geom:read-obj

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

The mesh in a Wavefront OBJ file, as a geom:solid. v lines are the vertices (a fourth w component is ignored) and f lines the facets, whose tokens may be v, v/vt, v/vt/vn or v//vn; an index is 1-based when positive and counts back from the vertices seen so far when negative. A facet may have any number of vertices -- OBJ quads stay quads, and geom:mesh fan-triangulates them like every other facet.

Every other record is read past: vn, vt, g, o, s, usemtl, mtllib and comments. A file naming several objects reads as ONE solid, which is what a solid is: a single boundary representation with one colour. Materials, texture coordinates and per-vertex normals are not kept -- geom has no slot for any of them.

CL-USER> (geom:read-obj "bunny.obj" :label "bunny")
#<GEOM:SOLID "bunny" 35947 vertices 69451 facets>
CL-USER> (geom:volume *)
7.700565237493941e-4

An OBJ carries its own units -- that bunny is 0.2 across, in metres -- so (scene:fit v) is what frames it and (scene:grid v :extent nil) is usually what you want beside it. A face wound clockwise seen from outside makes geom:volume subtract instead of add, so a negative volume means the file's winding is inverted.

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. Numbers are scanned character by character rather than through the reader, so exponent notation (1.30e-2) reads as a float everywhere -- read-from-string answers a symbol for that on the WASM backends.