bug#42406: Mouse-wheel scrolling can be flickering

[Konrad Podczeck]

I still see a problem with mouse wheel scrolling, for emacs from the 27 branch as well as for emacs from the master branch, when there are multiple frames open.

To reproduce: Start Emacs (from any of the two mentioned branches) with an init-file just containing:

(setq mouse-wheel-progressive-speed nil)

(setq default-frame-alist '((tool-bar-lines . 1)(width . 82)(height . 46)(left . 1)(top . 0)(font . "SF Mono-15")(line-spacing . 3)))

Open any longer file. Mouse wheel scrolling performance is fine (at least for the master branch). Now do C-x 5 2, to get a second frame. Using the mouse wheel, scroll up and down. Repeat C-x 5 2, about six times, and the scrolling performance becomes worse and worse.

Remark: If one uses the menu to turn off the toolbar, then the problem disappears.

Remark: Instead of customizing default-frame-alist, one can also put the following code in the init-file

(custom-set-variables

 '(display-buffer-base-action

   '((display-buffer-reuse-window display-buffer-pop-up-frame)

    (reusable-frames . t)))

 '(display-buffer-alist

   '(

    ("[.]"

     (display-buffer-reuse-window display-buffer-pop-up-frame)

     (pop-up-frame-parameters

       (tool-bar-lines . 1)

       (left . 1)

       (top . 0)

       (height . 46)

       (width . 82)

       (font . "SF Mono-15")

       (line-spacing . 3)

      ))))

)

to get the the same problem with different buffers.

Konrad

Am 10.10.2020 um 16:07 schrieb Konrad Podczeck <konrad.podczeck@univie.ac.at>:

Am 10.10.2020 um 11:51 schrieb Alan Third <alan@idiocy.org>:

On Thu, Jul 30, 2020 at 12:30:27PM +0200, Konrad Podczeck wrote:

Having taken a closer look, it seems to me now that what I called "flickering" is the following:

Mouse-wheel scroll downwards, so that the cursor becomes positioned
at the top row of the frame. Then release the mouse-wheel, but so
that inertia scrolling continues for a short time. After the
scrolling comes to rest, which is probably determined by the window
manager, there is an extra movement, governed probably by Emacs, to
make sure that it is not the case that only, say, half of a row is
visible at the top of the frame. It seems to me that it is this
extra movement which leads to what I called "flickering."

Sorry for the long delay. In standard Emacs usage you shouldn't ever
see half a line displayed at the top of the screen. Are you using
pixel scroll mode or something?

No

The only alternative I can think of is that the inertia just pushes it
over the edge to scroll one more line, but I don't think you would see
that as "flickering", just an extra scroll.

Yes, maybe “flickering” is saying to much, but I see a “light tremor”, at least with the customizations:

(setq mouse-wheel-progressive-speed nil)
(setq mouse-wheel-scroll-amount '(1 ((shift) . 1)))

Konrad

To disable inertia in Emacs do:

  (setq ns-use-mwheel-momentum nil)

-- 
Alan Third