function Text.screen_line_widthB(State, line_index, i)
  local line = State.lines[line_index]
  local line_cache = State.line_cache[line_index]
  local start_posB = line_cache.screen_line_starting_posB[i]
  local start_offsetB = Text.offset(line.dataB, start_posB)
  local screen_line
  if i < #line_cache.screen_line_starting_posB then
    local past_end_posB = line_cache.screen_line_starting_posB[i+1]
    local past_end_offsetB = Text.offset(line.dataB, past_end_posB)
    screen_line = string.sub(line.data, start_offsetB, past_end_offsetB-1)
  else
    screen_line = string.sub(line.data, start_pos)
  end
  local screen_line_text = App.newText(love.graphics.getFont(), screen_line)
  return App.width(screen_line_text)
end