NaniteReadbackManager.h

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// Copyright Epic Games, Inc. All Rights Reserved.
 
#pragma once
 
#include "CoreMinimal.h"
#include "RHIGPUReadback.h"
 
class FRDGBuilder;
class FRDGBuffer;
class FRDGPooledBuffer;
 
namespace Nanite
{
 
class FReadbackManager
{
public:
    FReadbackManager(uint32 InNumBuffers);
 
    uint32 PrepareRequestsBuffer(FRDGBuilder& GraphBuilder);
    
    struct FGPUStreamingRequest* LockLatest(uint32& OutNumStreamingRequestsClamped, uint32& OutNumStreamingRequests);
    void Unlock();
    
    void QueueReadback(FRDGBuilder& GraphBuilder);
 
    FRDGBuffer* GetStreamingRequestsBuffer(FRDGBuilder& GraphBuilder) const;
    uint32 GetBufferVersion() const;
    
private:
    struct FReadbackBuffer
    {
        TUniquePtr<FRHIGPUBufferReadback>   Buffer;
        uint32                              NumElements = 0u;
    };
 
    class FBufferSizeManager
    {
    public:
        FBufferSizeManager();
 
        void Update(uint32 NumRequests);
        uint32 GetSize();
 
    private:
        float CurrentSize;
        uint32 OverBudgetCounter = 0;
        uint32 UnderBudgetCounter = 0;
    };
 
    TRefCountPtr<FRDGPooledBuffer>  RequestsBuffer;
    TArray<FReadbackBuffer>         ReadbackBuffers;
 
    FReadbackBuffer*                LatestBuffer = nullptr;
    uint32                          NumBuffers = 0;
    uint32                          NumPendingBuffers = 0;
    uint32                          NextReadBufferIndex = 0;
    uint32                          BufferVersion = 0;
 
    FBufferSizeManager              BufferSizeManager;
};
 
 
} // namespace Nanite