[Webkit-unassigned] [Bug 221225] Implement WebXR getViewerPose and getPose

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=221225

--- Comment #13 from youenn fablet <youennf at gmail.com> ---
(In reply to Imanol Fernandez from comment #12)
> (In reply to youenn fablet from comment #10)
> > WebXRSpace was previously taking a Ref<WebXRSession> and this patch is
> > changing it to a WeakPtr<WebXRSession>.
> > With this change, WebXRSpace needs to handle the case of a null
> > WebXRSession, while previously, it was not possible. Can you describe why
> > this is good to do so?
> > 
> > Are we getting closer to spec? It seems this particular change could
> > potentially be observable (before GC, WebXRSpace does something, after GC it
> > does something different).
> 
> I made the change when I added
> https://immersive-web.github.io/webxr/#xrsession-viewer-reference-space in
> order to avoid a cycle between Session and the viewer reference space.

>From the spec I can see:
- Each XRSpace has a session which is set to the XRSession that created the XRSpace.
- Each XRSession has a viewer reference space, which is an XRReferenceSpace of type "viewer" with an identity transform origin offset.

It seems that as long as XRSpace is alive, its XRSession should be alive.
If XRSpace is never changing of XRSession, one possibility is to have:
- XRSession is RefCounted<XRSession>
- XRSpace is no longer a RefCounted<XRSpace>
- XRSpace stores a XRSession&
- XRSpace implements its ref/deref methods by calling ref/deref of its XRSession.

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