SoundGenerator.h

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// Copyright Epic Games, Inc. All Rights Reserved.
 
#pragma once
 
#include "AudioDeviceManager.h"
#include "CoreMinimal.h"
#include "Containers/MpscQueue.h"
#include "Templates/Function.h"
 
namespace Audio
{
    using AudioTaskQueueId = uint32;
}
 
// Parameters used for constructing a new ISoundGenerator.
struct FSoundGeneratorInitParams
{
    Audio::FDeviceId AudioDeviceID;
    uint64 AudioComponentId = 0;
    float SampleRate = 0.0f;
    int32 AudioMixerNumOutputFrames = 0;
    int32 NumChannels = 0;
    int32 NumFramesPerCallback = 0;
    uint64 InstanceID = 0;
    bool bIsPreviewSound = false;
    FString GraphName;
    float StartTime = 0.0f;
};
 
class ISoundGenerator
{
public:
    ENGINE_API ISoundGenerator();
    ENGINE_API virtual ~ISoundGenerator();
 
    // Called when a new buffer is required. 
    virtual int32 OnGenerateAudio(float* OutAudio, int32 NumSamples) = 0;
 
    // Returns the number of samples to render per callback
    virtual int32 GetDesiredNumSamplesToRenderPerCallback() const { return 1024; }
 
    // Optional. Called on audio generator thread right when the generator begins generating.
    virtual void OnBeginGenerate() {}
 
    // Optional. Called on audio generator thread right when the generator ends generating.
    virtual void OnEndGenerate() {}
 
    // Optional. Can be overridden to end the sound when generating is finished.
    virtual bool IsFinished() const { return false; }
 
    // Return the cost to render this sound generator. Derived classes can optionally
    // override this method.
    //
    // This is called repeatedly to track the cost and managing the maximum number
    // of concurrently rendering voices. 
    virtual float GetRelativeRenderCost() const { return 1.f; }
 
    // Retrieves the next buffer of audio from the generator, called from the audio mixer.
    // Returns the number of samples actually written. The remainder are untouched.
    ENGINE_API int32 GetNextBuffer(float* OutAudio, int32 NumSamples, bool bRequireNumberSamples = false);
 
    virtual Audio::AudioTaskQueueId GetSynchronizedRenderQueueId() const { return 0; }
 
protected:
 
    // Protected method to execute lambda in audio render thread
    // Used for conveying parameter changes or events to the generator thread.
    ENGINE_API void SynthCommand(TFunction<void()> Command);
 
private:
 
    ENGINE_API void PumpPendingMessages();
 
    // The command queue used to convey commands from game thread to generator thread 
    TMpscQueue<TUniqueFunction<void()>> CommandQueue;
 
    friend class USynthComponent;
};
 
// Null implementation of ISoundGenerator which no-ops audio generation
class FSoundGeneratorNull : public ISoundGenerator
{
public:
    virtual int32 OnGenerateAudio(float* OutAudio, int32 NumSamples) override
    {
        FMemory::Memzero(OutAudio, NumSamples * sizeof(float));
        return NumSamples;
    }
};
 
typedef TSharedPtr<ISoundGenerator, ESPMode::ThreadSafe> ISoundGeneratorPtr;