[Bug: 21.4.19] smooth vscroll-{up,down}

[David Kastrup]

Jérôme Bouat <jerome.bouat at wanadoo.fr> writes:

> But emacs can move smoothly the window,
> it is simply not mapped in 'next-line' function.
> For the expected result, make emacs evaluate:
> (dotimes (i 10) (set-window-vscroll nil (* i 0.1)) (sit-for 0.05))

It must be noted that while this Emacs (not XEmacs) code somewhat
works, it is not integrated with the display engine in a manner that
will cause sane and smooth recentering and cursor movement behavior.

Also, true smooth scrolling works by whole pixel amounts, not "line
fractions", and the scrolling happens at vertical retrace time for
best effect.

The complex display engine of Emacs (can't vouch for XEmacs) is not
all too well suited for this sort of pixel-based action.  If it were,
scrollbars would behave "more naturally" already.

-- 
David Kastrup, Kriemhildstr. 15, 44793 Bochum