Javascript 试图理解THREEJS中使用的回调函数

下面的代码来自一个THREE.JS示例；效果很好。我用three.js代码制作了自己的艺术画廊。我用来挂画的代码源于three.js示例：webgl\u materials\u texture\u manualmipmap.html

下面的代码可以工作，但我不理解MaterialPaint 1如何在回调函数中使用，因为在回调函数之后才完全定义MaterialPaint 1

谁能给我解释一下这是怎么回事吗。MaterialPaint 1是如何在回调函数中使用的，尽管它是在后面定义的，因为它在示例中工作得很好，但在我自己的代码中，我必须使用小提琴来加载绘画

var callbackPainting = function () {
  var image = texturePainting1.image;
  texturePainting2.image = image;
  texturePainting2.needsUpdate = true;
  scene1.add(meshCanvas1);
  scene2.add(meshCanvas2);
  var geometry = new THREE.PlaneGeometry(100, 100);
  var mesh1 = new THREE.Mesh(geometry, materialPainting1);
  var mesh2 = new THREE.Mesh(geometry, materialPainting2);
  addPainting(scene1, mesh1);
  addPainting(scene2, mesh2);

  function addPainting(zscene, zmesh) {
    zmesh.scale.x = image.width / 100;
    zmesh.scale.y = image.height / 100;
    zscene.add(zmesh);
    var meshFrame = new THREE.Mesh(geometry, new THREE.MeshBasicMaterial({
      color: 0x000000,
      polygonOffset: true,
      polygonOffsetFactor: 1,
      polygonOffsetUnits: 5
    }));
    meshFrame.scale.x = 1.1 * image.width / 100;
    meshFrame.scale.y = 1.1 * image.height / 100;
    zscene.add(meshFrame);
    var meshShadow = new THREE.Mesh(geometry, new THREE.MeshBasicMaterial({
      color: 0x000000,
      opacity: 0.75,
      transparent: true
    }));
    meshShadow.position.y = -1.1 * image.height / 2;
    meshShadow.position.z = -1.1 * image.height / 2;
    meshShadow.rotation.x = -Math.PI / 2;
    meshShadow.scale.x = 1.1 * image.width / 100;
    meshShadow.scale.y = 1.1 * image.height / 100;
    zscene.add(meshShadow);
    var floorHeight = -1.117 * image.height / 2;
    meshCanvas1.position.y = meshCanvas2.position.y = floorHeight;
  }
};
var texturePainting1 = THREE.ImageUtils.loadTexture("textures/758px-Canestra_di_frutta_(Caravaggio).jpg", THREE.UVMapping, callbackPainting),
  texturePainting2 = new THREE.Texture(),
  materialPainting1 = new THREE.MeshBasicMaterial({
    color: 0xffffff,
    map: texturePainting1
  }),
  materialPainting2 = new THREE.MeshBasicMaterial({
    color: 0xffccaa,
    map: texturePainting2
  });

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纹理加载是异步的；在加载纹理之前，不会执行回调函数。到那时，您的材质已经定义

然而，作为一个良好的实践，我会首先定义材料

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three.js r.66

阅读“提升”。嗨@WestLangley，如何检查纹理是否加载？？？@JothiKannan如果你有问题，你需要发表一篇帖子并询问社区。