--
-- Most of the time the viewport affects each pane's top and screen_top. An
-- exception is when you're editing a pane and you scroll the cursor inside
-- it. In that case we want to affect the viewport (for all panes) based on
-- the editable pane's screen_top.

  -- This little bit of state ensures we don't mess with a pane's screen_top
  -- if it was just used to update the viewport.
  Editable_cursor_pane_updated_screen_top = false

  if not Editable_cursor_pane_updated_screen_top then return true end

    if not eq(old_top, pane.screen_top1) then

    Editable_cursor_pane_updated_screen_top = not eq(old_top, pane.screen_top1)
    if Editable_cursor_pane_updated_screen_top then
--?       print('updating viewport based on screen top')