scene_system.hpp

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#ifndef FOOLSENGINE_SCENESYSTEM_H
#define FOOLSENGINE_SCENESYSTEM_H
 
#include <vector>
#include <memory>
#include <unordered_map>
#include <algorithm>
#include <cctype>
#include <type_traits>
 
#include <glm/glm.hpp>
#include <glm/gtc/quaternion.hpp>
 
#include "core/ecs_world.hpp"
#include "core/resource_database.hpp"
#include "scene_components.hpp"
#include "spatial_query_math.hpp"
#include "render_system.hpp"
#include "texture.hpp"
#include "input_system/input_system.hpp"
 
namespace ToyMaker {
 
    class SceneNodeCore;
    class SceneNode;
    class ViewportNode;
    class SceneSystem;

    enum class RelativeTo : uint8_t {
        PARENT=0, //< Compute relative to/on top of this node's parent's transform.
        // WORLD=1,
        // CAMERA=2,
    };

    NLOHMANN_JSON_SERIALIZE_ENUM(RelativeTo, {
        {RelativeTo::PARENT, "parent"},
    });

    enum SpecialEntity: EntityID {
        ENTITY_NULL = kMaxEntities,
    };

    extern const std::string kSceneRootName;

    class SceneNodeCore: public std::enable_shared_from_this<SceneNodeCore> {
    public:
        static void SceneNodeCore_del_(SceneNodeCore* sceneNode);

        virtual ~SceneNodeCore()=default;

        template <typename TComponent>
        void addComponent(const TComponent& component, const bool bypassSceneActivityCheck=false);

        void addComponent(const nlohmann::json& jsonComponent, const bool bypassSceneActivityCheck=false);

        template <typename TComponent>
        TComponent getComponent(const float simulationProgress=1.f) const;

        template <typename TComponent>
        bool hasComponent() const;

        bool hasComponent(const std::string& type) const;

        template <typename TComponent>
        void updateComponent(const TComponent& component);

        void updateComponent(const nlohmann::json& component);

        template <typename TComponent>
        void addOrUpdateComponent(const TComponent& component, const bool bypassSceneActivityCheck=false);

        void addOrUpdateComponent(const nlohmann::json& component, const bool bypassSceneActivityCheck=false);

        template <typename TComponent>
        void removeComponent();

        template <typename TSystem>
        void setEnabled(bool state);

        template <typename TSystem>
        bool getEnabled() const;

        EntityID getEntityID() const;

        WorldID getWorldID() const;

        UniversalEntityID getUniversalEntityID() const;

        std::weak_ptr<ECSWorld> getWorld() const;

        bool inScene() const;

        bool isActive() const;

        bool isAncestorOf(std::shared_ptr<const SceneNodeCore> sceneNode) const;

        bool hasNode(const std::string& pathToChild) const;
        
        void addNode(std::shared_ptr<SceneNodeCore> node, const std::string& where);

        std::vector<std::shared_ptr<SceneNodeCore>> getChildren();

        std::vector<std::shared_ptr<const SceneNodeCore>> getChildren() const;

        std::vector<std::shared_ptr<SceneNodeCore>> getDescendants();

        template <typename TObject=std::shared_ptr<SceneNode>>
        TObject getByPath(const std::string& where);

        template <typename TSceneNode=SceneNode>
        std::shared_ptr<TSceneNode> getNodeByID(EntityID entityID);

        std::string getPathFromAncestor(std::shared_ptr<const SceneNodeCore> ancestor) const;

        virtual std::shared_ptr<ViewportNode> getLocalViewport();

        virtual std::shared_ptr<const ViewportNode> getLocalViewport() const;

        std::shared_ptr<SceneNodeCore> getNode(const std::string& where);

        std::shared_ptr<SceneNodeCore> getParentNode();

        std::shared_ptr<const SceneNodeCore> getParentNode() const;

        std::shared_ptr<SceneNodeCore> removeNode(const std::string& where);

        std::vector<std::shared_ptr<SceneNodeCore>> removeChildren();

        std::string getName() const;

        void setName(const std::string& name);

        std::string getViewportLocalPath() const;

        inline void setPrototype_(std::shared_ptr<SceneNodeCore> prototype) { mPrototype=prototype; }
 
    protected:

        virtual void joinWorld(ECSWorld& world);

        static std::shared_ptr<SceneNodeCore> copy(const std::shared_ptr<const SceneNodeCore> other);

        template<typename ...TComponents>
        SceneNodeCore(const Placement& placement, const std::string& name, TComponents...components);

