) / Num_animation_frames
	end
end