update() {

		this.object.updateMatrixWorld( true );

		_normalMatrix.getNormalMatrix( this.object.matrixWorld );

		const matrixWorld = this.object.matrixWorld;

		const position = this.geometry.attributes.position;

		//

		const objGeometry = this.object.geometry;

		if ( objGeometry ) {

			const objPos = objGeometry.attributes.position;

			const objNorm = objGeometry.attributes.normal;

			let idx = 0;

			// for simplicity, ignore index and drawcalls, and render every normal

			for ( let j = 0, jl = objPos.count; j < jl; j ++ ) {

				_v1.fromBufferAttribute( objPos, j ).applyMatrix4( matrixWorld );

				_v2.fromBufferAttribute( objNorm, j );

				_v2.applyMatrix3( _normalMatrix ).normalize().multiplyScalar( this.size ).add( _v1 );

				position.setXYZ( idx, _v1.x, _v1.y, _v1.z );

				idx = idx + 1;

				position.setXYZ( idx, _v2.x, _v2.y, _v2.z );

				idx = idx + 1;

			}

		}

		position.needsUpdate = true;

	}
Updates the vertex normals preview based on the object's world transform.