光线投射Raycaster

        光线投射详细介绍可参考：https://en.wikipedia.org/wiki/Ray_casting，

        ThreeJS中，提供了Raycaster类，用于进行鼠标拾取，即：当三维场景中鼠标移动时，利用光线投射，可计算出鼠标划过了哪些物体。

        ThreeJS官方案例webgl_interactive_cubes演示了光线投射的具体应用，

        通过Raycaster类实例的intersectObjects方法，可以获取到与射线Ray相交的一组物体；

        通过Raycaster类实例的intersectObject方法，可以获取到与Ray射线相交的第一个物体，

        此外，在鼠标点击或移动时，我们是需要不断去更新Ray射线的，这样才能选中正确的3D物体，可以通过setFromCamera方法，来更新射线，

        接着，还有一个要解决的问题，就是这里的标准化设备坐标中的二维坐标，如何进行处理才是符合ThreeJS的接口规范的？

        核心代码如下，

const mousePosition = new THREE.Vector2(); //记录鼠标位置
//TODO:监听鼠标移动事件
function onPointerMove( event ) {
  mousePosition.x = ( event.clientX / window.innerWidth ) * 2 - 1;
  mousePosition.y = - ( event.clientY / window.innerHeight ) * 2 + 1;
}
document.addEventListener("mousemove",onPointerMove);

注意到：计算mousePosition.y的计算结果，相比mousePosition.x多乘了一个-1，这是因为屏幕坐标系和ThreeJS的XYZ空间直角坐标系，两者的Y轴是相反的。

3D场景鼠标交互案例

       下面来实现一个利用光线投射控制鼠标选中物体高亮显示的案例，主要效果如下：

①鼠标选中物体，高亮显示，

②鼠标离开物体，取消高亮显示，

         完整示例代码如下，

import * as THREE from "three";
import { OrbitControls } from "three/addons/controls/OrbitControls.js"; //轨道控制器
import { GUI } from "three/examples/jsm/libs/lil-gui.module.min.js"; //lil-gui调试工具
import { RGBELoader } from "three/examples/jsm/loaders/RGBELoader.js"; //HDR加载器
import { GLTFLoader } from "three/examples/jsm/loaders/GLTFLoader.js"; //GLTF加载器
import { DRACOLoader } from "three/examples/jsm/loaders/DRACOLoader.js";

const gui = new GUI();

//TODO:打印版本
console.warn("threejs版本:", THREE.REVISION);
//TODO:创建时钟
const clock = new THREE.Clock();
//TODO:创建场景
const scene = new THREE.Scene();
//TODO:创建透视相机
const camera = new THREE.PerspectiveCamera(
  45, //视角
  window.innerWidth / window.innerHeight,
  0.1, //近平面
  1000.0 //远平面
);

//TODO:创建渲染器
const renderer = new THREE.WebGLRenderer({ antialias: true });
renderer.setSize(window.innerWidth, window.innerHeight);

//TODO:轨道控制器
const orbitControls = new OrbitControls(camera, renderer.domElement);
//设置阻尼效果
// orbitControls.enableDamping = true;
orbitControls.update();

document.body.appendChild(renderer.domElement);

//TODO:添加光源
const light = new THREE.PointLight(0xffffff, 1000, 1000);
light.position.set(15, 15, 15);
scene.add(light);

scene.background = new THREE.Color(0xbfe3dd);


//TODO：添加3个球体
const ball1 = new THREE.SphereGeometry(1);
const ballMaterial = new THREE.MeshBasicMaterial({color:0xffff00});
const ballMesh1 = new THREE.Mesh(ball1,ballMaterial);
ballMesh1.geometry.scale(0.5,0.5,0.5);
ballMesh1.position.set(-1.0,-1.0,-1.0);

const ballMesh2 = new THREE.Mesh(ball1,ballMaterial);
ballMesh2.geometry.scale(0.5,0.5,0.5);
ballMesh2.position.set(1.0,-1.0,-1.0);

const ballMesh3 = new THREE.Mesh(ball1,ballMaterial);
ballMesh3.geometry.scale(0.5,0.5,0.5);
ballMesh3.position.set(1.0,1.0,-1.0);

const ballMesh4 = new THREE.Mesh(ball1,ballMaterial);
ballMesh4.geometry.scale(0.5,0.5,0.5);
ballMesh4.position.set(1.0,1.0,1.0);

scene.add(ballMesh1);
scene.add(ballMesh2);
scene.add(ballMesh3);
scene.add(ballMesh4);

//TODO:设置相机位置
camera.position.z = 5.0;
camera.position.y = 2.0;
camera.position.x = 2.0;
camera.lookAt(0, 0, 0);

