这在SpotLights内部用于计算阴影。
//Create a WebGLRenderer and turn on shadows in the renderer
const renderer = new THREE.WebGLRenderer();
renderer.shadowMap.enabled = true;
renderer.shadowMap.type = THREE.PCFSoftShadowMap; // default THREE.PCFShadowMap
//Create a SpotLight and turn on shadows for the light
const light = new THREE.SpotLight( 0xffffff );
light.castShadow = true; // default false
scene.add( light );
//Set up shadow properties for the light
light.shadow.mapSize.width = 512; // default
light.shadow.mapSize.height = 512; // default
light.shadow.camera.near = 0.5; // default
light.shadow.camera.far = 500 // default
light.shadow.focus = 1; // default
//Create a sphere that cast shadows (but does not receive them)
const sphereGeometry = new THREE.SphereGeometry( 5, 32, 32 );
const sphereMaterial = new THREE.MeshStandardMaterial( { color: 0xff0000 } );
const sphere = new THREE.Mesh( sphereGeometry, sphereMaterial );
sphere.castShadow = true; //default is false
sphere.receiveShadow = false; //default
scene.add( sphere );
//Create a plane that receives shadows (but does not cast them)
const planeGeometry = new THREE.PlaneGeometry( 20, 20, 32, 32 );
const planeMaterial = new THREE.MeshStandardMaterial( { color: 0x00ff00 } )
const plane = new THREE.Mesh( planeGeometry, planeMaterial );
plane.receiveShadow = true;
scene.add( plane );
//Create a helper for the shadow camera (optional)
const helper = new THREE.CameraHelper( light.shadow.camera );
scene.add( helper );
构造函数创建一个 [param:PerspectiveCamera PerspectiveCamera] 来管理阴影的世界视图
有关常用属性，请参阅基类 [page:LightShadow LightShadow]。
在光的世界里。这用于生成场景的深度图;从光的角度来看，其他物体背后的物体将处于阴影中。
默认值为 [page:PerspectiveCamera.near near] 裁剪平面为 `0.5` 的 [page:PerspectiveCamera]。
[page:PerspectiveCamera.fov fov] 裁剪平面将通过 [page:SpotLightShadow.update update] 方法跟踪所属 [page:SpotLight SpotLight] 的 [page:SpotLight.angle angle] 属性。
同样 [page:PerspectiveCamera.aspect aspect] 属性将跟踪 [page:LightShadow.mapSize mapSize] 的 aspect。
如果设置了灯光的 [page:SpotLight.distance distance] 属性，则 [page:PerspectiveCamera.far far]
裁剪平面将跟踪该值，否则默认为 `500`。
用于对焦阴影相机。相机的视野设置为聚光灯视野的百分比。范围为 `[0, 1]`。默认值为 `1.0`。
只读属性，用于检查给定对象是否为[name]类型。
有关常用方法，请参阅基础LightShadow类。
[link:https://github.com/mrdoob/three.js/blob/master/src/lights/[name].js src/lights/[name].js]