10.1.3 Change-space Notification Protocol

The purpose of the change-space notification protocol is to force a recalculation of the space occupied by potentially each pane in the pane hierarchy. The protocol is triggerred by a call to note-space-requirement-changed on a pane P. In McCLIM, we must therefore invalidate the stored space-requirement value and re-invoke compose-space on P. Finally, the parent of P must be notified recursively.

This process would be repeated for all the panes on a path from P to the top-level pane, if it weren't for the fact that some panes compute their space requirements independently of those of their children. Thus, we stop calling note-space-requirement-changed in the following cases:

• when P is a restraining-pane,
• when P is a top-level-sheet-pane, or
• when P has been given explicit values for :width and :height

In either of those cases, allocate-space is called.