        SceneNodeCore(const nlohmann::json& jsonSceneNode);

        SceneNodeCore(const SceneNodeCore& sceneObject);
 
        // /**
        //  * @brief Copy assignment operator.
        //  * 
        //  * @todo Sit down and figure out whether this operator will ever actually need to be used.
        //  */
        // BaseSceneNode& operator=(const BaseSceneNode& sceneObject);

        virtual void onCreated();

        virtual void onActivated();

        virtual void onDeactivated();

        virtual void onDestroyed();

        static void validateName(const std::string& nodeName);
 
    private:
        struct Key {};

        template<typename ...TComponents>
        SceneNodeCore(const Key&, const Placement& placement, const std::string& name, TComponents...components);

        enum StateFlags: uint8_t {
            ENABLED=0x1, //< This node is intended to be made active as soon as its added to the SceneSystem's scene tree.
            ACTIVE=0x2, //< This node is presently active on the SceneSystem's scene tree.
        };

        template <typename TObject, typename Enable=void>
        struct getByPath_Helper {
            static TObject get(std::shared_ptr<SceneNodeCore> rootNode, const std::string& where);
            static constexpr bool s_valid { false };
        };

        virtual std::shared_ptr<SceneNodeCore> clone() const;

        void copyDescendants(const SceneNodeCore& other);

        static void setParentViewport(std::shared_ptr<SceneNodeCore> node, std::shared_ptr<ViewportNode> newViewport);

        static std::shared_ptr<SceneNodeCore> disconnectNode(std::shared_ptr<SceneNodeCore> node);

        static bool detectCycle(std::shared_ptr<SceneNodeCore> node);

        static std::tuple<std::string, std::string> nextInPath(const std::string& where);

        void copyAndReplaceAttributes(const SceneNodeCore& other);

        void recomputeChildNameIndexMapping();

        std::string mName {};

        uint8_t mStateFlags { 0x00 | StateFlags::ENABLED };

        RelativeTo mRelativeTo{ RelativeTo::PARENT };

        std::shared_ptr<Entity> mEntity { nullptr };

        std::weak_ptr<SceneNodeCore> mParent {};

        std::weak_ptr<ViewportNode> mParentViewport {};

        std::unordered_map<std::string, std::size_t> mChildNameToNode {};

        std::vector<std::shared_ptr<SceneNodeCore>> mChildren {};

        std::shared_ptr<SceneNodeCore> mPrototype { nullptr };

        Signature mSystemMask {Signature{}.set()};
 
    friend class SceneSystem;
    template<typename TSceneNode>
    friend class BaseSceneNode;
    friend class ViewportNode;
    };
 

    template <typename TSceneNode>
    class BaseSceneNode: public SceneNodeCore {
    public:
 
    protected:
        template <typename ...TComponents>
        static std::shared_ptr<TSceneNode> create(const Key&, const Placement& placement, const std::string& name, TComponents...components);

        template <typename ...TComponents>
        static std::shared_ptr<TSceneNode> create(const Placement& placement, const std::string& name, TComponents...components);

        static std::shared_ptr<TSceneNode> create(const nlohmann::json& sceneNodeDescription);
 

        static std::shared_ptr<TSceneNode> copy(const std::shared_ptr<const TSceneNode> sceneNode);
        template <typename...TComponents>

        BaseSceneNode(const Key& key, const Placement& placement, const std::string& name, TComponents...components):
        SceneNodeCore{ key, placement, name, components... }
        {}

        template<typename ...TComponents>
        BaseSceneNode(const Placement& placement, const std::string& name, TComponents...components):
        SceneNodeCore{ placement, name, components... }
        {}

        BaseSceneNode(const nlohmann::json& nodeDescription) : SceneNodeCore { nodeDescription } {}

        BaseSceneNode(const SceneNodeCore& other): SceneNodeCore{ other } {}
 
    friend class SceneNodeCore;
    };

    class SceneNode: public BaseSceneNode<SceneNode>, public Resource<SceneNode> { 
    public:
        template <typename ...TComponents>
        static std::shared_ptr<SceneNode> create(const Placement& placement, const std::string& name, TComponents...components);
        static std::shared_ptr<SceneNode> create(const nlohmann::json& sceneNodeDescription);
        static std::shared_ptr<SceneNode> copy(const std::shared_ptr<const SceneNode> other);
 
        static inline std::string getResourceTypeName() { return "SceneNode"; }
 
    protected:
        template<typename ...TComponents>
        SceneNode(const Placement& placement, const std::string& name, TComponents...components):
        BaseSceneNode<SceneNode>{placement, name, components...},
        Resource<SceneNode>{0}
        {}
 
