Page load blocked on JS error TypeError: vrDisplay is null (thrown intermittently); causes Gecko to crash!

[caseyyee]

when opening in Firefox using windows MR. Seems to happen when headset is idle on not on my head.

Not exactly sure where it is originating from. Polyfill maybe?

[cvan]

This smells like a Firefox platform bug. If so, I can file a Bugzilla Gecko bug. Perhaps this could be solved in the meantime with a hack of adding an event listener for vrdisplayconnect: window.addEventListener('vrdisplayconnect', function () { getVRDisplays(); });

somewhat related: looks like the vrdisplayconnect event still fires every time upon page load if there's a VR display connected

also, could you paste a screenshot and/or JS Console errors/warnings?

[cvan]

@caseyyee: do you think this belongs in the initial milestone?

[caseyyee]

[caseyyee]

Actually, I think this might be C# code in Unity. Some types of errors are raised as alert boxes for some reason. I'll dig in.

@cvan its intermittent. I'll see if I can resolve, but I don't think we need to block.

Either way, the experience loads after you press OK anyways.

[cvan]

@caseyyee:

if you log each event in onUnity, what's the order of the events? I assume "Ready" is always getting fired first, yes?

try adding this to index.html:

          onProgress: unityProgress,
          handler: errorhandler
        });

        var errorhandler = function (msg, url, lineNo, columnNo, error) {
            console.error('Message: %s; URL: %s; Line: %s, Column: %s; Error:\n',
              msg,
              url,
              lineNo,
              columnNo,
              error);
          return false;
        };

[cvan]

from @kearwood:

call GetVRDisplays on load if you detect Firefox 58 and see if a VRDisplay is returned. Waiting for vrdisplayconnect before using GetVRDisplays is best in all other cases and in FF59+; however.

@caseyyee: can you try that?

[cvan]

having the headset on or off doesn't seem to affect this. I can't figure out reliable steps to reproduce this. @caseyyee: if you can, let me know.

[cvan]

additional follow up: I rebuilt the Unity project, and I encountered the issue immediately. and after I dismissed the alert prompt, Firefox Nightly crashed.

here's one of the crashes: https://crash-stats.mozilla.com/report/index/8b59877c-48ec-4d69-a5f4-9e2da0180208

looks like the crash happened at nsGlobalWindowInner::DispatchVRDisplayActivate(unsigned int, mozilla::dom::VRDisplayEventReason)

@kearwood: any ideas? (@caseyyee: looks like, regardless of the fix/workaround we discover, we ought to file a Gecko platform bug on Bugzilla for this.)

[delapuente]

It is worth solving or researching this issue bat not blocking on it so, moving to the next release.

[delapuente]

Can we retest this after merging #132 It is probable that PR can solve this too. But this is something we should address properly, talking to Unity folks to determine the exact order of the events.

[cvan]

also, I'll set a task item for me to file a Bugzilla bug. no matter how poorly I write my WebVR event listeners, I shouldn't be able to crash Gecko 💥!

[caseyyee]

works for me. reopen if you encounter this issue!