前置信息：

灯光从World到Scene的流程。

UE4 Lights UWorld to FScene [1]_spawnactor failed because of collision at the spaw_sh15285118586的博客-CSDN博客

 mesh从world到Scene流程，与灯光类似

void UStaticMeshComponent::CreateRenderState_Concurrent(FRegisterComponentContext* Context)
{LLM_SCOPE(ELLMTag::StaticMesh);Super::CreateRenderState_Concurrent(Context);
}

void UPrimitiveComponent::CreateRenderState_Concurrent(FRegisterComponentContext* Context)
{// Make sure cached cull distance is up-to-date if its zero and we have an LD cull distanceif( CachedMaxDrawDistance == 0.f && LDMaxDrawDistance > 0.f ){bool bNeverCull = bNeverDistanceCull || GetLODParentPrimitive();CachedMaxDrawDistance = bNeverCull ? 0.f : LDMaxDrawDistance;}Super::CreateRenderState_Concurrent(Context);UpdateBounds();// If the primitive isn't hidden and the detail mode setting allows it, add it to the scene.if (ShouldComponentAddToScene()){if (Context != nullptr){Context->AddPrimitive(this);}else{GetWorld()->Scene->AddPrimitive(this);}}// Components are either registered as static or dynamic in the streaming manager.// Static components are registered in batches the first frame the level becomes visible (or incrementally each frame when loaded but not yet visible). // The level static streaming data is never updated after this, and gets reused whenever the level becomes visible again (after being hidden).// Dynamic components, on the other hand, are updated whenever their render states change.// The following logic handles all cases where static components should fallback on the dynamic path.// It is based on a design where each component must either have bHandledByStreamingManagerAsDynamic or bAttachedToStreamingManagerAsStatic set.// If this is not the case, then the component has never been handled before.// The bIgnoreStreamingManagerUpdate flag is used to prevent handling component that are already in the update list or that don't have streaming data.if (!bIgnoreStreamingManagerUpdate && (Mobility != EComponentMobility::Static || bHandledByStreamingManagerAsDynamic || (!bAttachedToStreamingManagerAsStatic && OwnerLevelHasRegisteredStaticComponentsInStreamingManager(GetOwner())))){FStreamingManagerCollection* Collection = IStreamingManager::Get_Concurrent();if (Collection){Collection->NotifyPrimitiveUpdated_Concurrent(this);}}
}

void FScene::AddPrimitive(UPrimitiveComponent* Primitive)
{SCOPE_CYCLE_COUNTER(STAT_AddScenePrimitiveGT);SCOPED_NAMED_EVENT(FScene_AddPrimitive, FColor::Green);checkf(!Primitive->IsUnreachable(), TEXT("%s"), *Primitive->GetFullName());const float WorldTime = GetWorld()->GetTimeSeconds();// Save the world transform for next time the primitive is added to the scenefloat DeltaTime = WorldTime - Primitive->LastSubmitTime;if ( DeltaTime < -0.0001f || Primitive->LastSubmitTime < 0.0001f ){// Time was reset?Primitive->LastSubmitTime = WorldTime;}else if ( DeltaTime > 0.0001f ){// First call for the new frame?Primitive->LastSubmitTime = WorldTime;}checkf(!Primitive->SceneProxy, TEXT("Primitive has already been added to the scene!"));// Create the primitive's scene proxy.FPrimitiveSceneProxy* PrimitiveSceneProxy = Primitive->CreateSceneProxy();Primitive->SceneProxy = PrimitiveSceneProxy;if(!PrimitiveSceneProxy){// Primitives which don't have a proxy are irrelevant to the scene manager.return;}// Create the primitive scene info.FPrimitiveSceneInfo* PrimitiveSceneInfo = new FPrimitiveSceneInfo(Primitive, this);PrimitiveSceneProxy->PrimitiveSceneInfo = PrimitiveSceneInfo;// Cache the primitives initial transform.FMatrix RenderMatrix = Primitive->GetRenderMatrix();FVector AttachmentRootPosition = Primitive->GetActorPositionForRenderer();struct FCreateRenderThreadParameters{FPrimitiveSceneProxy* PrimitiveSceneProxy;FMatrix RenderMatrix;FBoxSphereBounds WorldBounds;FVector AttachmentRootPosition;FBoxSphereBounds LocalBounds;};FCreateRenderThreadParameters Params ={PrimitiveSceneProxy,RenderMatrix,Primitive->Bounds,AttachmentRootPosition,Primitive->GetLocalBounds()};// Help track down primitive with bad bounds way before the it gets to the RendererensureMsgf(!Primitive->Bounds.ContainsNaN(),TEXT("Nans found on Bounds for Primitive %s: Origin %s, BoxExtent %s, SphereRadius %f"), *Primitive->GetName(), *Primitive->Bounds.Origin.ToString(), *Primitive->Bounds.BoxExtent.ToString(), Primitive->Bounds.SphereRadius);INC_DWORD_STAT_BY( STAT_GameToRendererMallocTotal, PrimitiveSceneProxy->GetMemoryFootprint() + PrimitiveSceneInfo->GetMemoryFootprint() );// Verify the primitive is validVerifyProperPIEScene(Primitive, World);// Increment the attachment counter, the primitive is about to be attached to the scene.Primitive->AttachmentCounter.Increment();// Create any RenderThreadResources required and send a command to the rendering thread to add the primitive to the scene.FScene* Scene = this;// If this primitive has a simulated previous transform, ensure that the velocity data for the scene representation is correctTOptional<FTransform> PreviousTransform = FMotionVectorSimulation::Get().GetPreviousTransform(Primitive);ENQUEUE_RENDER_COMMAND(AddPrimitiveCommand)([Params = MoveTemp(Params), Scene, PrimitiveSceneInfo, PreviousTransform = MoveTemp(PreviousTransform)](FRHICommandListImmediate& RHICmdList){FPrimitiveSceneProxy* SceneProxy = Params.PrimitiveSceneProxy;FScopeCycleCounter Context(SceneProxy->GetStatId());SceneProxy->SetTransform(Params.RenderMatrix, Params.WorldBounds, Params.LocalBounds, Params.AttachmentRootPosition);// Create any RenderThreadResources required.SceneProxy->CreateRenderThreadResources();Scene->AddPrimitiveSceneInfo_RenderThread(PrimitiveSceneInfo, PreviousTransform);});}

