Stereo decoding

Left channel = delta(r, left) - delta(depth)
(left sidewall 45degree upwards)

Right channel = delta(r, right) + delta(depth)
(right sidewall 45degree downwards)

Imp

• vr_in, vr_out, vz_in, vz_out
  
• stylus shape: v_width -> v_depth
• ? fit(vr_in), fit(vr_out), fit(v_depth)
• ? diff(vr_in), diff(vr_out), diff(v_depth)
• vr_diff_in - vd_diff, vr_diff_out + vd_diff