• Formats - many 3D models formats, each one responding a problem
• Popular 3D Models Formats
  • OBJ 簡(jiǎn)單课舍、高效
  • FBX
  • STL
  • PLY
  • COLLADA
  • 3DS
  • GLTF 目前使用最多的

• GLTF

  • a format is becoming a standard and should cover most of our needs
  • it's for GL transmission format
  • it supports different sets of data like geometries, materials, cameras, lights, scene graph, animations, etc.
  • you can export various formats like json, binary, embed texture, etc.
  • most 3D softwares, game engines and libraries support it
  • the gltf team provides various models glTF-Sample-Models

• GLTF Formats - a GLTF file can have different formats

  • 我們可以參考這個(gè) Duck Model鹅颊，對(duì)應(yīng)了解一下以下幾種主要格式
  1. GLTF
  • the default format
  • .gltf - is a JSON that contains cameras, lights, scenes, materials, objects transformations, but no geometries nor textures
  • .bin - is a binary that usually contains the data like geometries(vertices position, UV coordinates, colors, etc.)
  • .png - is the texture
  • we load the .gltf file and the other files will be loaded automatically
  2. GLTF-BINARY
  • only one file
  • contains the all the data we talk about
  • binary
  • usually lighter
  • easier to load because only one file
  • hard to alter its data
  3. GLTF-DRACO
  • like the gltf default format, but the buffer data is compressed using the Draco algorithm
  • much lighter
  4. GLTF-EMBEDDED
  • one file can read
  • JSON
  • heavier

• Set up 場(chǎng)景配置（plane + lights），axesHelper非必選

  • 當(dāng)我們導(dǎo)入一個(gè)gltf文件時(shí)就漾，gltf會(huì)有真實(shí)的model郭毕，這些model通常會(huì)是 PBR material，PBR material 將會(huì)在three.js中創(chuàng)建 MeshStandardMaterial，所以我們需要 lights

  import * as THREE from 'three'
  import {OrbitControls} from 'three/addons/controls/OrbitControls.js'

  /**
   * scene
  */
  const scene = new THREE.Scene()

  /**
   * floor
  */
  const floor = new THREE.Mesh(
    new THREE.PlaneGeometry(10, 10),
    new THREE.MeshStandardMaterial({
      color: '#444444',
      metalness: 0.4,
      roughness: 0.5
    })
  )
  floor.receiveShadow = true
  floor.rotation.x = - Math.PI * 0.5
  scene.add(floor)

  /**
   * light
  */
  const ambientLight = new THREE.AmbientLight(0xffffff, 0.8)
  scene.add(ambientLight)

  const directionalLight = new THREE.DirectionalLight(0xffffff, 0.6)
  directionalLight.castShadow = true
  directionalLight.shadow.mapSize.set(1024, 1024)
  directionalLight.shadow.camera.far = 15
  directionalLight.shadow.camera.left = - 7
  directionalLight.shadow.camera.top = 7
  directionalLight.shadow.camera.right = 7
  directionalLight.shadow.camera.bottom = - 7
  directionalLight.position.set(- 5, 5, 0)
  scene.add(directionalLight)

  /**
   * camera
  */
  const camera = new THREE.PerspectiveCamera(
    75,
    window.innerWidth / window.innerHeight,
    0.1,
    100
  )
  camera.position.set(2, 2, 2)

  /**
   * renderer
  */
  const renderer = new THREE.WebGLRenderer()
  renderer.shadowMap.enabled = true
  renderer.shadowMap.type = THREE.PCFSoftShadowMap
  renderer.setSize(window.innerWidth, window.innerHeight)
  document.body.appendChild(renderer.domElement)

  window.addEventListener('resize', () => {
    camera.aspect = window.innerWidth / window.innerHeight
    camera.updateProjectionMatrix()

    renderer.setSize(window.innerWidth, window.innerHeight) 
    renderer.setPixelRatio(Math.min(window.devicePixelRatio, 2))   
  })

  /**
   * axesHelper
  */
  const axesHelper = new THREE.AxesHelper(5)
  scene.add(axesHelper)

  /**
   * control
  */
  const controls = new OrbitControls(camera, renderer.domElement)
  controls.enableDamping = true

  /**
   * render
  */
  const clock = new THREE.Clock()
  const tick = () => {
    let elapsedTime = clock.getElapsedTime()

    controls.update()
    requestAnimationFrame(tick)
    renderer.render(scene, camera)
  }
  tick()

set up.png

• Load the model in three.js, use the GLTFLoader

  • 這里用的是一個(gè) Duck Model 作為例子展示淹仑，內(nèi)置參數(shù)的結(jié)構(gòu)可參考下圖
  • the Mesh should be our duck
  • we don't need the PerspectiveCamera
  • the camera and the duck are in an Object3D
  • the Object3D has a scale set to small value

  import { GLTFLoader } from 'three/addons/loaders/GLTFLoader.js';

  /**
   * scene
  */
  ...

