Re: [PATCH v4] HID: hid-multitouch: support fine-grain orientation reporting

From: Peter Hutterer
Date: Wed Oct 11 2017 - 18:59:54 EST


On Wed, Oct 11, 2017 at 10:43:24PM +0200, Henrik Rydberg wrote:
> > > > , but I'd go for fixing the documentation. And re-reading it, it's not
> > > > clear that the doc tells us to have [0,90]. It mentions negative values
> > > > and out of ranges too, so we might just as well simply clarify that we
> > > > rather have [-90,90], with 0 being "north".
> > >
> > > ... I'd like the documentation fix to go in together in one go with this
> > > patch if possible.
> > >
> >
> > Sounds like a plan.
>
> How about this patch?
>
> Henrik
>
> ---
>
> From b14f92066dfab3f8a255ec7b5a30cb1a864dc62f Mon Sep 17 00:00:00 2001
> From: Henrik Rydberg <rydberg@xxxxxxxxxxx>
> Date: Wed, 11 Oct 2017 22:41:39 +0200
> Subject: [PATCH] Input: docs - clarify the usage of ABS_MT_ORIENTATION
>
> As more drivers start to support touch orientation, clarify how the
> value range should be set to match the expected behavior in
> userland.
>
> Signed-off-by: Henrik Rydberg <rydberg@xxxxxxxxxxx>
> ---
> Documentation/input/multi-touch-protocol.rst | 14 ++++++++------
> 1 file changed, 8 insertions(+), 6 deletions(-)
>
> diff --git a/Documentation/input/multi-touch-protocol.rst b/Documentation/input/multi-touch-protocol.rst
> index 8035868..a0c5c03 100644
> --- a/Documentation/input/multi-touch-protocol.rst
> +++ b/Documentation/input/multi-touch-protocol.rst
> @@ -269,15 +269,17 @@ ABS_MT_ORIENTATION
> The orientation of the touching ellipse. The value should describe a signed
> quarter of a revolution clockwise around the touch center. The signed value
> range is arbitrary, but zero should be returned for an ellipse aligned with
> - the Y axis of the surface, a negative value when the ellipse is turned to
> - the left, and a positive value when the ellipse is turned to the
> - right. When completely aligned with the X axis, the range max should be
> - returned.
> + the Y axis of the surface (north). A negative value should be returned when
> + the ellipse is turned to the left (west),

this bit is good.


> + with the smallest value reported
> + when aligned with the negative X axis. The largest value should be returned
> + when aligned with the positive X axis.

this bit is less precise than before, because 'smallest' doesn't mean
'minimum' but smallest value. so a device announcing -90,90 could think that
returning -120 is a good idea for X alignment. I liked the previous "When
completely aligned with the X axis, the range max should be returned.", it
was less ambiguous.

replacing 'smallest value'/'largest value' with -range_max/range_max should
be sufficient here.


> +
> + The value range should be specified as [-range_max, range_max].

I'd really like this to be [0, max] == can only detect one quarter/half and
[-max, +max] == can detect both directions. It's one extra bit of
information that may come in useful at some point.

> Touch ellipsis are symmetrical by default. For devices capable of true 360
> - degree orientation, the reported orientation must exceed the range max to
> + degree orientation, the reported orientation will exceed range_max, in order to
> indicate more than a quarter of a revolution. For an upside-down finger,
> - range max * 2 should be returned.
> + +- 2 * range_max should be returned.

ack to this bit

Cheers,
Peter

>
> Orientation can be omitted if the touch area is circular, or if the
> information is not available in the kernel driver. Partial orientation
> --
> 2.14.1
>