W3C home > Mailing lists > Public > public-geolocation@w3.org > August 2014

Re: Proposal to add unit quaternion representation to the Device Orientation event.

From: Rich Tibbett <richt@opera.com>
Date: Sun, 31 Aug 2014 08:13:22 +0200
Message-ID: <CAAsrAZC-DtU3odQ6Ccaej5-kUYen1Qp1n=LAEjOeaC6246iWRA@mail.gmail.com>
To: Tim Volodine <timvolodine@google.com>
Cc: "Mandyam, Giridhar" <mandyam@quicinc.com>, Mounir Lamouri <mounir@lamouri.fr>, public-geolocation <public-geolocation@w3.org>, Rob Manson <roBman@buildar.com>
On Fri, Aug 29, 2014 at 6:28 PM, Tim Volodine <timvolodine@google.com> wrote:
> The idea itself to provide screen adjusted orientation is nice, but I think
> there are some issues on the API / implementation level.
>
> From talking to Mounir I understand there can be multiple different screen
> orientations per 'window'. This is in contrast to Device Orientation where
> there is only one orientation per device (i.e. per browser process). In
> addition to that it is technically possible to change screen orientation
> while device orientation does not change so in that case screen adjusted
> angles should be updated as well. Device Orientation API would need to
> listen to screen orientation so would become more complicated and somewhat
> duplicate the Screen Orientation API.

This is very good feedback and I plan to incorporate this in to the
current proposals.

>
> If we provide a quaternion I think we can get away with minimal plumbing in
> javascript to compute screen orientation where needed:
> let's say q is the current device orientation quaternion and A current
> screen orientation angle then:
>
> screen_q = [cos(A/2) -n*sin(A/2)] * q   (quaternion multiplication)
> where n = q.Rotate([0 0 1])      (quaternion conjugation)
> (i.e. n is the normal to the screen)
>
> that way the Device Orientation / Screen Orientation APIs and their
> implementations can be kept separate.

It is just that nobody really does this right now. This is simply too
complex for common use cases such as applying simple CSS-based
transforms to on-screen objects.

Just this week http://www.google.com/teapot was released. You cannot
pour the tea correctly if you rotate your screen to landscape mode. On
devices that allow 180 degree screen rotation, the opposite action
pours the tea. It's amazing!

This is how device orientation is used today - broken unless you hold
your device in a very particular way. The average web developer should
not need to understand the nuanced dynamics of device orientation vs
screen orientation. At it's most basic level, it should just work the
same way in any screen orientation.

Google Engineers could fix the teapot pour on that page using the
solution you proposed above but that requires several orders of
magnitude more understanding of the mathematics of device orientation
and, in particular, quaternion multiplication to get it working
correctly.

It's just not feasible to expect *every web developer* to do that *all
the time*. Whenever they don't do that the device orientation
interaction will be broken.

The proposed alternative allows web developers to replace occurrences
of `.gamma` with `.screenGamma` in their code and the problem would be
solved equally well. _If_ they then need a quaternion or rotation
matrix then there is a straight-forward JavaScript function for that
at http://w3c.github.io/deviceorientation/spec-source-orientation.html#worked-example-2.

