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<h1>Canvas 纹理</h1>
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<p>这篇文章是此篇 <a href="textures.html">关于纹理</a> 文章的延续，如果你还没有读过，你或许应当从那篇开始。</p>
<p>在<a href="textures.html">上一篇讲解纹理的文章中</a>，我们主要使用图像文件来生成动态纹理，有时候我们想在运行时生成一个纹理。一种可行的方式是使用 <a href="/docs/#api/en/textures/CanvasTexture"><code class="notranslate" translate="no">CanvasTexture</code></a>。</p>
<p>Canvas纹理 使用一个<code class="notranslate" translate="no"><canvas></code> 作为它的输入， 如果你还不知道如何使用2D Canvas API来在画布上绘制内容，<a href="https://developer.mozilla.org/en-US/docs/Web/API/Canvas_API/Tutorial">MDN上有一篇很好的文章</a>。</p>
<p>我们来写一段简单的Canvas代码，这是一个在随机位置上绘制随机颜色的点的程序。</p>
<pre class="prettyprint showlinemods notranslate lang-js" translate="no">const ctx = document.createElement('canvas').getContext('2d');
document.body.appendChild(ctx.canvas);
ctx.canvas.width = 256;
ctx.canvas.height = 256;
ctx.fillStyle = '#FFF';
ctx.fillRect(0, 0, ctx.canvas.width, ctx.canvas.height);
function randInt(min, max) {
if (max === undefined) {
max = min;
min = 0;
}
return Math.random() * (max - min) + min | 0;
}
function drawRandomDot() {
ctx.fillStyle = `#${randInt(0x1000000).toString(16).padStart(6, '0')}`;
ctx.beginPath();
const x = randInt(256);
const y = randInt(256);
const radius = randInt(10, 64);
ctx.arc(x, y, radius, 0, Math.PI * 2);
ctx.fill();
}
function render() {
drawRandomDot();
requestAnimationFrame(render);
}
requestAnimationFrame(render);</pre>
<p>这实在太简单了。</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/canvas-random-dots.html"></iframe></div>
<a class="threejs_center" href="/manual/examples/canvas-random-dots.html" target="_blank">点击在新窗口打开</a>
</div>
<p></p>
<p>现在让我们用它来绘制纹理。我们会用从 <a href="textures.html">上一篇文章</a> 中绘制立方体纹理的例子开始。
我们将删除加载图像的代码，取而代之的是使用我们的Canvas，通过创建一个<a href="/docs/#api/en/textures/CanvasTexture"><code class="notranslate" translate="no">CanvasTexture</code></a>，然后把我们创建好的Canvas对象传入。</p>
<pre class="prettyprint showlinemods notranslate lang-js" translate="no">const cubes = []; // 我们使用这个数组来旋转这些立方体
-const loader = new THREE.TextureLoader();
-
+const ctx = document.createElement('canvas').getContext('2d');
+ctx.canvas.width = 256;
+ctx.canvas.height = 256;
+ctx.fillStyle = '#FFF';
+ctx.fillRect(0, 0, ctx.canvas.width, ctx.canvas.height);
+const texture = new THREE.CanvasTexture(ctx.canvas);
const material = new THREE.MeshBasicMaterial({
- map: loader.load('resources/images/wall.jpg'),
+ map: texture,
});
const cube = new THREE.Mesh(geometry, material);
scene.add(cube);
cubes.push(cube); // 添加到cube list中方便旋转</pre>
<p>然后调用代码，在我们的渲染循环中绘制一个随机点。</p>
<pre class="prettyprint showlinemods notranslate lang-js" translate="no">function render(time) {
time *= 0.001;
if (resizeRendererToDisplaySize(renderer)) {
const canvas = renderer.domElement;
camera.aspect = canvas.clientWidth / canvas.clientHeight;
camera.updateProjectionMatrix();
}
+ drawRandomDot();
+ texture.needsUpdate = true;
cubes.forEach((cube, ndx) => {
const speed = .2 + ndx * .1;
const rot = time * speed;
cube.rotation.x = rot;
cube.rotation.y = rot;
});
renderer.render(scene, camera);
requestAnimationFrame(render);
}</pre>
<p>我们只需要做额外的一件事，设置了 <a href="/docs/#api/en/textures/CanvasTexture"><code class="notranslate" translate="no">CanvasTexture</code></a> 的 <code class="notranslate" translate="no">needsUpdate</code>属性来告诉THREE.js来更新纹理画布的最新内容。</p>