        SceneNode(const nlohmann::json& jsonSceneNode):
        BaseSceneNode<SceneNode>{jsonSceneNode},
        Resource<SceneNode>{0}
        {}
 
        SceneNode(const SceneNode& sceneObject):
        BaseSceneNode<SceneNode>{sceneObject},
        Resource<SceneNode>{0}
        {}
    friend class BaseSceneNode<SceneNode>;
    };

    class ViewportNode: public BaseSceneNode<ViewportNode>, public Resource<ViewportNode> {
    public:
        struct RenderConfiguration {
            enum class ResizeType: uint8_t {
                OFF=0, //< No resize, render texture is rendered as is with no scaling.
                VIEWPORT_DIMENSIONS, //< Viewport transform configured per stretch mode and requested dimensions
                TEXTURE_DIMENSIONS, //< Texture result rendered in base dimensions, and then warped to fit request dimensions
            };

            enum class ResizeMode: uint8_t {
                FIXED_ASPECT=0, //< both, while retaining aspect ratio.
                EXPAND_VERTICALLY, //< Expand vertically if permitted by target dimensions, otherwise constrain to aspect.
                EXPAND_HORIZONTALLY, //< Expand horiontally if possible by target dimensions, otherwise constrain to aspect.
                EXPAND_FILL, //< No constraint in either dimension, expand to fill target dimensions always.
            };

            enum class UpdateMode: uint8_t {
                NEVER=0, //< No rerender takes place even when render is called for this viewport.
                ONCE, //< Update on next render frame, then set to UpdateMode::NEVER
                ON_FETCH, //< Update whenever a request for the texture is made, where frequency is entirely dependent on caller.
                ON_FETCH_CAP_FPS, //< Update on request, but ignore requests exceeding FPS cap.  Final frequency is constrained to the FPS cap configured for this viewport, but may be lower than it.
                ON_RENDER, //< Update every render call with no constraint, so frequency depends entirely on the render frequency of the application loop.
                ON_RENDER_CAP_FPS, //< Update on render call when fps cap isn't exceeded.  Final FPS may be lower than specified as a cap.
            };

            using RenderType = RenderSet::RenderType;

            ResizeType mResizeType { ResizeType::VIEWPORT_DIMENSIONS };
            ResizeMode mResizeMode { ResizeMode::EXPAND_HORIZONTALLY };

            RenderType mRenderType { RenderType::BASIC_3D };

            glm::u16vec2 mBaseDimensions { 800, 600 };

            glm::u16vec2 mComputedDimensions { 800, 600 };

            glm::u16vec2 mRequestedDimensions { 800, 600 };

            float mRenderScale { 1.f };

            UpdateMode mUpdateMode { UpdateMode::ON_RENDER_CAP_FPS };

            float mFPSCap { 60.f };
        };

        static std::shared_ptr<ViewportNode> create(const std::string& name, bool inheritsWorld, bool allowActionFlowThrough, const RenderConfiguration& renderConfiguration, std::shared_ptr<Texture> skybox);

        static std::shared_ptr<ViewportNode> create(const nlohmann::json& sceneNodeDescription);

        static std::shared_ptr<ViewportNode> copy(const std::shared_ptr<const ViewportNode> other);

        static inline std::string getResourceTypeName() { return "ViewportNode"; }

        void viewNextDebugTexture();

        void updateExposure(float newExposure);

        void updateGamma(float newGamma);

        float getExposure();

        float getGamma();

        std::shared_ptr<ViewportNode> getLocalViewport() override;

        virtual std::shared_ptr<const ViewportNode> getLocalViewport() const override;

        std::shared_ptr<Texture> fetchRenderResult(float simulationProgress);

        void setActiveCamera(const std::string& cameraPath);

        void setActiveCamera(std::shared_ptr<SceneNodeCore> cameraNode);

        RenderConfiguration getRenderConfiguration() const;

        void setRenderConfiguration(const RenderConfiguration& renderConfiguration);

        void setSkybox(std::shared_ptr<Texture> skybox);

        void setResizeType(RenderConfiguration::ResizeType type);

        void setResizeMode(RenderConfiguration::ResizeMode mode);

        void setRenderScale(float renderScale);

        void setUpdateMode(RenderConfiguration::UpdateMode updateMode);

        void setFPSCap(float fpsCap);

        void requestDimensions(glm::u16vec2 requestedDimensions);

