Two-finger width setting on Dell XPS 15 9650

[Vahe Oughourlian]

On Mon, Jun 19, 2017 at 5:58 PM Peter Hutterer <peter.hutterer at who-t.net>
wrote:

> On Fri, Jun 16, 2017 at 05:48:31PM +0000, Vahe Oughourlian wrote:
> > On Thu, Jun 15, 2017 at 3:23 PM Peter Hutterer <peter.hutterer at who-t.net
> >
> > wrote:
> >
> > > On Tue, Jun 13, 2017 at 01:46:12AM +0000, Vahe Oughourlian wrote:
> > > > I'm working with a Dell XPS 15 9650 using libinput. Using the
> Synaptics
> > > > driver, a property is available to set the maximum distance two
> fingers
> > > may
> > > > be apart before a two-finger scroll can be triggered, called
> "Synaptics
> > > > Two-Finger Width." At the moment, two fingers anywhere on the
> touchpad
> > > will
> > > > switch it over to a two-finger scroll.
> > > >
> > > > I ran across a post from Peter Hutterer (
> > > >
> > >
> https://who-t.blogspot.de/2016/04/why-libinput-doesnt-have-lot-of-config.html
> > > )
> > > > discussing the intention to minimize options in libinput, and there
> > > doesn't
> > > > seem to be a setting that affects this behavior that I could find.
> Given
> > > > that, is the most appropriate thing to file a bug for this particular
> > > > trackpad to have a reasonable default added for this device, or is
> this a
> > > > setting libinput eventually intends to support? Or is this setting
> > > already
> > > > available?
> > >
> > > it's not an available configuration, no. But the main question is what
> > > you're actually trying to achive? I'm assuming that any finger distance
> > > limits are not the issue per se but that there's something else that
> > > affects
> > > how you can interact.
> > >
> > > Cheers,
> > >    Peter
> > >
> > >
> > There are a couple common cases:
> >
> > 1. My left thumb may drift onto the upper left corner of the touchpad (in
> > the usual home-row typing position) while my right hand is controlling
> the
> > touchpad. Despite the 70mm-ish distance between the fingers, the next
> > cursor motion by the right hand is treated as a two-finger scroll.
>
> https://bugs.freedesktop.org/show_bug.cgi?id=99703
>
> > 2. I often use the physical click as part of a drag-and-highlight. While
> > there are dead zones at the bottom of the mouse for the virtual buttons,
> if
> > my thumb isn't quite low enough on the right hand, the moment before
> > actually clicking the physical button underneath the trackpad will turn
> > into a two-finger scroll. This also can occur at the end of the click as
> > I'm lifting the thumb, and the next motion is a scroll.
>
> not quite the same but similar to the bug above. I think that's something
> we'd have to revisit once we manage to get a hand on 99703
>

Sure, I'll keep an eye on 99703 and give it a shot when it comes out.


>
> > My intention was to set the distance between two fingers such that they'd
> > have to be much closer together (within 20mm, for example) to avoid these
> > accidental scroll events.
>
> tbh, I don't think that's the right solution and that's also why there's no
> config option for it. Any distance-based guessing of intentions should
> always be internal to libinput because once we expose the option we'll have
> to keep it around forever. And exposing an option promises behaviour.
>

Completely agree. Mostly this is me working backwards from an existing
option in the old version to find a possible solution.


>
> I think fixing 99703 will remove most of your issues.
>

I'm not sure in this case. While it looks like 99703 will solve the case
mid-movement, it doesn't really address the cases at the start of the
movement when two fingers are on the pad.


>
> > One thing I have also noticed on other trackpads (on other OSes,
> > admittedly) is that both fingers seem to have to be in motion to trigger
> a
> > two finger scroll, whereas I seem to be able to trigger a two-finger
> scroll
> > on the Dell's trackpad by moving one finger while two fingers are on the
> > trackpad at a time. Perhaps that's the solution here?
>
> yeah, that's been a long-standing feature of the 2fg scroll on linux. not
> sure we can/should get rid of that.
>

I'm entirely sympathetic to your perspective here about changing existing
and expected behavior, and no doubt you'd hear from a cadre of unhappy
users if the behavior were to change. However, I'd like to push back here.
I think two fingers moving gives significantly more intention to the
gesture, and as I'm seeing in my experience, it's happening enough
unintentionally to me to raise the question. I don't think it makes sense
from a user perspective to have any two touch points anywhere on the pad
trigger a scroll.

Adding a configuration seems like the wrong solution per the direction the
project is taking, but changing the existing behavior is also undesirable.
What kind of consideration might move you to change this scroll behavior?


>
> Cheers,
>    Peter
>
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