[PATCH v2] protocol: Extend wl_touch with touchpoint shape event

[Andreas Pokorny]

Hi,
Some questions below..

On Wed, Apr 6, 2016 at 11:52 PM, Peter Hutterer <peter.hutterer at who-t.net>
wrote:

> On Wed, Apr 06, 2016 at 10:17:35AM -0700, Dennis Kempin wrote:
> > On Tue, Apr 5, 2016 at 5:26 PM, Peter Hutterer <peter.hutterer at who-t.net>
> wrote:
> > > On Tue, Apr 05, 2016 at 01:09:31PM -0700, Dennis Kempin wrote:
> > >> [...]
> > >> +      </description>
> > >> +      <arg name="id" type="int" summary="the unique ID of this touch
> point"/>
> > >> +      <arg name="major" type="fixed" summary="length of the major
> > >> axis in surface coordinates"/>
> > >> +      <arg name="minor" type="fixed" summary="length of the minor
> > >> axis in surface coordinates"/>
> > >> +      <arg name="orientation" type="fixed"
> > >> +           summary="angle between major axis and surface x-axis in
> degrees"/>
> > >> +    </event>
>

Jumping on the major/minor train. Is there no interest in pressure values?
It seems that more accurate touchscreens that may offer reproducible
pressure values
become mainstream..


> > [...]

> > Maybe we could include a fallback event for devices that do not have
> > good support?
> > One that would only use a single value to describe the size of a
> > touch, normalized
> > to 0..1. In practice, I do not think we could put any more requirements
> on this
> > value. There is no way for us to tell how tell if a device is using
> > the full range
> > (0 to reported max axis value), and in a bad case we might end up with
> that
> > size being in the range of 0 to 0.1.
> >
> > Let me know what you think about this.
>
> I'm mostly thinking about how to enable this in libinput from a technical
> perspective, and the obvious solution would be whitelisting or blacklisting
> devices, combined with the calibration you use as well.
>
> the fallback wouldn't be normalized but simply skipping it where we can't
> be
> sure. to do that, we need to do one thing though: split up the events into
> area and orientation as separate events. we can send orientation even when
> the area is unknown.
>
> how does that sound?
>

Are you referring to libinput events or wayland events here? Why would
splitting the events help?
I have also seen touchscreens just offering a major axis and an
orientation. That is an edge
case but even there we could have finger-heuristic to estimate a minor
value..

@Dennis: I am curious how complex the contact size calibration function in
chrome os is.

regards
Andreas
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