tree control & drawing

[Alan Shouls]

Hi,

I am working on the tree control under OSX and currently looking at 
the highlight. I have added support for bitmap highlights so it is 
possible to have a gradient highlight that you get in the left had 
column of Finder windows and many Apple applications. To do this I 
have added some new methods to the tree control

     virtual void SetHighlightImage(const wxImage &);
     virtual void SetUnfocusedHighlightImage(const wxImage &);

There is some tom-foolery to cache a correctly scaled bitmap within 
in the tree control (wxImage and wxBitmap make it easy). The results 
don't look bad (heres a screeny)

   http://users.softpress.com/alan/Resources/treetest1.png

One of the things is that has become apparent to me that it is 
impossible to write a subclass or hook into any events to make it 
possible to override drawing behaviour in the base-class.

The drawing of an individual item is achieved through 'PaintItem'. 
This method is not virtual and there are no events that I can hook 
into. For me the only way to work with it is to modify the 
'wxGenericTreeCtrl' its self. To my mind the code could easily be 
split across a few methods that could themselves be virtual. What I 
am thinking is that painting an item could be done though

  PaintItemBackground
  PaintItemHighlight
  PaintItemContents

Or something like this. Obviously it would be possible to create a 
set of events etc. to do the same, Generally when working with a 
framework I would make some sub-class that encapsulated whatever 
modifications to the appearance / behaviour that I needed and the 
process of incorporating some of this into the framework its self is 
a fight for another day. This is not really possible with the tree 
control with wx.

I believe that moves are afoot to base the tree control on the 
databrowser so it may not be the case that making modifications to 
the treecontrol on wx are appropriate - so these questions may be a 
little academic. If on the other hand it does not get there I would 
like to be able to have something that I can offer to the wx 
community.

Best regards

Alan Shouls