unreal gpuscene

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TypeOffsetTable 是 Primitive Type 相同 Primitive 的结束偏移，不是开始偏移，第一个类型开始偏移是 0，第一个类型结束偏移，是第一个类型的个数

Source\Runtime\Renderer\Private\RendererScene.cpp

FTypeOffsetTableEntry& NextEntry = TypeOffsetTable[TypeIndex];

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Primitives SOA 数据，不会修改这个数据结构，PersistentPrimitiveIdToIndexMap 是进行二次映射，映射到 Primitives，PersistentPrimitiveIdToIndexMap 下标索引和 Primitives 一致，PersistentPrimitiveIdToIndexMap 下标索引内容，对应 Primitives 索引

Primitives[SourceIndex]->PackedIndex 表示应该放置的数组下标

Source\Runtime\Renderer\Private\RendererScene.cpp

FPersistentPrimitiveIndex MovedPersisitentIndex = Primitives[DestIndex]->PersistentIndex;

PersistentPrimitiveIdToIndexMap[MovedPersisitentIndex.Index] = SourceIndex;

Primitives[SourceIndex]->PackedIndex = DestIndex;

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需要更新 instance 条件，UpdatedInstances 和 AddedLocalPrimitiveSceneInfos

PendingAllocateInstanceIds.Reserve(UpdatedInstances.Num() + AddedLocalPrimitiveSceneInfos.Num());

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primitive 更新条件 AddedPrimitiveSceneInfos 和 UpdatedTransforms 和 UpdatedInstances，不太明白为什么 UpdatedInstances 更新需要修改 primitive

const int32 SceneInfosContainerReservedSize = AddedPrimitiveSceneInfos.Num() + UpdatedTransforms.Num() + UpdatedInstances.Num();

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GPUSceneInstanceSceneDataRW 是 float4 的 soa

Saved\ShaderDebugInfo\PCD3D_SM6\Global\FGPUSceneSetInstancePrimitiveIdCS\0\GPUSceneDataManagement.usf

RWStructuredBuffer<float4> GPUSceneInstanceSceneDataRW;
float4 LoadInstanceSceneDataElement(uint Index)
{
    return GPUSceneInstanceSceneDataRW[Index];
}

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Source\Runtime\Engine\Public\InstanceUniformShaderParameters.h

ENGINE_API void Build

    (

        uint32 PrimitiveId,

        uint32 RelativeId,

        uint32 InstanceFlags,

        uint32 LastUpdateFrame,

        uint32 CustomDataCount,

        float RandomID,

        bool bIsVisible = true

    );

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Source\Runtime\Renderer\Private\GPUScene.cpp

InstanceUploadInfo.InstanceSceneDataBuffers = PrimitiveSceneInfo->GetInstanceSceneDataBuffers();

        if (InstanceUploadInfo.InstanceSceneDataBuffers)

        {

            const FInstanceSceneDataBuffers::FReadView InstanceSceneDataBuffers = InstanceUploadInfo.InstanceSceneDataBuffers->GetReadView();

            InstanceUploadInfo.NumInstances = InstanceUploadInfo.InstanceSceneDataBuffers->GetNumInstances();

            InstanceUploadInfo.InstanceFlags = PackFlags(InstanceSceneDataBuffers.Flags);

            InstanceUploadInfo.InstanceLightShadowUVBias = InstanceSceneDataBuffers.InstanceLightShadowUVBias;

            InstanceUploadInfo.InstanceCustomData = InstanceSceneDataBuffers.InstanceCustomData;

            InstanceUploadInfo.InstanceRandomID = InstanceSceneDataBuffers.InstanceRandomIDs;

            InstanceUploadInfo.InstanceHierarchyOffset = InstanceSceneDataBuffers.InstanceHierarchyOffset;

            InstanceUploadInfo.InstancePayloadExtension = InstanceSceneDataBuffers.InstancePayloadExtension;

            InstanceUploadInfo.InstanceLocalBounds = InstanceSceneDataBuffers.InstanceLocalBounds;

#if WITH_EDITOR

            InstanceUploadInfo.InstanceEditorData = InstanceSceneDataBuffers.InstanceEditorData;

#endif

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UploadDataSourceAdapter  cpu 信息获取读写封装

PrimitiveUploader gpu 数据读写封装

Source\Runtime\Renderer\Private\GPUScene.cpp

            ParallelForTemplate(TEXT("GPUScene Upload Primitives Task"), TaskContext.NumPrimitiveDataUploads, 1, [&TaskContext, &UploadDataSourceAdapter](int32 ItemIndex)

            {

                FOptionalTaskTagScope TaskTagScope(ETaskTag::EParallelRenderingThread);

                FVector4f* DstData = static_cast<FVector4f*>(TaskContext.PrimitiveUploader->GetRef(ItemIndex));

                UploadDataSourceAdapter.GetPrimitiveShaderData(ItemIndex, DstData);

            }, bExecuteInParallel ? EParallelForFlags::None : EParallelForFlags::ForceSingleThread);

        }