bug#42406: Mouse-wheel scrolling can be flickering

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bug#42406: Mouse-wheel scrolling can be flickering

Konrad Podczeck
Mouse-wheel scroll and then suddenly release the mouse-wheel, so that thereafter the text scrolled still moves for a short time. During that time, the text flickers.

(In case this is platform-dependent, I use the NS-port of Emacs 27.0.91/pretest)




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bug#42406: Mouse-wheel scrolling can be flickering

Alan Third
On Fri, Jul 17, 2020 at 05:36:10PM +0200, Konrad Podczeck wrote:
> Mouse-wheel scroll and then suddenly release the mouse-wheel, so
> that thereafter the text scrolled still moves for a short time.
> During that time, the text flickers.
>
> (In case this is platform-dependent, I use the NS-port of Emacs
> 27.0.91/pretest)

Emacs 28 will use a different method of drawing to the screen that
should, hopefully, not flicker. Can you please try out a build from
master and see if it's any better?
--
Alan Third



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bug#42406: Mouse-wheel scrolling can be flickering

Konrad Podczeck
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."


For how to enable/disable "inertia scrolling, see

https://support.apple.com/en-nz/guide/mac-help/unac899/mac


> Am 22.07.2020 um 22:16 schrieb Alan Third <[hidden email]>:
>
> On Sun, Jul 19, 2020 at 10:29:20PM +0200, Konrad Podczeck wrote:
>> For me, there is no difference with Emacs 28. To see this best, make the following customizations:
>>
>> (setq mouse-wheel-progressive-speed nil)
>> (setq mouse-wheel-scroll-amount '(1 ((shift) . 1)))
>>
>> (and make sure that in the Mouse Options part of the Accessibilty
>> panel of the general System Preferences of MacOS, scrolling with
>> inertia is enabled.)
>
> What version of macOS are you using? I can't get momentum working here
> any more and I don't have any option that I can see in the system
> preferences to turn it on or off.
>
> I can't think of any reason that momentum scrolling should flicker
> when normal scrolling doesn't, they use the exact same mechanism.
>
> Does it happen when you run emacs -Q?
> --
> Alan Third




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bug#42406: Mouse-wheel scrolling can be flickering

Alan Third
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."

I'm afraid I don't follow. The NS port doesn't let you scroll by part
of a line by default. Are you using pixel-scroll-mode or similar?

If I use pixel-scroll-mode I can see some flickering of the mode line
after scrolling has ceased (as you say, when it rolls back or forth to
show a whole line), but only in Emacs 27, Emacs 28 is fine.

> For how to enable/disable "inertia scrolling, see
>
> https://support.apple.com/en-nz/guide/mac-help/unac899/mac

Thanks, strangely I don't see what they describe there... My Mac must
have something odd going on... :/
--
Alan Third