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396 lines
23 KiB
396 lines
23 KiB
2 years ago
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<!DOCTYPE html><html lang="zh"><head>
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<meta charset="utf-8">
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<title>自定义缓冲几何体</title>
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<meta name="viewport" content="width=device-width, user-scalable=no, minimum-scale=1.0, maximum-scale=1.0">
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<meta name="twitter:card" content="summary_large_image">
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<meta name="twitter:site" content="@threejs">
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<meta name="twitter:title" content="Three.js – 自定义缓冲几何体">
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<meta property="og:image" content="https://threejs.org/files/share.png">
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<link rel="shortcut icon" href="/files/favicon_white.ico" media="(prefers-color-scheme: dark)">
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<link rel="shortcut icon" href="/files/favicon.ico" media="(prefers-color-scheme: light)">
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<link rel="stylesheet" href="/manual/resources/lesson.css">
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<link rel="stylesheet" href="/manual/resources/lang.css">
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<!-- Import maps polyfill -->
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<!-- Remove this when import maps will be widely supported -->
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<script async src="https://unpkg.com/es-module-shims@1.3.6/dist/es-module-shims.js"></script>
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<script type="importmap">
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{
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"imports": {
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"three": "../../build/three.module.js"
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}
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}
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</script>
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<link rel="stylesheet" href="/manual/zh/lang.css">
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</head>
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<body>
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<div class="container">
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<div class="lesson-title">
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<h1>自定义缓冲几何体</h1>
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</div>
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<div class="lesson">
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<div class="lesson-main">
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<p>在three.js中， <a href="/docs/#api/zh/core/BufferGeometry"><code class="notranslate" translate="no">BufferGeometry</code></a> 是用来代表所有几何体的一种方式。 <a href="/docs/#api/zh/core/BufferGeometry"><code class="notranslate" translate="no">BufferGeometry</code></a> 本质上是一系列 <a href="/docs/#api/zh/core/BufferAttribute"><code class="notranslate" translate="no">BufferAttribute</code></a>s 的 <em>名称</em> 。每一个 <a href="/docs/#api/zh/core/BufferAttribute"><code class="notranslate" translate="no">BufferAttribute</code></a> 代表一种类型数据的数组：位置，法线，颜色，uv，等等…… 这些合起来， <a href="/docs/#api/zh/core/BufferAttribute"><code class="notranslate" translate="no">BufferAttribute</code></a>s 代表每个顶点所有数据的 <em>并行数组</em> 。</p>
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<div class="threejs_center"><img src="../resources/threejs-attributes.svg" style="width: 700px"></div>
