Function evalQ

js/decimation.js:555–561

(q, v, x, y, z)

      // This plane contains the edge and is perpendicular to the face,
      // so it constrains the vertex to lie on the crease line.
      let px = ny*edz - nz*edy;
      let py = nz*edx - nx*edz;
      let pz = nx*edy - ny*edx;
      const plen = Math.sqrt(px*px + py*py + pz*pz);
      if (plen < 1e-10) continue; // edge parallel to face normal — degenerate
      px /= plen; py /= plen; pz /= plen;
      const d = -(px*positions[va*3] + py*positions[va*3+1] + pz*positions[va*3+2]);
      // Scale by sqrtW: addPlaneQ accumulates (a²,ab,…) so scaling inputs by √w yields w×(a²,ab,…)
      addPlaneQ(quadrics, va, px*sqrtW, py*sqrtW, pz*sqrtW, d*sqrtW);
      addPlaneQ(quadrics, vb, px*sqrtW, py*sqrtW, pz*sqrtW, d*sqrtW);