bug#42406: Mouse-wheel scrolling can be flickering

[martin rudalics]

> To clarify my observation: If I comment out just the two calls to
> wset_update_mode_line that are in window_scroll_pixel_based, then the
> mouse wheel scrolling problem with multiple frames goes away, but the
> problem with scrolling via the scroll bars remains; if I comment out
> all five calls to wset_update_mode which are in window.c, then in
> addition the scroll-bar problem goes away (with multiple frames). I
> just wanted to know whether Martin has an idea which of the remaining
> three calls (when they are not out-commented) could be responsible for
> the scroll-bar problem.

I suppose it happens via 'scroll-bar-toolkit-scroll' calling
'scroll-bar-drag-1' calling 'set-window-start' so commenting out the

  wset_update_mode_line (w);
  /* Bug#15957.  */

occurrence in Fset_window_start should cut it.

martin