Auto-resizing columns in Really Big Tree Views

[Guy Harris <gharris flashcom net>]

(As the tree view stuff is still under development - and as what I'm
asking for may require changes to it - I'm assuming, perhaps
incorrectly, that this question is best asked on "gtk-devel-list" not
"gtk-list".)

Context:

If you're unfamiliar with Ethereal, it's a GUI packet capture/analysis
program:

	http://www.ethereal.com

along the lines of Network Associate's Sniffer, or Microsoft's Network
Monitor, or the old "tcpview" which was a Motif-based analyzer built out
of old tcpdump source.

It has 3 panes (like all three of the analyzers mentioned); the topmost
pane is a list of all packets (currently implemented with a GtkCList),
the middle pane is a tree showing a the fields in the currently-selected
packet, and the bottom pane is a hex/ASCII dump of the data in the
currently-selected packet.

In Ethereal, I'd like to have some columns in the packet-list pane
auto-resize, from the user's point of view, *without* having the tree
view widget iterating over all the rows.

I want to avoid that because there could be a *LOT* of rows (one packet
capture has 138,673 packets in it; I really don't want to have the tree
view widget go through all 138,673 rows call back to the model - which
would be implemented by Ethereal itself, rather than by a data structure
storing the text for the columns, as storing the text for all those
columns, rather than generating them on the fly by dissecting the packet
when it's to be displayed, significantly increases the memory
requirement for that capture file).

It looks as if "gtk_tree_view_calc_size()" will, in fact, iterate over
all rows in the model, and, for each row, iterate over all columns in
the view.

Is there any way to have Ethereal supply the column widths, which it can
do for most columns, *and* have the widths it supplies take into account
the widths of the titles, so that if, for example, you have a capture
with one packet in it, so that the largest value of the "packet number"
column is 1, it can supply a width large enough to hold the title "No."
for that column?

For one column, the "packet information" column, which give a short
summary of the packet contents at the topmost protocol layer, it won't
know the column width; I'd like to avoid, when reading the capture file
in, generating the data in that column, as that would significantly slow
down reading large capture files.  Instead, I'd like, if possible, to
resize that column *when it's displayed*, so that if you scroll the
packet list down and make visible a row with a longer "information"
column than any rows that have been seen so far, the column gets wider. 
(That column is probably going to be the rightmost column, so the visual
effect should only be the appearance of, or a change in the length of, a
horizontal scrollbar.)