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<p>上面提到，我们有四个属性：<code class="notranslate" translate="no">position</code>, <code class="notranslate" translate="no">normal</code>, <code class="notranslate" translate="no">color</code>, <code class="notranslate" translate="no">uv</code> 。
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它们指的是 <em>并行数组</em> ，代表每个属性的第N个数据集属于同一个顶点。index=4的顶点被高亮表示贯穿所有属性的平行数据定义一个顶点。</p>
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<p>这就告诉我们，这是一个方块的数据图，高亮的地方代表一个角。</p>
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<div class="threejs_center"><img src="../resources/cube-faces-vertex.svg" style="width: 500px"></div>
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<p>考虑下方块的单个角，不同的面都需要一个不同的法线。法线是面朝向的信息。在图中，在方块的角周围用箭头表示的法线，代表共用顶点位置的面需要指向不同方向的法线。</p>
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<p>同理，一个角在不同的面需要不同的UVs。UVs是用来指定纹理区域中，画在相应顶点位置三角形的纹理坐标。你可以看到，绿色的面需要顶点的UV对应于F纹理的右上角，蓝色的面需要的UV对应于F纹理的左上角，红色的面需要的UV对应于F纹理的左下角。</p>
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<p>一个简单的 <em>顶点</em> 是所有组成部分的集合。如果顶点需要其中任一部分变得不同，那么它必须是一个不同的顶点。</p>
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<p>举一个简单的例子，让我们创建一个使用 <a href="/docs/#api/zh/core/BufferGeometry"><code class="notranslate" translate="no">BufferGeometry</code></a> 的方块。方块很有趣，因为它看起来在角的地方共用顶点但实际上不是。在我们的例子中，我们将列出所有顶点数据，然后转化成并行数组，最后用它们创建 <a href="/docs/#api/zh/core/BufferAttribute"><code class="notranslate" translate="no">BufferAttribute</code></a>s 并添加到 <a href="/docs/#api/zh/core/BufferGeometry"><code class="notranslate" translate="no">BufferGeometry</code></a> 。</p>
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<p>我们从方块所需的所有数据开始。再次记住如果顶点有任何独一无二的部分，它必须是不同的顶点。像这里创建一个方块需要36个顶点，每个面2个三角形，每个三角形3个顶点，6个面=36个顶点。</p>
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<pre class="prettyprint showlinemods notranslate lang-js" translate="no">const vertices = [
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// front
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{ pos: [-1, -1, 1], norm: [ 0, 0, 1], uv: [0, 0], },
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{ pos: [ 1, -1, 1], norm: [ 0, 0, 1], uv: [1, 0], },
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{ pos: [-1, 1, 1], norm: [ 0, 0, 1], uv: [0, 1], },
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{ pos: [-1, 1, 1], norm: [ 0, 0, 1], uv: [0, 1], },
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{ pos: [ 1, -1, 1], norm: [ 0, 0, 1], uv: [1, 0], },
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{ pos: [ 1, 1, 1], norm: [ 0, 0, 1], uv: [1, 1], },
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// right
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{ pos: [ 1, -1, 1], norm: [ 1, 0, 0], uv: [0, 0], },
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{ pos: [ 1, -1, -1], norm: [ 1, 0, 0], uv: [1, 0], },
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{ pos: [ 1, 1, 1], norm: [ 1, 0, 0], uv: [0, 1], },
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{ pos: [ 1, 1, 1], norm: [ 1, 0, 0], uv: [0, 1], },
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{ pos: [ 1, -1, -1], norm: [ 1, 0, 0], uv: [1, 0], },
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{ pos: [ 1, 1, -1], norm: [ 1, 0, 0], uv: [1, 1], },
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// back
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{ pos: [ 1, -1, -1], norm: [ 0, 0, -1], uv: [0, 0], },
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{ pos: [-1, -1, -1], norm: [ 0, 0, -1], uv: [1, 0], },
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{ pos: [ 1, 1, -1], norm: [ 0, 0, -1], uv: [0, 1], },
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{ pos: [ 1, 1, -1], norm: [ 0, 0, -1], uv: [0, 1], },
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{ pos: [-1, -1, -1], norm: [ 0, 0, -1], uv: [1, 0], },
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{ pos: [-1, 1, -1], norm: [ 0, 0, -1], uv: [1, 1], },
