XCEngine/engine/src/Scene/ModelSceneInstantiation.cpp

#include <XCEngine/Scene/ModelSceneInstantiation.h>

#include <XCEngine/Components/GameObject.h>
#include <XCEngine/Components/MeshFilterComponent.h>
#include <XCEngine/Components/MeshRendererComponent.h>
#include <XCEngine/Core/Asset/ResourceManager.h>
#include <XCEngine/Scene/Scene.h>

namespace XCEngine {

namespace {

using namespace Components;
using namespace Resources;

Containers::String MakeNodeName(const ModelNode& node, Core::uint32 nodeIndex) {
    if (!node.name.Empty()) {
        return node.name;
    }

    return Containers::String(("ModelNode_" + std::to_string(nodeIndex)).c_str());
}

Containers::String MakeMeshObjectName(const Containers::String& nodeName, Core::uint32 meshBindingOffset) {
    return Containers::String(
        (std::string(nodeName.CStr()) + "_Mesh" + std::to_string(meshBindingOffset)).c_str());
}

AssetRef MakeSubAssetRef(const AssetRef& modelAssetRef, LocalID localID, ResourceType resourceType) {
    AssetRef ref;
    ref.assetGuid = modelAssetRef.assetGuid;
    ref.localID = localID;
    ref.resourceType = resourceType;
    return ref;
}

void SetErrorMessage(Containers::String* outErrorMessage, const Containers::String& message) {
    if (outErrorMessage != nullptr) {
        *outErrorMessage = message;
    }
}

bool AttachMeshBinding(
    GameObject& targetObject,
    const Model& model,
    const AssetRef& modelAssetRef,
    const ModelMeshBinding& meshBinding,
    Containers::String* outErrorMessage,
    std::vector<GameObject*>* outMeshObjects) {
    if (!modelAssetRef.IsValid()) {
        SetErrorMessage(outErrorMessage, "Model asset ref is required when instantiating mesh bindings.");
        return false;
    }

    auto* meshFilter = targetObject.GetComponent<MeshFilterComponent>();
    if (meshFilter == nullptr) {
        meshFilter = targetObject.AddComponent<MeshFilterComponent>();
    }

    auto* meshRenderer = targetObject.GetComponent<MeshRendererComponent>();
    if (meshRenderer == nullptr) {
        meshRenderer = targetObject.AddComponent<MeshRendererComponent>();
    }

    meshFilter->SetMeshAssetRef(MakeSubAssetRef(modelAssetRef, meshBinding.meshLocalID, ResourceType::Mesh));

    const auto& materialBindings = model.GetMaterialBindings();
    const Core::uint32 materialBindingEnd = meshBinding.materialBindingStart + meshBinding.materialBindingCount;
    if (materialBindingEnd > materialBindings.Size()) {
        SetErrorMessage(outErrorMessage, "Model mesh binding references material bindings outside the model range.");
        return false;
    }

    for (Core::uint32 materialBindingIndex = meshBinding.materialBindingStart;
         materialBindingIndex < materialBindingEnd;
         ++materialBindingIndex) {
        const ModelMaterialBinding& materialBinding = materialBindings[materialBindingIndex];
        meshRenderer->SetMaterialAssetRef(
            static_cast<size_t>(materialBinding.slotIndex),
            MakeSubAssetRef(modelAssetRef, materialBinding.materialLocalID, ResourceType::Material));
    }

    if (outMeshObjects != nullptr) {
        outMeshObjects->push_back(&targetObject);
    }
    return true;
}

} // namespace

bool InstantiateModelHierarchy(
    Components::Scene& scene,
    const Resources::Model& model,
    const Resources::AssetRef& modelAssetRef,
    Components::GameObject* parent,
    ModelSceneInstantiationResult* outResult,
    Containers::String* outErrorMessage) {
    if (!model.IsValid()) {
        SetErrorMessage(outErrorMessage, "Model is invalid.");
        return false;
    }

    if (!model.HasRootNode()) {
        SetErrorMessage(outErrorMessage, "Model does not have a root node.");
        return false;
    }

    const auto& nodes = model.GetNodes();
    const auto& meshBindings = model.GetMeshBindings();
    if (model.GetRootNodeIndex() >= nodes.Size()) {
        SetErrorMessage(outErrorMessage, "Model root node index is outside the node range.");
        return false;
    }

