Source/WebCore/webaudio/ConvolverNode.cpp

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 * Copyright (C) 2010, Google Inc. All rights reserved.
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#include "config.h"

#if ENABLE(WEB_AUDIO)

#include "ConvolverNode.h"

#include "AudioBuffer.h"
#include "AudioContext.h"
#include "AudioNodeInput.h"
#include "AudioNodeOutput.h"
#include "Reverb.h"

// Note about empirical tuning:
// The maximum FFT size affects reverb performance and accuracy.
// If the reverb is single-threaded and processes entirely in the real-time audio thread,
// it's important not to make this too high.  In this case 8192 is a good value.
// But, the Reverb object is multi-threaded, so we want this as high as possible without losing too much accuracy.
// Very large FFTs will have worse phase errors.  Given these constraints 16384 is a good compromise.
const size_t MaxFFTSize = 16384;

namespace WebCore {

ConvolverNode::ConvolverNode(AudioContext* context, double sampleRate)
    : AudioNode(context, sampleRate)
{
    addInput(adoptPtr(new AudioNodeInput(this)));
    addOutput(adoptPtr(new AudioNodeOutput(this, 2)));
    
    setType(NodeTypeConvolver);
    
    initialize();
}

ConvolverNode::~ConvolverNode()
{
    uninitialize();
}

void ConvolverNode::process(size_t framesToProcess)
{
    AudioBus* outputBus = output(0)->bus();
    ASSERT(outputBus);

    // Synchronize with possible dynamic changes to the impulse response.
    if (m_processLock.tryLock()) {
        if (!isInitialized() || !m_reverb.get())
            outputBus->zero();
        else {
            // Process using the convolution engine.
            // Note that we can handle the case where nothing is connected to the input, in which case we'll just feed silence into the convolver.
            // FIXME:  If we wanted to get fancy we could try to factor in the 'tail time' and stop processing once the tail dies down if
            // we keep getting fed silence.
            m_reverb->process(input(0)->bus(), outputBus, framesToProcess);
        }
        
        m_processLock.unlock();
    } else {
        // Too bad - the tryLock() failed.  We must be in the middle of setting a new impulse response.
        outputBus->zero();
    }
}

void ConvolverNode::reset()
{
    MutexLocker locker(m_processLock);
    if (m_reverb.get())
        m_reverb->reset();
}

void ConvolverNode::initialize()
{
    if (isInitialized())
        return;
        
    AudioNode::initialize();
}

void ConvolverNode::uninitialize()
{
    if (!isInitialized())
        return;

    m_reverb.clear();
    AudioNode::uninitialize();
}

void ConvolverNode::setBuffer(AudioBuffer* buffer)
{
    ASSERT(isMainThread());
    
    ASSERT(buffer);
    if (!buffer)
        return;

    unsigned numberOfChannels = buffer->numberOfChannels();
    size_t bufferLength = buffer->length();

    // The current implementation supports up to four channel impulse responses, which are interpreted as true-stereo (see Reverb class).
    bool isBufferGood = numberOfChannels > 0 && numberOfChannels <= 4 && bufferLength;
    ASSERT(isBufferGood);
    if (!isBufferGood)
        return;

    // Wrap the AudioBuffer by an AudioBus. It's an efficient pointer set and not a memcpy().
    // This memory is simply used in the Reverb constructor and no reference to it is kept for later use in that class.
    AudioBus bufferBus(numberOfChannels, bufferLength, false);
    for (unsigned i = 0; i < numberOfChannels; ++i)
        bufferBus.setChannelMemory(i, buffer->getChannelData(i)->data(), bufferLength);
    
    // Create the reverb with the given impulse response.
    bool useBackgroundThreads = !context()->isOfflineContext();
    OwnPtr<Reverb> reverb = adoptPtr(new Reverb(&bufferBus, AudioNode::ProcessingSizeInFrames, MaxFFTSize, 2, useBackgroundThreads));

    {
        // Synchronize with process().
        MutexLocker locker(m_processLock);
        m_reverb = reverb.release();
        m_buffer = buffer;
    }
}

AudioBuffer* ConvolverNode::buffer()
{
    ASSERT(isMainThread());
    return m_buffer.get();
}

} // namespace WebCore

#endif // ENABLE(WEB_AUDIO)