<p>这样，我们就有了一个用Canvas绘制纹理的立方体。</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/canvas-textured-cube.html"></iframe></div>
<a class="threejs_center" href="/manual/examples/canvas-textured-cube.html" target="_blank">点击在新窗口打开</a>
</div>
<p></p>
<p>请注意，如果你想使用THREE.js绘制到Canvas中，你最好用 <code class="notranslate" translate="no">RenderTarget</code>，在 <a href="rendertargets.html">这篇文章</a> 中有提到。</p>
<p>纹理画布的一个常见用法是在场景中绘制文本。例如，你想把一个人的名字放在他们角色上面作为一个徽标(Badge)，你也许需要使用Canvas来绘制徽标纹理。</p>
<p>让我们创建一个有3个人的场景，并给每个人绘制一个徽标或者标签(Label)。</p>
<p>让我们用上面的例子，移除所有相关的立方体。然后设置背景为白色，然后添加两个<a href="lights.html">灯光</a>。</p>
<pre class="prettyprint showlinemods notranslate lang-js" translate="no">const scene = new THREE.Scene();
+scene.background = new THREE.Color('white');
+
+function addLight(position) {
+ const color = 0xFFFFFF;
+ const intensity = 1;
+ const light = new THREE.DirectionalLight(color, intensity);
+ light.position.set(...position);
+ scene.add(light);
+ scene.add(light.target);
+}
+addLight([-3, 1, 1]);
+addLight([ 2, 1, .5]);</pre>
<p>让我们写一些代码以使用2D Canvas绘制标签</p>
<pre class="prettyprint showlinemods notranslate lang-js" translate="no">+function makeLabelCanvas(size, name) {
+ const borderSize = 2;
+ const ctx = document.createElement('canvas').getContext('2d');
+ const font = `${size}px bold sans-serif`;
+ ctx.font = font;
+ // 测量一下name有多长
+ const doubleBorderSize = borderSize * 2;
+ const width = ctx.measureText(name).width + doubleBorderSize;
+ const height = size + doubleBorderSize;
+ ctx.canvas.width = width;
+ ctx.canvas.height = height;
+
+ // 注意，调整画布后需要重新修改字体
+ ctx.font = font;
+ ctx.textBaseline = 'top';
+
+ ctx.fillStyle = 'blue';
+ ctx.fillRect(0, 0, width, height);
+ ctx.fillStyle = 'white';
+ ctx.fillText(name, borderSize, borderSize);
+
+ return ctx.canvas;
+}</pre>
<p>然后我们将用一个圆柱体作为身体，一个球体作为头部，一个平面作为标签来制作一个简单的人。</p>
<p>首先我们开始制作共享几何体。</p>
<pre class="prettyprint showlinemods notranslate lang-js" translate="no">+const bodyRadiusTop = .4;
+const bodyRadiusBottom = .2;
+const bodyHeight = 2;
+const bodyRadialSegments = 6;
+const bodyGeometry = new THREE.CylinderGeometry(
+ bodyRadiusTop, bodyRadiusBottom, bodyHeight, bodyRadialSegments);
+
+const headRadius = bodyRadiusTop * 0.8;
+const headLonSegments = 12;
+const headLatSegments = 5;
+const headGeometry = new THREE.SphereGeometry(
+ headRadius, headLonSegments, headLatSegments);
+
+const labelGeometry = new THREE.PlaneGeometry(1, 1);</pre>
<p>然后我们写一个函数把这些部分组合成一个人。</p>
<pre class="prettyprint showlinemods notranslate lang-js" translate="no">+function makePerson(x, size, name, color) {
+ const canvas = makeLabelCanvas(size, name);
+ const texture = new THREE.CanvasTexture(canvas);
+ // 因为我们的Canvas长宽都不太可能是2的倍数，所以将filtering设置合理一些
+ texture.minFilter = THREE.LinearFilter;
+ texture.wrapS = THREE.ClampToEdgeWrapping;
+ texture.wrapT = THREE.ClampToEdgeWrapping;
+
+ const labelMaterial = new THREE.MeshBasicMaterial({
+ map: texture,
+ side: THREE.DoubleSide,
+ transparent: true,
+ });
+ const bodyMaterial = new THREE.MeshPhongMaterial({
+ color,
+ flatShading: true,
+ });
+
+ const root = new THREE.Object3D();
+ root.position.x = x;
+
+ const body = new THREE.Mesh(bodyGeometry, bodyMaterial);
+ root.add(body);
+ body.position.y = bodyHeight / 2;
+
+ const head = new THREE.Mesh(headGeometry, bodyMaterial);
+ root.add(head);
+ head.position.y = bodyHeight + headRadius * 1.1;
+
+ const label = new THREE.Mesh(labelGeometry, labelMaterial);
+ root.add(label);
