Correctly propagate end value for exponential ramp

third_party/WebKit/Source/modules/webaudio/AudioParamTimeline.cpp

Index: third_party/WebKit/Source/modules/webaudio/AudioParamTimeline.cpp
diff --git a/third_party/WebKit/Source/modules/webaudio/AudioParamTimeline.cpp b/third_party/WebKit/Source/modules/webaudio/AudioParamTimeline.cpp
index 2fad553577e2bc4fe97550976828c048aadfa4ba..3abcc72ffb0b1de2a4fa53e33eabff78734a8053 100644
--- a/third_party/WebKit/Source/modules/webaudio/AudioParamTimeline.cpp
+++ b/third_party/WebKit/Source/modules/webaudio/AudioParamTimeline.cpp
@@ -410,11 +410,6 @@ float AudioParamTimeline::valuesForFrameRangeImpl(
         float value1 = event.value();
         double time1 = event.time();
 
-        // If the current event is SetValue, set the default value too so that it appears as if
-        // SetValue were actually run for any corner caes where we want to use the default value.
-        if (event.type() == ParamEvent::SetValue)
-            value = value1;
-

[Raymond Toy, 2016/01/06 22:05:02]

I think this is actually incorrect and was just a workaround for exponentialRamp
starting at the correct value when the start and end values have different
signs.

         float value2 = nextEvent ? nextEvent->value() : value1;
         double time2 = nextEvent ? nextEvent->time() : endFrame / sampleRate + 1;
 
@@ -473,6 +468,9 @@ float AudioParamTimeline::valuesForFrameRangeImpl(
             if (value1 * value2 <= 0) {
                 // It's an error if value1 and value2 have opposite signs or if one of them is zero.
                 // Handle this by propagating the previous value.
+                if (writeIndex < fillToFrame)
+                    value = value1;
+
                 for (; writeIndex < fillToFrame; ++writeIndex)
                     values[writeIndex] = value;
             } else {
@@ -516,7 +514,6 @@ float AudioParamTimeline::valuesForFrameRangeImpl(
             switch (event.type()) {
             case ParamEvent::SetValue:
             case ParamEvent::LinearRampToValue:
-            case ParamEvent::ExponentialRampToValue:
                 {
                     currentFrame = fillToEndFrame;
 
@@ -529,6 +526,19 @@ float AudioParamTimeline::valuesForFrameRangeImpl(
                     break;
                 }
 
+            case ParamEvent::ExponentialRampToValue:
+                {
+                    currentFrame = fillToEndFrame;
+
+                    // Simply stay at a constant value from the last time.  We don't want to use the
+                    // value of the event in case value1 * value2 < 0.  In that case we should
+                    // propagate the previous value, which is in |value|.
+                    for (; writeIndex < fillToFrame; ++writeIndex)
+                        values[writeIndex] = value;
+
+                    break;
+                }
+
             case ParamEvent::SetTarget:
                 {
                     // Exponential approach to target value with given time constant.