computeBoundingSphere method 
    
      
  
void
computeBoundingSphere(
)
      override
     
    
    
  Implementation
  @override
	void computeBoundingSphere() {
		if ( this.boundingSphere == null ) {
			this.boundingSphere = BoundingSphere();
		}
		final geometryCount = _geometryCount;
		final boundingSphere = this.boundingSphere;
		final active = _active;
		boundingSphere?.empty();
		for (int i = 0; i < geometryCount; i ++ ) {
			if ( active[ i ] == false ) continue;
			getMatrixAt( i, _matrix );
			getBoundingSphereAt( i, _sphere ).applyMatrix4( _matrix );
			boundingSphere?.union( _sphere );
		}
	}