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// left
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{ pos: [-1, -1, -1], norm: [-1, 0, 0], uv: [0, 0], },
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{ pos: [-1, -1, 1], norm: [-1, 0, 0], uv: [1, 0], },
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{ pos: [-1, 1, -1], norm: [-1, 0, 0], uv: [0, 1], },
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{ pos: [-1, 1, -1], norm: [-1, 0, 0], uv: [0, 1], },
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{ pos: [-1, -1, 1], norm: [-1, 0, 0], uv: [1, 0], },
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{ pos: [-1, 1, 1], norm: [-1, 0, 0], uv: [1, 1], },
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// top
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{ pos: [ 1, 1, -1], norm: [ 0, 1, 0], uv: [0, 0], },
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{ pos: [-1, 1, -1], norm: [ 0, 1, 0], uv: [1, 0], },
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{ pos: [ 1, 1, 1], norm: [ 0, 1, 0], uv: [0, 1], },
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{ pos: [ 1, 1, 1], norm: [ 0, 1, 0], uv: [0, 1], },
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{ pos: [-1, 1, -1], norm: [ 0, 1, 0], uv: [1, 0], },
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{ pos: [-1, 1, 1], norm: [ 0, 1, 0], uv: [1, 1], },
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// bottom
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{ pos: [ 1, -1, 1], norm: [ 0, -1, 0], uv: [0, 0], },
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{ pos: [-1, -1, 1], norm: [ 0, -1, 0], uv: [1, 0], },
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{ pos: [ 1, -1, -1], norm: [ 0, -1, 0], uv: [0, 1], },
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{ pos: [ 1, -1, -1], norm: [ 0, -1, 0], uv: [0, 1], },
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{ pos: [-1, -1, 1], norm: [ 0, -1, 0], uv: [1, 0], },
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{ pos: [-1, -1, -1], norm: [ 0, -1, 0], uv: [1, 1], },
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];
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</pre>
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<p>然后我们能将它们全部转换成3个并行数组</p>
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<pre class="prettyprint showlinemods notranslate lang-js" translate="no">const positions = [];
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const normals = [];
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const uvs = [];
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for (const vertex of vertices) {
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positions.push(...vertex.pos);
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normals.push(...vertex.norm);
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uvs.push(...vertex.uv);
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}
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</pre>
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<p>最终我们能创建一个 <a href="/docs/#api/zh/core/BufferGeometry"><code class="notranslate" translate="no">BufferGeometry</code></a> ，然后为每个数组创建一个 <a href="/docs/#api/zh/core/BufferAttribute"><code class="notranslate" translate="no">BufferAttribute</code></a> 并添加到 <a href="/docs/#api/zh/core/BufferGeometry"><code class="notranslate" translate="no">BufferGeometry</code></a> 。</p>
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<pre class="prettyprint showlinemods notranslate lang-js" translate="no"> const geometry = new THREE.BufferGeometry();
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const positionNumComponents = 3;
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const normalNumComponents = 3;
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const uvNumComponents = 2;
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geometry.setAttribute(
