xrshim.js

{
	const REALAPI_URL = 'https://raw.githack.com/MozillaReality/webxr-ios-js/develop/dist/webxr.js';

	const API = [
		'XR',
		'XRSession',
		'XRRenderState',
		'XRFrame',
		'XRSpace',
		'XRReferenceSpace',
		'XRBoundedReferenceSpace',
		'XRView',
		'XRViewport',
		'XRRigidTransform',
		'XRPose',
		'XRViewerPose',
		'XRInputSource',
		'XRInputSourceArray',
		'XRWebGLLayer',
		'XRSessionEvent',
		'XRInputSourceEvent',
		'XRInputSourcesChangeEvent',
		'XRReferenceSpaceEvent'
	];

	// Note: Currently (10/28/2019) EventTarget can't be extended on Safari
	//	 unlike FireFox and Chrome. So declaring our own here for now.
	//       But we don't expose so "navigator.xr instanceof EventTarget" will end up
	//       being false out of this scope. Any problems with this limitation?
	class EventTarget {
		addEventListener() {
			// @TODO: Relax this add/remove/dispatch event limitations?
			throw new Error('Shim: We don\'t expect user adds event before stating session.');
		}
		removeEventListener() {
			throw new Error('Shim: We don\'t expect user removes event before stating session.');
		}
		dispatchEvent() {
			throw new Error('Shim: We don\'t expect user dispatches event before stating session.');
		}
	}

	const install = () => {
		for (const name of API) {
			if (window[name] !== undefined) { continue; }
			switch (name) {
				case 'XR':
					installXR();
					break;
				case 'XRRenderState':
				case 'XRFrame':
				case 'XRView':
				case 'XRViewport':
				case 'XRRigidTransform':
				case 'XRPose':
				case 'XRInputSource':
				case 'XRInputSourceArray':
				case 'XRWebGLLayer':
					window[name] = class {
						constructor() {
							// Note: XRRigidTransform should be able to be instanciated by user
							//       even before starting session but prohibiting as Shim limitation so far.
							throw new Error('Shim: We don\'t expect user instanciates XR classes');
						}
					};
					break;
				case 'XRSession':
				case 'XRSpace':
					window[name] = class extends EventTarget {
						constructor() {
							throw new Error('Shim: We don\'t expect user instanciates XR classes');
						}
					};
					break;
				case 'XRReferenceSpace':
					window[name] = class extends XRSpace {
						constructor() {
							throw new Error('Shim: We don\'t expect user instanciates XR classes');
						}
					};
					break;
				case 'XRBoundedReferenceSpace':
					window[name] = class extends XRReferenceSpace {
						constructor() {
							throw new Error('Shim: We don\'t expect user instanciates XR classes');
						}
					};
					break;
				case 'XRViewerPose':
					window[name] = class extends XRPose {
						constructor() {
							throw new Error('Shim: We don\'t expect user instanciates XR classes');
						}
					};
					break;
				case 'XRSessionEvent':
				case 'XRInputSourceEvent':
				case 'XRInputSourcesChangeEvent':
				case 'XRReferenceSpaceEvent':
					window[name] = class extends Event {
						constructor() {
							throw new Error('Shim: We don\'t expect user instanciates XR classes');
						}
					};
					break;
				default:
					console.error('Unknown API name, ', name);
			};
		}
		if (navigator.xr === undefined) { navigator.xr = new XR(); }
	};

	const installXR = () => {
		let instanciated = false;
		window.XR = class extends EventTarget {
			constructor() {
				super();
				// Note: Allow instance creation only once and refuse from out of this scope.
				if (instanciated) {
					throw new Error('Shim: We don\'t expect user instanciates XR classes');
				}
				instanciated = true;
			}
			isSessionSupported(mode) {
				// Note: We support only immersive-ar mode for now.
				//       See https://github.com/MozillaReality/webxr-ios-js/pull/34#discussion_r334910337
				return Promise.resolve(mode === 'immersive-ar');
			}
			requestSession(mode, opts) {
				console.log("going to load from ", REALAPI_URL)
				return new Promise((resolve, reject) => {
					// Note: Uninstall fake XR classes here because the polyfill declares them.
					//       Until the polyfill is loaded they are undefined.
					//       Can this cause any problems?
					uninstall();

					const script = document.createElement('script');
					script.setAttribute('src', REALAPI_URL);
					script.setAttribute('type', 'text/javascript');

					let loaded = false;
					const loadFunction = () => {
						if (loaded) return;
						loaded = true;
						console.log("now the script is really loaded", navigator.xr);
						navigator.xr.requestSession(mode, opts).then(resolve).catch(reject);
					};
					script.onload = loadFunction;
					script.onreadystatechange = loadFunction;
					document.getElementsByTagName('head')[0].appendChild(script);
				});
			}
			get ondevicechange() { return null; }
			set ondevicechange(value) {
				// @TODO: Relax this limitation?
				throw new Error('Shim: We don\'t expect user sets devicechange event before starting session.');
			}
		};
	};

	const uninstall = () => {
		for (const name of API) {
			delete window[name];
		}
		delete navigator.xr;
	};

	install();
}