Re: Gtk scrollbar: thumb too short

[Luc Teirlinck]

Miles Bader wrote:

   I think that if this is the worry, it's groundless, because the emacs
   extensions are just that -- extensions, which extrapolate existing
   behavior, not really arbitrary differences in details, which is the
   usual case of problems arising with lookalike implemenations.

It is a little bit more complicated than that.  The Emacs behavior
would be an alternative behavior, not an extension.  There are two
unrelated issues:

1. overscrolling versus non-overscrolling.  As Owen pointed out to me,
   GTK already supports both.  That is not the issue we are
   discussing.

2. A character based approach versus a pixel based approach.

Two applications, Emacs and PixelStuff start out with exactly one
window height (say sixty lines) full of stuff.  Both allow
overscrolling to put the last line at the top.  In Emacs, the thumb
covers the entire length of the scrollbar, because all text is
visible, in PixelStuff it covers approximately half (60/119) of the
scrollbar.  We scroll to the bottom.  In PixelStuff, the thumb stays
the same size and moves smoothly to the bottom, until it hits the
bottom, exactly when the last line of real text gets at the top.  In
Emacs, the thumb shrinks gradually to a size determined by (amount of
characters on the last line) / (total amount of characters).  This is
different behavior, not an extension of behavior.

A user of PixelStuff using Emacs for the first time will conclude that
Emacs does not allow overscrolling, because the thumb already is at
the bottom, so no downward scrolling is possible.  An Emacs user using
PixelStuff for the first time will conclude that he is only looking
at half of the real text.

Sincerely,

Luc.