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'position',
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new THREE.BufferAttribute(new Float32Array(positions), positionNumComponents));
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geometry.setAttribute(
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'normal',
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new THREE.BufferAttribute(new Float32Array(normals), normalNumComponents));
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geometry.setAttribute(
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'uv',
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new THREE.BufferAttribute(new Float32Array(uvs), uvNumComponents));
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</pre>
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<p>注意名字很重要。你必须将属性的名字命名成three.js所期望的(除非你正在创建自定义着色器)，在这里是 <code class="notranslate" translate="no">position</code>、 <code class="notranslate" translate="no">normal</code> 和 <code class="notranslate" translate="no">uv</code> 。如果你想要设置顶点颜色则命名属性为 <code class="notranslate" translate="no">color</code> 。</p>
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<p>在上面我们创建了3个JavaScript原生数组， <code class="notranslate" translate="no">positions</code>, <code class="notranslate" translate="no">normals</code> 和 <code class="notranslate" translate="no">uvs</code> 。
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然后我们将他们转换为 <code class="notranslate" translate="no">Float32Array</code> 的类型数组<a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray">TypedArrays</a>。 <a href="/docs/#api/zh/core/BufferAttribute"><code class="notranslate" translate="no">BufferAttribute</code></a> 是类型数组而不是原生数组。同时 <a href="/docs/#api/zh/core/BufferAttribute"><code class="notranslate" translate="no">BufferAttribute</code></a> 需要你设定每个顶点有多少组成成分。对于位置和法线，每个顶点我们需要3个组成成分，x、y和z。对于UVs我们需要2个，u和v。</p>
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<p></p><div translate="no" class="threejs_example_container notranslate">
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<div><iframe class="threejs_example notranslate" translate="no" style=" " src="/manual/examples/resources/editor.html?url=/manual/examples/custom-buffergeometry-cube.html"></iframe></div>
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<a class="threejs_center" href="/manual/examples/custom-buffergeometry-cube.html" target="_blank">点击此处在新标签页中打开</a>
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</div>
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<p></p>
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<p>那会是大量的数据。我们可以做点改善，可以用索引来代表顶点。看回我们的方块数据，每个面由2个三角形组成，每个三角形3个顶点，总共6个，但是其中2个是完全一样的；同样的位置，同样的法线，和同样的uv。因此，我们可以移除匹配的顶点，然后用索引代表他们。首先我们移除匹配的顶点。</p>
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<pre class="prettyprint showlinemods notranslate lang-js" translate="no">const vertices = [
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// front
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{ pos: [-1, -1, 1], norm: [ 0, 0, 1], uv: [0, 0], }, // 0
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{ pos: [ 1, -1, 1], norm: [ 0, 0, 1], uv: [1, 0], }, // 1
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{ pos: [-1, 1, 1], norm: [ 0, 0, 1], uv: [0, 1], }, // 2
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-
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- { pos: [-1, 1, 1], norm: [ 0, 0, 1], uv: [0, 1], },
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- { pos: [ 1, -1, 1], norm: [ 0, 0, 1], uv: [1, 0], },
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{ pos: [ 1, 1, 1], norm: [ 0, 0, 1], uv: [1, 1], }, // 3
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// right
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{ pos: [ 1, -1, 1], norm: [ 1, 0, 0], uv: [0, 0], }, // 4
