computeNormal method
void
computeNormal()
Implementation
void computeNormal() {
final vA = this.v1!.position;
final vB = this.v2!.position;
final vC = this.v3!.position;
_cb.subVectors( vC, vB );
_ab.subVectors( vA, vB );
_cb.cross( _ab ).normalize();
this.normal.copy( _cb );
}