bug#42406: Mouse-wheel scrolling can be flickering

[Eli Zaretskii]

> Date: Thu, 10 Dec 2020 22:10:28 +0000
> From: Alan Third <alan@idiocy.org>
> Cc: 42406@debbugs.gnu.org
> 
> What appears to be happening is that scrolling with the mouse, and
> also using C-v or M-v causes every frame to update the cursor and
> clear the internal border, which in turn causes them all to be drawn
> to the screen at once, which is pretty slow.
> 
> (It also appears to do something with scrollbars which helped me find a
> subtle redrawing bug.)
> 
> Scrolling through the buffer by using C-n to move down line by line
> only updates the frame being displayed. I'm not sure what's going on,
> it appears to be system independent code doing this.

Any pointers to the code which causes all the frames to be updated in
C-v/M-v case?