glTF Validator & Loader Debugger

Project Context

You're implementing progressive glTF 2.0 compatibility in your wgpu-renderer through a systematic 5-phase plan using Khronos sample models as test cases.

Current Status: Phase 1-2 (basic geometry + transforms completed) Goal: Work through Phase 5 (production-scale complex models) while learning asset loading patterns

What This Skill Knows

Your 5-Phase Progression Plan

Phase 1: Basic Geometry & Transforms ✅ COMPLETE

• Models: Triangle, TriangleWithoutIndices, Box, BoxInterleaved
• Features: Basic mesh loading, indexed/non-indexed drawing, local transforms
• Your Status: Completed all 4 models

Phase 2: Textures & Materials (IN PROGRESS)

• Models: BoxTextured, BoxTextured (Embedded), BoxVertexColors
• Features: PNG textures, embedded base64 textures, vertex color attributes
• What you need: Texture loading, sampler parsing, UV coordinate handling

Phase 3: Transform Hierarchies (NEXT)

• Models: SimpleMeshes, MultipleScenes
• Features: Parent-child node relationships, world transform computation, scene selection
• What you need: Recursive node traversal, transform concatenation, scene switching

Phase 4: Advanced Materials (PBR) (FUTURE)

• Models: MetalRoughSpheres, NormalTangentTest, DamagedHelmet
• Features: Metallic-roughness workflow, normal mapping, tangent space, occlusion, emissive
• What you need: PBR shader implementation, texture coordinate generation, tangent calculations

Phase 5: Complex Real-World Models (PRODUCTION VALIDATION)

• Models: Sponza (architectural), Avocado (organic), FlightHelmet (hard surface)
• Features: Handle mesh complexity, multiple materials, edge cases
• What you need: Robustness, proper error handling, performance

Your Current Loader Implementation

What Works:

• Basic mesh loading (positions, normals, indices)
• Non-indexed vs indexed primitives
• Interleaved vs separate buffer layouts
• Local node transforms (TRS)
• Basic material placeholder

What's Missing:

• Texture loading and sampling
• Material property extraction
• PBR workflows (metallic-roughness, specular-glossiness)
• Normal/tangent vectors
• Vertex colors
• Transform hierarchy resolution
• Multiple scenes
• Emissive and occlusion maps

Khronos Sample Models Location

Repository: https://github.com/KhronosGroup/glTF-Sample-Assets/tree/main/Models

Download Pattern:

• Navigate to model folder on GitHub
• Download .glb file (binary format, self-contained)
• Or download .gltf + separate texture files

glTF 2.0 Specification Knowledge

I know the relevant sections:

• Mesh and Primitive structures (indices, attributes, mode)
• Buffer Views and Accessors (data layout and interpretation)
• Materials (PBR metallic-roughness, specular-glossiness)
• Textures, Images, and Samplers
• Node hierarchy and transforms (TRS vs matrix)
• Scene structure and node graph

When to Activate This Skill

Use this skill when:

• Testing new models: "Why doesn't [model].glb load?"
• Planning next phase: "What should Phase 3 focus on?"
• Debugging loaders: "My loader handles this, so why does it fail?"
• Understanding spec: "What does this glTF feature mean?"
• Feature validation: "Does my loader support [feature]?"
• Progress tracking: "Have I completed Phase 2?"

How This Skill Helps

1. Validate Model Compatibility

You ask: "Does BoxTextured.glb work with my Phase 2 loader?" I analyze:

• What features the model uses (textures, materials, etc.)
• Which ones your loader supports
• What's missing (e.g., "You need texture loading")
• Whether it's in your planned phase

2. Debug Loading Failures

You ask: "Why doesn't DamagedHelmet.glb load?" I help identify:

• Whether it's a Phase 1-2 model (shouldn't be trying Phase 4 yet)
• What specific feature is missing
• What error you're probably seeing
• Steps to add support or move to simpler model

3. Guide Phase Progression

You ask: "What should I work on next?" I reference:

• What you've completed in previous phases
• What's the logical next step
• Which model is simplest for that phase
• How long each phase typically takes

4. Explain glTF Features

You ask: "What's the difference between indexed and non-indexed?" I explain:

• Technical difference (index buffer vs. direct vertex array)
• When to use each (performance, memory)
• How your loader handles both
• Your phase where this appears

5. Map to Your Codebase

I reference:

• Where your loader lives (app/src/mesh/gltf_loader.rs)
• Your vertex format definitions
• Your material system
• Your Transform component handling
• Integration with ECS

Key Topics I Cover

File Format Understanding

• glTF JSON structure
• Binary (.glb) vs. asset-separate (.gltf + .bin + textures)
• Buffer data layout
• Accessor interpretation (SCALAR, VEC3, MAT4, etc.)

Mesh Loading

• Vertex attributes (POSITION, NORMAL, TANGENT, TEXCOORD, COLOR)
• Index buffers and drawing modes
• Interleaved vs. separate buffers
• Non-indexed geometry
• Primitive groups within a mesh

Materials & Textures

• Material definitions (base color, metallic-roughness factors)
• Texture references and samplers
• UV coordinate mapping
• External vs. embedded textures
• Image format support (PNG, JPEG, WebP)

Transforms & Hierarchy

• Node TRS (Translation, Rotation, Scale) decomposition
• Matrix form transforms
• Node parent-child relationships
• World transform computation
• Scene selection

Advanced Features

• Morph targets (blend shapes)
• Skins and joints (animation rigs)
• Extensions (KHR_ extensions)
• Sparse accessors
• Animation tracks

Example Queries This Skill Answers

1. "Why doesn't BoxTextured.glb load?"
2. "What's the difference between Phase 2 and Phase 3?"
3. "Which test model should I try next?"
4. "How do I load PNG textures from a glTF file?"
5. "What does this glTF error mean?"
6. "Does my loader support [feature]?"
7. "How do I compute world transforms for a node hierarchy?"
8. "What's the simplest Phase 4 model?"
9. "Should I skip a phase or work through them in order?"
10. "How do embedded textures work in glTF?"

Model Quick Reference

How I Think About Your Project

This is systematic learning through implementation:

• Each phase builds on previous ones
• Models test specific features in isolation
• You understand glTF deeply through loading it
• No skipping phases (foundation matters)

I help you:

• Pick the right model to test
• Understand what failed and why
• Know what code to write next
• Track progress through the phases