Immersive Web Newsletter 1,

Recent Spec Changes - 2019-01-01
At the start of this year there were significant changes to the Immersive
Web. Here are some of the significant merged PRs.

Edit on Github
<https://github.com/immersive-web/administrivia/blob/master/newsletter/2019-01-01-Recent_Spec_Changes-agenda.md>
.

   - Add XRRenderState to the spec
   <https://github.com/immersive-web/webxr/pull/458> - Merged Mon Jan 28
   2019 - spec

Also fixed a minor inconsistency in the explainer regarding the name of the
associated dictionary.


   - Describe the identity reference space
   <https://github.com/immersive-web/webxr/pull/459> - Merged Fri Jan 11
   2019 - explainer

This adds a new reference space type that takes the place of passing null
as the mechanism to return identity poses. Move to handle it with a new
space like this was due the desire to allow the originOffset to still be
used even in situations with no tracking.

Nell and I had a question about whether or not the included code sample is
something that belongs in the spec and/or explainer, since it's a pretty
specific case and the purpose of this doc is not to teach anyone quaternion
math. Still, it seems like a good demonstration of why this new type
matters. Thoughts?


   - Handle pose queries in a more generalized fashion
   <https://github.com/immersive-web/webxr/pull/460> - Merged Tue Jan 15
   2019 - spec,explainer

This PR is intended to pave the way for making it easier to introduce new
types of pose tracking functionality in the future by making how we query
poses for almost everything more generalized. (The viewer pose is still
special because it's the only thing that needs the views array, but even
there this change makes it less of an outlier.) Ideally this change will
make it much easier to reason about adding things like anchors in the
future, and also serves to set the stage for #384 as well as fixing the
frame-bound concern brought up in that issue.


   - Make outputContext part of the XRRenderState
   <https://github.com/immersive-web/webxr/pull/504> - Merged Fri Feb 08
   2019 - explainer

This was discussed at the Jan 2019 F2F as part of a broader topic of
refactoring output contexts. Making output contexts mutable as described in
the PR was seen as non-controversial while other aspects of the discussion
did not reach an agreement.

Change moves setting the outputContext from a session-creation time event
that was then immutable to part of the XRRenderState, which allows it to be
changed at any point. outputContext's can still only be associated with a
single session at a time, so it will be removed from any previous session
when reassigned.


   - Spec XRPresentationContext creation
   <https://github.com/immersive-web/webxr/pull/501> - Merged Wed Feb 06
   2019 - spec

fixes XRPresentationContext should be a dictionary (
https://github.com/immersive-web/webxr/issues/449)


   - Update explainer.md <https://github.com/immersive-web/webxr/pull/508>
   - Merged Tue Feb 05 2019 - explainer,copy-change

taken the liberty of updating a bunch of relatively minor grammatical
changes and minor working updates, such as splitting up very long sentences
...only 1 or 2 actual edits of any semantics ..really nice explainer! just
requesting pull for these edits


   - Added XRPose and related refactors to the spec
   <https://github.com/immersive-web/webxr/pull/496> - Merged Wed Feb 13
   2019 - spec

refactoring


   - Introduce spec internal concept and start to use Infra spec definitions
   <https://github.com/immersive-web/webxr/pull/518> - Merged Tue Feb 12
   2019 - spec

This change defines a spec internal concept, XR device, distinguished from
the XR object's XR device internal slot. The XR device concept is not
exposed to the script surface but just used by spec internal algorithms.
The XR device concept represents an XR device and the XR object's XR device
internal slot can hold an XR device.

This change moves the definition of the list of supported modes from XR
object's XR device internal slot to XR device concept. This makes us be
able to define XR device's states under the concept rather than the
platform object's internal slot and write algorithm steps that reference
those states more easly.

This change specifies navigator.xr attribute's getter and the creation of
XR object associated with a Navigator object.

This change introduces the Infra spec defintions to define XR object's
properties and algorithm steps: select an XR device, supportsSeesionMode()
method, requestSession() method for this particular PR. (More to come.)


