Bug 1788188 - Implement missing framerate methods in the WebXR spec. r=emilio

In particular this adds an initial implementation for the
updateTargetFrameRate method and adds the supportedFrameRates
and frameRate attributes to the XRSession.

Differential Revision: https://phabricator.services.mozilla.com/D156063

dom/vr/XRSession.cpp

@@ -231,6 +231,13 @@ XRRenderState* XRSession::RenderState() { return mActiveRenderState; }
 
 XRInputSourceArray* XRSession::InputSources() { return mInputSources; }
 
+Nullable<float> XRSession::GetFrameRate() { return {}; }
+
+void XRSession::GetSupportedFrameRates(JSContext*,
+                                       JS::MutableHandle<JSObject*> aRetVal) {
+  aRetVal.set(nullptr);
+}
+
 // https://immersive-web.github.io/webxr/#apply-the-pending-render-state
 void XRSession::ApplyPendingRenderState() {
   if (mPendingRenderState == nullptr) {
@@ -393,6 +400,31 @@ already_AddRefed<Promise> XRSession::RequestReferenceSpace(
   return promise.forget();
 }
 
+already_AddRefed<Promise> XRSession::UpdateTargetFrameRate(float aRate,
+                                                           ErrorResult& aRv) {
+  nsCOMPtr<nsIGlobalObject> global = GetParentObject();
+  NS_ENSURE_TRUE(global, nullptr);
+
+  RefPtr<Promise> promise = Promise::Create(global, aRv);
+  NS_ENSURE_TRUE(!aRv.Failed(), nullptr);
+
+  if (mEnded) {
+    promise->MaybeRejectWithInvalidStateError(
+        "UpdateTargetFrameRate can not be called on an XRSession that has "
+        "ended.");
+    return promise.forget();
+  }
+
+  // https://immersive-web.github.io/webxr/#dom-xrsession-updatetargetframerate
+  // TODO: Validate the rate with the frame rates supported from the device.
+  // We add a no op for now to avoid JS exceptions related to undefined method.
+  // The spec states that user agent MAY use rate to calculate a new display
+  // frame rate, so it's fine to let the default frame rate for now.
+
+  promise->MaybeResolve(JS::UndefinedHandleValue);
+  return promise.forget();
+}
+
 XRRenderState* XRSession::GetActiveRenderState() const {
   return mActiveRenderState;
 }

dom/vr/XRSession.h

@@ -67,6 +67,9 @@ class XRSession final : public DOMEventTargetHelper, public nsARefreshObserver {
   XRVisibilityState VisibilityState() const;
   XRRenderState* RenderState();
   XRInputSourceArray* InputSources();
+  Nullable<float> GetFrameRate();
+  void GetSupportedFrameRates(JSContext* aJSContext,
+                              JS::MutableHandle<JSObject*> aRetval);
 
   // WebIDL Methods
   void UpdateRenderState(const XRRenderStateInit& aNewState, ErrorResult& aRv);
@@ -76,6 +79,8 @@ class XRSession final : public DOMEventTargetHelper, public nsARefreshObserver {
                                 mozilla::ErrorResult& aError);
   void CancelAnimationFrame(int32_t aHandle, mozilla::ErrorResult& aError);
   already_AddRefed<Promise> End(ErrorResult& aRv);
+  already_AddRefed<Promise> UpdateTargetFrameRate(float aRate,
+                                                  ErrorResult& aRv);
 
   // WebIDL Events
   IMPL_EVENT_HANDLER(end);

dom/webidl/WebXR.webidl

@@ -43,12 +43,16 @@ interface XRSession : EventTarget {
   readonly attribute XRVisibilityState visibilityState;
   [SameObject] readonly attribute XRRenderState renderState;
   [SameObject] readonly attribute XRInputSourceArray inputSources;
+  readonly attribute float? frameRate;
+  readonly attribute Float32Array? supportedFrameRates;
 
   // Methods
   [Throws]
   void updateRenderState(optional XRRenderStateInit state = {});
   [NewObject]
   Promise<XRReferenceSpace> requestReferenceSpace(XRReferenceSpaceType type);
+  [NewObject]
+  Promise<void> updateTargetFrameRate(float rate);
 
   [Throws]
   long requestAnimationFrame(XRFrameRequestCallback callback);