applyMatrix4( matrix ) {

		// transform of empty box is an empty box.
		if ( this.isEmpty() ) return this;

		// NOTE: I am using a binary pattern to specify all 2^3 combinations below
		_points[ 0 ].set( this.min.x, this.min.y, this.min.z ).applyMatrix4( matrix ); // 000
		_points[ 1 ].set( this.min.x, this.min.y, this.max.z ).applyMatrix4( matrix ); // 001
		_points[ 2 ].set( this.min.x, this.max.y, this.min.z ).applyMatrix4( matrix ); // 010
		_points[ 3 ].set( this.min.x, this.max.y, this.max.z ).applyMatrix4( matrix ); // 011
		_points[ 4 ].set( this.max.x, this.min.y, this.min.z ).applyMatrix4( matrix ); // 100
		_points[ 5 ].set( this.max.x, this.min.y, this.max.z ).applyMatrix4( matrix ); // 101
		_points[ 6 ].set( this.max.x, this.max.y, this.min.z ).applyMatrix4( matrix ); // 110
		_points[ 7 ].set( this.max.x, this.max.y, this.max.z ).applyMatrix4( matrix ); // 111

		this.setFromPoints( _points );

		return this;

	}
Transforms this bounding box by the given 4x4 transformation matrix.

@param {Matrix4} matrix - The transformation matrix.
@return {Box3} A reference to this bounding box.