AudioBusSubsystem.h

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// Copyright Epic Games, Inc. All Rights Reserved.
 
#pragma once
 
#include "DSP/MultithreadedPatching.h"
#include "Misc/TVariant.h"
#include "Subsystems/AudioEngineSubsystem.h"
#include "Templates/TypeHash.h"
#include "UObject/StrongObjectPtr.h"
 
#include "AudioBusSubsystem.generated.h"
 
class UAudioBus;
 
namespace Audio
{
    // Forward declarations 
    class FMixerAudioBus;
    class FMixerSourceManager;
 
    struct FAudioBusKey
    {
        uint32 ObjectId = INDEX_NONE; // from a corresponding UObject (UAudioBus) if applicable
        uint32 InstanceId = INDEX_NONE;
 
        FAudioBusKey()
            : InstanceId(InstanceIdCounter++)
        {
        }
 
        // For construction with a given UObject unique id 
        FAudioBusKey(uint32 InObjectId)
            : ObjectId(InObjectId)
        {
        }
 
        const bool IsValid() const
        {
            return ObjectId != INDEX_NONE || InstanceId != INDEX_NONE;
        }
 
        inline friend uint32 GetTypeHash(const FAudioBusKey& Key)
        {
            return HashCombineFast(Key.ObjectId, Key.InstanceId);
        }
                
        inline friend bool operator==(const FAudioBusKey& InLHS, const FAudioBusKey& InRHS) 
        {
            return (InLHS.ObjectId == InRHS.ObjectId) && (InLHS.InstanceId == InRHS.InstanceId);
        }
 
        inline friend bool operator!=(const FAudioBusKey& InLHS, const FAudioBusKey& InRHS) 
        {
            return !(InLHS == InRHS);
        }
        
 
    private:
        static AUDIOMIXER_API std::atomic<uint32> InstanceIdCounter;
    };
}
 
UCLASS(MinimalAPI)
class UAudioBusSubsystem : public UAudioEngineSubsystem
{
    GENERATED_BODY()
 
public:
    AUDIOMIXER_API UAudioBusSubsystem();
    virtual ~UAudioBusSubsystem() = default;
 
    //~ Begin USubsystem interface
    AUDIOMIXER_API virtual bool ShouldCreateSubsystem(UObject* Outer) const override;
    AUDIOMIXER_API virtual void Initialize(FSubsystemCollectionBase& Collection) override;
    AUDIOMIXER_API virtual void Deinitialize() override;
    //~ End USubsystem interface
 
    // Audio bus API from FMixerDevice
    UE_DEPRECATED(5.6, "Use the StartAudioBus version that requires an AudioBus name.")
    AUDIOMIXER_API void StartAudioBus(Audio::FAudioBusKey InAudioBusKey, int32 InNumChannels, bool bInIsAutomatic);
 
    AUDIOMIXER_API void StartAudioBus(Audio::FAudioBusKey InAudioBusKey, const FString& InAudioBusName, int32 InNumChannels, bool bInIsAutomatic);
    AUDIOMIXER_API void StopAudioBus(Audio::FAudioBusKey InAudioBusKey);
    AUDIOMIXER_API bool IsAudioBusActive(Audio::FAudioBusKey InAudioBusKey) const;
    
    AUDIOMIXER_API Audio::FPatchInput AddPatchInputForAudioBus(Audio::FAudioBusKey InAudioBusKey, int32 InFrames, int32 InChannels, float InGain = 1.f);
    AUDIOMIXER_API Audio::FPatchOutputStrongPtr AddPatchOutputForAudioBus(Audio::FAudioBusKey InAudioBusKey, int32 InFrames, int32 InChannels, float InGain = 1.f);
 
    AUDIOMIXER_API Audio::FPatchInput AddPatchInputForSoundAndAudioBus(uint64 SoundInstanceID, Audio::FAudioBusKey AudioBusKey, int32 InFrames, int32 NumChannels, float InGain = 1.f);
    AUDIOMIXER_API Audio::FPatchOutputStrongPtr AddPatchOutputForSoundAndAudioBus(uint64 SoundInstanceID, Audio::FAudioBusKey AudioBusKey, int32 InFrames, int32 NumChannels, float InGain = 1.f);
    AUDIOMIXER_API void ConnectPatches(uint64 SoundInstanceID);
    AUDIOMIXER_API void RemoveSound(uint64 SoundInstanceID);
 
    AUDIOMIXER_API void InitDefaultAudioBuses();
    AUDIOMIXER_API void ShutdownDefaultAudioBuses();
 
private:
    struct FActiveBusData
    {
        Audio::FAudioBusKey BusKey = 0;
        int32 NumChannels = 0;
        bool bIsAutomatic = false;
    };
 
    TArray<TStrongObjectPtr<UAudioBus>> DefaultAudioBuses; 
    // The active audio bus list accessible on the game thread
    TMap<Audio::FAudioBusKey, FActiveBusData> ActiveAudioBuses_GameThread;
 
    struct FPendingConnection
    {
        using FPatchVariant = TVariant<Audio::FPatchInput, Audio::FPatchOutputStrongPtr>;
        FPatchVariant PatchVariant;
        Audio::FAudioBusKey AudioBusKey;
        int32 BlockSizeFrames = 0;
        int32 NumChannels = 0;
        bool bIsAutomatic = false;
    };
 
    void AddPendingConnection(uint64 SoundInstanceID, FPendingConnection&& PendingConnection);
 
    struct FSoundInstanceConnections
    {
        TArray<FPendingConnection> PendingConnections;
    };
 
    TArray<FPendingConnection> ExtractPendingConnectionsIfReady(uint64 SoundInstanceID);
 
    TMap<uint64, FSoundInstanceConnections> SoundInstanceConnectionMap;
    FCriticalSection Mutex;
};