        ActionDispatch& getActionDispatch();

        bool handleAction(std::pair<ActionDefinition, ActionData> pendingAction);

        bool disallowsHandledActionPropagation() const { return mPreventHandledActionPropagation; }

        ~ViewportNode() override;

        inline uint32_t getViewportLoadOrdinal() const { return mViewportLoadOrdinal; }
 
    protected:
        ViewportNode(const Placement& placement, const std::string& name):
        BaseSceneNode<ViewportNode>{placement, name},
        Resource<ViewportNode>{0},
        mViewportLoadOrdinal { SDL_GetTicks() }
        {}
        ViewportNode(const nlohmann::json& jsonSceneNode):
        BaseSceneNode<ViewportNode>{jsonSceneNode},
        Resource<ViewportNode>{0},
        mViewportLoadOrdinal { SDL_GetTicks() }
        {}
        ViewportNode(const ViewportNode& sceneObject):
        BaseSceneNode<ViewportNode>{sceneObject},
        Resource<ViewportNode>{0},
        mViewportLoadOrdinal { SDL_GetTicks() }
        {}

        std::shared_ptr<ECSWorld> mOwnWorld { nullptr };

        void onActivated() override;

        void onDeactivated() override;

        void joinWorld(ECSWorld& world) override;
 
    private:
        static std::shared_ptr<ViewportNode> create(const Key& key, const std::string& name, bool inheritsWorld, const RenderConfiguration& renderConfiguration, std::shared_ptr<Texture> skybox);

        ViewportNode(const Key& key, const Placement& placement, const std::string& name):
        BaseSceneNode<ViewportNode>{key, Placement{}, name},
        Resource<ViewportNode>{0}
        {(void)placement; /*prevent unused parameter warnings*/}

        std::shared_ptr<SceneNodeCore> clone() const override;

        void createAndJoinWorld();

        void registerDomainCamera(std::shared_ptr<SceneNodeCore> cameraNode);

        void unregisterDomainCamera(std::shared_ptr<SceneNodeCore> cameraNode);
        std::shared_ptr<SceneNodeCore> findFallbackCamera();

        std::vector<std::shared_ptr<ViewportNode>> getActiveDescendantViewports();

        std::vector<std::weak_ptr<ECSWorld>> getActiveDescendantWorlds();

        uint32_t render(float simulationProgress, uint32_t variableStep);

        void render_(float simulationProgress);

        inline SDL_Rect getCenteredViewportCoordinates() const {
            return {
                mRenderConfiguration.mRequestedDimensions.x/2 - mRenderConfiguration.mComputedDimensions.x/2, mRenderConfiguration.mRequestedDimensions.y/2 - mRenderConfiguration.mComputedDimensions.y/2,
                mRenderConfiguration.mComputedDimensions.x, mRenderConfiguration.mComputedDimensions.y
            };
        }

        struct ViewportChildComp_ {
            bool operator() (const std::shared_ptr<ViewportNode>& one, const std::shared_ptr<ViewportNode>& two) const {
                return one->getViewportLoadOrdinal() < two->getViewportLoadOrdinal();
            }
        };

        uint32_t mViewportLoadOrdinal { std::numeric_limits<uint32_t>::max() };

        uint32_t mNLifetimeChildrenAdded { 0 };

        ActionDispatch mActionDispatch {};

        bool mActionFlowthrough { false };

        bool mPreventHandledActionPropagation { true };

        std::set<std::shared_ptr<ViewportNode>, ViewportChildComp_> mChildViewports {};

        std::shared_ptr<SceneNodeCore> mActiveCamera { nullptr };

        std::set<std::shared_ptr<SceneNodeCore>, std::owner_less<std::shared_ptr<SceneNodeCore>>> mDomainCameras {};

        RenderSetID mRenderSet;

        std::shared_ptr<Texture> mTextureResult { nullptr };

        RenderConfiguration mRenderConfiguration {};

        uint32_t mTimeSinceLastRender { static_cast<uint32_t>(1000/mRenderConfiguration.mFPSCap) };
 
    friend class BaseSceneNode<ViewportNode>;
    friend class SceneNodeCore;
    friend class SceneSystem;
    };

    class SceneSystem: public System<SceneSystem, std::tuple<>, std::tuple<Placement, SceneHierarchyData, Transform>> {
    public:
        explicit SceneSystem(std::weak_ptr<ECSWorld> world):
        System<SceneSystem, std::tuple<>, std::tuple<Placement, SceneHierarchyData, Transform>> { world }
        {}

