ThreeJS学习|创建第一个三维场景

vlambda
2020-08-16

ThreeJS学习|创建第一个三维场景

概述

由于自己需要学点ThreeJS相关的东西，因此就用推文的形式记录自己所学。乐忠于寻求一起学习的朋友 ThreeJS学习|创建第一个三维场景（部分代码来源于教材，有删改！）

ThreeJS

如今浏览器的功能越来越强大,而且这些功能可以通过 JavaScript直接调用。你可以用HTML5标签轻松地添加视频和音频,而且可以在HTML5画布上创建各种交互组件。现在这个功能集合里又有了一个新成员,即支持 WebGL。通过 WebGL,你可以直接使用显卡的计算资源,创建高性能的二维和三维计算机图形,然后在 JavaScript里直接使用 WebGL编程,创建三维场景并生成动画,这个过程非常复杂,而且容易出错。Three js库可以简化这个过程。

Threejs可以帮助我们的地方如下:

创建简单的和复杂的三维图形
在三维场景中生成动画、移动物体
在物体上应用纹理和材质
从三维建模软件中加载图形
创建基于样条曲线的二维图形

创建场景

1.创建HTML页面框架

首先需要创建一个HTML框架，这样后面的代码只需要在此基础上添加即可。HTML页面框架如下所示。

<!DOCTYPE html>
<html>
<head> <title>Example 01.01 - Basic skeleton</title> <script type="text/javascript" src="../libs/three.js"></script> <script type="text/javascript" src="../libs/jquery-1.9.0.js"></script> <style> body { margin: 0; overflow: hidden; }</style></head><body>
<div id="WebGL-output"></div>
<script type="text/javascript">
 function init() { } window.onload = init</script></body></html>

从上述代码可以看出这个框架是一个非常简单的HTML页面,上面只有寥寥几个元素。在<head>元素里我们会加载本书示例中用到的外部 JavaScript库。当我们写 Three js程序代码时,会把 Three js渲染器的输出指向这个元素。在前面的代码片段里,你会看到已经有几行 JavaScript代码了这一小段代码的作用是在页面加载结束时,使用 jQuery调用一个匿名的 JavaScript函数。我们所有的 Threejs程序代码都写在这个匿名函数里。

2.渲染并展示三维图像

现在需要在第一步创建的场景中添加对象，本次添加几个物体和一个相机。

<script type="text/javascript">
 // once everything is loaded, we run our Three.js stuff. function init() {
 // create a scene, that will hold all our elements such as objects, cameras and lights. var scene = new THREE.Scene();
 // create a camera, which defines where we're looking at. var camera = new THREE.PerspectiveCamera(45, window.innerWidth / window.innerHeight, 0.1, 1000);
 // create a render and set the size var renderer = new THREE.WebGLRenderer(); renderer.setClearColorHex(); renderer.setClearColor(new THREE.Color(0xEEEEEE)); renderer.setSize(window.innerWidth, window.innerHeight);
 // show axes in the screen var axes = new THREE.AxisHelper(20); scene.add(axes);
 // create the ground plane var planeGeometry = new THREE.PlaneGeometry(60, 20); var planeMaterial = new THREE.MeshBasicMaterial({color: 0xcccccc}); var plane = new THREE.Mesh(planeGeometry, planeMaterial);
 // rotate and position the plane plane.rotation.x = -0.5 * Math.PI; plane.position.x = 15; plane.position.y = 0; plane.position.z = 0;
 // add the plane to the scene scene.add(plane);
 // create a cube var cubeGeometry = new THREE.BoxGeometry(4, 4, 4); var cubeMaterial = new THREE.MeshBasicMaterial({color: 0xff0000, wireframe: true}); var cube = new THREE.Mesh(cubeGeometry, cubeMaterial);
 // position the cube cube.position.x = -4; cube.position.y = 3; cube.position.z = 0;
 // add the cube to the scene scene.add(cube);
 // create a sphere var sphereGeometry = new THREE.SphereGeometry(4, 20, 20); var sphereMaterial = new THREE.MeshBasicMaterial({color: 0x7777ff, wireframe: true}); var sphere = new THREE.Mesh(sphereGeometry, sphereMaterial);
 // position the sphere sphere.position.x = 20; sphere.position.y = 4; sphere.position.z = 2;
 // add the sphere to the scene scene.add(sphere);
 // position and point the camera to the center of the scene camera.position.x = -30; camera.position.y = 40; camera.position.z = 30; camera.lookAt(scene.position);
 // add the output of the renderer to the html element document.getElementById("WebGL-output").appendChild(renderer.domElement);
 // render the scene renderer.render(scene, camera); } window.onload = init;</script>

