Resource: GLTF Format

Compared with FBX, which is only applied to the animation system, Arche's loading of GLTF is more comprehensive.

note

Currently GLTF loaded animation assets can only be used with GPUSkinnedMeshRenderer, because GLTF animation transforms are resolved as per Entity transforms.

The loading of GLTF requires the use of the GLTFLoader loader, which uses the open source tinygltf. When loading data, you need to specify a root entity, and the entities created by the loader will be mounted under the entity according to the child-parent relationship:

class GLTFLoader {
public:
    std::vector<std::unique_ptr<Image>> images;
    std::vector<SampledTexture2DPtr> textures;
    std::vector<MaterialPtr> materials;
    std::vector<std::vector<std::pair<MeshPtr, MaterialPtr>>> renderers;
    std::vector<GPUSkinnedMeshRenderer::SkinPtr> skins;
    
    GLTFLoader(wgpu::Device& device);
    
    void loadFromFile(std::string filename, EntityPtr defaultSceneRoot, float scale = 1.0f);
};

Therefore, when using, you can load GLTF resources as follows:

auto modelEntity = rootEntity->createChild();
auto loader = loader::GLTFLoader(_device);
loader.loadFromFile("Models/sponza/sponza.gltf", modelEntity);

In tinygltf, tinygltf::Model represents all the resources used by the modified GLTF file, and a GLTF file can contain multiple scenes, Therefore, the specific scene to be loaded can be selected through tinygltf::Scene, and the scene is related to the node tree of Entity. Therefore, when loading, first read all resources from tinygltf::Model, these resources are reusable data, which can be used in other scenarios:

void GLTFLoader::loadScene(tinygltf::Model& gltfModel) {
    ...
    
    // Load images
    loadImages(gltfModel);
    
    // Load textures && samplers
    loadTextures(gltfModel);
    
    // Load materials
    loadMaterials(gltfModel);
    
    // Load meshes
    loadMeshes(gltfModel);
    
    ...
}

Then build a specific scene based on tinygltf::Scene:

void GLTFLoader::loadScene(tinygltf::Model& gltfModel) {
    ...
    
    // Load nodes && scenes
    const tinygltf::Scene &scene = gltfModel.scenes[gltfModel.defaultScene > -1 ? gltfModel.defaultScene : 0];
    for (size_t i = 0; i < scene.nodes.size(); i++) {
        const tinygltf::Node node = gltfModel.nodes[scene.nodes[i]];
        loadNode(nullptr, node, scene.nodes[i], gltfModel);
    }
    
    // Load animations
    if (gltfModel.animations.size() > 0) {
        loadAnimations(gltfModel);
    }
    loadSkins(gltfModel);
    for (auto node : _linearNodes) {
        // Assign skins
        if (node.second.second > -1) {
            node.second.first->getComponent<GPUSkinnedMeshRenderer>()->setSkin(skins[node.second.second]);
        }
        // Initial pose
        auto mesh = node.second.first->getComponent<GPUSkinnedMeshRenderer>();
        if (mesh) {
            mesh->update(0);
        }
    }
}