update( { renderer } ) {

		const renderTarget = renderer.getRenderTarget();

		if ( this.scope === ScreenNode.VIEWPORT ) {

			if ( renderTarget !== null ) {

				viewportVec.copy( renderTarget.viewport );

			} else {

				renderer.getViewport( viewportVec );

				viewportVec.multiplyScalar( renderer.getPixelRatio() );

			}

		} else {

			if ( renderTarget !== null ) {

				screenSizeVec.width = renderTarget.width;
				screenSizeVec.height = renderTarget.height;

			} else {

				renderer.getDrawingBufferSize( screenSizeVec );

			}

		}

	}
`ScreenNode` implements {@link Node#update} to retrieve viewport and size information
from the current renderer.

@param {NodeFrame} frame - A reference to the current node frame.