Bug 897092 - Fix setTargetAtTime glitch. r=ehsan

--HG--
extra : rebase_source : 8b1162e7721637df2b8a2faad849609d3177369b

content/media/AudioEventTimeline.h

@@ -160,7 +160,9 @@ class AudioEventTimeline
 {
 public:
   explicit AudioEventTimeline(float aDefaultValue)
-    : mValue(aDefaultValue)
+    : mValue(aDefaultValue),
+      mComputedValue(aDefaultValue),
+      mLastComputedValue(aDefaultValue)
   {
   }
 
@@ -186,7 +188,7 @@ public:
   {
     // Silently don't change anything if there are any events
     if (mEvents.IsEmpty()) {
-      mValue = aValue;
+      mLastComputedValue = mComputedValue = mValue = aValue;
     }
   }
 
@@ -237,9 +239,29 @@ public:
     mEvents.Clear();
   }
 
+  static bool TimesEqual(int64_t aLhs, int64_t aRhs)
+  {
+    return aLhs == aRhs;
+  }
+
+  // Since we are going to accumulate error by adding 0.01 multiple time in a
+  // loop, we want to fuzz the equality check in GetValueAtTime.
+  static bool TimesEqual(double aLhs, double aRhs)
+  {
+    const float kEpsilon = 0.0000000001f;
+    return fabs(aLhs - aRhs) < kEpsilon;
+  }
+
+  template<class TimeType>
+  float GetValueAtTime(TimeType aTime)
+  {
+    mComputedValue = GetValueAtTimeHelper(aTime);
+    return mComputedValue;
+  }
+
   // This method computes the AudioParam value at a given time based on the event timeline
   template<class TimeType>
-  float GetValueAtTime(TimeType aTime) const
+  float GetValueAtTimeHelper(TimeType aTime)
   {
     const AudioTimelineEvent* previous = nullptr;
     const AudioTimelineEvent* next = nullptr;
@@ -252,7 +274,8 @@ public:
       case AudioTimelineEvent::LinearRamp:
       case AudioTimelineEvent::ExponentialRamp:
       case AudioTimelineEvent::SetValueCurve:
-        if (aTime == mEvents[i].template Time<TimeType>()) {
+        if (TimesEqual(aTime, mEvents[i].template Time<TimeType>())) {
+          mLastComputedValue = mComputedValue;
           // Find the last event with the same time
           do {
             ++i;
@@ -261,13 +284,14 @@ public:
 
           // SetTarget nodes can be handled no matter what their next node is (if they have one)
           if (mEvents[i - 1].mType == AudioTimelineEvent::SetTarget) {
-            // Follow the curve, without regard to the next node
+            // Follow the curve, without regard to the next event, starting at
+            // the last value of the last event.
             return ExponentialApproach(mEvents[i - 1].template Time<TimeType>(),
-                                       mValue, mEvents[i - 1].mValue,
+                                       mLastComputedValue, mEvents[i - 1].mValue,
                                        mEvents[i - 1].mTimeConstant, aTime);
           }
 
-          // SetValueCurve events can be handled no mattar what their next node is (if they have one)
+          // SetValueCurve events can be handled no matter what their event node is (if they have one)
           if (mEvents[i - 1].mType == AudioTimelineEvent::SetValueCurve) {
             return ExtractValueFromCurve(mEvents[i - 1].template Time<TimeType>(),
                                          mEvents[i - 1].mCurve,
@@ -306,8 +330,8 @@ public:
 
     // SetTarget nodes can be handled no matter what their next node is (if they have one)
     if (previous->mType == AudioTimelineEvent::SetTarget) {
-      // Follow the curve, without regard to the next node
-      return ExponentialApproach(previous->template Time<TimeType>(), mValue, previous->mValue,
+      return ExponentialApproach(previous->template Time<TimeType>(),
+                                 mLastComputedValue, previous->mValue,
                                  previous->mTimeConstant, aTime);
     }
 
@@ -540,6 +564,10 @@ private:
   // being a bottleneck.
   nsTArray<AudioTimelineEvent> mEvents;
   float mValue;
+  // This is the value of this AudioParam we computed at the last call.
+  float mComputedValue;
+  // This is the value of this AudioParam at the last tick of the previous event.
+  float mLastComputedValue;
 };
 
 }

content/media/webaudio/AudioParamTimeline.h

@@ -50,7 +50,7 @@ public:
   // getting the value of an a-rate AudioParam for each tick inside an
   // AudioNodeEngine implementation.
   template<class TimeType>
-  float GetValueAtTime(TimeType aTime, size_t aCounter = 0) const
+  float GetValueAtTime(TimeType aTime, size_t aCounter = 0)
   {
     MOZ_ASSERT(aCounter < WEBAUDIO_BLOCK_SIZE);
     MOZ_ASSERT(!aCounter || !HasSimpleValue());

content/media/webaudio/compiledtest/TestAudioEventTimeline.cpp

@@ -314,6 +314,15 @@ void TestAfterLastTargetValueEventWithValueSet()
 
   timeline.SetValue(50.f);
   timeline.SetTargetAtTime(20.0f, 1.0, 5.0, rv);
+
+  // When using SetTargetValueAtTime, Timeline become stateful: the value for
+  // time t may depend on the time t-1, so we can't just query the value at a
+  // time and get the right value. We have to call GetValueAtTime for the
+  // previous times.
+  for (double i = 0.0; i < 9.99; i+=0.01) {
+    timeline.GetValueAtTime(i);
+  }
+
   is(timeline.GetValueAtTime(10.), (20.f + (50.f - 20.f) * expf(-9.0f / 5.0f)), "Return the value after SetValue and the last SetTarget event based on the curve");
 }
 

content/media/webaudio/test/test_audioParamSetTargetAtTime.html

@@ -10,8 +10,8 @@
 <pre id="test">
 <script class="testbody" type="text/javascript">
 
-var V0 = 0.1;
-var V1 = 0.9;
+var V0 = 0.9;
+var V1 = 0.1;
 var T0 = 0;
 var TimeConstant = 10;