glb-chunks

A GLB's two chunks, read and written, and its accessors read back. The GLB container module new readers and writers use (skinned-glb, and Dramatis's VRM writer, hair reader and gates), so a check reads exports with the reader the shipped code uses. Pure: no DOM, no engine, synchronous. tosijs-3d/glb-chunks.

Reading, readGlb:

• under 12 bytes, a bad magic or a version other than 2 throws "not a GLB";
• a file shorter than its header's length, or a chunk running past it, throws "truncated GLB" (a short read, not a corrupt file);
• the first JSON chunk wins, and so does the first BIN chunk;
• the binary chunk is optional (bin: null); no JSON chunk throws.

Writing, writeGlb: the JSON padded with spaces and the binary chunk with zeros, to 4 bytes; a null or empty binary chunk is left out, as the spec allows a GLB with no buffer.

Accessors, accessorBytes / accessorValues / readVec3: tightly packed, strided views de-interleaved, sparse accessors applied (one with no bufferView starts from zeros, as glTF says), every read bounds-checked against its buffer view.