graph drawing tool
on_node = function(sx,sy)
	local result
	for _,node in ipairs(Surface) do
		if node.type == 'text' then
			if sx >= node.x and sx < node.x + node.w then
				if sy >= node.y and sy < node.y + node_height(node) then
					result = inner(result, node)
				end
			end
		end
	end
	return result
end