having this as a request on an open session may cause extra dialogs to user

[blairmacintyre]

Having the configuration of world tracking that this be a call on the session will allow it to be updated while the session is running, which is good

 planeDetectionState : {
   enabled : true
 }

BUT, it also means that the call may happen after a UA has asked the user if they will approve WebXR starting, which may require another dialog.

Can we change this to add something like:

navigator.xr.requestSession('immersive-ar', {worldKnowledge: true})
      .then(onSessionStarted)
      .catch(err => {
        // May fail for a variety of reasons. Probably just want to
        // render the scene normally without any tracking at this point.
        window.requestAnimationFrame(onDrawFrame);
      });

We could still support popping up permissions if sensing state is called when permissions haven't been requested. So

function onSessionStarted(session) {
  // Store the session for use later.
  xrSession = session;
  xrSession.updateWorldSensingState({
      planeDetectionState : {
         enabled : true
     })

could pop up permissions if worldKnowledge hasn't been requested. This would, however, that updateWorldSensingState is a Promise, since it could fail:

xrSession.updateWorldSensingState({
      planeDetectionState : {
         enabled : true
     }).then(stateUpdated)
      .catch(err => {
        // May fail for a variety of reasons, depending on the implementation and the 
        // permissions granted by the user, or the capabilities of the platform
      });

Also, two other things here:

1. for the option for requestSession, I suggest worldKnowledge, meaning "this page has access to world knowledge". The sensing and tracking will happen regardless, in the platform, even if it's not available to this app.

2. I change updateWorldTrackingState to updateWorldSensingState because tracking is about "tracking changes and motion", while sensing is broader (e.g., detecting static structure, etc).

UPDATE: Changed a bit of the text above for clarity. This is also discussed in #7

[blairmacintyre]

hey @toji look, another candidate for requestSession options! 😎

[blairmacintyre]

@johnpallett @bialpio comments welcome. I am probably going to start fiddling with an implementation later today (I hope)

[bialpio]

Link to PR: immersive-web/webxr#689.

[bialpio]

Closing this issue, I will be reworking the explainer to address this concern. The core API seems to be moving away from configuring the session at run-time, so this proposal makes sense.