D3D12ConstantBuffer.h

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// Copyright Epic Games, Inc. All Rights Reserved.
 
#pragma once
 
#include "D3D12RHICommon.h"
#if D3D12RHI_USE_CONSTANT_BUFFER_VIEWS
#include "D3D12View.h"
#endif
 
class FD3D12FastConstantAllocator;
class FD3D12ResourceLocation;
 
// Chunk size for global constant buffer shadow data. Should always be a multiple of 256
#define GLOBAL_CONSTANT_BUFFER_CHUNK_SIZE 512
 
class FD3D12ConstantBuffer : public FD3D12DeviceChild
{
public:
    FD3D12ConstantBuffer(FD3D12Device* InParent, FD3D12FastConstantAllocator& InAllocator);
    virtual ~FD3D12ConstantBuffer();
 
    FORCEINLINE_DEBUGGABLE void UpdateConstant(const uint8* Data, uint16 Offset, uint16 InSize)
    {
        // Make sure we have enough memory in our shadow data
        const uint32 RequiredSize = (uint32)Offset + (uint32)InSize;
        if ((uint32)ShadowData.Num() < RequiredSize)
        {
            // Make sure we grow in chunks to prevent too many reallocs
            const uint32 SizeToGrowTo = Align(RequiredSize, GLOBAL_CONSTANT_BUFFER_CHUNK_SIZE);
            ShadowData.SetNumZeroed(SizeToGrowTo);
        }
 
        FMemory::Memcpy(ShadowData.GetData() + Offset, Data, InSize);
        CurrentUpdateSize = FMath::Max(RequiredSize, CurrentUpdateSize);
 
        bIsDirty = true;
    }
 
    FORCEINLINE void Reset() { CurrentUpdateSize = 0; }
 
    bool Version(FD3D12ResourceLocation& BufferOut, bool bDiscardSharedConstants);
 
#if D3D12RHI_USE_CONSTANT_BUFFER_VIEWS
    inline D3D12_CPU_DESCRIPTOR_HANDLE GetOfflineCpuHandle() const { return View->GetOfflineCpuHandle(); }
#endif
 
protected:
#if D3D12RHI_USE_CONSTANT_BUFFER_VIEWS
    FD3D12ConstantBufferView* View = nullptr;
#endif
 
    TArray<uint8> ShadowData;
    
    uint32  CurrentUpdateSize;
 
    uint32  TotalUpdateSize;
    
    // Indicates that a constant has been updated but this one hasn't been flushed.
    bool bIsDirty;
 
    FD3D12FastConstantAllocator& Allocator;
};