在本示例中我们定义了 scene(场景)、 camera(相机)和 renderer(渲染器)。变量 scene是一个容器,用来保存并跟踪所有我们想渲染的物体。我们想要渲染的球体和方块会在本例后面添加到这个 scene变量中。在这个例子中我们还创建了一个 camera变量。 camera变量定义了我们能够在渲染好的 scene里看到什么。接下来,我们定义了一个renderer对象。renderer对象负责计算指定相机角度下,浏览器中 scene的样子。在这个示例里我们创建了一个WebGLRenderer对象,使用计算机上的显卡来渲染场景。

3.添加材质、灯光和阴影

添加材质的前提是添加一个光源，然后在原有基础上修改即可。

// add spotlight for the shadowsvar spotLight = new THREE.SpotLight(0xffffff);spotLight.position.set(-40, 60, -10);spotLight.castShadow = true;scene.add(spotLight);

通过 SpotLight方法创建一个光源,并从( spotLight. position.set(-40,60,-10)位置处照射我们的场景。如果我们现在就渲染场景,那么结果跟之前的场景没什么区别。原因是不同的材质对光源的反应并不相同。我们在前一个示例中用的基础材质(调用 Mesh BasicMaterialO方法)不会对场景中的光源产生反应,而只会以指定的颜色渲染物体。所以我们不得不改变 plane、 sphere和cube的材质。

<!DOCTYPE html>
<html>
<head> <title>Example 01.03 - Materials and light</title> <script type="text/javascript" src="../libs/three.js"></script> <script type="text/javascript" src="../libs/stats.js"></script> <script type="text/javascript" src="../libs/dat.gui.js"></script> <style> body { /* set margin to 0 and overflow to hidden, to go fullscreen */ margin: 0; overflow: hidden; }</style></head><body>
<!-- Div which will hold the Output --><div id="WebGL-output"></div>
<!-- Javascript code that runs our Three.js examples --><script type="text/javascript">
 // once everything is loaded, we run our Three.js stuff. function init() {
 // create a scene, that will hold all our elements such as objects, cameras and lights. var scene = new THREE.Scene();
 // create a camera, which defines where we're looking at. var camera = new THREE.PerspectiveCamera(45, window.innerWidth / window.innerHeight, 0.1, 1000);
 // create a render and set the size var renderer = new THREE.WebGLRenderer();
 renderer.setClearColor(new THREE.Color(0xEEEEEE, 1.0)); renderer.setSize(window.innerWidth, window.innerHeight); renderer.shadowMapEnabled = true;
 // create the ground plane var planeGeometry = new THREE.PlaneGeometry(60, 20); var planeMaterial = new THREE.MeshLambertMaterial({color: 0xffffff}); var plane = new THREE.Mesh(planeGeometry, planeMaterial); plane.receiveShadow = true;
 // rotate and position the plane plane.rotation.x = -0.5 * Math.PI; plane.position.x = 15; plane.position.y = 0; plane.position.z = 0;
 // add the plane to the scene scene.add(plane);
 // create a cube var cubeGeometry = new THREE.BoxGeometry(4, 4, 4); var cubeMaterial = new THREE.MeshLambertMaterial({color: 0xff0000}); var cube = new THREE.Mesh(cubeGeometry, cubeMaterial); cube.castShadow = true;
 // position the cube cube.position.x = -4; cube.position.y = 3; cube.position.z = 0;
 // add the cube to the scene scene.add(cube);
 var sphereGeometry = new THREE.SphereGeometry(4, 20, 20); var sphereMaterial = new THREE.MeshLambertMaterial({color: 0x7777ff}); var sphere = new THREE.Mesh(sphereGeometry, sphereMaterial); sphere.castShadow = true;
 // position the sphere sphere.position.x = 20; sphere.position.y = 4; sphere.position.z = 2;

 // add the sphere to the scene scene.add(sphere);
 // position and point the camera to the center of the scene camera.position.x = -30; camera.position.y = 40; camera.position.z = 30; camera.lookAt(scene.position);
 // add spotlight for the shadows var spotLight = new THREE.SpotLight(0xffffff); spotLight.position.set(-40, 60, -10); spotLight.castShadow = true; scene.add(spotLight);
 // add the output of the renderer to the html element document.getElementById("WebGL-output").appendChild(renderer.domElement);
 // call the render function renderer.render(scene, camera); } window.onload = init;</script></body></html>