nx_bvhfk.nx

nx_bvhfk.nx -- BVH FORWARD KINEMATICS: joint tree + channel rotations -> WORLD-SPACE positions. WHY THIS IS THE RUNG THAT MATTERS: parsing a BVH gets you a hierarchy; PLAYING it is what DanceXR does. Our exceed is not playback -- it is that nx_pose_retarget already inverts our sovereign FK (joint POSITIONS -> our rig's FK angles), and nx_pose_coach / nx_pose_naturalness already SCORE a pose track. The one missing link was world-space positions out of a BVH. This organ is that link, so third-party mocap can drive OUR rig -- including VRM, which appears nowhere in DanceXR's format set. THE FK CORE (fk_eval + the integer matrix substrate) LIVES IN nx_bvhfk_lib.nx since 2026-08-13 -- extracted on the second consumer (nx_clipcheck's bvh self-clearance control). The KAT below is the extraction's value-identity proof: bone-length isometry on real third-party data. *THE HARDEST TOOTH IS BONE-LENGTH INVARIANCE. A rotation is an isometry: |child - parent| MUST equal |offset|, at every frame, for every joint. A rest-pose test passes even if the rotation path is a no-op; a length test fails the moment a matrix is mis-scaled, mis-composed, or drifts in fixed point. It is the implied hidden quantity that physics demands, and it is checked here against REAL third-party data, not only a fixture. 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. usage: nx_bvhfk pos <file.bvh> <frame> world x y z per joint nx_bvhfk lens <file.bvh> <frame> measured bone length vs declared |offset| per joint nx_bvhfk --kat selftest: 6 teeth, 3 of them anti-vacuity license_tier: ORIGINAL No hw writes (Rule 26). expect_exit: 0