Outliner widget

[Gary Benson <gary inauspicious org>]

Hi all,

Over the past few weeks I've been contemplating writing an outliner for
GNOME, the core of which will be an outliner widget which I'm about to try
and write; the screenshot on http://www.outliners.com/ gives a fair idea
of what I'm intending (a picture tells a thousand words and all that).  
Currently I'm a little lost as to where to start, and I'd appreciate some
feedback on my current thoughts.

Initially, I thought that a tree view would be a good starting point, but
I've become convinced that it would be very hard to implement what I want
with one. My current thinking involves a recursive tree of three custom
widgets that mirror the organisation of the data being represented.

The highest level widget, Outline, would be a scrolled window containing
an OutlineGroup, which would simply be a vertical box containing
OutlineElements. The OutlineElement itself would be the lowest level
widget comprising the arrow on the left (used both as a drag handle and to
hide the subtree), and a GtkTextView on the right, below which would
optionally be an OutlineGroup (see crappy ASCII art below).

 +-------+------------------+
 |       | +--------------+ |
 | Arrow | | GtkTextView  | |
 |       | +--------------+ |
 |       | | OutlineGroup | |
 |       | +--------------+ |
 +-------+------------------+

Now for the questions:

What would be good parent classes be for my three widgets?

The arrow would probably be a toggle button. Is it possible to make it so
that double-clicking is required to toggle it, so that single click may be
used to select the subtree? Is it possible to override the renderer for a
widget or do I need to make a custom one? Is it possible to make the arrow
stay at the top of its hbox cell or do I need a fixed container in there?

Folding would probably be accomplished by enclosing the GtkTextView/
OutlineGroup vbox in an event box and setting its height to that of a line 
of text when folded. Does this sound reasonable or is there a better way?

Thanks in advance,
Gary

[ gary inauspicious org ][ GnuPG 85A8F78B ][ http://inauspicious.org/ ]