Source/WebCore/Modules/webaudio/AudioSummingJunction.h

/*
 * Copyright (C) 2012, Google Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
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 * 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
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS'' AND ANY
 * 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
 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
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 */

#pragma once

#include "AudioBus.h"
#include <wtf/HashSet.h>
#include <wtf/Vector.h>

namespace WebCore {

class AudioContext;
class AudioNodeOutput;

// An AudioSummingJunction represents a point where zero, one, or more AudioNodeOutputs connect.

class AudioSummingJunction {
public:
    explicit AudioSummingJunction(AudioContext&);
    virtual ~AudioSummingJunction();

    // Can be called from any thread.
    AudioContext& context() { return m_context.get(); }

    // This must be called whenever we modify m_outputs.
    void changedOutputs();

    // This copies m_outputs to m_renderingOutputs. Please see comments for these lists below.
    // This must be called when we own the context's graph lock in the audio thread at the very start or end of the render quantum.
    void updateRenderingState();

    // Rendering code accesses its version of the current connections here.
    unsigned numberOfRenderingConnections() const { return m_renderingOutputs.size(); }
    AudioNodeOutput* renderingOutput(unsigned i) { return m_renderingOutputs[i]; }
    const AudioNodeOutput* renderingOutput(unsigned i) const { return m_renderingOutputs[i]; }
    bool isConnected() const { return numberOfRenderingConnections() > 0; }

    virtual bool canUpdateState() = 0;
    virtual void didUpdate() = 0;

protected:
    Ref<AudioContext> m_context;

    // m_outputs contains the AudioNodeOutputs representing current connections which are not disabled.
    // The rendering code should never use this directly, but instead uses m_renderingOutputs.
    HashSet<AudioNodeOutput*> m_outputs;

    // numberOfConnections() should never be called from the audio rendering thread.
    // Instead numberOfRenderingConnections() and renderingOutput() should be used.
    unsigned numberOfConnections() const { return m_outputs.size(); }

    // m_renderingOutputs is a copy of m_outputs which will never be modified during the graph rendering on the audio thread.
    // This is the list which is used by the rendering code.
    // Whenever m_outputs is modified, the context is told so it can later update m_renderingOutputs from m_outputs at a safe time.
    // Most of the time, m_renderingOutputs is identical to m_outputs.
    Vector<AudioNodeOutput*> m_renderingOutputs;

    // m_renderingStateNeedUpdating keeps track if m_outputs is modified.
    bool m_renderingStateNeedUpdating;
};

} // namespace WebCore