NaniteOwnershipVisibilitySceneExtension.h

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// Copyright Epic Games, Inc. All Rights Reserved.
 
#pragma once
 
#include "SceneExtensions.h"
#include "PrimitiveSceneInfo.h" // FPersistentPrimitiveIndex
 
class FRDGBuffer;
 
namespace Nanite
{
 
// This scene extension keeps track of nanite primitives that have bOwnerNoSee or bOnlyOwnerSee enabled on them.
// It then creates a bitmask GPU buffer to efficiently hide such primitives in the relevant views.
class FOwnershipVisibilitySceneExtension : public ISceneExtension
{
    DECLARE_SCENE_EXTENSION(RENDERER_API, FOwnershipVisibilitySceneExtension);
public:
    using ISceneExtension::ISceneExtension;
 
    static bool ShouldCreateExtension(FScene& Scene);
 
    //~ Begin ISceneExtension Interface.
    virtual ISceneExtensionUpdater* CreateUpdater() override;
    virtual ISceneExtensionRenderer* CreateRenderer(FSceneRendererBase& InSceneRenderer, const FEngineShowFlags& EngineShowFlags) override;
    //~ End ISceneExtension Interface.
 
    const TArray<FPersistentPrimitiveIndex>& GetPrimitivesWithOwnership() const;
    int32 GetMaxPersistentPrimitiveIndex() const;
 
private:
 
    // Private updater class for handling adding and removal of primitives.
    class FUpdater : public ISceneExtensionUpdater
    {
        DECLARE_SCENE_EXTENSION_UPDATER(FUpdater, FOwnershipVisibilitySceneExtension);
    public:
        FUpdater(FOwnershipVisibilitySceneExtension& InSceneExtension) : SceneExtension(InSceneExtension) {}
 
        //~ Begin ISceneExtensionUpdater Interface.
        virtual void PreSceneUpdate(FRDGBuilder& GraphBuilder, const FScenePreUpdateChangeSet& ChangeSet, FSceneUniformBuffer& SceneUniforms) override;
        virtual void PostSceneUpdate(FRDGBuilder& GraphBuilder, const FScenePostUpdateChangeSet& ChangeSet) override;
        //~ End ISceneExtensionUpdater Interface.
 
    private:
        FOwnershipVisibilitySceneExtension& SceneExtension;
    };
 
    // Private "renderer" class, creating a bit array buffer with one bit per primitive per view.
    class FRenderer : public ISceneExtensionRenderer
    {
        DECLARE_SCENE_EXTENSION_RENDERER(FRenderer, FOwnershipVisibilitySceneExtension);
    public:
        FRenderer(FSceneRendererBase& InSceneRenderer, FOwnershipVisibilitySceneExtension& InSceneExtension)
            : ISceneExtensionRenderer(InSceneRenderer), SceneExtension(InSceneExtension) {
        }
 
        //~ Begin ISceneExtensionRenderer Interface.
        virtual void UpdateViewData(FRDGBuilder& GraphBuilder, const FRendererViewDataManager& ViewDataManager) override;
        virtual void UpdateSceneUniformBuffer(FRDGBuilder& GraphBuilder, FSceneUniformBuffer& SceneUniforms) override;
        //~ End ISceneExtensionRenderer Interface.
 
    private:
        FOwnershipVisibilitySceneExtension& SceneExtension;
        FRDGBuffer* OwnershipHiddenPrimitivesBitArrayBuffer = nullptr;
    };
 
    TArray<FPersistentPrimitiveIndex> NanitePrimitivesWithOwnership;
};
 
} // namespace Nanite