        static std::string getSystemTypeName() { return "SceneSystem"; }

        bool isSingleton() const override { return true; }

        template<typename TObject=std::shared_ptr<SceneNode>>
        TObject getByPath(const std::string& where);

        template <typename TSceneNode>
        std::shared_ptr<TSceneNode> getNodeByID(const UniversalEntityID& universalEntityID);

        std::vector<std::shared_ptr<SceneNodeCore>> getNodesByID(const std::vector<UniversalEntityID>& universalEntityIDs);

        std::shared_ptr<SceneNodeCore> getNode(const std::string& where);

        std::shared_ptr<SceneNodeCore> removeNode(const std::string& where);

        void addNode(std::shared_ptr<SceneNodeCore> node, const std::string& where);

        std::weak_ptr<ECSWorld> getRootWorld() const;

        ViewportNode& getRootViewport() const;

        void onApplicationInitialize(const ViewportNode::RenderConfiguration& rootViewportRenderConfiguration);

        void onApplicationStart();

        void onApplicationEnd();

        void simulationStep(uint32_t simStepMillis, std::vector<std::pair<ActionDefinition, ActionData>> triggeredActions={});

        void variableStep(float simulationProgress, uint32_t simulationLagMillis, uint32_t variableStepMillis, std::vector<std::pair<ActionDefinition, ActionData>> triggeredActions={});

        void updateTransforms();

        uint32_t render(float simulationProgress, uint32_t variableStep);
 
    private:
        class SceneSubworld: public System<SceneSubworld, std::tuple<Placement>, std::tuple<Transform, SceneHierarchyData>> {
        public:
            explicit SceneSubworld(std::weak_ptr<ECSWorld> world):
            System<SceneSubworld, std::tuple<Placement>, std::tuple<Transform, SceneHierarchyData>> { world }
            {}
            static std::string getSystemTypeName() { return "SceneSubworld"; }
        private:
            void onEntityUpdated(EntityID entityID) override;
        };

        template <typename TSceneNode, typename Enable=void>
        struct getNodeByID_Helper {
            static std::shared_ptr<TSceneNode> get(const UniversalEntityID& universalEntityID, SceneSystem& sceneSystem);
        };

        bool isActive(std::shared_ptr<const SceneNodeCore> sceneNode) const;

        bool isActive(UniversalEntityID UniversalEntityID) const;

        bool inScene(std::shared_ptr<const SceneNodeCore> sceneNode) const;

        bool inScene(UniversalEntityID UniversalEntityID) const;

        void markDirty(UniversalEntityID UniversalEntityID);

        std::vector<std::shared_ptr<ViewportNode>> getActiveViewports();

        std::vector<std::weak_ptr<ECSWorld>> getActiveWorlds();

        Transform getLocalTransform(std::shared_ptr<const SceneNodeCore> sceneNode) const;

        Transform getCachedWorldTransform(std::shared_ptr<const SceneNodeCore> sceneNode) const;

        void updateHierarchyDataInsertion(std::shared_ptr<SceneNodeCore> insertedNode);

        void updateHierarchyDataRemoval(std::shared_ptr<SceneNodeCore> removedNode);

        void nodeAdded(std::shared_ptr<SceneNodeCore> sceneNode);

        void nodeRemoved(std::shared_ptr<SceneNodeCore> sceneNode);

        void nodeActivationChanged(std::shared_ptr<SceneNodeCore> sceneNode, bool state);

        void activateSubtree(std::shared_ptr<SceneNodeCore> sceneNode);

        void deactivateSubtree(std::shared_ptr<SceneNodeCore> sceneNode);

        void onWorldEntityUpdate(UniversalEntityID UniversalEntityID);

        std::shared_ptr<SceneNodeCore> getNodeByID(const UniversalEntityID& universalEntityID);

        std::shared_ptr<ViewportNode> mRootNode{ nullptr };

        std::map<UniversalEntityID, std::weak_ptr<SceneNodeCore>, std::less<UniversalEntityID>> mEntityToNode {};

        std::set<UniversalEntityID, std::less<UniversalEntityID>> mActiveEntities {};

        std::set<UniversalEntityID, std::less<UniversalEntityID>> mComputeTransformQueue {};
 
    friend class SceneNodeCore;
    };
 
 
    template <typename TSceneNode>
    template <typename ...TComponents>
    std::shared_ptr<TSceneNode> BaseSceneNode<TSceneNode>::create(const Placement& placement, const std::string& name, TComponents...components) {
        std::shared_ptr<SceneNodeCore> newNode ( new TSceneNode(placement, name, components...), &SceneNodeCore_del_);
        newNode->onCreated();
        return std::static_pointer_cast<TSceneNode>(newNode);
    }
 
