GainNode.cpp   [plain text]

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#include "config.h"

#if ENABLE(WEB_AUDIO)

#include "GainNode.h"

#include "AudioBus.h"
#include "AudioNodeInput.h"
#include "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
{
    m_gain = AudioParam::create(context, "gain", 1.0, 0.0, 1.0);

    addInput(std::make_unique<AudioNodeInput>(this));
    addOutput(std::make_unique<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.
            if (!m_lastGain && m_lastGain == m_gain->value()) {
                // If the gain is 0 (and we've converged on dezippering), just zero the bus and set
                // the silence hint.
                outputBus->zero();
            } else
                outputBus->copyWithGainFrom(*inputBus, &m_lastGain, gain()->value());
        }
    }
}

void GainNode::reset()
{
    // Snap directly to desired gain.
    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)