浅谈three.js

来源：互联网发布：怎么看淘宝行业数据编辑：程序博客网时间：2024/06/01 10:53

THREE.js可以这么理解three+js，three代表3维世界，js即javascript,这是一个让我们可以在浏览器中绘制3D效果的javascript库，通过webgl为html5 canvas提供硬件3D加速渲染，这样Web开发人员就可以借助系统显卡来在浏览器里更流畅地展示3D场景和模型了.

THREE.js中有三个主要的概念，相机（Camera）、场景（Scene）、Renderer（渲染器）

1.照相机（Camera）

学习Camera之前我们先了解一下THREE.js中使用的坐标系，如图所示：

构造函数
OrthographicCamera(left, right, top, bottom, near, far);
实例说明
camera = new THREE.OrthographicCamera(-2, 2, 1.5, -1.5, 1, 10);
camera.position.set(0, 0, 5);
var cubeGeometry = new THREE.CubeGeometry(1,1,1); //创建一个正方体
var material = new THREE.MeshBasicMaterial({ color : 0xff0000, wireframe : true });
var cube = new THREE.Mesh(cubeGeometry, material);
scene.add(cube);
renderer.render(scene, camera);
但是这里有一个很奇怪的问题，命名创建的是一个长度为1的正方体，为啥投影是长方体？这里canvas面板的长宽比是2:1，但是相机的（right-left）/(top-bottom)比例是4：3，因此 垂直方向上面被压缩了，所以显示的是一个长方体。
将（right-left）/(top-bottom)的比例同样调整为2:1
camera = new THREE.OrthographicCamera(-2, 2, 1, -1, 1, 10);
2.光源(Light)
光是自然界中常见的现象，我们把正在发光的物体成为光源。与光相对立的是阴影，光被物体 
遮挡住了便形成了阴影。根据光照的效果不同，THREE.js中抽象除了几种不同的光源。
•   聚光灯(THREE.SpotLight)
•   平行光源(THREE.DirectionalLight)
•   环境光源(THREE.AmbientLight)
•   半球光源(THREE.HemisphereLight)
•   点光源(THREE.PointLight)
•   聚光灯(SpotLight)
聚光灯像某个方向进行照射的光源，其光照范围呈圆锥状。
构造函数
SpotLight(color, intensity,distance, angle, penumbra, decay);
color：光的颜色
intensity：光的强度
distance：光能照射的最远的距离，按照光的强度按照距离呈线性衰减。
angle：照射的中心点到圆锥上边距的夹角
decay：光线衰减的速率
除了构造函数中的几个属性之外，SpotLight还有一个很重要的属性target，点光源聚焦的地方 ，该属性值是一个Object3D的实例，将target的值设置为一个运动中的物体可以让点光源跟随物体的运动而运动。
THREE.js中只有聚光灯(SpotLight)和平行光源(DirectionalLight)可以产生阴影，这里看看如何让聚光灯产生阴影。 
1>.告诉renderer需要渲染阴影
var renderer = new THREE.WEBGLRenderer();
renderer.shadowMapEnabled = true; or renderer.shadowMap.enabled = true;
2>.告诉THREE.js哪些物体会投射阴影，哪些物体会接收阴影
cubeMesh.castShadow = true; //cubeMesh会在其他的物体上面投射阴影
floorMesh.receiveShadow = true; //floorMesh会接收其他物体在其上投射的阴影
3>.添加聚光灯
var spotLight = new THREE.SpotLight();
spotLight.angle = Math.PI / 8;
spotLight.exponent = 30;
spotLight.position = new THREE.Vector3(40, 60, -50);
scene.add(spotLight);
4>.设置阴影相关的属性
spotLight.castShadow = true;
spotLight.shadow.camera.near = 500;
spotLight.shadow.camera.far = 4000;
spotLight.shadow.camera.fov = 30;
near, far, fov设置投影的区域

5>.设置阴影贴图大小
spotLight.shadow.mapSize.width = 1024;
spotLight.shadow.mapSize.height = 1024;
设置阴影贴图大小，如果发现阴影的边界呈块状，说明阴影贴图太小了，需要设置更大的值
总结实例:
<!DOCTYPE html>
 
<html>
 
<head>
    <title>Example 03.04 - Directional Light</title>
    <script type="text/javascript" src="../libs/three.js"></script>
    <script type="text/javascript" src="../libs/jquery-1.9.0.js"></script>
    <script type="text/javascript" src="../libs/stats.js"></script>
    <script type="text/javascript" src="../libs/dat.gui.js"></script>
    <style>
        body {
            margin: 0;
            overflow: hidden;
        }
    </style>
</head>
<body>
 
