书接上回，这里讨论贴图的运用！！！

// 创建球网格
  const ball = MeshBuilder.CreateSphere('ball',{diameter:1},scene)
  ball.position = new Vector3(0,1,0)
  // 创建PRB材质
  const ballMat = new PBRMaterial('pbr',scene)

  // albedoTexture 反照率贴图
  ballMat.albedoTexture = new Texture('./textures/aerial_beach_02_diff_4k.jpg',scene)

  // 法线贴图
  ballMat.bumpTexture = new Texture('./textures/aerial_beach_02_nor_gl_4k.jpg',scene)
  ballMat.invertNormalMapX = true
  ballMat.invertNormalMapY = true

  // ao贴图
  ballMat.metallicTexture = new Texture('./textures/aerial_beach_02_ao_4k.jpg',scene)
  ballMat.useAmbientOcclusionFromMetallicTextureRed = true
  ballMat.useRoughnessFromMetallicTextureGreen = true
  ballMat.useMetallnessFromMetallicTextureBlue = true

  // 发光贴图
  ballMat.emissiveTexture = new Texture('./textures/emissive.jpg',scene)
  // 默认是黑色 不发光
  ballMat.emissiveColor = new Color3(1,1,1)
  // 发光强度
  ballMat.emissiveIntensity = 1
  // 材质接收到的环境光强度
  ballMat.environmentIntensity = 0.25
  // 发光层
  const glowLayer  = new GlowLayer('glow',scene)
  glowLayer.intensity = 1

  // 应用材质
  ball.material = ballMat;