Thank you Eli,

I just realized I forgot to be clear about my question.
The problem is that after evaluating the code, here,
after starting from emacs -Q, the vscroll value is still
zero.

So I was wondering what is the value when doing

> M-: (window-vscroll nil t)
>
after evaluating the example code.

So Eli, when you say it works, do you mean that
vscroll value is 300?

Thanks again...

On Sun, 5 Nov 2023 at 17:20, Eli Zaretskii <eliz@gnu.org> wrote:

> > From: dalanicolai <dalanicolai@gmail.com>
> > Date: Sun, 5 Nov 2023 16:49:04 +0100
> >
> > It works when I simply load my Emacs configuration, but for some
> > reason it does not work when I start from emacs -Q.
> >
> > Although I guess vscroll should be working on lines smaller than the
> > screen, just for testing I now display 3 'spaces' and then try to set
> > vscroll as follows:
> >
> >  (progn
> >    (pop-to-buffer "example")
> >    (dotimes (i 3)
> >      (let ((o (make-overlay (point)
> >                             (progn (insert " ")
> >                                    (point)))))
> >        (insert "\n")
> >        (overlay-put o 'display `(space . (:width (600) :height (800))))
> >        (overlay-put o 'face (list :background (pcase (% i 3)
> >                                                 (0 "red")
> >                                                 (1 "green")
> >                                                 (2 "blue"))))))
> >    (goto-char (point-min))
> >
> >    (set-window-vscroll nil 300 t))
> >
> > I have tested it on Emacs 29.1 and 28.3.
> >
> > I wonder if this is a bug, or if I am missing something.  Could you
> > please evaluate the above code starting from emacs -Q, and confirm
> > this is a bug (or tell me what I am missing)?
>
> Works for me in "emacs -Q".
>