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{ pos: [ 1, -1, -1], norm: [ 1, 0, 0], uv: [1, 0], }, // 5
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-
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- { pos: [ 1, 1, 1], norm: [ 1, 0, 0], uv: [0, 1], },
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- { pos: [ 1, -1, -1], norm: [ 1, 0, 0], uv: [1, 0], },
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{ pos: [ 1, 1, 1], norm: [ 1, 0, 0], uv: [0, 1], }, // 6
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{ pos: [ 1, 1, -1], norm: [ 1, 0, 0], uv: [1, 1], }, // 7
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// back
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{ pos: [ 1, -1, -1], norm: [ 0, 0, -1], uv: [0, 0], }, // 8
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{ pos: [-1, -1, -1], norm: [ 0, 0, -1], uv: [1, 0], }, // 9
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-
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- { pos: [ 1, 1, -1], norm: [ 0, 0, -1], uv: [0, 1], },
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- { pos: [-1, -1, -1], norm: [ 0, 0, -1], uv: [1, 0], },
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{ pos: [ 1, 1, -1], norm: [ 0, 0, -1], uv: [0, 1], }, // 10
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{ pos: [-1, 1, -1], norm: [ 0, 0, -1], uv: [1, 1], }, // 11
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// left
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{ pos: [-1, -1, -1], norm: [-1, 0, 0], uv: [0, 0], }, // 12
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{ pos: [-1, -1, 1], norm: [-1, 0, 0], uv: [1, 0], }, // 13
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-
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- { pos: [-1, 1, -1], norm: [-1, 0, 0], uv: [0, 1], },
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- { pos: [-1, -1, 1], norm: [-1, 0, 0], uv: [1, 0], },
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{ pos: [-1, 1, -1], norm: [-1, 0, 0], uv: [0, 1], }, // 14
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{ pos: [-1, 1, 1], norm: [-1, 0, 0], uv: [1, 1], }, // 15
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// top
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{ pos: [ 1, 1, -1], norm: [ 0, 1, 0], uv: [0, 0], }, // 16
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{ pos: [-1, 1, -1], norm: [ 0, 1, 0], uv: [1, 0], }, // 17
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-
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- { pos: [ 1, 1, 1], norm: [ 0, 1, 0], uv: [0, 1], },
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- { pos: [-1, 1, -1], norm: [ 0, 1, 0], uv: [1, 0], },
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{ pos: [ 1, 1, 1], norm: [ 0, 1, 0], uv: [0, 1], }, // 18
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{ pos: [-1, 1, 1], norm: [ 0, 1, 0], uv: [1, 1], }, // 19
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// bottom
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{ pos: [ 1, -1, 1], norm: [ 0, -1, 0], uv: [0, 0], }, // 20
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{ pos: [-1, -1, 1], norm: [ 0, -1, 0], uv: [1, 0], }, // 21
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-
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- { pos: [ 1, -1, -1], norm: [ 0, -1, 0], uv: [0, 1], },
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- { pos: [-1, -1, 1], norm: [ 0, -1, 0], uv: [1, 0], },
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{ pos: [ 1, -1, -1], norm: [ 0, -1, 0], uv: [0, 1], }, // 22
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{ pos: [-1, -1, -1], norm: [ 0, -1, 0], uv: [1, 1], }, // 23
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];
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</pre>
