Re: Scrolling over images/tall lines

[Eli Zaretskii <eliz@gnu.org>]

> From: Yuan Fu <casouri@gmail.com>
> Date: Tue, 3 Nov 2020 13:06:49 -0500
> Cc: emacs-devel@gnu.org
> 
> > 
> > Why can't you achieve the same by leaving window-start at its original
> > place (2) and setting vscroll to get the display you want, like this:
> > 
> > +----------------------+
> > |                      |
> > |        image         |
> > |                      |
> > |                      |
> > +------window top--------------+--
> > ||                      |      | ^
> > |+----------------------+      | | vscroll (negative)
> > |(2)=======line==========      | v
> > |==========line==========      |
> > |==========line==========      |
> > 
> > Did you try this method?
> 
> I did, but (set-window-vscroll nil -20 t) returned 0 and didn’t have any effect, so I thought that’s not a valid thing to do.

Can you show a simple example of code where it doesn't work?  I'll
have a look; AFAICT it should work.

> And that feels worse than setting window-start and vscroll in the same time too, because with a negative vscroll you don’t even know where to start the glyph matrix.

??? Of course we know where to start the glyph matrix.  And Lisp
programs shouldn't be bothered by that anyway.