Implement GLTF Model Loader Example with Scene Hierarchy Mapping

[Copilot]

This PR implements a comprehensive GLTF model loader example that demonstrates how to load GLTF models and map their scene hierarchy to the ULRE engine's SceneNode system, as requested in the issue.

Overview

The implementation provides a complete foundation for GLTF loading while focusing on mesh geometry rendering and maintaining extensibility for future features like materials, textures, and animations.

Key Features

Scene Hierarchy Mapping

• GLTF Node → SceneNode: Each GLTF node corresponds to an engine SceneNode, preserving the complete hierarchy
• GLTF Mesh → Special SceneNode: Each GLTF mesh is wrapped as a container SceneNode
• GLTF Primitive → Independent Mesh: Each GLTF primitive creates an independent Primitive/Mesh with MeshComponent

Architecture Design

GLTF File Structure    →    ULRE Engine Objects
├── GLTFScene         →    Scene
├── GLTFNode          →    SceneNode (hierarchy preserved)
├── GLTFMesh          →    Special SceneNode (container)
│   └── GLTFPrimitive →    Primitive + Mesh + MeshComponent
└── GLTFMaterial      →    Material + MaterialInstance (extensible)

Current Implementation

• ✅ Basic GLTF data structure definitions following GLTF 2.0 specification
• ✅ Scene hierarchy mapping with complete node relationship preservation
• ✅ Vertex position data extraction and Primitive creation
• ✅ Bounding box calculation from GLTF accessor data
• ✅ Integration with existing Material/Pipeline/MeshComponent systems
• ✅ Comprehensive logging and debugging support

Future Extension Points

The implementation includes complete data structures for future development:

• Material System: PBR metallic/roughness support with GLTFMaterial structure
• Texture System: Image loading and sampler configuration with GLTFTexture, GLTFImage, GLTFSampler
• Animation System: Keyframe animation with GLTFAnimation, GLTFAnimationChannel
• Skeletal Animation: Bone weights and joints with GLTFSkin structure
• Vertex Attributes: Ready for normal, UV, color, and bone data

Files Added

1. example/Basic/GLTFLoaderTest.cpp - Main implementation following existing code patterns
2. example/Basic/triangle.gltf - Simple test GLTF file with single triangle
3. example/Basic/complex_scene.gltf - Multi-node hierarchy test case
4. example/Basic/GLTF_README.md - Comprehensive usage documentation
5. example/Basic/IMPLEMENTATION_SUMMARY.md - Architecture analysis and extension guide

Usage Example

class MyApp : public WorkObject {
    bool Init() override {
        GLTFLoader* loader = new GLTFLoader(this);
        loader->InitializeRenderResources();
        loader->LoadFromFile("model.gltf");
        loader->BuildSceneHierarchy(GetScene(), GetSceneRoot());
        return true;
    }
};

Code Quality

• Follows existing codebase patterns (WorkObject, Material, Pipeline, MeshComponent)
• Comprehensive error handling and logging with scene hierarchy visualization
• Clear separation of concerns with extensible architecture
• Well-documented with inline comments and usage examples
• Consistent with GLTF 2.0 specification

The implementation provides immediate mesh rendering capability while establishing a solid foundation for future GLTF feature development in the ULRE engine.

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