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<p>现在我们有24个唯一的顶点。然后我们为36个要画的顶点设定36个索引，通过调用 <a href="/docs/#api/zh/core/BufferGeometry.setIndex"><code class="notranslate" translate="no">BufferGeometry.setIndex</code></a> 并传入索引数组来创建12个三角形。</p>
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<pre class="prettyprint showlinemods notranslate lang-js" translate="no">geometry.setAttribute(
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'position',
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new THREE.BufferAttribute(positions, positionNumComponents));
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geometry.setAttribute(
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'normal',
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new THREE.BufferAttribute(normals, normalNumComponents));
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geometry.setAttribute(
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'uv',
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new THREE.BufferAttribute(uvs, uvNumComponents));
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+geometry.setIndex([
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+ 0, 1, 2, 2, 1, 3, // front
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+ 4, 5, 6, 6, 5, 7, // right
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+ 8, 9, 10, 10, 9, 11, // back
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+ 12, 13, 14, 14, 13, 15, // left
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+ 16, 17, 18, 18, 17, 19, // top
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+ 20, 21, 22, 22, 21, 23, // bottom
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+]);
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</pre>
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<p></p><div translate="no" class="threejs_example_container notranslate">
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<div><iframe class="threejs_example notranslate" translate="no" style=" " src="/manual/examples/resources/editor.html?url=/manual/examples/custom-buffergeometry-cube-indexed.html"></iframe></div>
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<a class="threejs_center" href="/manual/examples/custom-buffergeometry-cube-indexed.html" target="_blank">点击此处在新标签页中打开</a>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
<p></p>
|
||
|
|
<p>如果你没有提供法线数据的话， <a href="/docs/#api/zh/core/BufferGeometry"><code class="notranslate" translate="no">BufferGeometry</code></a> 有个方法<a href="/docs/#api/zh/core/BufferGeometry#computeVertexNormals"><code class="notranslate" translate="no">computeVertexNormals</code></a>可以用来计算法线。不幸的是，因为如果顶点的其他数据不同的话，位置数据不能被共享，调用 <code class="notranslate" translate="no">computeVertexNormals</code> 会让你的几何体像球面或者圆筒一样连接自身。</p>
|
||
|
|
<div class="spread">
|
||
|
|
<div>
|
||
|
|
<div data-diagram="bufferGeometryCylinder"></div>
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
<p>对于上面的圆筒，法线是通过 <code class="notranslate" translate="no">computeVertexNormals</code> 方法创建的。
|
||
|
|
如果你仔细观察会发现在圆筒上有条缝。这是因为在圆筒的开始和结束的地方没有办法共享顶点数据，需要不同的UVs，所以该方法不知道它们是同样的顶点以平滑过度。只要知道一点，解决方法是应用自己的法线数据。</p>
|
||
|
|
<p>我们同样可以在一开始使用类型数组<a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray">TypedArrays</a>取代JavaScript的原生数组。
|
||
|
|
缺点是你必须在一开始定义数组的大小。当然那不是很难，但是使用原生数组我们只需要用 <code class="notranslate" translate="no">push</code> 将数据加入数组并最后通过 <code class="notranslate" translate="no">length</code> 查看数组大小。使用类型数组我们没有这样的方法，所以需要记录添加的数据。</p>
|
||
|
|
<p>在这个例子，提前计算数组长度很简单，因为我们一开始使用一大块静态数据。</p>
|
||
|
|
<pre class="prettyprint showlinemods notranslate lang-js" translate="no">-const positions = [];
|
||
|
|
-const normals = [];
|
||
|
|
-const uvs = [];
|
||
|
|
+const numVertices = vertices.length;
|
||
|
|
+const positionNumComponents = 3;
|
||
|
|
+const normalNumComponents = 3;
|
||
|
|
+const uvNumComponents = 2;
|
||
|
|
+const positions = new Float32Array(numVertices * positionNumComponents);
|
||
|
|
+const normals = new Float32Array(numVertices * normalNumComponents);