+ label.position.y = bodyHeight * 4 / 5;
+ label.position.z = bodyRadiusTop * 1.01;
+
+ // 如果单位是米， 那这里0.01就是将标签的尺寸转化为厘米
+ const labelBaseScale = 0.01;
+ label.scale.x = canvas.width * labelBaseScale;
+ label.scale.y = canvas.height * labelBaseScale;
+
+ scene.add(root);
+ return root;
+}</pre>
<p>在上面你可以看到，我们把身体、头部、标签放在了一个根<a href="/docs/#api/en/core/Object3D"><code class="notranslate" translate="no">Object3D</code></a> 上并且调整了他们的位置。这样如果我们想移动人的话直接移动根对象就可以了。身体是2个单位的高度，如果1个单位等于1米，那么上面的代码会尝试用厘米为单位制作标签，它们使用厘米作为宽高，以更好的适合文本。</p>
<p>然后我们可以制作带标签的人</p>
<pre class="prettyprint showlinemods notranslate lang-js" translate="no">+makePerson(-3, 32, 'Purple People Eater', 'purple');
+makePerson(-0, 32, 'Green Machine', 'green');
+makePerson(+3, 32, 'Red Menace', 'red');</pre>
<p>剩下的就是添加 <a href="/docs/#examples/controls/OrbitControls"><code class="notranslate" translate="no">OrbitControls</code></a> 这样我们就可以移动相机了。</p>
<pre class="prettyprint showlinemods notranslate lang-js" translate="no">import * as THREE from 'three';
+import {OrbitControls} from 'three/addons/controls/OrbitControls.js';</pre>
<pre class="prettyprint showlinemods notranslate lang-js" translate="no">const fov = 75;
const aspect = 2; // Canvas默认值
const near = 0.1;
-const far = 5;
+const far = 50;
const camera = new THREE.PerspectiveCamera(fov, aspect, near, far);
-camera.position.z = 2;
+camera.position.set(0, 2, 5);
+const controls = new OrbitControls(camera, canvas);
+controls.target.set(0, 2, 0);
+controls.update();</pre>
<p>然后我们得到了一些简单的标签。</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/canvas-textured-labels.html"></iframe></div>
<a class="threejs_center" href="/manual/examples/canvas-textured-labels.html" target="_blank">点击在新窗口打开</a>
</div>
<p></p>
<p>注意事项：</p>
<ul>
<li>如果你过度放大，标签的分辨率会降低。</li>
</ul>
<p>没有简单的解决方案，还有更复杂的字体渲染技术，据我所知没有插件可以解决这个问题。另外，还需要用户下载字体数据文件，这会变得很慢。</p>
<p>一种方案是增加标签的分辨率，尝试让尺寸变成现在的2倍，然后设置 <code class="notranslate" translate="no">labelBaseScale</code> 是现在的一半。</p>
<ul>
<li>名字越长，标签越长。</li>
</ul>
<p>如果你想解决这个问题，你需要指定标签的固定大小，然后挤压文本。</p>
<p>这很容易做到。传入一个基本宽度并缩放文本以适应。</p>
<pre class="prettyprint showlinemods notranslate lang-js" translate="no">-function makeLabelCanvas(size, name) {
+function makeLabelCanvas(baseWidth, size, name) {
const borderSize = 2;
const ctx = document.createElement('canvas').getContext('2d');
const font = `${size}px bold sans-serif`;
ctx.font = font;
// 测量一下name有多长
+ const textWidth = ctx.measureText(name).width;
const doubleBorderSize = borderSize * 2;
- const width = ctx.measureText(name).width + doubleBorderSize;
+ const width = baseWidth + doubleBorderSize;
const height = size + doubleBorderSize;
ctx.canvas.width = width;
ctx.canvas.height = height;
// 注意，调整画布后需要重新修改字体
ctx.font = font;
- ctx.textBaseline = 'top';
+ ctx.textBaseline = 'middle';
+ ctx.textAlign = 'center';
ctx.fillStyle = 'blue';
ctx.fillRect(0, 0, width, height);
+ // 缩放以适应，但是不要拉伸
+ const scaleFactor = Math.min(1, baseWidth / textWidth);
+ ctx.translate(width / 2, height / 2);
+ ctx.scale(scaleFactor, 1);
ctx.fillStyle = 'white';
ctx.fillText(name, borderSize, borderSize);
return ctx.canvas;
}</pre>
<p>然后我们可以传入预期标签的长度</p>
<pre class="prettyprint showlinemods notranslate lang-js" translate="no">-function makePerson(x, size, name, color) {
- const canvas = makeLabelCanvas(size, name);
+function makePerson(x, labelWidth, size, name, color) {
+ const canvas = makeLabelCanvas(labelWidth, size, name);
...
