geom:read-stl

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

The mesh in an STL file, as a geom:solid. Both dialects are read and which one a file is written in is decided from the file's own shape, never from its extension and never from its first word: a binary writer putting solid <name> in its 80-byte header is routine. An ASCII file opens with the token solid and carries facet or endsolid on its next line; anything else is binary.

STL is a triangle soup with no index table, so the solid carries three vertices per facet -- 8,954 triangles come back as 26,862 vertices. The per-facet normal the file stores is ignored: geom computes Newell's from the geometry, and half the writers in the world store zeros there.

CL-USER> (geom:read-stl "part.stl" :color (geom:vec3 0.45 0.7 0.92))
#<GEOM:SOLID 26862 vertices 8954 facets>
CL-USER> (geom:volume *)
16.084489098307944

A binary file's twelve float32s a triangle are moved by one read-sequence over a packed single-float array, so reading one costs no per-number arithmetic at all; an ASCII file is scanned character by character like geom:read-obj.

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. The dialect test reads the file's shape rather than its length: one code path, identical on all four, and it needs no size at all.