//TODO:利用光线投射,使用鼠标选中Mesh
const rayCaster = new THREE.Raycaster();
const mousePosition = new THREE.Vector2(); //记录鼠标位置
const hightLightColor = new THREE.Color(0xff0000);//高亮颜色
const highlightMaterial = new THREE.MeshBasicMaterial({color:hightLightColor});
const lastSelected = {
  originMaterial:null,//被选中的3D物体的material
  instance:null,//被选中的3D物体
}
//TODO:监听鼠标移动事件
function onPointerMove( event ) {
  mousePosition.x = ( event.clientX / window.innerWidth ) * 2 - 1;
  mousePosition.y = - ( event.clientY / window.innerHeight ) * 2 + 1;
}
document.addEventListener("mousemove",onPointerMove);


//TODO:还原上一次被选中的3D物体
function resetLastSelected(){
  if(lastSelected.instance && lastSelected.originMaterial){
    lastSelected.instance.material = lastSelected.originMaterial;
    lastSelected.instance = null;
    lastSelected.originMaterial = null;
  }
}

function pick3DObject(){
  // 通过摄像机和鼠标位置更新射线_[使用一个新的原点和方向来更新射线。]
  rayCaster.setFromCamera(mousePosition,camera);
  /**
   * objects —— 检测和射线相交的一组物体。
     recursive —— 若为true，则同时也会检测所有物体的后代。否则将只会检测对象本身的相交部分。默认值为true。
   */
  const interscets = rayCaster.intersectObjects(scene.children,false);
  if(interscets.length>0){
    const interscetObject = interscets[ 0 ].object;
    console.log("interscets::",interscetObject);
    //TODO:还原上一次选中的3D物体
    resetLastSelected();
    if(interscetObject){
      //TODO:鼠标选中3D物体,设置高亮效果
      //记录当前被选中的物体
      lastSelected.instance = interscetObject;
      lastSelected.originMaterial = interscetObject.material;
      //设置高亮
      interscetObject.material = highlightMaterial;
    }
  }else{
    //TODO:鼠标离开3D物体,还原Material
    resetLastSelected();
  }
}

//TODO:创建坐标辅助器
// const axesHelper = new THREE.AxesHelper(5);
// scene.add(axesHelper);

//TODO:渲染函数
function animate() {
  requestAnimationFrame(animate);
  //TODO:旋转立方体
  // mesh.rotation.x += 0.01;
  // mesh.rotation.y += 0.01;
  pick3DObject();
  //TODO:更新轨道控制器
  orbitControls.update();
  //TODO:渲染
  renderer.render(scene, camera);
}
window.onresize = function () {
  //TODO:重置渲染器宽高比
  renderer.setSize(window.innerWidth, window.innerHeight);
  //TODO:重置相机宽高比
  camera.aspect = window.innerWidth / window.innerHeight;
  //TODO:更新相机投影矩阵
  camera.updateProjectionMatrix();
};

animate();

//TODO:lil-gui添加调试按钮
const myObject = {
  // myBoolean: true,
  fullScreenBtnFunction: function () {
    document.body.requestFullscreen();
  },
  exitFullScreenBtnFunction: function () {
    document.exitFullscreen();
  },
  wireframeMode: false,
  renderMode: 1,
  colorSpace: 0,
};

gui.add(myObject, "fullScreenBtnFunction").name("全屏显示"); // Button
gui.add(myObject, "exitFullScreenBtnFunction").name("退出全屏"); // Button
//TODO:开启/关闭线框模式
gui
  .add(myObject, "wireframeMode")
  .name("线框模式")
  .onChange(function (value) {
    console.log(value);
    mesh.material.wireframe = value;
  });
// gui.add(myObject, "myString"); // Text Field
// gui.add(myObject, "myNumber"); // Number Field

//TODO:控制Mesh网格正反面显示模式
gui
  .add(myObject, "renderMode", { 双面模式: 0, 正面模式: 1, 背面模式: 2 })
  .name("三角形正反面显示模式")
  .onChange(function (value) {
    console.log(value);
    switch (value) {
      case 0: {
        triangleMesh.material.side = THREE.DoubleSide;
        break;
      }
      case 1: {
        triangleMesh.material.side = THREE.FrontSide;
        break;
      }
      case 2: {
        triangleMesh.material.side = THREE.BackSide;
        break;
      }
    }
  });

//TODO:控制颜色空间
gui
  .add(myObject, "colorSpace", {
    NoColorSpace: 0,
    SRGBColorSpace: 1,
    LinearSRGBColorSpace: 2,
  })
  .onChange((value) => {
    console.log("修改颜色空间::", value);
    switch (value) {
      case 0: {
        diffuseMap.colorSpace = THREE.NoColorSpace;
        break;
      }
      case 1: {
        diffuseMap.colorSpace = THREE.SRGBColorSpace;
        break;
      }
      case 2: {
        diffuseMap.colorSpace = THREE.LinearSRGBColorSpace;
        break;
      }
    }
  });