Merge pull request #248 from jsantell/unresolved-displays

Set a timeout on getVRDisplays() to handle scenario where the promise never resolves. Fixes #199

README.md

@@ -92,6 +92,19 @@ WebVRConfig = {
   // gl.ARRAY_BUFFER_BINDING, gl.ELEMENT_ARRAY_BUFFER_BINDING,
   // and gl.TEXTURE_BINDING_2D for texture unit 0.
   DIRTY_SUBMIT_FRAME_BINDINGS: true // Default: false.
+
+  // When set to true, this will cause a polyfilled VRDisplay to always be
+  // appended to the list returned by navigator.getVRDisplays(), even if that
+  // list includes a native VRDisplay.
+  ALWAYS_APPEND_POLYFILL_DISPLAY: false,
+
+  // There are scenarios where the native WebVR API exists, and instead of returning
+  // 0 VR displays when none are detected, `navigator.getVRDisplays()`'s promise never
+  // resolves. This results in the polyfill hanging and not being able to provide fallback
+  // displays, so set a timeout in milliseconds to stop waiting for a response
+  // and just use polyfilled displays.
+  // https://bugs.chromium.org/p/chromium/issues/detail?id=727969
+  GET_VR_DISPLAYS_TIMEOUT: 1000,
 }
 ```
 

src/main.js

@@ -68,7 +68,15 @@ window.WebVRConfig = Util.extend({
   // When set to true, this will cause a polyfilled VRDisplay to always be
   // appended to the list returned by navigator.getVRDisplays(), even if that
   // list includes a native VRDisplay.
-  ALWAYS_APPEND_POLYFILL_DISPLAY: false
+  ALWAYS_APPEND_POLYFILL_DISPLAY: false,
+
+  // There are scenarios where the native WebVR API exists, and instead of returning
+  // 0 VR displays when none are detected, `navigator.getVRDisplays()`'s promise never
+  // resolves. This results in the polyfill hanging and not being able to provide fallback
+  // displays, so set a timeout in milliseconds to stop waiting for a response
+  // and just use polyfilled displays.
+  // https://bugs.chromium.org/p/chromium/issues/detail?id=727969
+  GET_VR_DISPLAYS_TIMEOUT: 1000,
 }, window.WebVRConfig);
 
 if (!window.WebVRConfig.DEFER_INITIALIZATION) {

src/util.js

@@ -30,6 +30,25 @@ Util.lerp = function(a, b, t) {
   return a + ((b - a) * t);
 };
 
+/**
+ * Light polyfill for `Promise.race`. Returns
+ * a promise that resolves when the first promise
+ * provided resolves.
+ *
+ * @param {Array<Promise>} promises
+ */
+Util.race = function(promises) {
+  if (Promise.race) {
+    return Promise.race(promises);
+  }
+
+  return new Promise(function (resolve, reject) {
+    for (var i = 0; i < promises.length; i++) {
+      promises[i].then(resolve, reject);
+    }
+  });
+};
+
 Util.isIOS = (function() {
   var isIOS = /iPad|iPhone|iPod/.test(navigator.platform);
   return function() {

src/webvr-polyfill.js

@@ -159,23 +159,29 @@ WebVRPolyfill.prototype.getVRDisplays = function() {
   this.populateDevices();
   var polyfillDisplays = this.displays;
 
-  if (this.nativeWebVRAvailable) {
-    return this.nativeGetVRDisplaysFunc.call(navigator).then(function(nativeDisplays) {
-      if (window.WebVRConfig.ALWAYS_APPEND_POLYFILL_DISPLAY) {
-        return nativeDisplays.concat(polyfillDisplays);
-      } else {
-        return nativeDisplays.length > 0 ? nativeDisplays : polyfillDisplays;
-      }
-    });
-  } else {
-    return new Promise(function(resolve, reject) {
-      try {
-        resolve(polyfillDisplays);
-      } catch (e) {
-        reject(e);
-      }
-    });
+  if (!this.nativeWebVRAvailable) {
+    return Promise.resolve(polyfillDisplays);
   }
+
+  // Set up a race condition if this browser has a bug where
+  // `navigator.getVRDisplays()` never resolves.
+  var vrDisplaysNative = this.nativeGetVRDisplaysFunc.call(navigator);
+  var timeout = new Promise(function(resolve) {
+    setTimeout(function() {
+      resolve([])
+    }, window.WebVRConfig.GET_VR_DISPLAYS_TIMEOUT);
+  }).then(function (displays) {
+    console.warn('Native WebVR implementation detected, but `getVRDisplays()` failed to resolve. Falling back to polyfill.');
+    return displays;
+  });
+
+  return Util.race([vrDisplaysNative, timeout]).then(function(nativeDisplays) {
+    if (window.WebVRConfig.ALWAYS_APPEND_POLYFILL_DISPLAY) {
+      return nativeDisplays.concat(polyfillDisplays);
+    } else {
+      return nativeDisplays.length > 0 ? nativeDisplays : polyfillDisplays;
+    }
+  });
 };
 
 WebVRPolyfill.prototype.getVRDevices = function() {