    template <typename TSceneNode>
    template <typename ...TComponents>
    std::shared_ptr<TSceneNode> BaseSceneNode<TSceneNode>::create(const Key& key, const Placement& placement, const std::string& name, TComponents...components) {
        std::shared_ptr<SceneNodeCore> newNode( new TSceneNode(key, placement, name, components...), &SceneNodeCore_del_);
        newNode->onCreated();
        return std::static_pointer_cast<TSceneNode>(newNode);
    }
 
    template <typename TSceneNode>
    std::shared_ptr<TSceneNode> BaseSceneNode<TSceneNode>::create(const nlohmann::json& sceneNodeDescription) {
        std::shared_ptr<SceneNodeCore> newNode{ new TSceneNode{ sceneNodeDescription }, &SceneNodeCore_del_};
        newNode->onCreated();
        return std::static_pointer_cast<TSceneNode>(newNode);
    }
 
    template <typename TSceneNode>
    std::shared_ptr<TSceneNode> BaseSceneNode<TSceneNode>::copy(const std::shared_ptr<const TSceneNode> sceneNode) {
        std::shared_ptr<SceneNodeCore> newNode { SceneNodeCore::copy(sceneNode) };
        newNode->onCreated();
        return std::static_pointer_cast<TSceneNode>(newNode);
    }
 
    template<typename ...TComponents>
    std::shared_ptr<SceneNode> SceneNode::create(const Placement& placement, const std::string& name,  TComponents...components) {
        return BaseSceneNode<SceneNode>::create<TComponents...>(placement, name, components...);
    }
 
    template <typename TObject>
    TObject SceneNodeCore::getByPath(const std::string& where) {
        return getByPath_Helper<TObject>::get(shared_from_this(), where);
    }
 
    template <typename TObject>
    TObject SceneSystem::getByPath(const std::string& where) {
        return mRootNode->getByPath<TObject>(where);
    }
 
    template <typename TSceneNode>
    inline std::shared_ptr<TSceneNode> SceneSystem::getNodeByID(const UniversalEntityID& universalEntityID) {
        return SceneSystem::getNodeByID_Helper<TSceneNode>(universalEntityID, *this);
    }
 
    // Fail retrieval in cases where no explicitly defined object by path
    // method exists
    template <typename TObject, typename Enable>
    TObject SceneNodeCore::getByPath_Helper<TObject, Enable>::get(std::shared_ptr<SceneNodeCore> rootNode, const std::string& where) {
        static_assert(false && "No Object-by-Path method for this type exists");
        return TObject{}; // this is just to shut the compiler up about no returned value
    }
 
    template <typename TSceneNode, typename Enable>
    std::shared_ptr<TSceneNode> SceneSystem::getNodeByID_Helper<TSceneNode, Enable>::get(const UniversalEntityID& universalEntityID, SceneSystem& sceneSystem) {
        static_assert(false && "No scene node of this type exists");
        return std::shared_ptr<TSceneNode>{};
    }
 
    template <typename TSceneNode>
    struct SceneSystem::getNodeByID_Helper<TSceneNode, typename std::enable_if_t<std::is_base_of<SceneNodeCore, TSceneNode>::value>> {
        std::shared_ptr<TSceneNode> get(const UniversalEntityID& universalEntityID, SceneSystem& sceneSystem) {
            return std::static_pointer_cast<TSceneNode>(sceneSystem.getNodeByID(universalEntityID));
        }
    };
 
    template <typename TObject>
    struct SceneNodeCore::getByPath_Helper<std::shared_ptr<TObject>, typename std::enable_if_t<std::is_base_of<SceneNodeCore, TObject>::value>> {
        static std::shared_ptr<TObject> get(std::shared_ptr<SceneNodeCore> rootNode, const std::string& where) {
            return std::static_pointer_cast<TObject>(rootNode->getNode(where));
        }
        static constexpr bool s_valid { true };
    };
 
    template <typename ...TComponents>
    SceneNodeCore::SceneNodeCore(const Placement& placement, const std::string& name, TComponents...components) {
        validateName(name);
        mName = name;
        mEntity = std::make_shared<Entity>(
            ECSWorld::createEntityPrototype<Placement, SceneHierarchyData, Transform, ObjectBounds, AxisAlignedBounds, TComponents...>(
                placement,
                SceneHierarchyData{},
                Transform{glm::mat4{1.f}},
                ObjectBounds {},
                AxisAlignedBounds {},
                components...
            )
        );
    }
 
