bug#42406: Mouse-wheel scrolling can be flickering

[martin rudalics]

>>   > Performance does not degrade when only the two calls of
>>   > wset_update_mode_line you mentioned are commented out. However, with
>>   > just commenting out these two instances, I still have a scroll
>>   > performance problem when scrolling by using the scroll-bars. Could you
>>   > also identify the instance concerning this?
>>
>> I forgot how Emacs precisely handles that.  Maybe Eli can tell.
>
> See scroll-bar-toolkit-scroll.  Basically, it calls
> scroll-up/scroll-down.

Then something else must come into play here.  I don't see where
'scroll-bar-toolkit-scroll' forces a mode line update.

martin