geom:read-gltf

(geom:read-gltf path &key color label)

The scene in a glTF 2.0 file, as a list of geom:solids -- one per mesh primitive, each coloured by its material's baseColorFactor (:color overrides them all). Both carriers are read: a .glb (JSON chunk + BIN chunk) and a .gltf whose buffers are .bin files beside it or base64 data: URIs. A remote (http:) buffer URI is refused -- this is a file reader, not a fetcher.

A glTF is a scene, not a mesh, and the node hierarchy survives the read: each glTF node becomes a geom:node posed by its translation/rotation/matrix, every solid is attached under its node, and the answer is the flat list -- so scene:add splices it, geom:bounds measures it as one, and each solid's geom:world-transform carries its parents. A multi-part model's parts land where its nodes say.

A node's scale is baked into its primitives' vertices, accumulated down the tree with each child's translation scaled by the product above it -- geom:transform is rigid by decision, so a 2x-scaled node's cube measures 8x the volume rather than carrying a scale the measurements cannot see. That composition is exact for uniform scales; a non-uniform scale above a rotated child would shear, which no rigid transform can represent, and is refused by name.

CL-USER> (geom:read-gltf "Duck.glb")
(#<GEOM:SOLID "LOD3spShape" 2399 vertices 4212 facets>)
CL-USER> (geom:volume (first *))
1.1957991851442398

The JSON goes through rontolisp:json-parse; the buffers through read-sequence over packed arrays, which is exactly what a bufferView is -- POSITION is one native transfer, indices another. Only a base64 data: URI is decoded by Lisp arithmetic, float32 assembly included, so an embedded multi-megabyte buffer is the slow path.

What is refused by name

A silent partial read of a glTF is worse than a refusal, so each of these names itself: a primitive mode other than triangles, sparse accessors, any extensionsRequired entry (Draco and meshopt compression arrive this way), skins, animations, and glTF 1.x. Textures, per-vertex normals and texture coordinates are read past -- a solid has one colour and computes its own normals.

Backend support

Every backend that has a filesystem: the interpreter, a compiled .class/.jar, WASM Preview 1 and the WASI 0.3 component, with the same answer on all four.