Re: Logitech high-resolution scrolling..

From: Linus Torvalds
Date: Tue Oct 30 2018 - 12:29:39 EST

On Mon, Oct 29, 2018 at 11:27 PM Peter Hutterer
<peter.hutterer@xxxxxxxxx> wrote:
> Other issues I found with an MX Anywhere 2S is that on slow scroll and in
> ratchet mode we get some scroll jitter. In ratchet mode we can get this
> sequence if you scroll just past the notch and it snaps back:
> [1, 1, 1, 1, 1, 1, 1, 1, -1]
> That's quite easy to trigger. In free-wheel mode we may get the same for
> slow motion due to human finger jitter (the Anywhere 2S didn't have HW
> jitter, but other devices may). So a perceived-consistent scroll motion may
> really look like this:
> [1, 1, 1, 1, 1, -1, 1, 1]
> Hard to triggger but when it does, it feels like we're dropping events.
> The former isn't that much of an issue as long as the ratchet is enabled so
> you get the haptic feedback and we (usually) don't drop events.

Both of these actually argue that doing the reset on direction change
can be a real problem.

But equally clearly, _not_ doing the reset is unacceptable too.

I wonder if there's some docs on what Logitech does internally in the
mouse. It might involve a timeout (ie "if not moving for a while, do
the rounding _and_ reset), which would probably be too expensive to do
on the host side.