   - Add XRSession.viewerSpace and tidy XRSpace explanations
   <https://github.com/immersive-web/webxr/pull/491> - Merged Mon Feb 04
   2019 - explainer

This PR addresses a few related things I noticed now that the getPose()
changes have landed

   1. We were missing a section that focused on the descriptions of XRSpace
   and XRPose themselves. I added this to spatial-tracking-explainer.md and
   moved the XRRigidTransform and XRRay types to be together in that
   document's idl section
   2. Having an XRSpace representing the viewer would be really handy for a
   few reasons. First, it would allow pose data to be queried relative to the
   viewer, such as "where are the hands relative to the headset?", without
   having to do extra matrix math. Second, it's easier to describe the
   consistent targetRaySpace for 'gaze' based input sources. Third, it becomes
   one of the XRSpaces from which hit testing can be done (See PR #493).
   3. With both of the above changes in the spatial-tracking-explainer.md,
   it made sense to move some of the smaller subsections around so content was
   grouped in a more sensible manner.
   4. Added a check on the results of getPose() in the explainer sample code
   5. While I was at it, this fixes #478 in the explainer, though the
   actual spec will still need updating.
   6. Fixed a few typos, too.


   - Adding an explainer for real-world hit testing
   <https://github.com/immersive-web/webxr/pull/493> - Merged Mon Feb 04
   2019 - explainer

This PR contains an explainer with a proposal for adding real-world hit
testing to WebXR. It builds strongly on the great work done by
@lincolnfrog, @judax, @blairmacinyre, and others to clearly define the
problem space. While it is expected that hit-testing will often be used to
create anchors, this PR does not include a proposal for an anchors API;
that will come in a subsequent PR but still needs a bit more design work.

Rather than a long-winded PR description, I'm hoping that the explainer
stands on its own. Please don't hesitate to call out areas that are unclear.

For clarity's sake, the base for this PR is the input-explainer-cleanup
branch in PR #492


   - Restructures input-explainer.md to improve clarity and prep for
   hit-testing proposal <https://github.com/immersive-web/webxr/pull/492> -
   Merged Mon Feb 04 2019 - explainer

While working on the proposal for adding hit testing to WebXR, it became
clear that to easily explain the new hit testing concepts, the input
explainer needed a bit of house keeping. I ended up moving a large portion
of the document content around, so it may be easier to just view the new
version of the document rather than the diff.

The intent with this PR is to clarify the descriptions of existing
functionality, not to introduce changes in that functionality. That said, I
expect we may uncover shared misunderstandings through the cleaner text, so
please do call out things that don't match your expectations. I also
removed the grab-and-drag sample code for the moment; it makes a
reappearance in the hit-testing-explainer in PR #493

For ease of diffing, the base for this PR is adding-viewerSpace branch
behind PR #491


   - Narrow application of the 'unstable' markup in the spec
   <https://github.com/immersive-web/webxr/pull/510> - Merged Wed Feb 06
   2019 - spec,copy-change

Previously the entire spec was contained in one big "unstable" section.
This update changes that to only apply to sections of the spec that the
editors (conservatively) feel may still see breaking changes.

Sections not marked "unstable" are *not* considered "done". They are
expected to still see updates to prose, algorithm improvements, and new
additive functionality, but are not likely to have
backwards-compatibility-breaking changes made to them going forward.


   - Describe exceptions that updateRenderState may throw.
   <https://github.com/immersive-web/webxr/pull/511> - Merged Wed Feb 06
   2019 - spec

Based on some observations made while attempting to implement
updateRenderState in Chrome.


   - Specify that frame callbacks are not called without a base layer
   <https://github.com/immersive-web/webxr/pull/512> - Merged Tue Feb 12
   2019 - spec

Pretty self-explanatory. We shouldn't execute callbacks if there's no
render target, especially since that facilitates tracking the user
movements without an associated visual changes.