    ModelSceneInstantiationResult localResult;
    localResult.nodeObjects.resize(nodes.Size(), nullptr);
    for (Core::uint32 nodeIndex = 0; nodeIndex < nodes.Size(); ++nodeIndex) {
        const ModelNode& node = nodes[nodeIndex];
        localResult.nodeObjects[nodeIndex] = scene.CreateGameObject(MakeNodeName(node, nodeIndex).CStr(), nullptr);
        if (localResult.nodeObjects[nodeIndex] == nullptr) {
            SetErrorMessage(outErrorMessage, "Failed to create a model node game object.");
            return false;
        }

        auto* transform = localResult.nodeObjects[nodeIndex]->GetTransform();
        transform->SetLocalPosition(node.localPosition);
        transform->SetLocalRotation(node.localRotation);
        transform->SetLocalScale(node.localScale);
    }

    for (Core::uint32 nodeIndex = 0; nodeIndex < nodes.Size(); ++nodeIndex) {
        const ModelNode& node = nodes[nodeIndex];
        GameObject* nodeObject = localResult.nodeObjects[nodeIndex];
        if (nodeObject == nullptr) {
            continue;
        }

        if (node.parentIndex >= 0) {
            const Core::uint32 parentIndex = static_cast<Core::uint32>(node.parentIndex);
            if (parentIndex >= localResult.nodeObjects.size() || localResult.nodeObjects[parentIndex] == nullptr) {
                SetErrorMessage(outErrorMessage, "Model node references an invalid parent index.");
                return false;
            }

            nodeObject->SetParent(localResult.nodeObjects[parentIndex], false);
        } else if (parent != nullptr) {
            nodeObject->SetParent(parent, false);
        }
    }

    for (Core::uint32 nodeIndex = 0; nodeIndex < nodes.Size(); ++nodeIndex) {
        const ModelNode& node = nodes[nodeIndex];
        GameObject* nodeObject = localResult.nodeObjects[nodeIndex];
        if (nodeObject == nullptr || node.meshBindingCount == 0u) {
            continue;
        }

        const Core::uint32 meshBindingEnd = node.meshBindingStart + node.meshBindingCount;
        if (meshBindingEnd > meshBindings.Size()) {
            SetErrorMessage(outErrorMessage, "Model node references mesh bindings outside the model range.");
            return false;
        }

        if (node.meshBindingCount == 1u) {
            if (!AttachMeshBinding(
                    *nodeObject,
                    model,
                    modelAssetRef,
                    meshBindings[node.meshBindingStart],
                    outErrorMessage,
                    &localResult.meshObjects)) {
                return false;
            }
            continue;
        }

        const Containers::String nodeName = MakeNodeName(node, nodeIndex);
        for (Core::uint32 meshBindingIndex = node.meshBindingStart; meshBindingIndex < meshBindingEnd; ++meshBindingIndex) {
            GameObject* meshObject = scene.CreateGameObject(
                MakeMeshObjectName(nodeName, meshBindingIndex - node.meshBindingStart).CStr(),
                nodeObject);
            if (meshObject == nullptr) {
                SetErrorMessage(outErrorMessage, "Failed to create an auxiliary mesh binding game object.");
                return false;
            }

            if (!AttachMeshBinding(
                    *meshObject,
                    model,
                    modelAssetRef,
                    meshBindings[meshBindingIndex],
                    outErrorMessage,
                    &localResult.meshObjects)) {
                return false;
            }
        }
    }

    localResult.rootObject = localResult.nodeObjects[model.GetRootNodeIndex()];
    if (outResult != nullptr) {
        *outResult = std::move(localResult);
    }
    return true;
}

bool InstantiateModelHierarchy(
    Components::Scene& scene,
    const Containers::String& modelPath,
    Components::GameObject* parent,
    ModelSceneInstantiationResult* outResult,
    Containers::String* outErrorMessage) {
    ResourceManager& resourceManager = ResourceManager::Get();
    const ResourceHandle<Resources::Model> modelHandle = resourceManager.Load<Resources::Model>(modelPath);
    if (!modelHandle.IsValid()) {
        SetErrorMessage(outErrorMessage, Containers::String("Failed to load model asset: ") + modelPath);
        return false;
    }

    AssetRef modelAssetRef;
    if (!resourceManager.TryGetAssetRef(modelPath, ResourceType::Model, modelAssetRef)) {
        SetErrorMessage(outErrorMessage, Containers::String("Failed to resolve model asset ref: ") + modelPath);
        return false;
    }

    return InstantiateModelHierarchy(scene, *modelHandle, modelAssetRef, parent, outResult, outErrorMessage);
}

} // namespace XCEngine