def build_screen_image(edit_buffer)
      working_region = edit_buffer[left_margin..right_margin]

      if (mask = @options[:secret_mask])
        mask[0] * working_region.length
      else
        working_region
      end.ljust(active_width)
    end
def build_screen_image(edit_buffer)
      working_region = edit_buffer[left_margin..right_margin]

      if (mask = @options[:secret_mask])
        mask[0] * working_region.length
      else
        working_region
      end.ljust(active_width)
    end
Compute what should be on the screen.