<!-- SOLIDIVISM · part 297 -->
 {number} focalLength - Values for focal length and film gauge must have the same unit.
	 */
	setFocalLength( focalLength ) {

		/** see {@link http://www.bobatkins.com/photography/technical/field_of_view.html} */
		const vExtentSlope = 0.5 * this.getFilmHeight() / focalLength;

		this.fov = RAD2DEG * 2 * Math.atan( vExtentSlope );
		this.updateProjectionMatrix();

	}

	/**
	 * Returns the focal length from the current {@link PerspectiveCamera#fov} and
	 * {@link PerspectiveCamera#filmGauge}.
	 *
	 * @return {number} The computed focal length.
	 */
	getFocalLength() {

		const vExtentSlope = Math.tan( DEG2RAD * 0.5 * this.fov );

		return 0.5 * this.getFilmHeight() / vExtentSlope;

	}

	/**
	 * Returns the current vertical field of view angle in degrees considering {@link PerspectiveCamera#zoom}.
	 *
	 * @return {number} The effective FOV.
	 */
	getEffectiveFOV() {

		return RAD2DEG * 2 * Math.atan(
			Math.tan( DEG2RAD * 0.5 * this.fov ) / this.zoom );

	}

	/**
	 * Returns the width of the image on the film. If {@link PerspectiveCamera#aspect} is greater than or
	 * equal to one (landscape format), the result equals {@link PerspectiveCamera#filmGauge}.
	 *
	 * @return {number} The film width.
	 */
	getFilmWidth() {

		// film not completely covered in portrait format (aspect < 1)
		return this.filmGauge * Math.min( this.aspect, 1 );

	}

	/**
	 * Returns the height of the image on the film. If {@link PerspectiveCamera#aspect} is greater than or
	 * equal to one (landscape format), the result equals {@link PerspectiveCamera#filmGauge}.
	 *
	 * @return {number} The film width.
	 */
	getFilmHeight() {

		// film not completely covered in landscape format (aspect > 1)
		return this.filmGauge / Math.max( this.aspect, 1 );

	}

	/**
	 * Computes the 2D bounds of the camera's viewable rectangle at a given distance along the viewing direction.
	 * Sets `minTarget` and `maxTarget` to the coordinates of the lower-left and upper-right corners of the view rectangle.
	 *
	 * @param {number} distance - The viewing distance.
	 * @param {Vector2} minTarget - The lower-left corner of the view rectangle is written into this vector.
	 * @param {Vector2} maxTarget - The upper-right corner of the view rectangle is written into this vector.
	 */
	getViewBounds( distance, minTarget, maxTarget ) {

		_v3$1.set( -1, -1, 0.5 ).applyMatrix4( this.projectionMatrixInverse );

		minTarget.set( _v3$1.x, _v3$1.y ).multiplyScalar( - distance / _v3$1.z );

		_v3$1.set( 1, 1, 0.5 ).applyMatrix4( this.projectionMatrixInverse );

		maxTarget.set( _v3$1.x, _v3$1.y ).multiplyScalar( - distance / _v3$1.z );

	}

	/**
	 * Computes the width and height of the camera's viewable rectangle at a given distance along the viewing direction.
	 *
	 * @param {number} distance - The viewing distance.
	 * @param {Vector2} target - The target vector that is used to store result where x is width and y is height.
	 * @returns {Vector2} The view size.
	 */
	getViewSize( distance, target ) {

		this.getViewBounds( distance, _minTarget, _maxTarget );

		return target.subVectors( _maxTarget, _minTarget );

	}

	/**
	 * Sets an offset in a larger frustum. This is useful for multi-window or
	 * multi-monitor/multi-machine setups.
	 *
	 * For example, if you have 3x2 monitors and each monitor is 1920x1080 and
	 * the monitors are in grid like this
	 *```
	 *   +---+---+---+
	 *   | A | B | C |
	 *   +---+---+---+
	 *   | D | E | F |
	 *   +---+---+---+
	 *```
	 * then for each monitor you would call it like this:
	 *```js
	 * const w = 1920;
	 * const h = 1080;
	 * const fullWidth = w * 3;
	 * const fullHeight = h * 2;
	 *
	 * // --A--
	 * camera.setViewOffset( fullWidth, fullHeight, w * 0, h * 0, w, h );
	 * // --B--
	 * camera.setViewOffset( fullWidth, fullHeight, w * 1, h * 0, w, h );
	 * // --C--
	 * camera.setViewOffset( fullWidth, fullHeight, w * 2, h * 0, w, h );
	 * // --D--
	 * camera.setViewOffset( fullWidth, fullHeight, w * 0, h * 1, w, h );
	 * // --E--
	 * camera.setViewOffset( fullWidth, fullHeight, w * 1, h * 1, w, h );
	 * // --F--
	 * camera.setViewOffset( fullWidth, fullHeight, w * 2, h * 1, w, h );
	 * ```
	 *
	 * Note there is no reason monitors have to be the same size or in a grid.
	 *
	 * @param {number} fullWidth - The full width of multiview setup.
	 * @param {number} fullHeight - The full height of multiview setup.
	 * @param {number} x - The horizontal offset of the subcamera.
	 * @param {number} y - The vertical offset of the subcamera.
	 * @param {number} width - The width of subcamera.
	 * @param {number} height - The height of subcamera.
	 */
	setViewOffset( fullWidth, fullHeight, x, y, width, height ) {

		this.aspect = fullWidth / fullHeight;

		if ( this.view === null ) {

			this.view = {
				enabled: true,
				fullWidth: 1,
				fullHeight: 1,
				offsetX: 0,
				offsetY: 0,
				width: 1,
				height: 1
			};

		}

		this.view.enabled = true;
		this.view.fullWidth = fullWidth;
		this.view.fullHeight =