Re: scroll-down with pixel transition

[Tak Kunihiro]

GOAL: Pixel-level vertical scrolling up and down

> I'm still not sure what you mean by "overshoot", but if that's the
> extra full-line scroll for each of the 10 iterations

Yes, that's what I meant!

> then you see the same in the snippet you shown that scrolls in the
> other direction, if you look carefully.

This I do not see (even with careful look).  At least, following lines
give me pixel-level and smooth scrolling.  Not for you?

(dotimes (ii 10)
  (vertical-motion 1)
  (dolist (vs (number-sequence 1 (1- (frame-char-height))))
    (set-window-vscroll nil vs t) (sit-for 0.02))
  (scroll-up 1) (sit-for 0.02))

> Changing that (probably as some special optional mode) will require
> changes in the display engine on the C level and in probably also in
> the line-moving commands in simple.el.  Patches welcome.

Let's say the lines above give smooth scrolling.  If so, to make Emacs
scroll both up and down with pixel-to-pixel resolution, requirement is
that `set-window-vscroll' accepts negative number.