get normal() {
    if (this._n === undefined) {
      let u = vec3.sub([], this.v2.xyz, this.v1.xyz);
      let v = vec3.sub([], this.v3.xyz, this.v1.xyz);
      this._n = vec3.cross([], u, v);
    }
    return this._n;
  }
/**
   * The unit surface normal vector for this Tri.
   * @return {vec3}
   */
The unit surface normal vector for this Tri.
@return {vec3}
The unit surface normal vector for this Tri . @return { vec3 }
get normal() {
    if (this._n === undefined) {
      let u = vec3.sub([], this.v2.xyz, this.v1.xyz);
      let v = vec3.sub([], this.v3.xyz, this.v1.xyz);
      this._n = vec3.cross([], u, v);
    }
    return this._n;
  }
get normal ( ) { if ( this . _n === undefined ) { let u = vec3 . sub ( [ ] , this . v2 . xyz , this . v1 . xyz ) ; let v = vec3 . sub ( [ ] , this . v3 . xyz , this . v1 . xyz ) ; this . _n = vec3 . cross ( [ ] , u , v ) ; } return this . _n ; }
The unit surface normal vector for this Tri.
The unit surface normal vector for this Tri .