tick_spec = function(lo, hi)
	-- given an interval of numbers, return a nice set of ticks to draw for the interval
	-- the ticks will try to be at multiples of 10, or some multiple of a power of 10
	-- we don't want to overwhelm the viewer, so we'll aim for between 2 and 4 ticks
	-- the ticks will be specified as a low and high value, and a delta between consecutive ticks
	local anchorlo, scale = approximate(lo, order_of_magnitude(hi-lo))
	local anchorhi = approximate_up(hi, order_of_magnitude(hi-lo))
--	print('---', lo, hi, order_of_magnitude(hi-lo), anchorlo, anchorhi, scale)
	while (anchorhi-anchorlo)/scale < 4 do
--		print('a', anchorlo, anchorhi, scale, (anchorhi-anchorlo)/scale)
		scale = scale/2
	end
	while (anchorhi-anchorlo)/scale > 8 do
--		print('b', scale, (anchorhi-anchorlo)/scale)
		scale = scale*2
	end
--	print('c', scale, (anchorhi-anchorlo)/scale)
	while vy(anchorlo-scale) > Menu_bar_height+20 do
		anchorlo = anchorlo-scale
	end
	while vy(anchorhi+scale) < App.screen.height-20 do
		anchorhi = anchorhi+scale
	end
--	print('d', scale, (anchorhi-anchorlo)/scale)
	return anchorlo, anchorhi, scale
end

approximate_up = function(n, zeros)
	-- turn n into a number with n zeros
	-- step 1: scale down
	for i=1,zeros do
		n = n/10
	end
	n = math.ceil(n)
	if n == 0 then n = 1 end
	-- step 2: scale back up
	local magnitude = 1
	for i=1,zeros do
		n = n*10
		magnitude = magnitude*10
	end
	return n, magnitude
end

test_approximate_up = function()
	check_eq(approximate_up(12, 1), 20, 'easy case')
	-- when scale down ends up at 0
	check_eq(approximate_up(2, 1), 10, 'below 5')
	check_eq(approximate_up(7, 1), 10, 'above 5')
end

copy_viewport = function(v)
	return {x=v.x, y=v.y, w=v.w, h=v.h, zoom=v.zoom}
end

Save_viewport = nil  -- save one previous position sometimes

from_viewport = function(state)
	local result = {}
	for k,v in pairs(state) do
		if Viewport[k] then
			result[k] = Viewport[k]
		end
	end
	return result
end

surface_bounds = function(nodes)
	local minx,miny,maxx,maxy
	for _,node in pairs(nodes) do
		if minx == nil or node.x < minx then
			minx = node.x
		end
		if maxx == nil or node.x > maxx then
			maxx = node.x
		end
		if miny == nil or node.y < miny then
			miny = node.y
		end
		if maxy == nil or node.y > maxy then
			maxy = node.y
		end
	end
	return minx,miny,maxx+600,maxy+600
end

wait_for_response = function()
	local response
	repeat
		love.timer.sleep(0.01)
		response = live.receive_from_app()
	until response
	return response
end

load_from_iterator = function(f)
	local result = {}
	local i,line,drawing = 0, ''
	while true do
		local line = f()
		if line == nil then break end
		table.insert(result, line)
	end
	if #result == 0 then
		table.insert(result, '')
	end
	return result
end

Ticks_font = love.graphics.newFont(12)

approximate = function(n, zeros)
	-- turn n into a number with n zeros
	for i=1,zeros do
		n = n/10
	end
	n= math.floor(n)
	local magnitude = 1
	for i=1,zeros do
		n = n*10
		magnitude = magnitude*10
	end
	return n, magnitude
end

order_of_magnitude = function(n)
	return math.floor(math.log(n)/math.log(10))
end