[Metasounds] Operator precaching mechanism.

#jira UE-185725, UE-179996,
#rb phil.popp
#swarm https://p4-swarm.epicgames.net/reviews/27703580

[CL 28775007 by maxwell hayes in ue5-main branch]

Engine/Plugins/Runtime/Metasound/Source/MetasoundEngine/Private/MetasoundOperatorCacheSubsystem.cpp

@@ -0,0 +1,131 @@
+// Copyright Epic Games, Inc. All Rights Reserved.
+#include "MetasoundOperatorCacheSubsystem.h"
+
+#include "AudioMixerDevice.h"
+#include "MetasoundGenerator.h"
+#include "MetasoundGeneratorModule.h"
+#include "MetasoundOperatorCache.h"
+#include "Modules/ModuleManager.h"
+#include "Misc/Optional.h"
+
+static TOptional<Metasound::FMetasoundGeneratorInitParams> CreateInitParams(UMetaSoundSource* InMetaSound, const FSoundGeneratorInitParams& InParams)
+{
+	using namespace Metasound;
+	using namespace Metasound::Frontend;
+	using namespace Metasound::Engine;
+	using namespace Metasound::SourcePrivate;
+
+	if (!ensure(InMetaSound))
+	{
+		return {}; // InMetaSound was null
+	}
+
+	if (ensure(!InMetaSound->IsDynamic()))
+	{
+		return {}; // we cannot precache dynamic metasounds
+	}
+
+	FOperatorSettings InSettings = InMetaSound->GetOperatorSettings(static_cast<FSampleRate>(InParams.SampleRate));
+	FMetasoundEnvironment Environment = InMetaSound->CreateEnvironment(InParams);
+
+	FOperatorBuilderSettings BuilderSettings = FOperatorBuilderSettings::GetDefaultSettings();
+	// Graph analyzer currently only enabled for preview sounds (but can theoretically be supported for all sounds)
+	BuilderSettings.bPopulateInternalDataReferences = InParams.bIsPreviewSound;
+
+	return FMetasoundGeneratorInitParams
+	{
+		InSettings,
+		MoveTemp(BuilderSettings),
+		{}, // Graph, retrieved from the FrontEnd Registry in FOperatorPool::BuildAndAddOperator()
+		Environment,
+		InMetaSound->GetName(),
+		InMetaSound->GetOutputAudioChannelOrder(),
+		{}, // DefaultParameters
+		true, // bBuildSynchronous
+		{} // DataChannel
+	};
+}
+
+bool UMetaSoundCacheSubsystem::ShouldCreateSubsystem(UObject* Outer) const
+{
+	return !IsRunningDedicatedServer();
+}
+
+void UMetaSoundCacheSubsystem::Initialize(FSubsystemCollectionBase& Collection)
+{
+	using namespace Audio;
+	using namespace Metasound;
+
+	BuildParams = MakeUnique<FSoundGeneratorInitParams>();
+	const FMixerDevice* MixerDevice = GetMixerDevice();
+
+	if (BuildParams && ensure(MixerDevice))
+	{
+		BuildParams->AudioDeviceID = GetAudioDeviceHandle().GetDeviceID();
+		BuildParams->SampleRate = MixerDevice->GetSampleRate();
+		BuildParams->AudioMixerNumOutputFrames = MixerDevice->GetNumOutputFrames();
+		BuildParams->NumChannels = MixerDevice->GetNumDeviceChannels();
+		BuildParams->NumFramesPerCallback = 0;
+		BuildParams->InstanceID = 0;
+	}
+}
+
+void UMetaSoundCacheSubsystem::Update()
+{
+#if METASOUND_OPERATORCACHEPROFILER_ENABLED
+	using namespace Metasound;
+	if (TSharedPtr<FOperatorPool> OperatorPool = FModuleManager::GetModuleChecked<IMetasoundGeneratorModule>("MetasoundGenerator").GetOperatorPool())
+	{
+		OperatorPool->UpdateHitRateTracker();
+	}
+#endif // #if METASOUND_OPERATORCACHEPROFILER_ENABLED
+}
+
+void UMetaSoundCacheSubsystem::PrecacheMetaSound(UMetaSoundSource* InMetaSound, int32 InNumInstances)
+{
+	using namespace Audio;
+	using namespace Metasound;
+
+	TSharedPtr<FOperatorPool> OperatorPool;
+	IMetasoundGeneratorModule* Module = FModuleManager::GetModulePtr<IMetasoundGeneratorModule>("MetasoundGenerator");
+	if (ensure(Module))
+	{
+		OperatorPool = Module->GetOperatorPool();
+	}
+
+	const FMixerDevice* MixerDevice = GetMixerDevice();
+
+	if (!ensure(MixerDevice && InMetaSound && BuildParams && OperatorPool))
+	{
+		return;
+	}
+
+	if (!ensure(InNumInstances > 0))
+	{
+		return;
+	}
+
+	InMetaSound->InitResources();
+	BuildParams->GraphName = InMetaSound->GetOwningAssetName();
+
+	if (InMetaSound->IsDynamic())
+	{
+		return;
+	}
+
+	TOptional<FMetasoundGeneratorInitParams> InitParams = CreateInitParams(InMetaSound, *BuildParams);
+	if (!InitParams.IsSet())
+	{
+		return;
+	}
+	
+
+	TUniquePtr<FOperatorBuildData> Data = MakeUnique<FOperatorBuildData>(
+		  MoveTemp(InitParams.GetValue())
+		, InMetaSound->GetRegistryKey()
+		, FSoftObjectPath(InMetaSound->GetOwningAsset())
+		, InNumInstances
+	);
+
+	OperatorPool->BuildAndAddOperator(MoveTemp(Data));
+}