[PATCH xf86-input-libinput] Up the scroll dist value for touchpads

[Peter Hutterer]

On Thu, Mar 05, 2015 at 09:51:17AM +0100, Hans de Goede wrote:
> Hi,
> 
> On 04-03-15 22:46, Peter Hutterer wrote:
> >On Wed, Mar 04, 2015 at 01:15:31PM +0100, Hans de Goede wrote:
> >>Hi,
> >>
> >>On 04-03-15 06:00, Peter Hutterer wrote:
> >>>For source FINGER and CONTINUOUS, the axis value is the same as relative
> >>>motion - but scrolling in X usually doesn't have the same speed as finger
> >>>movement, it's a lot coarser.
> >>>
> >>>We don't know ahead of time where we'll get the scroll events from. Set a
> >>>default scroll distance of 15 and multiply any wheel clicks we get by this
> >>>value.
> >>>
> >>>Signed-off-by: Peter Hutterer <peter.hutterer at who-t.net>
> >>>---
> >>>15 is more-or-less a magic value, it feels just right on my box here
> >>
> >>Hmm, this is somewhat different from what we discussed in our mail conversation.
> >
> >indeed, I had that first, then compared it to the evdev driver and decided
> >that this one is the better approach after all, explanation below.
> >
> >>First of all the problem most users are reporting and I'm seeing myself is not
> >>that mouse wheel scrolling is too slow (which this patch seems to imply), but
> >>rather that finger scrolling is much too fast, see e.g.:
> >>
> >>https://bugzilla.redhat.com/show_bug.cgi?id=1198467
> >>
> >>What I understood from our discussion on this is that the idea for
> >>mouse wheel scrolling was to emulate discrete-value number of button
> >>4 / 5 clicks and let X do the translation into scrolling axis, giving
> >>us the exact same scroll wheel speed as the evdev driver.
> >>
> >>That and for finger scroll events actually make things slower by applying
> >>a multiplication factor < 1.0 .
> >
> >X has two ways for a driver to submit scroll events: buttons 4-7 or data in
> >a scroll valuator. Because clients may rely on either of those methods
> >exclusively, the server emulates the other method.
> >
> >If set up, a driver defines a scroll distance. A valuator movement of that
> >scroll distance is equivalent to one mouse wheel click, and vice versa.
> >So if the driver sends a button 5 click, the server emulates a
> ><distance> motion event. If the driver sends a <distance> motion event, the
> >server emulates a button 4 click. The distance accumulates in the server, so
> >if you send <distance/2> twice, the server will only emulate the click event
> >on the second event.
> >
> >This is what the scroll distance does here - a movement of 15 on the
> >touchpad is now equivalent to a mouse wheel click. So this patch does slow
> >down the touchpad scrolling while leaving the mouse wheel as-is.
> >
> >This is a better approach (and a smaller diff) than the button click
> >approach I suggested initially because it gives us some smooth scrolling on
> >the wheel as well. A REL_WHEEL value of 2 will now result in a single smooth
> >scroll event that can be used for speed calculation. Posting the button
> >events directly would prevent that.
> >
> >Ideally we could just leave the scroll distance at 1 for devices that only
> >have mouse wheels but we don't know this at device init time. Hence the
> >default distance optimized for touchpads, then we multiply by that distance
> >for wheel clicks. The actual value of the scroll distance is meaningless,
> >it's just a reference to know how many "scroll units" a motion event
> >represents. IIRC synaptics currently uses a default of 100 and that's in
> >device coordinates.
> >
> >So in short, this patch does what we want, it slows down touchpad scrolling
> >while leaving wheel scrolling as-is.
> 
> Ah thanks for the explanation. Xorg sometimes has too many levels of
> indirection making things confusing...
> 
> Given the above this patch is:
> 
> Reviewed-by: Hans de Goede <hdegoede at redhat.com>
> 
> Regards,
> 
> Hans
> 
> p.s.
> 
> We should probably create an updated Fedora package for this, and push it as
> an F-22 update, making it close:
> https://bugzilla.redhat.com/show_bug.cgi?id=1198467
> 
> I can take care of that if you want me to. Please let me know either way.

already building in koji, thanks for the review

Cheers,
   Peter