From: Josef Wolf <jw@...>
Date: 2009-09-09T06:30:23+09:00
Subject: Re: Zoomable TkCanvas?

On Wed, Sep 09, 2009 at 05:29:47AM +0900, Joel VanderWerf wrote:

Thanks for your patience with me, Joel!

> Josef Wolf wrote:
>> But how do I override the methods to create the items? In Perl/Tk, that
>> would be easy, since item creation is done via canvas methods.  But in
>> Ruby/Tk, items are created via their own classes (e.g. TkcLine.new(args)
>> or something). There don't seem to exist methods in the Canvas class to
>> create items, which could easily be overridden.
>
> Maybe subclass (or delegate to) the Tk classes:
>
> class MyRectangle < TkcRectangle
>   def initialize(x,y,w,h)
>     super(...) # adjust args depending on zoom level etc.
>   end
> end

That would result in:
 - lots of new subclasses, polluting namespaces
 - lots of code duplication
 - it would not be a drop-in replacement: one would have to change the
   class names of the items when switching from standard canvas to the
   improved canvas

Maybe extending TkcItem would be a better solution.  Something like:

   class TkcItem
     alias orig_initialize initialize
     def initialize(parent, *args)
       # do whatever we need
       orig_initialize parent, args
     end
   end

Opinions?