box_height = function(node)
	-- return the height of a node. The result is scaled.
  local y = 0
  for i=1,#node.editor.lines do
    local line = node.editor.lines[i]
    if node.editor.line_cache[i] == nil then
      node.editor.line_cache[i] = {}
    end
    node.editor.line_cache[i].fragments = nil
    node.editor.line_cache[i].screen_line_starting_pos = nil
    Text.compute_fragments(node.editor, i)
    Text.populate_screen_line_starting_pos(node.editor, i)
--    y = y + node.scaled_fontsize*#node.editor.line_cache[i].screen_line_starting_pos
    y = y + math.floor(node.editor.line_height)*#node.editor.line_cache[i].screen_line_starting_pos
  end
  return y
end