    template <typename ...TComponents>
    SceneNodeCore::SceneNodeCore(const Key&, const Placement& placement, const std::string& name, TComponents...components) {
        mName = name;
        mEntity = std::make_shared<Entity>(
            ECSWorld::createEntityPrototype<Placement, SceneHierarchyData, Transform, ObjectBounds, AxisAlignedBounds, TComponents...>(
                placement,
                SceneHierarchyData{},
                Transform{glm::mat4{1.f}},
                ObjectBounds {},
                AxisAlignedBounds{},
                components...
            )
        );
    }
 
    template <typename TComponent>
    void SceneNodeCore::addComponent(const TComponent& component, bool bypassSceneActivityCheck) {
        mEntity->addComponent<TComponent>(component);
 
        // NOTE: required because even though this node's entity's signature changes, it
        // is disabled by default on any systems it is eligible for. We need to activate
        // the node according to its system mask
        if(!bypassSceneActivityCheck && isActive()) {
            mEntity->enableSystems(mSystemMask);
        }
        // NOTE: no removeComponent() equivalent required, as systems that depend on the removed
        // component will automatically have this entity removed from their list, and hence
        // be disabled
    }
 
    template <typename TComponent>
    TComponent SceneNodeCore::getComponent(const float simulationProgress) const {
        return mEntity->getComponent<TComponent>(simulationProgress);
    }
 
    template <typename TComponent>
    bool SceneNodeCore::hasComponent() const {
        return mEntity->hasComponent<TComponent>();
    }
 
    template <typename TComponent>
    void SceneNodeCore::updateComponent(const TComponent& component) {
        mEntity->updateComponent<TComponent>(component);
    }
 
    template <typename TComponent>
    void SceneNodeCore::addOrUpdateComponent(const TComponent& component, const bool bypassSceneActivityCheck) {
        if(!hasComponent<TComponent>()) {
            addComponent<TComponent>(component, bypassSceneActivityCheck);
            return;
        }
        updateComponent<TComponent>(component);
    }
 
    template <typename TComponent>
    void SceneNodeCore::removeComponent() {
        mEntity->removeComponent<TComponent>();
    }
 
    template <typename TSystem>
    bool SceneNodeCore::getEnabled() const {
        return mEntity->isEnabled<TSystem>();
    }
 
    template <typename TSystem>
    void SceneNodeCore::setEnabled(bool state) {
        const SystemType systemType { mEntity->getWorld().lock()->getSystemType<TSystem>() };
        mSystemMask.set(systemType, state);
 
        // since the system mask has been changed, we'll want the scene
        // to talk to ECS and make this node visible to the system that
        // was enabled, if eligible
        if(state == true && isActive()){
            mEntity->enableSystems(mSystemMask);
        }
    }
 
    // Specialization for when the scene system itself is marked
    // enabled or disabled
    template <>
    inline void SceneNodeCore::setEnabled<SceneSystem>(bool state) {
        const SystemType systemType { mEntity->getWorld().lock()->getSystemType<SceneSystem>() };
        // TODO: enabled entities are tracked in both SceneSystem's 
        // mActiveNodes and ECS getEnabledEntities, which is 
        // redundant and may eventually cause errors
        mSystemMask.set(systemType, state);
        //TODO: More redundancy. Why?
        mStateFlags = state? (mStateFlags | SceneNodeCore::StateFlags::ENABLED): (mStateFlags & ~SceneNodeCore::StateFlags::ENABLED);
        mEntity->getWorld().lock()->getSystem<SceneSystem>()->nodeActivationChanged(
            shared_from_this(),
            state
        );
    }
 
    // Prevent removal of components essential to a scene node
    template <>
    inline void SceneNodeCore::removeComponent<Placement>() {
        assert(false && "Cannot remove a scene node's Placement component");
    }
    template <>
    inline void SceneNodeCore::removeComponent<Transform>() {
        assert(false && "Cannot remove a scene node's Transform component");
    }
 
    template <typename TSceneNode>
    std::shared_ptr<TSceneNode> SceneNodeCore::getNodeByID(EntityID entityID) {
        return getWorld().lock()->getSystem<SceneSystem>()->getNodeByID<TSceneNode>({getWorldID(), entityID});
    }

    NLOHMANN_JSON_SERIALIZE_ENUM(ViewportNode::RenderConfiguration::ResizeType, {
        {ViewportNode::RenderConfiguration::ResizeType::OFF, "off"},
        {ViewportNode::RenderConfiguration::ResizeType::VIEWPORT_DIMENSIONS, "viewport-dimensions"},
        {ViewportNode::RenderConfiguration::ResizeType::TEXTURE_DIMENSIONS, "texture-dimensions"},
    });

