From: Clifford Heath <cjh_nospam@...>
Date: 2002-07-26T09:10:16+09:00
Subject: Re: GUI's and the Rouge, Part III (yes, finally) 1/2

Benjamin Peterson wrote:
> I agree strongly that asynchronous, hierarchical
> message passing is a vital part of GUI infrastructure.
> I was under the impression that it revolutionized GUI
> programming quite a while back, though.

Nearly all existing GUI toolkits use some kind of asynchronous
messaging within a hierarchy, but no others that I'm aware of
(having been away from GUIs for a couple of years now) combine
the characteristics of:
* Rich messaging - you define strong message types with arbitrary
  content (in OpenUI that means potentially nested arrays of
  structures of...)
* Hierarchical propagation against handlers having the appearance
  of dynamically-bound methods that receive the message parameters,
* Message broadcast down towards the leaf nodes that's transparent
  to the current delivery node.

In other words, sufficient power in the messaging system that no
widget needs to directly address any other.

Most GUI toolkits make minimal or no use of the hierarchy for message
propagation. Messages are normally of one of the limited standard
types, and there are ad-hoc broadcast mechanisms if any.

--
Clifford Heath