Re: Gtk scrollbar: thumb too short

[Richard Stallman]

    > That is unnecessarily complicated.  I think the position value that
    > users see is thumb_start / trough_pixels.  That is much simpler
    > and it is visually evident.

    For the normal case, these two approaches are the same.

The two models are mathematically equivalent in the normal case, but I
conjecture that the simple one is the way users really understand it.
In unusual cases, where the two models disagree, preserving the simple
model will seem natural.  Preserving the complex model will seem
unnatural.

    But in more complicated cases, your approach isn't possible. 

Of course it is possible.  Emacs already does it, with some toolkits.

    You get a situation where the correct size of the thumb cannot 
    fit into the trough with that starting position, which gives
    you two choices:

     - Make the thumb go out of the trough.

I think there is a misnunderstanding here.  Nobody proposed this.  You
said that some themes might do this, as a consequence of how the code
works; I responded it is no problem if they do.

     - Shrink the thumb to a smaller size than it should be.
       While less of a problem than the previous approach,
       it strikes me as a little strange. Also, you still have
       to consider what happens when you reach some minimum 
       size for the handlebar.

This is what should happen.  This is what Emacs already does
on some platforms.  (What is the "handlebar"?)

    I'm not sure that presenting this simple model to the user
    is compatible with allowing the user to drag the scrollbar thumb
    to overscroll.

They must be compatible; they already work together on other
platforms.  It is somewhat hard to grab the thumb when most of the
thumb is off-screen, but it should not be impossible.

    You have to decide whether dragging the scrollbar to the bottom:

     - Scrolls to last page of the document

Dragging it to the bottom of the trough should scroll to the last full
page.  Dragging it beyond the bottom should show less than a full
page.

    (Note that by allowing the user to drag the thumb to overscroll,
    no matter how you do it, you make the operation of scrolling
    to the last page of the document a precision operation rather

That is true, but the amount of precision required is no more than for
scrolling at any other place in the document.  Emacs has worked this
way for many years, and we have not heard a complaint.