A = function()
	B()
	-- TODO: ugly that we're manipulating editor objects twice
	compute_layout(Page, Page.x,Page.y, Surface)
	compute_layout(Page2, Page2.x,Page2.y, Surface)
	-- continue the pipeline
	love.graphics.setFont(love.graphics.newFont(scale(20)))  -- editor objects implicitly depend on current font

    x repeated down arrow near bottom pans down

    ✓ repeated down arrow near bottom pans down

    x repeated down arrow near bottom pans down

    ✓ repeated down arrow near bottom pans down

	if node == skip_updating then return end

	if node == skip_updating then return end

			node.editor.screen_top1, node.editor.top = schema1_of_y(node.editor, scale(Viewport.y-node.y))
--? 			print('modified screen_top to', node.editor.screen_top1.line, 'at', node.editor.top, 'vpx')
		else
			-- adjust editor to start rendering near top of viewport
--? 			print(Viewport.y)
			node.editor.top = Viewport.y%node.editor.line_height
			if node.editor.top > 0 then node.editor.top = node.editor.top - node.editor.line_height end
--? 			print('top', node.editor.top)

		node.editor.top = node.editor.top + Menu_bar_height

		node.editor.screen_top1, node.editor.top = schema1_of_y(node.editor, scale(Viewport.y-node.y))

		node.editor.screen_top1, node.editor.top = schema1_of_y(node.editor, scale(Viewport.y-node.y))

A = function(skip_updating_screen_top_for)

A = function()

	B(skip_updating_screen_top_for)

	B()

		love.graphics.line(25, i*100, 75, i*100)

			print('cursor before', Cursor_node.editor.cursor1.line, Cursor_node.editor.cursor1.pos)

--? 			print('edit', old_top.line, '=>', Cursor_node.editor.screen_top1.line)

			print('cursor after', Cursor_node.editor.cursor1.line, Cursor_node.editor.cursor1.pos)

			if not eq(Cursor_node.editor.screen_top1, old_top) then
--? 				print('modifying Viewport', Viewport.y, 'based on', Cursor_node.y, Cursor_node.editor.screen_top1.line, Cursor_node.editor.line_height)
				Viewport.y = Cursor_node.y + y_of_schema1(Cursor_node.editor, Cursor_node.editor.screen_top1)/Viewport.zoom
--? 				print('modified Viewport', Viewport.y)
				-- Most of the time, we update the screen_top of nodes from Viewport.y.
				-- But here we went the other way.
				-- It's very important to avoid creating a recurrence, to avoid running
				-- both sides of this feedback loop in a single frame. These apps are
				-- not very numerically precise (e.g. we force text lines to start at
				-- integer pixels regardless of zoom, because that keeps text crisp),
				-- and the computations of Viewport.y and node.top will almost certainly
				-- not converge. The resulting bugs are extremely difficult to chase
				-- down.
				-- The optional skip_updating_screen_top_for arg ensures we don't run
				-- the other side of the feedback loop.
				A(--[[skip updating screen_top for]] Cursor_node)
				return
			end

			pan_viewport_to_contain_cursor(Cursor_node)

		print('cursor before', Cursor_node.editor.cursor1.line, Cursor_node.editor.cursor1.pos)
		print('cursor after', Cursor_node.editor.cursor1.line, Cursor_node.editor.cursor1.pos)
		pan_viewport_to_contain_cursor(Cursor_node)

B = function(skip_updating_screen_top_for)

--	print('B')

B = function()

B = function()

	-- recompute various aspects based on the current viewport settings
	for _,obj in ipairs(Surface) do
		if obj.type == 'line' then
			obj.zdata = {}
			for i=1,#obj.data,2 do
				table.insert(obj.zdata, vx(obj.data[i]))
				table.insert(obj.zdata, vy(obj.data[i+1]))
			end
		elseif obj.type == 'bezier' then
			zdata = {}
			for i=1,#obj.data,2 do
				table.insert(zdata, vx(obj.data[i]))
				table.insert(zdata, vy(obj.data[i+1]))
			end
			obj.zdata = love.math.newBezierCurve(zdata):render()
		elseif obj.type == 'text' then
			if obj.w then

				update_editor_box(obj, skip_updating_screen_top_for)

			else
				obj.text = love.graphics.newText(love.graphics.getFont(), obj.data)
			end
		end
	end