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Three.js学习之网格

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前言

　　小编之前发布过关于几何形状和材质，相信大家看过学习之后，我们就能使用他们来创建物体了。最常用的一种物体就是网格（Mesh），网格是由顶点、边、面等组成的物体；其他物体包括线段（Line）、骨骼（Bone）、粒子系统（ParticleSystem）等。创建物体需要指定几何形状和材质，其中，几何形状决定了物体的顶点位置等信息，材质决定了物体的颜色、纹理等信息。

1.创建网格

　　在前几篇中，我们学习了如何创建几何形状与材质，而网格的创建非常简单，只要把几何形状与材质传入其构造函数。最常用的物体是网格（Mesh），它代表包含点、线、面的几何体，其构造函数是：

Mesh(geometry, material)

　　下面，让我们通过一个具体的例子了解如何创建网格：

var material = new THREE.MeshLambertMaterial({

 color: 0xffff00

});

var geometry = new THREE.CubeGeometry(1, 2, 3);

var mesh = new THREE.Mesh(geometry, material);

scene.add(mesh);

　　如果material和geometry之后不会复用的话，也可以合在一起写为：

var mesh = new THREE.Mesh(new THREE.CubeGeometry(1, 2, 3),

 new THREE.MeshLambertMaterial({

  color: 0xffff00

 })

);

scene.add(mesh);

　　添加光照后，得到的效果为：

　　如果不指定material，则每次会随机分配一种wireframe为true的材质，每次刷新页面后的颜色是不同的，一种可能的效果是：

　　源码：

<!DOCTYPE html>
<html>
 <head>
  <meta charset="UTF-8">
  <title>3.js测试9.1</title> 
 </head>
 <body onload="init()">
  <canvas id="mainCanvas" width="400px" height="300px" ></canvas>
 </body>
 <script type="text/javascript" src="js/three.min.js"></script>
 <script type="text/javascript">
  function init() {
   var renderer = new THREE.WebGLRenderer({
    canvas: document.getElementById('mainCanvas')
   });
   renderer.setClearColor(0x000000);
   var scene = new THREE.Scene();
   
   // camera
   var camera = new THREE.OrthographicCamera(-2.5, 2.5, 1.875, -1.875, 0.1, 100);
   camera.position.set(5, 5, 20);
   camera.lookAt(new THREE.Vector3(0, 0, 0));
   scene.add(camera);
   
   var material = new THREE.MeshLambertMaterial({
    color: 0xffff00
   });
//   var material = new THREE.MeshBasicMaterial({
//    color: 0xffff00,
//    wireframe: true
//   });
   var geometry = new THREE.CubeGeometry(1, 2, 3);
   var mesh = new THREE.Mesh(geometry, material);
   scene.add(mesh);
   
   var light = new THREE.DirectionalLight(0xffffff);
   light.position.set(20, 10, 5);
   scene.add(light);
   
   // render
   renderer.render(scene, camera);
  }
 </script>
</html>
 

2.修改属性

　　2.1 修改材质

　　除了在构造函数中指定材质，在网格被创建后，也能对材质进行修改：

var material = new THREE.MeshLambertMaterial({

 color: 0xffff00

});

var geometry = new THREE.CubeGeometry(1, 2, 3);

var mesh = new THREE.Mesh(geometry, material);

 scene.add(mesh);

mesh.material = new THREE.MeshLambertMaterial({

 color: 0xff0000

});

　　最终显示的颜色是红色：

　　源码：

<!DOCTYPE html>
<html>
 <head>
  <meta charset="UTF-8">
  <title>3.js测试9.2</title> 
 </head>
 <body onload="init()">
  <canvas id="mainCanvas" width="400px" height="300px" ></canvas>
 </body>
 <script type="text/javascript" src="js/three.min.js"></script> 
 <script type="text/javascript">
  function init() {
   var renderer = new THREE.WebGLRenderer({
    canvas: document.getElementById('mainCanvas')
   });
   renderer.setClearColor(0x000000);
   var scene = new THREE.Scene();
   
