Re: Gtk scrollbar: thumb too short

[Luc Teirlinck <teirllm@dms.auburn.edu>]

Owen Taylor wrote:

      Stefan Monnier seemed to think that invisible text would make
      computing the end scroll position of the scrollbar very hard. 
      That implied to me that Emacs computed scrollbars based on total 
      characters not visible characters; but I didn't research the
      point.

In a certain sense that actually seems correct.

I only claim that the actual behavior seems consistent.  It is not at
all clear what the ideal behavior is supposed to be.  It seems to
depend on personal taste.

There are two main ways to "hide" text, selective display and the
"invisible" text and overlay property.  Both seem to behave the same
way.  Selective display is the most convenient to experiment with.

Set scroll-conservatively to 1000 or such, so that lines come into
view one by one.  Take some piece of heavily indented code and do 
M-1 C-x $  Just start scrolling with C-n or the down-arrow key.
Watch the scroll-bar.

If a 

...

line representing invisible text comes into view then everything
depends on the size of the invisible text.  If it represents a large
chunk of invisible code, the effect on the scrollbar is dramatic,
otherwise it is negligible.  In other words, it gives you an idea of
the amount of actual (indented) code you are scrolling through.

Bug or feature?  I do not know whether there is a "correct" answer to
that question.  It depends on what the user is trying to do and on the
user's taste and expectations.  But it seems predictable.  Somehow, it
looks OK to me, but it is very well possible that the only reason why
is that it is the (only) behavior I am used to.  (I seldom get
confronted with invisible text outside of Emacs.)

Sincerely,

Luc.