|
||
|
|
+const uvs = new Float32Array(numVertices * uvNumComponents);
|
||
|
|
+let posNdx = 0;
|
||
|
|
+let nrmNdx = 0;
|
||
|
|
+let uvNdx = 0;
|
||
|
|
for (const vertex of vertices) {
|
||
|
|
- positions.push(...vertex.pos);
|
||
|
|
- normals.push(...vertex.norm);
|
||
|
|
- uvs.push(...vertex.uv);
|
||
|
|
+ positions.set(vertex.pos, posNdx);
|
||
|
|
+ normals.set(vertex.norm, nrmNdx);
|
||
|
|
+ uvs.set(vertex.uv, uvNdx);
|
||
|
|
+ posNdx += positionNumComponents;
|
||
|
|
+ nrmNdx += normalNumComponents;
|
||
|
|
+ uvNdx += uvNumComponents;
|
||
|
|
}
|
||
|
|
|
||
|
|
geometry.setAttribute(
|
||
|
|
'position',
|
||
|
|
- new THREE.BufferAttribute(new Float32Array(positions), positionNumComponents));
|
||
|
|
+ new THREE.BufferAttribute(positions, positionNumComponents));
|
||
|
|
geometry.setAttribute(
|
||
|
|
'normal',
|
||
|
|
- new THREE.BufferAttribute(new Float32Array(normals), normalNumComponents));
|
||
|
|
+ new THREE.BufferAttribute(normals, normalNumComponents));
|
||
|
|
geometry.setAttribute(
|
||
|
|
'uv',
|
||
|
|
- new THREE.BufferAttribute(new Float32Array(uvs), uvNumComponents));
|
||
|
|
+ new THREE.BufferAttribute(uvs, uvNumComponents));
|
||
|
|
|
||
|
|
geometry.setIndex([
|
||
|
|
0, 1, 2, 2, 1, 3, // front
|
||
|
|
4, 5, 6, 6, 5, 7, // right
|
||
|
|
8, 9, 10, 10, 9, 11, // back
|
||
|
|
12, 13, 14, 14, 13, 15, // left
|
||
|
|
16, 17, 18, 18, 17, 19, // top
|
||
|
|
20, 21, 22, 22, 21, 23, // bottom
|
||
|
|
]);
|
||
|
|
</pre>
|
||
|
|
<p></p><div translate="no" class="threejs_example_container notranslate">
|
||
|
|
<div><iframe class="threejs_example notranslate" translate="no" style=" " src="/manual/examples/resources/editor.html?url=/manual/examples/custom-buffergeometry-cube-typedarrays.html"></iframe></div>
|
||
|
|
<a class="threejs_center" href="/manual/examples/custom-buffergeometry-cube-typedarrays.html" target="_blank">点击此处在新标签页中打开</a>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
<p></p>
|
||
|
|
<p>一个使用类型数组的好理由，是如果你想动态更新顶点数据的任何一部分。</p>
|
||
|
|
<p>因为想不起动态更新顶点数据的好例子，所以我决定创建一个球面并从中央开始进进出出地移动每个四边形。但愿它是个有用的例子。</p>
|
||
|
|
<p>这里是用来产生球面的位置和索引数据的代码。代码共享了四边形内的顶点数据，但是四边形之间的没有共享，因为我们需要分别地移动每个四边形。</p>
|
||
|
|
<p>因为我懒，所以我通过3个 <a href="/docs/#api/zh/core/Object3D"><code class="notranslate" translate="no">Object3D</code></a> 对象的层级关系，计算球面的点。关于如何计算在这篇文章有解释<a href="optimize-lots-of-objects.html">the article on optimizing lots of objects</a>。</p>
|
||
|
|
<pre class="prettyprint showlinemods notranslate lang-js" translate="no">function makeSpherePositions(segmentsAround, segmentsDown) {
|
||
|
|
const numVertices = segmentsAround * segmentsDown * 6;
|
||
|
|
const numComponents = 3;
|
||
|
|
const positions = new Float32Array(numVertices * numComponents);
|
||
|
|
const indices = [];
|
||
|
|
|
||
|
|
const longHelper = new THREE.Object3D();
|
||
|
|
const latHelper = new THREE.Object3D();
|
||
|
|
const pointHelper = new THREE.Object3D();
|
||
|
|
longHelper.add(latHelper);
|
||
|
|
latHelper.add(pointHelper);
|
||
|
|
pointHelper.position.z = 1;
|
||
|
|
const temp = new THREE.Vector3();
|
||
|
|
|
||
|
|
function getPoint(lat, long) {
|
||
|
|
latHelper.rotation.x = lat;
|
||
|
|
longHelper.rotation.y = long;
|
||
|
|
longHelper.updateMatrixWorld(true);
|
||
|
|
return pointHelper.getWorldPosition(temp).toArray();
|
||
|
|
}
|
||
|
|
|
||
|
|
let posNdx = 0;
|
||
|
|
let ndx = 0;
|
||
|
|
for (let down = 0; down < segmentsDown; ++down) {
|
||
|
|
const v0 = down / segmentsDown;
|
||
|
|
const v1 = (down + 1) / segmentsDown;
|
||
|
|
const lat0 = (v0 - 0.5) * Math.PI;
|
||
|
|
const lat1 = (v1 - 0.5) * Math.PI;
|
||
|
|
|
||
|
|
for (let across = 0; across < segmentsAround; ++across) {
|
||
|
|
const u0 = across / segmentsAround;
|
||
|
|
const u1 = (across + 1) / segmentsAround;
|
||
|
|
const long0 = u0 * Math.PI * 2;
|
||
|
|
const long1 = u1 * Math.PI * 2;
|
||
|
|
|
||
|
|
