WebXR: Set isPresenting flag before dispatching sessionstart event

[KabirSheemul]

Description of the problem

While starting an XR session, sessionstart event is dispatched from WebXRManager.js after a successful XR session has been established. After that, the isPresenting flag is set to true. As a result when we add an event listener for sessionstart, in the callback function isPresenting is returning false.

function onRequestReferenceSpace( value ) {
    referenceSpace = value;
    animation.setContext( session );
    animation.start();
    scope.dispatchEvent( { type: 'sessionstart' } );
    scope.isPresenting = true;
}

Is this behavior intentional? I think we should set the flag true before dispatching the event.

Three.js version

• r112

[Mugen87]

If the order is changed, it's also necessary to switch the order when sessionend is fired. Meaning isPresenting should be set to false first and then sessionend is dispachted.

[timothyallan]

If the order is changed, it's also necessary to switch the order when sessionend is fired.
Meaning isPresenting should be set to false first and then sessionend is dispachted.

This would solve some hacks I'm currently doing. In particular, I currently have to do a timeout hack on sessionend to get around this. My canvas needs to be resized after the session is ended, but I can't resize it as presenting is true still on sessionend.