code: private static boolean inCone(int i, int j, int n, int[] verts, int[] indices) {
          int pi = (indices[i] & 0x0fffffff) * 4;
          int pj = (indices[j] & 0x0fffffff) * 4;
          int pi1 = (indices[next(i, n)] & 0x0fffffff) * 4;
          int pin1 = (indices[prev(i, n)] & 0x0fffffff) * 4;
          // If P[i] is a convex vertex [ i+1 left or on (i-1,i) ].
          if (leftOn(verts, pin1, pi, pi1)) {
              return left(verts, pi, pj, pin1) && left(verts, pj, pi, pi1);
          }
          // Assume (i-1,i,i+1) not collinear.
          // else P[i] is reflex.
          return !(leftOn(verts, pi, pj, pi1) && leftOn(verts, pj, pi, pin1));
      }
docs: polygon P in the neighborhood of the i endpoint.