nx_bvhfk_lib.nx

nx_bvhfk_lib.nx -- SHARED BVH FORWARD-KINEMATICS CORE (fk_eval + integer matrix substrate). Extracted 2026-08-13 when the SECOND consumer appeared (nx_clipcheck's bvh self-clearance control lane needs world positions per frame) rather than copy-pasting the FK into it -- Rule 15, and the standing law: EXTRACT THE FIX, DON'T RE-TYPE IT. The functions below are MOVED VERBATIM from nx_bvhfk.nx; that organ's KAT (bone-length isometry proven on real third-party mocap) remains the proof that this extraction is value-identical. SEMANTICS (BVH is specific and easy to get subtly wrong): world_rot[j] = world_rot[parent] * R_local[j] world_pos[j] = world_pos[parent] + world_rot[parent] * offset[j] R_local is the product of that joint's rotation channels IN THE ORDER THE FILE LISTS THEM (commonly ZXY, but the file decides -- never the convention). The root additionally consumes its position channels as a translation. UNITS: positions in file units x B_SCALE (1000) -- BVH does not state its unit; the convention is centimetres, so we do not claim mm. Angles arrive as millidegrees and are converted to the it_* integer-trig circle (25736 units) -- never to floats. license_tier: ORIGINAL No hw writes (Rule 26).