  /**
   * model
  */
  const gltfLoder = new GLTFLoader()
  gltfLoder.load(
    '../public/models/Duck/glTF/Duck.gltf',
    (gltf) => {
      // success
      console.log(gltf);
    }
  )

gltf 結(jié)構(gòu).png

• There are many ways can add the duck to our scene

  • add the whole scene in our scene
  • add the children of the scene to our scene and ignore the PerspectiveCamera
  • filter the children before adding to the scene
  • add only the Mesh and end up with a duck with a wrong scale, position and rotation
  • open the file at a 3D software clean it and export again

• Add the Object3D to our scene and ignore the unused PerspectiveCamera

  1. mesh 結(jié)構(gòu)較為單一丙挽，例如上面的 Duck Model

  // duck
  gltfLoader.load(
    '../public/models/Duck/glTF/Duck.gltf',
    (gltf) => {
      // console.log(gltf.scene);
  
      scene.add(gltf.scene.children[0])
    }
  )
  

  Duck model.png
  2. mesh 結(jié)構(gòu)復(fù)雜的，也就是有多個(gè)mesh組成的 FlightHelmet Model

  // flightHelmet
  gltfLoader.load(
    '../public/models/FlightHelmet/glTF/FlightHelmet.gltf',
    (gltf) => {
      // console.log(gltf.scene);
  
      // 不可用匀借，取值過(guò)程會(huì)移動(dòng)原數(shù)組數(shù)據(jù)颜阐，導(dǎo)致循環(huán)混亂
      // for (const child of gltf.scene.children) {  
      //   scene.add(child)
      // }
  
      // 可用
      // while(gltf.scene.children.length) {
      //   scene.add(gltf.scene.children[0])
      // }
  
      const children = [...gltf.scene.children]
      for (const child of children) {
        scene.add(child)
      }
    }
  )
  

  FlightHelmet結(jié)構(gòu).png
  
  
  FlightHelmet model.png

• Draco Compression

  • the draco verion can be lighter than the default version(gltf)
  • compression is applied to the buffer data(typically the geometry)
  • draco is not exclusive to gltf but they got the popular at the same time and implementation went faster with gltf exports

  • Take the /draco/ folder and copy it to your statistic floder (node_modules/three/examples/jsm/libs/draco)

  • when we use the DRACOLoader, the geometries are lighter but has to load the DRACOLoader and the decoder(上一步，我們需要移動(dòng)至public文件夾的部分)

  import {DRACOLoader} from 'three/addons/loaders/DRACOLoader.js'

  /**
   * model
   * **/
  const dracoLoader = new DRACOLoader()  // 必須寫(xiě)在實(shí)例化gltfLoader之前
  dracoLoader.setDecoderPath('/public/draco/')  // 根據(jù)自己項(xiàng)目的結(jié)構(gòu) provide the path to our dracoLoader

  const gltfLoader = new GLTFLoader()
  gltfLoader.setDRACOLoader(dracoLoader)  // provide the dracoLoader instance to gltfLoader

  // duck
  gltfLoader.load(
    '../public/models/Duck/glTF-Draco/Duck.gltf',
    (gltf) => {  
      scene.add(gltf.scene.children[0])
    }
  )

Draco loader.png

• Animations - gltf can load animation Fox Model

  • to load a gltf object contains a animations property composed of multiple AnimationClip - 可以理解為關(guān)鍵幀的合集
  • we need to create an AnimationMixer, it's like a player 播放器
  • add on of the AnimationClips to the mixer and then call the play()
  • update the mixer on each frame
    
    animation.png

  /**
   * model
   */
  ...
  let mixer = null
  // fox
  gltfLoader.load(
    '../public/models/Fox/glTF/Fox.gltf',
    (gltf) => {
      // console.log(gltf);

      gltf.scene.scale.set(0.025, 0.025, 0.025)
      scene.add(gltf.scene)

      // animation
      mixer = new THREE.AnimationMixer(gltf.scene)
      const action = mixer.clipAction(gltf.animations[0])
      // console.log(action);
      action.play()
    }
  )

/**
 * render
 */
const clock = new THREE.Clock()
let previousTime = 0
const tick = () => {
  const elapsedTime = clock.getElapsedTime()
  const deltaTime = elapsedTime - previousTime
  previousTime = elapsedTime

  // update mixer
  mixer && mixer.update(deltaTime)

  ...
}
tick()

animation fox model.png