Remove unnecessary attribute "gain" in AudioBuffer and AudioBufferSourceNode interfaces

Source/modules/webaudio/AudioBufferSourceNode.cpp

 /*
  * Copyright (C) 2010, Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1.  Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 47 matching lines @@
 AudioBufferSourceNode::AudioBufferSourceNode(AudioContext* context, float sampleRate)
     : AudioScheduledSourceNode(context, sampleRate)
     , m_buffer(nullptr)
     , m_isLooping(false)
     , m_loopStart(0)
     , m_loopEnd(0)
     , m_virtualReadIndex(0)
     , m_isGrain(false)
     , m_grainOffset(0.0)
     , m_grainDuration(DefaultGrainDuration)
-    , m_lastGain(1.0)
     , m_pannerNode(0)
 {
     ScriptWrappable::init(this);
     setNodeType(NodeTypeAudioBufferSource);
 
-    m_gain = AudioParam::create(context, "gain", 1.0, 0.0, 1.0);
     m_playbackRate = AudioParam::create(context, "playbackRate", 1.0, 0.0, MaxRate);
 
     // Default to mono.  A call to setBuffer() will set the number of output channels to that of the buffer.
     addOutput(adoptPtr(new AudioNodeOutput(this, 1)));
 
     initialize();
 }
 
 AudioBufferSourceNode::~AudioBufferSourceNode()
 {
@@ skipping 41 matching lines @@
 
         for (unsigned i = 0; i < outputBus->numberOfChannels(); ++i)
             m_destinationChannels[i] = outputBus->channel(i)->mutableData();
 
         // Render by reading directly from the buffer.
         if (!renderFromBuffer(outputBus, quantumFrameOffset, bufferFramesToProcess)) {
             outputBus->zero();
             return;
         }
 
-        // Apply the gain (in-place) to the output bus.
-        float totalGain = gain()->value() * m_buffer->gain();
-        outputBus->copyWithGainFrom(*outputBus, &m_lastGain, totalGain);

[Raymond Toy, 2014/04/07 20:17:12]

Do we still need to do some kind of copy here or does outputBus already contain
the desired data?

[KhNo, 2014/04/08 02:27:16]

It is just for applying gain to outputBus itself.
First parameter is outputBus.
Inside of copyWithGainFrom() it is filtered out if targetGain and lastMixGain
are same.
We don't need to do this.

         outputBus->clearSilentFlag();
     } else {
         // Too bad - the tryLock() failed.  We must be in the middle of changing buffers and were already outputting silence anyway.
         outputBus->zero();
     }
 }
 
 // Returns true if we're finished.
 bool AudioBufferSourceNode::renderSilenceAndFinishIfNotLooping(AudioBus*, unsigned index, size_t framesToProcess)
 {
@@ skipping 342 matching lines @@
 void AudioBufferSourceNode::finish()
 {
     clearPannerNode();
     ASSERT(!m_pannerNode);
     AudioScheduledSourceNode::finish();
 }
 
 } // namespace WebCore
 
 #endif // ENABLE(WEB_AUDIO)