}
-makePerson(-3, 32, 'Purple People Eater', 'purple');
-makePerson(-0, 32, 'Green Machine', 'green');
-makePerson(+3, 32, 'Red Menace', 'red');
+makePerson(-3, 150, 32, 'Purple People Eater', 'purple');
+makePerson(-0, 150, 32, 'Green Machine', 'green');
+makePerson(+3, 150, 32, 'Red Menace', 'red');</pre>
<p>我们将文本居中并缩放以适应标签的尺寸。</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/canvas-textured-labels-scale-to-fit.html"></iframe></div>
<a class="threejs_center" href="/manual/examples/canvas-textured-labels-scale-to-fit.html" target="_blank">点击在新窗口打开</a>
</div>
<p></p>
<p>上面我们为每一个纹理使用了单独的Canvas，是否为每个纹理使用单独的Canvas取决于你。如果你需要经常单独更新它们，每个纹理一个Canvas是一个比较好的选择。如果它们很少或者从不更新，那么你可以用一个Canvas，通过THREE.js来生成多个纹理。让我们更改上面的代码来完成这一点。</p>
<pre class="prettyprint showlinemods notranslate lang-js" translate="no">+const ctx = document.createElement('canvas').getContext('2d');
function makeLabelCanvas(baseWidth, size, name) {
const borderSize = 2;
- const ctx = document.createElement('canvas').getContext('2d');
const font = `${size}px bold sans-serif`;
...
}
+const forceTextureInitialization = function() {
+ const material = new THREE.MeshBasicMaterial();
+ const geometry = new THREE.PlaneGeometry();
+ const scene = new THREE.Scene();
+ scene.add(new THREE.Mesh(geometry, material));
+ const camera = new THREE.Camera();
+
+ return function forceTextureInitialization(texture) {
+ material.map = texture;
+ renderer.render(scene, camera);
+ };
+}();
function makePerson(x, labelWidth, size, name, color) {
const canvas = makeLabelCanvas(labelWidth, size, name);
const texture = new THREE.CanvasTexture(canvas);
// 因为我们的Canvas长宽都不太可能是2的倍数，所以将filtering设置合理一些
texture.minFilter = THREE.LinearFilter;
texture.wrapS = THREE.ClampToEdgeWrapping;
texture.wrapT = THREE.ClampToEdgeWrapping;
+ forceTextureInitialization(texture);
...</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/canvas-textured-labels-one-canvas.html"></iframe></div>
<a class="threejs_center" href="/manual/examples/canvas-textured-labels-one-canvas.html" target="_blank">点击在新窗口打开</a>
</div>
<p></p>
<p>另一个问题是标签并不总是面向相机，如果你使用标签作为徽标，这可能是一件好事。
如果你使用标签来放置3D游戏中玩家的名字，也许你希望标签总是面对相机。
具体内容在 <a href="billboards.html">广告牌(Billboards)文章</a> 有覆盖到。</p>
<p>特别是对于标签，<a href="align-html-elements-to-3d.html">另一种解决方案是使用HTML</a>，
本文中的标签是 <em>位于3D场景中</em> ，如果你想要他们被其他对象遮挡是很好的，因为 <a href="align-html-elements-to-3d.html">HTML 标签</a> 总是在最上层。
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