constructor( light ) {

			//- Internals
			const scope = this;
			const doRenderLabel = light.name !== undefined && light.name !== '';
			let userAutoClearSetting; //Holds the initial position and dimension of the HUD

			const frame = {
				x: 10,
				y: 10,
				width: 256,
				height: 256
			};
			const camera = new THREE.OrthographicCamera( window.innerWidth / - 2, window.innerWidth / 2, window.innerHeight / 2, window.innerHeight / - 2, 1, 10 );
			camera.position.set( 0, 0, 2 );
			const scene = new THREE.Scene(); //HUD for shadow map

			const shader = THREE.UnpackDepthRGBAShader;
			const uniforms = THREE.UniformsUtils.clone( shader.uniforms );
			const material = new THREE.ShaderMaterial( {
				uniforms: uniforms,
				vertexShader: shader.vertexShader,
				fragmentShader: shader.fragmentShader
			} );
			const plane = new THREE.PlaneGeometry( frame.width, frame.height );
			const mesh = new THREE.Mesh( plane, material );
			scene.add( mesh ); //Label for light's name

			let labelCanvas, labelMesh;

			if ( doRenderLabel ) {

				labelCanvas = document.createElement( 'canvas' );
				const context = labelCanvas.getContext( '2d' );
				context.font = 'Bold 20px Arial';
				const labelWidth = context.measureText( light.name ).width;
				labelCanvas.width = labelWidth;
				labelCanvas.height = 25; //25 to account for g, p, etc.

				context.font = 'Bold 20px Arial';
				context.fillStyle = 'rgba( 255, 0, 0, 1 )';
				context.fillText( light.name, 0, 20 );
				const labelTexture = new THREE.Texture( labelCanvas );
				labelTexture.magFilter = THREE.LinearFilter;
				labelTexture.minFilter = THREE.LinearFilter;
				labelTexture.needsUpdate = true;
				const labelMaterial = new THREE.MeshBasicMaterial( {
					map: labelTexture,
					side: THREE.DoubleSide
				} );
				labelMaterial.transparent = true;
				const labelPlane = new THREE.PlaneGeometry( labelCanvas.width, labelCanvas.height );
				labelMesh = new THREE.Mesh( labelPlane, labelMaterial );
				scene.add( labelMesh );

			}

			function resetPosition() {

				scope.position.set( scope.position.x, scope.position.y );

			} //- API
			// Set to false to disable displaying this shadow map


			this.enabled = true; // Set the size of the displayed shadow map on the HUD

			this.size = {
				width: frame.width,
				height: frame.height,
				set: function ( width, height ) {

					this.width = width;
					this.height = height;
					mesh.scale.set( this.width / frame.width, this.height / frame.height, 1 ); //Reset the position as it is off when we scale stuff

					resetPosition();

				}
			}; // Set the position of the displayed shadow map on the HUD

			this.position = {
				x: frame.x,
				y: frame.y,
				set: function ( x, y ) {

					this.x = x;
					this.y = y;
					const width = scope.size.width;
					const height = scope.size.height;
					mesh.position.set( - window.innerWidth / 2 + width / 2 + this.x, window.innerHeight / 2 - height / 2 - this.y, 0 );
					if ( doRenderLabel ) labelMesh.position.set( mesh.position.x, mesh.position.y - scope.size.height / 2 + labelCanvas.height / 2, 0 );

				}
			};

			this.render = function ( renderer ) {

				if ( this.enabled ) {

					//Because a light's .shadowMap is only initialised after the first render pass
					//we have to make sure the correct map is sent into the shader, otherwise we
					//always end up with the scene's first added shadow casting light's shadowMap
					//in the shader
					//See: https://github.com/mrdoob/three.js/issues/5932
					uniforms.tDiffuse.value = light.shadow.map.texture;
					userAutoClearSetting = renderer.autoClear;
					renderer.autoClear = false; // To allow render overlay

					renderer.clearDepth();
					renderer.render( scene, camera );
					renderer.autoClear = userAutoClearSetting; //Restore user's setting

				}

			};

			this.updateForWindowResize = function () {

				if ( this.enabled ) {

					camera.left = window.innerWidth / - 2;
					camera.right = window.innerWidth / 2;
					camera.top = window.innerHeight / 2;
					camera.bottom = window.innerHeight / - 2;
					camera.updateProjectionMatrix();
					this.update();

				}

			};

			this.update = function () {

				this.position.set( this.position.x, this.position.y );
				this.size.set( this.size.width, this.size.height );

			}; //Force an update to set position/size


			this.update();

		}
This is a helper for visualising a given light's shadow map.
It works for shadow casting lights: DirectionalLight and SpotLight.
It renders out the shadow map and displays it on a HUD.

Example usage:
	1) Import ShadowMapViewer into your app.

	2) Create a shadow casting light and name it optionally:
		let light = new DirectionalLight( 0xffffff, 1 );
		light.castShadow = true;
		light.name = 'Sun';

	3) Create a shadow map viewer for that light and set its size and position optionally:
		let shadowMapViewer = new ShadowMapViewer( light );
		shadowMapViewer.size.set( 128, 128 );	//width, height  default: 256, 256
		shadowMapViewer.position.set( 10, 10 );	//x, y in pixel	 default: 0, 0 (top left corner)

	4) Render the shadow map viewer in your render loop:
		shadowMapViewer.render( renderer );

	5) Optionally: Update the shadow map viewer on window resize:
		shadowMapViewer.updateForWindowResize();

	6) If you set the position or size members directly, you need to call shadowMapViewer.update();