positions.set(getPoint(lat0, long0), posNdx); posNdx += numComponents;
|
||
|
|
positions.set(getPoint(lat1, long0), posNdx); posNdx += numComponents;
|
||
|
|
positions.set(getPoint(lat0, long1), posNdx); posNdx += numComponents;
|
||
|
|
positions.set(getPoint(lat1, long1), posNdx); posNdx += numComponents;
|
||
|
|
|
||
|
|
indices.push(
|
||
|
|
ndx, ndx + 1, ndx + 2,
|
||
|
|
ndx + 2, ndx + 1, ndx + 3,
|
||
|
|
);
|
||
|
|
ndx += 4;
|
||
|
|
}
|
||
|
|
}
|
||
|
|
return {positions, indices};
|
||
|
|
}
|
||
|
|
</pre>
|
||
|
|
<p>然后我们像这样调用。</p>
|
||
|
|
<pre class="prettyprint showlinemods notranslate lang-js" translate="no">const segmentsAround = 24;
|
||
|
|
const segmentsDown = 16;
|
||
|
|
const {positions, indices} = makeSpherePositions(segmentsAround, segmentsDown);
|
||
|
|
</pre>
|
||
|
|
<p>因为返回的位置数据是单位球面位置，所以它们跟我们需要的法线数据完全一样，我们只需要复制它们。</p>
|
||
|
|
<pre class="prettyprint showlinemods notranslate lang-js" translate="no">const normals = positions.slice();
|
||
|
|
</pre>
|
||
|
|
<p>然后我们像之前一样设置属性</p>
|
||
|
|
<pre class="prettyprint showlinemods notranslate lang-js" translate="no">const geometry = new THREE.BufferGeometry();
|
||
|
|
const positionNumComponents = 3;
|
||
|
|
const normalNumComponents = 3;
|
||
|
|
|
||
|
|
+const positionAttribute = new THREE.BufferAttribute(positions, positionNumComponents);
|
||
|
|
+positionAttribute.setUsage(THREE.DynamicDrawUsage);
|
||
|
|
geometry.setAttribute(
|
||
|
|
'position',
|
||
|
|
+ positionAttribute);
|
||
|
|
geometry.setAttribute(
|
||
|
|
'normal',
|
||
|
|
new THREE.BufferAttribute(normals, normalNumComponents));
|
||
|
|
geometry.setIndex(indices);
|
||
|
|
</pre>
|
||
|
|
<p>我已经高亮一些区别。我们保存了位置属性的引用。
|
||
|
|
同时我们标记它为动态。这是提示THREE.js我们将会经常改变属性的内容。</p>
|
||
|
|
<p>在我们的渲染循环中，每一帧我们基于它们的法线更新位置</p>
|
||
|
|
<pre class="prettyprint showlinemods notranslate lang-js" translate="no">const temp = new THREE.Vector3();
|
||
|
|
|
||
|
|
...
|
||
|
|
|
||
|
|
for (let i = 0; i < positions.length; i += 3) {
|
||
|
|
const quad = (i / 12 | 0);
|
||
|
|
const ringId = quad / segmentsAround | 0;
|
||
|
|
const ringQuadId = quad % segmentsAround;
|
||
|
|
const ringU = ringQuadId / segmentsAround;
|
||
|
|
const angle = ringU * Math.PI * 2;
|
||
|
|
temp.fromArray(normals, i);
|
||
|
|
temp.multiplyScalar(THREE.MathUtils.lerp(1, 1.4, Math.sin(time + ringId + angle) * .5 + .5));
|
||
|
|
temp.toArray(positions, i);
|
||
|
|
}
|
||
|
|
positionAttribute.needsUpdate = true;
|
||
|
|
</pre>
|
||
|
|
<p>我们设置 <code class="notranslate" translate="no">positionAttribute.needsUpdate</code> 告诉THREE.js更新我们的改变。</p>
|
||
|
|
<p></p><div translate="no" class="threejs_example_container notranslate">
|
||
|
|
<div><iframe class="threejs_example notranslate" translate="no" style=" " src="/manual/examples/resources/editor.html?url=/manual/examples/custom-buffergeometry-dynamic.html"></iframe></div>
|
||
|
|
<a class="threejs_center" href="/manual/examples/custom-buffergeometry-dynamic.html" target="_blank">点击此处在新标签页中打开</a>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
<p></p>
|
||
|
|
<p>我希望这些例子能对如何使用 <a href="/docs/#api/zh/core/BufferGeometry"><code class="notranslate" translate="no">BufferGeometry</code></a> 直接创建你自己的几何体和如何动态更新 <a href="/docs/#api/zh/core/BufferAttribute"><code class="notranslate" translate="no">BufferAttribute</code></a> 的内容发挥作用。</p>
|
||
|
|
<!-- needed in English only to prevent warning from outdated translations -->
|
||
|
|
<p><a href="resources/threejs-geometry.svg"></a>
|
||
|
|
<a href="custom-geometry.html"></a></p>
|
||
|
|
<p><canvas id="c"></canvas></p>
|
||
|
|
<script type="module" src="../resources/threejs-custom-buffergeometry.js"></script>
|
||
|
|
|
||
|
|
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
<script src="/manual/resources/prettify.js"></script>
|
||
|
|
<script src="/manual/resources/lesson.js"></script>
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
</body></html>
|