fix: skip unsupported mesh attributes instead of throwing

[nixoletas]

Summary

• Skip unsupported mesh attributes (e.g. TEXCOORD_4+, custom attributes) gracefully instead of throwing GLTFUnarchiveError.NotSupported
• Fixes the "unable to load renderable" error when loading standard glTF 2.0 GLB files that include attributes beyond what SceneKit supports

Problem

GLB files exported from tools like Sketchfab may include more than 4 texture coordinate sets (TEXCOORD_0 through TEXCOORD_4). The attributeMap in GLTFTypes.swift only maps up to TEXCOORD_3, so when loadAttributes() encounters TEXCOORD_4, it throws:

GLTFUnarchiveError.NotSupported("loadMesh: user defined semantic is not supported: TEXCOORD_4")

Since SceneKit only uses 2 UV sets anyway, these extra attributes can be safely ignored.

Fix

Changed loadAttributes() in GLTFUnarchiver.swift to continue (with a debug print) instead of throw when encountering unmapped attributes. This matches how other glTF loaders handle unsupported attributes — they skip gracefully rather than failing the entire mesh.

Also fixed the same pattern in the commented-out legacy code block for consistency.

Test plan

• Tested with GLB files from Sketchfab containing TEXCOORD_4 attribute
• Models load correctly on iOS with SceneKit after this fix
• No visual difference since SceneKit ignores the extra UV sets anyway

🤖 Generated with Claude Code