Moiré torus
Geometry
Two families of nested ovals stand in for the torus. Family A holds N rings of radius r_i = r0 + i·Δ, each drawn as a circle squashed by the eccentricity e and left unrotated.
A_i : (x,y) = r_i (cos t, (1−e) sin t)B_i : (x,y) = o + r_i R(δ) (cos t, (1−e) sin t)
Family B repeats the same construction rotated by δ and displaced by o = (offset cos45°, offset sin45°·0.6), so its rings sit a hair out of register with A. Where the two families cross, the small angle produces broad moiré beats that sweep along the bands; a smaller δ widens the beats, a larger one tightens them.
B is drawn under a wedge clip — the sector from sector angle spanning sector span — so interference is confined to one arc of the ring and a quiet region of plain A rings remains for contrast. Drag to slide B bodily across A.