Working with Quads in Three.js for GLTF Export

Based on the available information about BufferAttributes in Three.js, I can provide some guidance on your question about exporting quad data using GLTFExporter.

Understanding BufferAttributes Limitations

Three.js BufferAttributes are designed with specific expectations about data structure. The position attribute in BufferGeometry typically has an itemSize of 3 (for x, y, z coordinates). Changing this to 4 would not be interpreted as quad data, but rather as a position with an additional component (like x, y, z, w).

Potential Approach

Instead of modifying the position attribute's itemSize, you would likely need to:

1. Keep the standard position attribute with itemSize of 3
2. Store your quad data in a custom attribute or in the index buffer
3. Modify the GLTFExporter to interpret and export this data appropriately

Challenges

The main challenges with this approach include:

• The GLTF format itself is primarily designed for triangle-based meshes
• Three.js rendering pipeline expects triangles
• Custom modifications to GLTFExporter would need to handle the conversion from your quad representation to a format compatible with GLTF

Suggested Implementation

You might consider:

JAVASCRIPTCopied
// Create geometry with standard position attributes
const geometry = new THREE.BufferGeometry();
const positions = new Float32Array([...]);  // x,y,z coordinates
geometry.setAttribute('position', new THREE.BufferAttribute(positions, 3));

// Store quad indices in a custom attribute or in a specific format in the index buffer
const quadIndices = new Uint16Array([...]);  // indices for quads
geometry.setIndex(new THREE.BufferAttribute(quadIndices, 1));

// Add custom user data to indicate this should be treated as quads
geometry.userData.isQuadMesh = true;

Then modify the GLTFExporter to check for this custom flag and handle the export accordingly.

Note that this is a complex modification that would require deep understanding of both Three.js internals and the GLTF format specification. You may need to study the source code of GLTFExporter in detail to implement such changes.