<div id="Stats-output">
</div>
<!-- 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 () {
    var stats = initStats();
    // 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(0xEEEEEE, 1.0);
    renderer.setSize(window.innerWidth, window.innerHeight);
    renderer.shadowMapEnabled = true;
    // create the ground plane
    var planeGeometry = new THREE.PlaneGeometry(600, 200, 20, 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 = -5
    plane.position.z = 0
    // add the plane to the scene
    scene.add(plane);
    // create a cube
    var cubeGeometry = new THREE.CubeGeometry(4, 4, 4);
    var cubeMaterial = new THREE.MeshLambertMaterial({color: 0xff3333});
    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);
    // position the sphere
    sphere.position.x = 20;
    sphere.position.y = 0;
    sphere.position.z = 2;
    sphere.castShadow = true;
    // add the sphere to the scene
    scene.add(sphere);
    // position and point the camera to the center of the scene
    camera.position.x = -35;
    camera.position.y = 30;
    camera.position.z = 25;
    camera.lookAt(new THREE.Vector3(10, 0, 0));
    // add subtle ambient lighting
    var ambiColor = "#1c1c1c";
    var ambientLight = new THREE.AmbientLight(ambiColor);
    scene.add(ambientLight);
    var target = new THREE.Object3D();
    target.position = new THREE.Vector3(5, 0, 0);
    var pointColor = "#ff5808";
    var directionalLight = new THREE.DirectionalLight(pointColor);
    directionalLight.position.set(-40, 60, -10);
    directionalLight.castShadow = true;
    directionalLight.shadowCameraNear = 2;
    directionalLight.shadowCameraFar = 200;
    directionalLight.shadowCameraLeft = -50;
    directionalLight.shadowCameraRight = 50;
    directionalLight.shadowCameraTop = 50;
    directionalLight.shadowCameraBottom = -50;
 
    directionalLight.distance = 0;
    directionalLight.intensity = 0.5;
    directionalLight.shadowMapHeight = 1024;
    directionalLight.shadowMapWidth = 1024;
    scene.add(directionalLight);
    // add a small sphere simulating the pointlight
    var sphereLight = new THREE.SphereGeometry(0.2);
    var sphereLightMaterial = new THREE.MeshBasicMaterial({color: 0xac6c25});
    var sphereLightMesh = new THREE.Mesh(sphereLight, sphereLightMaterial);
    sphereLightMesh.castShadow = true;
    sphereLightMesh.position = new THREE.Vector3(3, 20, 3);
    scene.add(sphereLightMesh);
    // add the output of the renderer to the html element
    $("#WebGL-output").append(renderer.domElement);
    // call the render function
    var step = 0;
    // used to determine the switch point for the light animation
    var invert = 1;
    var phase = 0;
    var controls = new function () {
        this.rotationSpeed = 0.03;
        this.bouncingSpeed = 0.03;
        this.ambientColor = ambiColor;
        this.pointColor = pointColor;
        this.intensity = 0.5;
        this.distance = 0;
        this.exponent = 30;
        this.angle = 0.1;
        this.debug = false;
        this.castShadow = true;
        this.onlyShadow = false;
        this.target = "Plane";
    }
    var gui = new dat.GUI();
    gui.addColor(controls, 'ambientColor').onChange(function (e) {
        ambientLight.color = new THREE.Color(e);
    });
    gui.addColor(controls, 'pointColor').onChange(function (e) {
        directionalLight.color = new THREE.Color(e);
    });
    gui.add(controls, 'intensity', 0, 5).onChange(function (e) {
        directionalLight.intensity = e;
    });
    gui.add(controls, 'distance', 0, 200).onChange(function (e) {
        directionalLight.distance = e;
    });
    gui.add(controls, 'debug').onChange(function (e) {
        directionalLight.shadowCameraVisible = e;
    });
    gui.add(controls, 'castShadow').onChange(function (e) {
        directionalLight.castShadow = e;
    });
    gui.add(controls, 'onlyShadow').onChange(function (e) {
        directionalLight.onlyShadow = e;
    });
    gui.add(controls, 'target', ['Plane', 'Sphere', 'Cube']).onChange(function (e) {
        console.log(e);
        switch (e) {
            case "Plane":
                directionalLight.target = plane;
                break;
            case "Sphere":
                directionalLight.target = sphere;
                break;
            case "Cube":
                directionalLight.target = cube;
                break;
        }
    });
    render();
    function render() {
        stats.update();
        // rotate the cube around its axes
        cube.rotation.x += controls.rotationSpeed;
        cube.rotation.y += controls.rotationSpeed;
        cube.rotation.z += controls.rotationSpeed;
        // bounce the sphere up and down
        step += controls.bouncingSpeed;
        sphere.position.x = 20 + ( 10 * (Math.cos(step)));
        sphere.position.y = 2 + ( 10 * Math.abs(Math.sin(step)));
        sphereLightMesh.position.z = -8;
        sphereLightMesh.position.y = +(27 * (Math.sin(step / 3)));
        sphereLightMesh.position.x = 10 + (26 * (Math.cos(step / 3)));
        directionalLight.position = sphereLightMesh.position;
        // render using requestAnimationFrame
        requestAnimationFrame(render);
        renderer.render(scene, camera);
    }
 
    function initStats() {
        var stats = new Stats();
        stats.setMode(0); // 0: fps, 1: ms
        // Align top-left
        stats.domElement.style.position = 'absolute';
        stats.domElement.style.left = '0px';
        stats.domElement.style.top = '0px';
        $("#Stats-output").append(stats.domElement);
        return stats;
    }
});
</script>
</body>
</html>

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