什么是导航立方体？

导航立方体是一个交互式的3D控件，它允许用户通过点击和拖动立方体的各个面来改变3D视图的方向。这是一种非常直观的方式，让用户能够轻松地在3D空间中导航。

创建导航立方体

下面是一个基本的步骤，说明如何使用Three.js创建一个导航立方体：

 // 创建场景var scene = new THREE.Scene();// 创建相机var camera = new THREE.PerspectiveCamera(75, window.innerWidth / window.innerHeight, 0.1, 1000);camera.position.z = 5;// 创建渲染器var renderer = new THREE.WebGLRenderer();renderer.setSize(window.innerWidth, window.innerHeight);renderer.setClearColor(0xffffff); // set to whitedocument.body.appendChild(renderer.domElement);// 创建立方体的几何体var geometry = new THREE.BoxGeometry(1, 1, 1);// 创建立方体的每个面的材质const CANVAS_SIZE = 256;var materials = [];['上', '下', '左', '右', '前', '后'].forEach(function(text) {// 创建一个canvas元素var canvas = document.createElement('canvas');canvas.width = CANVAS_SIZE;canvas.height = CANVAS_SIZE;// 获取canvas的2d绘图上下文var context = canvas.getContext('2d');// context.fillStyle = '#f0f0f0';  // 设置填充颜色为白色context.fillStyle = '#f6fcff';  // 设置填充颜色为白色context.fillRect(0, 0, canvas.width, canvas.height);  // 填充整个canvas// 在canvas上绘制文字context.fillStyle = 'black';  // 将文字颜色改为红色// context.font = 'bold 200px serif';  // 将文字大小改为96pxcontext.font = "bold 100px arial";context.textAlign = 'center';  // 设置文字对齐方式为居中context.textBaseline = 'middle';  // 设置文字基线为中线context.fillText(text, canvas.width / 2, canvas.height / 2);  // 将文字绘制在canvas的中心// 创建一个纹理// 使用canvas作为纹理var texture = new THREE.Texture(canvas);texture.needsUpdate = true;// 创建材质并添加到材质数组中// var material = new THREE.MeshStandardMaterial({ map: texture, color: 0xa5e3ff, emissive: 0xeb780a }); // Set material color to white// materials.push(material);// 使用MeshStandardMaterial以支持高光效果var material = new THREE.MeshStandardMaterial({ map: texture, color: 0xffffff, emissive: 0x000000 });materials.push(material);});// 创建立方体var cube = new THREE.Mesh(geometry, materials);cube.position.set(-0.5, -0.5, -0.5); // Set the position to the corner of the cube// scene.add(cube);// 添加光源var light = new THREE.AmbientLight(0xffffff);scene.add(light);// 添加平行光源var directionalLight = new THREE.DirectionalLight(0xffffff, 1);directionalLight.position.set(1, 1, 1).normalize();scene.add(directionalLight);// 鼠标悬停高亮效果var raycaster = new THREE.Raycaster();var mouse = new THREE.Vector2();function onMouseMove(event) {// 计算鼠标位置的归一化设备坐标mouse.x = (event.clientX / window.innerWidth) * 2 - 1;mouse.y = -(event.clientY / window.innerHeight) * 2 + 1;// 通过相机和鼠标位置更新射线raycaster.setFromCamera(mouse, camera);// 计算物体和射线的交点var intersects = raycaster.intersectObjects([cube]);// 遍历交点，将相应面的材质高亮for (var i = 0; i < materials.length; i++) {materials[i].emissive.set(0x000000); // 清除之前的高亮}if (intersects.length > 0) {var index = intersects[0].face.materialIndex;materials[index].emissive.set("#eb780a"); // 设置高亮}}function onClick(event) {// 处理点击事件，你可以在这里添加你的逻辑}// 添加事件监听器document.addEventListener('mousemove', onMouseMove, false);document.addEventListener('click', onClick, false);// 添加坐标系var axesHelper = new THREE.AxesHelper(2);axesHelper.position.copy(cube.position); // Set the position to match the cube// scene.add(axesHelper);// 创建一个包含立方体和坐标系的组var group = new THREE.Group();group.add(cube);group.add(axesHelper);scene.add(group);// 渲染函数function render() {requestAnimationFrame(render);group.rotation.x += 0.01;group.rotation.y += 0.01;renderer.render(scene, camera);}// 调用渲染函数
render();