On Sun, Feb 21, 2016 at 2:04 PM Peter Hutterer <peter.hutterer@xxxxxxxxx> wrote:
>
> On Thu, Feb 18, 2016 at 10:19:30AM -0800, Dmitry Torokhov wrote:
> > On Tue, Feb 09, 2016 at 01:56:05PM -0800, Charles Mooney wrote:
> > > Hello all,
> > >
> > > I'm currently working with a touchpad vendor with a new device that
> > > supports a limited form of hover detection. Their sensor is able to
> > > detect the presence or absence of a finger/hand/palm hovering over the
> > > sensor without touching it, but is unable to report any more details
> > > about it. This is a more limited form of hover detection than some
> > > devices which attach a hover state to each finger they see, and can
> > > even report x/y coordinates to hovering finger.
> > >
> > > Instead of using ABS_MT_DISTANCE, it appears that the correct event to
> > > use would be ABS_DISTANCE, since the value is not tied to a specific
> > > finger. I would like to check with you all about how this value is
> > > intended to be used, because it's not quite as obvious to me as I
> > > first thought.
> > >
> > > We need to handle three basic states:
> > > 1. At least one finger is touching the pad.
> > > 2. Something is hovering, but nothing is actually touching.
> > > 3. Nothing is touching the pad and nothing is detected hovering over it either
> > >
> > > It's seems clear to me that an ABS_DISTANCE of zero should indicate
> > > state #1 and that any other legal positive value should indicate state
> > > #2, but I'm less clear on what the best way to handle state #3 is.
> > > Currently, I think the best strategy would be to use a value of
> > > ABS_DISTANCE = -1 to indicate that there are no fingers seen (hovering
> > > or otherwise), does that make sense?
> > >
> > > If not this, how else would you suggest that this ought to be done?
> >
> > As we discussed in person, I believe that reporting an "out of bounds"
> > value for ABS_DISTANCE when we have to use single-touch mode and thus do
> > not have a good way to invalidate a contact, is the easiest option.
> > Alternative would be to invent another SYN event, which I'd rather not.
> >
> > So for devices that support hovering but can not report individual
> > hovering contacts we should declare 0..N as ABS_DISTANCE range and report
> > following values:
> >
> > - 0 when a finger is actually touching
> > - 1..N for hovering fingers
> > - return X < 0 or X > N when no fingers are detected at all; in
> > practice I think we should simply report -1 in this case.
> >
> > Benjamin, Peter, Henrik, any concerns?
>
> on the touchpads that support hovering we're already using BTN_TOOL_FINGER
> together with ABS_DISTANCE, without needing out-of-range reports.
> BTN_TOUCH is the signal when a finger is physically touching (or ABS_PRESSURE
> if it exists and clients care about it).
>
> So the sequence Charles should send is:
>
> 3) <nothing> :)
> 2)
> EV_ABS ABS_DISTANCE <d> # for d > 0
> EV_KEY BTN_TOOL_FINGER 1
> EV_SYN SYN_REPORT 0
> 1)
> EV_ABS ABS_DISTANCE 0
> EV_ABS ABS_X <x>
> EV_ABS ABS_Y <y>
> ...
> EV_KEY BTN_TOUCH 1
> EV_SYN SYN_REPORT 0
> 2)
> EV_ABS ABS_DISTANCE <d> # for d > 0
> EV_KEY BTN_TOUCH 0
> EV_SYN SYN_REPORT 0
> 3)
> EV_KEY BTN_TOOL_FINGER 0
> EV_SYN SYN_REPORT 0
>
> This should work with at least libinput, though I have to check what happens
> when you don't send x/y on the first event. I think this would need a patch
> in libinput, but that's doable. And it's the same sequence we also use for
> e.g. pen tools that support hovering as well.
>
> Cheers,
> Peter
Hi Peter,
It looks like you're suggesting to use "BTN_TOOL_FINGER" as a signal
as to weather or not the value in "ABS_DISTANCE" is valid or not.
1. No finger detected anywhere:
BTN_TOOL_FINGER = 0
ABS_DISTANCE = n/a
2. Finger seen hovering but not touching:
BTN_TOOL_FINGER = 1
ABS_DISTANCE > 0
2. Finger touching:
BTN_TOOL_FINGER = 1
ABS_DISTANCE = 0
Am I understanding that correctly?
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