 AddedPrimitiveSceneInfos 会在后面创建LumenSceneData用到。

void FScene::AddPrimitiveSceneInfo_RenderThread(FPrimitiveSceneInfo* PrimitiveSceneInfo, const TOptional<FTransform>& PreviousTransform)
{check(IsInRenderingThread());check(PrimitiveSceneInfo->PackedIndex == INDEX_NONE);check(AddedPrimitiveSceneInfos.Find(PrimitiveSceneInfo) == nullptr);AddedPrimitiveSceneInfos.FindOrAdd(PrimitiveSceneInfo);if (PreviousTransform.IsSet()){OverridenPreviousTransforms.Update(PrimitiveSceneInfo, PreviousTransform.GetValue().ToMatrixWithScale());}
}

LumenSceneData创建流程

Engine/Source/Runtime/Renderer/Private/DeferredShadingRenderer.cpp

Scene->UpdateAllPrimitiveSceneInfos(GraphBuilder, true);

void FScene::UpdateAllPrimitiveSceneInfos(FRDGBuilder& GraphBuilder, bool bAsyncCreateLPIs)
{TArray<FPrimitiveSceneInfo*> AddedLocalPrimitiveSceneInfos;AddedLocalPrimitiveSceneInfos.Reserve(AddedPrimitiveSceneInfos.Num());for (FPrimitiveSceneInfo* SceneInfo : AddedPrimitiveSceneInfos){AddedLocalPrimitiveSceneInfos.Add(SceneInfo);}AddedLocalPrimitiveSceneInfos.Sort(FPrimitiveArraySortKey());while (AddedLocalPrimitiveSceneInfos.Num()){int32 StartIndex = AddedLocalPrimitiveSceneInfos.Num() - 1;for (int AddIndex = StartIndex; AddIndex < AddedLocalPrimitiveSceneInfos.Num(); AddIndex++){FPrimitiveSceneInfo* PrimitiveSceneInfo = AddedLocalPrimitiveSceneInfos[AddIndex];int32 PrimitiveIndex = PrimitiveSceneInfo->PackedIndex;FPrimitiveSceneProxy* SceneProxy = PrimitiveSceneInfo->Proxy;if (ShouldPrimitiveOutputVelocity(SceneProxy, GetShaderPlatform())){PrimitiveSceneInfo->bRegisteredWithVelocityData = true;// We must register the initial LocalToWorld with the velocity state. // In the case of a moving component with MarkRenderStateDirty() called every frame, UpdateTransform will never happen.VelocityData.UpdateTransform(PrimitiveSceneInfo, PrimitiveTransforms[PrimitiveIndex], PrimitiveTransforms[PrimitiveIndex]);}DistanceFieldSceneData.AddPrimitive(PrimitiveSceneInfo);LumenAddPrimitive(PrimitiveSceneInfo);}}
}

// Add function is a member of FScene, because it needs to add the primitive to all FLumenSceneData at once
void FScene::LumenAddPrimitive(FPrimitiveSceneInfo* InPrimitive)
{LLM_SCOPE_BYTAG(Lumen);if (DefaultLumenSceneData->bTrackAllPrimitives){const FPrimitiveSceneProxy* Proxy = InPrimitive->Proxy;bool bTrackPrimitveForLumenScene = TrackPrimitiveForLumenScene(Proxy);for (FLumenSceneDataIterator LumenSceneData = GetLumenSceneDataIterator(); LumenSceneData; ++LumenSceneData){// We copy this flag over when creating per-view lumen scene data, validate that it's still the samecheck(LumenSceneData->bTrackAllPrimitives == DefaultLumenSceneData->bTrackAllPrimitives);LumenSceneData->PrimitivesToUpdateMeshCards.Add(InPrimitive->GetIndex());if (bTrackPrimitveForLumenScene){ensure(!LumenSceneData->PendingAddOperations.Contains(InPrimitive));ensure(!LumenSceneData->PendingUpdateOperations.Contains(InPrimitive));LumenSceneData->PendingAddOperations.Add(InPrimitive);}}}
}