root/Source/modules/webaudio/GainNode.cpp

DEFINITIONS

1. m_sampleAccurateGainValues
2. process
3. checkNumberOfChannelsForInput

/*
 * Copyright (C) 2010, Google Inc. All rights reserved.
 *
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 *
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 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS BE LIABLE FOR ANY
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#include "config.h"

#if ENABLE(WEB_AUDIO)

#include "modules/webaudio/GainNode.h"

#include "platform/audio/AudioBus.h"
#include "modules/webaudio/AudioNodeInput.h"
#include "modules/webaudio/AudioNodeOutput.h"

namespace WebCore {

GainNode::GainNode(AudioContext* context, float sampleRate)
    : AudioNode(context, sampleRate)
    , m_lastGain(1.0)
    , m_sampleAccurateGainValues(AudioNode::ProcessingSizeInFrames) // FIXME: can probably share temp buffer in context
{
    ScriptWrappable::init(this);
    m_gain = AudioParam::create(context, "gain", 1.0, 0.0, 1.0);

    addInput(adoptPtr(new AudioNodeInput(this)));
    addOutput(adoptPtr(new AudioNodeOutput(this, 1)));

    setNodeType(NodeTypeGain);

    initialize();
}

void GainNode::process(size_t framesToProcess)
{
    // FIXME: for some cases there is a nice optimization to avoid processing here, and let the gain change
    // happen in the summing junction input of the AudioNode we're connected to.
    // Then we can avoid all of the following:

    AudioBus* outputBus = output(0)->bus();
    ASSERT(outputBus);

    if (!isInitialized() || !input(0)->isConnected())
        outputBus->zero();
    else {
        AudioBus* inputBus = input(0)->bus();

        if (gain()->hasSampleAccurateValues()) {
            // Apply sample-accurate gain scaling for precise envelopes, grain windows, etc.
            ASSERT(framesToProcess <= m_sampleAccurateGainValues.size());
            if (framesToProcess <= m_sampleAccurateGainValues.size()) {
                float* gainValues = m_sampleAccurateGainValues.data();
                gain()->calculateSampleAccurateValues(gainValues, framesToProcess);
                outputBus->copyWithSampleAccurateGainValuesFrom(*inputBus, gainValues, framesToProcess);
            }
        } else {
            // Apply the gain with de-zippering into the output bus.
            outputBus->copyWithGainFrom(*inputBus, &m_lastGain, gain()->value());
        }
    }
}

// FIXME: this can go away when we do mixing with gain directly in summing junction of AudioNodeInput
//
// As soon as we know the channel count of our input, we can lazily initialize.
// Sometimes this may be called more than once with different channel counts, in which case we must safely
// uninitialize and then re-initialize with the new channel count.
void GainNode::checkNumberOfChannelsForInput(AudioNodeInput* input)
{
    ASSERT(context()->isAudioThread() && context()->isGraphOwner());

    ASSERT(input && input == this->input(0));
    if (input != this->input(0))
        return;

    unsigned numberOfChannels = input->numberOfChannels();

    if (isInitialized() && numberOfChannels != output(0)->numberOfChannels()) {
        // We're already initialized but the channel count has changed.
        uninitialize();
    }

    if (!isInitialized()) {
        // This will propagate the channel count to any nodes connected further downstream in the graph.
        output(0)->setNumberOfChannels(numberOfChannels);
        initialize();
    }

    AudioNode::checkNumberOfChannelsForInput(input);
}

} // namespace WebCore

#endif // ENABLE(WEB_AUDIO)