viewport( x, y, width, height ) {

		const viewport = this._tempVec4.set( x, y, width, height );

		if ( this.currentViewport.equals( viewport ) === false ) {

			const { gl } = this;

			gl.viewport( viewport.x, viewport.y, viewport.z, viewport.w );
			this.currentViewport.copy( viewport );

		}

	}
Specifies the viewport.

@param {number} x - The x-coordinate of the lower left corner of the viewport.
@param {number} y - The y-coordinate of the lower left corner of the viewport.
@param {number} width - The width of the viewport.
@param {number} height - The height of the viewport.