- Rich

>
>
> On Thu, Aug 28, 2014 at 11:07 AM, Rich Tibbett <richt@opera.com> wrote:
>>
>> On Sun, Aug 3, 2014 at 9:53 PM, Mandyam, Giridhar <mandyam@quicinc.com>
>> wrote:
>> > Having heard no objections, I am going to ask Tim/Rich in their capacity
>> > as Editors of the DeviceOrientation spec to create an ED with the
>> > quarternion proposal incorporated.
>> >
>> > Note that Mounir has posted to the public-fx list a suggestion to
>> > incorporate this into the Geometry specification:  see
>> > http://lists.w3.org/Archives/Public/public-fx/2014JulSep/0076.html.  Thanks
>> > for Mounir for doing this.  If this feature is incorporated into the
>> > Geometry spec, the editors can adjust the DeviceOrientation specification
>> > accordingly.
>>
>> While I think is a good addition it does not solve the underlying
>> issue of getting DeviceOrientation to work when a device's display
>> rotates away from its default orientation. In addition, this is
>> already a solvable problem for web developers. We have provided code
>> examples to transform the provided 'alpha', 'beta' and 'gamma'
>> attributes to a Unit Quaternion (and a Rotation Matrix) in the
>> "Alternate device orientation representations" annex within the latest
>> editor's draft @
>>
>> https://w3c.github.io/deviceorientation/spec-source-orientation.html#worked-example-2.
>>
>> My concern here is that giving web developers a Quaternion
>> representation of the device orientation still relies on them to
>> correctly transform that Quaternion relative to screen orientation
>> angle changes in order for their applications to work in any screen
>> orientation. Given that we still require web developers to apply their
>> own screen orientation transform to this fixed device frame quaternion
>> I wonder if this only partially solves the problems web developers are
>> having.
>>
>> I would rather we provided screen-adjusted device orientation values
>> on DeviceOrientation Event objects and let web developers construct
>> their own Quaternions and/or Rotation Matrices in JavaScript for now.
>> This issue has been discussed on public-webapps@ starting at
>> http://lists.w3.org/Archives/Public/public-webapps/2014JulSep/0203.html
>> and on the W3C DeviceOrientation Github issue tracker at
>> https://github.com/w3c/deviceorientation/issues/4. Currently we have
>> seen tentative support from Mozilla (and Opera) for this approach.
>> What do other browser implementers feel about prioritizing this
>> addition above and perhaps instead of adding a Quaternion
>> representation to the spec?
>>
>> I have made a pull request for adding 'screenAlpha', 'screenBeta' and
>> 'screenGamma' attributes to the DeviceOrientationEvent interface at
>> https://github.com/w3c/deviceorientation/pull/10. I also currently
>> have a tentative Chromium patch ready to add these attributes pending
>> general consensus on this mailing list.
>>
>> - Rich
>>
>> >
>> > Thanks,
>> >
>> > -Giri
>> >
>> > -----Original Message-----
>> > From: Mandyam, Giridhar [mailto:mandyam@quicinc.com]
>> > Sent: Thursday, July 24, 2014 8:40 AM
>> > To: Mounir Lamouri; Tim Volodine; public-geolocation
>> > Cc: Rich Tibbett; Rob Manson
>> > Subject: RE: Proposal to add unit quaternion representation to the
>> > Device Orientation event.
>> >
>> > Hi Mounir,
>> > It just went to Last Call:
>> > http://www.w3.org/TR/2014/WD-geometry-1-20140626/.  I wonder if we bring
>> > this in at this point.
>> >
>> > One possibility is to suggest this as a change to the Geometry I/F
>> > Module Level 1 spec prior to the August 7 deadline for LC comments, and go
>> > ahead and list the quaternion interface in DeviceOrientation until it is
>> > adopted in the Geometry I/F.
>> >
>> > Does anyone else have opinions on Mounir's suggestion?
>> >
>> > -Giri
>> >
>> > -----Original Message-----
>> > From: Mounir Lamouri [mailto:mounir@lamouri.fr]
>> > Sent: Thursday, July 24, 2014 8:30 AM
>> > To: Mandyam, Giridhar; Tim Volodine; public-geolocation
>> > Cc: Rich Tibbett; Rob Manson
>> > Subject: Re: Proposal to add unit quaternion representation to the
>> > Device Orientation event.
>> >
>> > Giri, should we investigate adding this to
>> > http://dev.w3.org/fxtf/geometry/ ?
>> >
>> > -- Mounir
>> >
>> > On Thu, 24 Jul 2014, at 22:43, Mandyam, Giridhar wrote:
>> >> If there are no objections to this proposal provided to the mailing
>> >> list by 5 PM US Pacific Time, August 1, 2014, then I will request the
>> >> editors (Tim and Rich) to include this proposal in the
>> >> DeviceOrientation spec.
>> >>
>> >> Thanks,
>> >>
>> >> -Giri
>> >>
>> >> -----Original Message-----
>> >> From: Mounir Lamouri [mailto:mounir@lamouri.fr]
>> >> Sent: Thursday, July 17, 2014 3:05 AM
>> >> To: Tim Volodine; public-geolocation
>> >> Cc: Rich Tibbett; Rob Manson; Mandyam, Giridhar
>> >> Subject: Re: Proposal to add unit quaternion representation to the
>> >> Device Orientation event.
>> >>
>> >> On Thu, 17 Jul 2014, at 00:29, Tim Volodine wrote:
>> >> > Proposed interface changes:
>> >> >
>> >> > [Callback, NoInterfaceObject]
>> >> > interface OrientationQuaternion {
>> >> >   readonly attribute double x;
>> >> >   readonly attribute double y;
>> >> >   readonly attribute double z;
>> >> >   readonly attribute double w;
>> >> > }
>> >>
>> >> That sounds great! Should we consider adding DOMQuaternion to
>> >> http://dev.w3.org/fxtf/geometry/ instead of creating it inside this
>> >> spec?
>> >>
>> >> -- Mounir
>> >>
>> >
>
>
Received on Sunday, 31 August 2014 06:13:50 UTC

This archive was generated by hypermail 2.4.0 : Friday, 17 January 2020 19:51:08 UTC