BufferGeometry Attribute Replacement Behavior

Based on the information available, it appears you've encountered an issue with dynamic BufferGeometry updates in Three.js. When you increase the vertex count and replace attributes, the mesh disappears from direct rendering but remains visible in shadow maps.

This behavior suggests that when you replace a BufferAttribute with a new one that has a larger size, there might be some internal state that isn't fully updated. The fact that deleting all attributes first resolves the issue supports this theory.

While the documentation doesn't explicitly address this specific scenario, your workaround of deleting attributes before setting new ones is a valid approach. When dealing with dynamic geometries where the vertex count changes, it's safer to completely remove the existing attributes before adding new ones with different sizes.

Your implementation should look like this:

JAVASCRIPTCopied
// When vertex count changes
this.clearGroups();

// Delete all existing attributes first
for (const key of Object.keys(this.attributes)) {
    this.deleteAttribute(key);
}

// Add new group and attributes
this.addGroup(groupStart, groupCount, 0);
const indexAttribute = new BufferAttribute(new Uint32Array(indices), 1);
this.setIndex(indexAttribute);
const positionAttribute = new BufferAttribute(new Float32Array(verticesCount * 3), 3);
this.setAttribute('position', positionAttribute);

This approach ensures a clean slate before setting up the new geometry configuration, preventing any potential conflicts between the old and new attribute data.