    NLOHMANN_JSON_SERIALIZE_ENUM(ViewportNode::RenderConfiguration::ResizeMode, {
        {ViewportNode::RenderConfiguration::ResizeMode::FIXED_ASPECT,"fixed-aspect"},
        {ViewportNode::RenderConfiguration::ResizeMode::EXPAND_VERTICALLY, "expand-vertically"},
        {ViewportNode::RenderConfiguration::ResizeMode::EXPAND_HORIZONTALLY, "expand-horizontally"},
        {ViewportNode::RenderConfiguration::ResizeMode::EXPAND_FILL, "expand-fill"},
    });

    NLOHMANN_JSON_SERIALIZE_ENUM(ViewportNode::RenderConfiguration::UpdateMode, {
        {ViewportNode::RenderConfiguration::UpdateMode::NEVER, "never"},
        {ViewportNode::RenderConfiguration::UpdateMode::ONCE, "once"},
        {ViewportNode::RenderConfiguration::UpdateMode::ON_FETCH, "on-fetch"},
        {ViewportNode::RenderConfiguration::UpdateMode::ON_RENDER, "on-render"},
        {ViewportNode::RenderConfiguration::UpdateMode::ON_RENDER_CAP_FPS, "on-render-cap-fps"},
    });

    NLOHMANN_JSON_SERIALIZE_ENUM(ViewportNode::RenderConfiguration::RenderType, {
        {ViewportNode::RenderConfiguration::RenderType::BASIC_3D, "basic-3d"},
        {ViewportNode::RenderConfiguration::RenderType::ADDITION, "addition"},
    });

    inline void to_json(nlohmann::json& json, const ViewportNode::RenderConfiguration& renderConfiguration) {
        json = {
            {"base_dimensions", nlohmann::json::array({renderConfiguration.mBaseDimensions.x, renderConfiguration.mBaseDimensions.y})},
            {"update_mode", renderConfiguration.mUpdateMode},
            {"resize_type", renderConfiguration.mResizeType},
            {"resize_mode", renderConfiguration.mResizeMode},
            {"render_scale", renderConfiguration.mRenderScale},
            {"render_type", renderConfiguration.mRenderType},
            {"fps_cap", renderConfiguration.mFPSCap},
        };
    }

    inline void from_json(const nlohmann::json& json, ViewportNode::RenderConfiguration& renderConfiguration) {
        assert(json.find("base_dimensions") != json.end() && "Viewport descriptions must contain the \"base_dimensions\" size 2 array of Numbers attribute");
        json.at("base_dimensions")[0].get_to(renderConfiguration.mBaseDimensions.x);
        json.at("base_dimensions")[1].get_to(renderConfiguration.mBaseDimensions.y);
        json.at("render_type").get_to(renderConfiguration.mRenderType);
        renderConfiguration.mRequestedDimensions = renderConfiguration.mBaseDimensions;
        renderConfiguration.mComputedDimensions = renderConfiguration.mBaseDimensions;
        assert(renderConfiguration.mBaseDimensions.x > 0 && renderConfiguration.mBaseDimensions.y > 0 && "Base dimensions cannot include a 0 in either dimension");
 
        assert(json.find("update_mode") != json.end() && "Viewport render configuration must include the \"update_mode\" enum attribute");
        json.at("update_mode").get_to(renderConfiguration.mUpdateMode);
 
        assert(json.find("resize_type") != json.end() && "Viewport render configuration must include the \"resize_type\" enum attribute");
        json.at("resize_type").get_to(renderConfiguration.mResizeType);
 
        assert(json.find("resize_mode") != json.end() && "Viewport render configuration must include the \"resize_mode\" enum attribute");
        json.at("resize_mode").get_to(renderConfiguration.mResizeMode);
 
        assert(json.find("render_scale") != json.end() && "Viewport render configuration must include the \"render_scale\" float attribute");
        json.at("render_scale").get_to(renderConfiguration.mRenderScale);
        assert(renderConfiguration.mRenderScale > 0.f && "Render scale must be a positive non-zero decimal number");
 
        assert(json.find("fps_cap") != json.end() && "Viewport must include the \"fps_cap\" float attribute");
        json.at("fps_cap").get_to(renderConfiguration.mFPSCap);
        assert(renderConfiguration.mFPSCap > 0.f && "FPS cap must be a positive non-zero decimal number");
    }
 
}
 
#endif