Re: [boost] Re: C++ GUI - another view

From: Mathew Robertson (mathew.robertson_at_[hidden])
Date: 2004-09-21 17:22:26

> I am not looking into embedding any intelligent objects in  the 'canvas' to
> begin with, however I am trying to keep that in mind. The component approach
> of ATL/WTL is very interesting from that point of view, wherein you add your
> messaging by multiple derivation, combined with CRTP. This Might be a very
> useful mechanism to make dumb drawing objects intelligent. For example, if I
> had a dumb line, it should be possible to 'attach' a class that can detect
> if that line is being grabbed with the mouse and so on.

Its an interesting idea - except that I personally think that all events should be available to be handled from the 'line', at runtime, so that you can dynamically hook up events.  By 'attaching' the 'grab' property to a line, you have constrained the line to never being able to dynamically hook up a different type of event.

The bigest issue that you will have with attaching events to a simple item, such as a line, is that there is a fundamental limit on the number of window handles available in the system - and this limit is quite low under win32.  To implement this design, your canvas will have to synthesise events like MouseEnter, MouseLeave, etc

regards,
Mathew Robertson