bug#42406: Mouse-wheel scrolling can be flickering

[Alan Third]

On Tue, Dec 15, 2020 at 07:54:49PM +0100, martin rudalics wrote:
> >> I haven't looked into it but can't running that code be simply
> >> suppressed when no internal border should be drawn anyway?  That is,
> >> when the width is zero which should be the default.
> >
> > The default is 2 on the NS port, and on non-GTK X builds it would
> > appear to be 1.
> >
> > I'm inclined to just leave it as-is. If people want to try setting it
> > to zero themselves they can, because as you say it doesn't do anything
> > if it's 0.
> 
> So if Konrad sets the 'internal-border-width' frame parameter to 0 the
> slowdown should not happen.  Right?

The cursor is still redrawn, so it may make no difference.

The NS port has two drawing paths, on older macs and Gnustep it draws
and the screen is updated piecemeal. On newer macs it draws to an
offscreen buffer and then that buffer is drawn to the screen. Drawing
the buffer to the screen is very slow.

It depends what Konrad's system is doing whether it will make much
difference, but I suspect he's using the off-screen buffer path so the
cursor redraw will force the whole frame update anyway.

-- 
Alan Third