   // camera
   var camera = new THREE.OrthographicCamera(-2.5, 2.5, 1.875, -1.875, 0.1, 100);
   camera.position.set(5, 5, 20);
   camera.lookAt(new THREE.Vector3(0, 0, 0));
   scene.add(camera);
   
   var material = new THREE.MeshLambertMaterial({
    color: 0xffff00
   });
   var geometry = new THREE.CubeGeometry(1, 2, 3);
   var mesh = new THREE.Mesh(geometry, material);
   scene.add(mesh);
   
   mesh.material = new THREE.MeshLambertMaterial({
    color: 0xff0000
   });
   
   var light = new THREE.DirectionalLight(0xffffff);
   light.position.set(20, 10, 5);
   scene.add(light);
   
   // render
   renderer.render(scene, camera);
  }
 </script>
</html>

　　2.2 位置、缩放、旋转

　　位置、缩放、旋转是物体三个常用属性。由于THREE.Mesh基础自THREE.Object3D，因此包含scale、rotation、position三个属性。它们都是THREE.Vector3实例，因此修改其值的方法是相同的，这里以位置为例。

　　THREE.Vector3有x、y、z三个属性，如果只设置其中一个属性，则可以用以下方法：

mesh.position.z = 1;

　　如果需要同时设置多个属性，可以使用以下两种方法：

mesh.position.set(1.5, -0.5, 0);

　　或者：

mesh.position = new THREE.Vector3(1.5, -0.5, 0);

　　缩放对应的属性是scale，旋转对应的属性是rotation，具体方法与上例相同，分别表示沿x、y、z三轴缩放或旋转。

 

　　源码：

<!DOCTYPE html>
<html>
 <head>
  <meta charset="UTF-8">
  <title>3.js测试9.3</title>
 </head>
 <body onload="init()">
  <canvas id="mainCanvas" width="400px" height="300px" ></canvas>
 </body>
 <script type="text/javascript" src="js/three.min.js"></script>
 <script type="text/javascript">
  function init() {
   var renderer = new THREE.WebGLRenderer({
    canvas: document.getElementById('mainCanvas')
   });
   renderer.setClearColor(0x000000);
   var scene = new THREE.Scene();
   
   // camera
   var camera = new THREE.OrthographicCamera(-2.5, 2.5, 1.875, -1.875, 0.1, 100);
   camera.position.set(5, 5, 20);
   camera.lookAt(new THREE.Vector3(0, 0, 0));
   scene.add(camera);
   
   var material = new THREE.MeshLambertMaterial({
    color: 0xffff00
   });
   var geometry = new THREE.CubeGeometry(1, 2, 3);
   var mesh = new THREE.Mesh(geometry, material);
   scene.add(mesh);
   
   mesh.position.set(1.5, -0.5, 0);
   mesh.position = new THREE.Vector3(1.5, -0.5, 0);
   mesh.position.z = 1;
   
   var light = new THREE.DirectionalLight(0xffffff);
   light.position.set(20, 10, 5);
   scene.add(light);
   
   drawAxes(scene);
   
   // render
   renderer.render(scene, camera);
  }
  
  function drawAxes(scene) {
   // x-axis
   var xGeo = new THREE.Geometry();
   xGeo.vertices.push(new THREE.Vector3(0, 0, 0));
   xGeo.vertices.push(new THREE.Vector3(1, 0, 0));
   var xMat = new THREE.LineBasicMaterial({
    color: 0xff0000
   });
   var xAxis = new THREE.Line(xGeo, xMat);
   scene.add(xAxis);
   
   // y-axis
   var yGeo = new THREE.Geometry();
   yGeo.vertices.push(new THREE.Vector3(0, 0, 0));
   yGeo.vertices.push(new THREE.Vector3(0, 1, 0));
   var yMat = new THREE.LineBasicMaterial({
    color: 0x00ff00
   });
   var yAxis = new THREE.Line(yGeo, yMat);
   scene.add(yAxis);
   
   // z-axis
   var zGeo = new THREE.Geometry();
   zGeo.vertices.push(new THREE.Vector3(0, 0, 0));
   zGeo.vertices.push(new THREE.Vector3(0, 0, 1));
   var zMat = new THREE.LineBasicMaterial({
    color: 0x00ccff
   });
   var zAxis = new THREE.Line(zGeo, zMat);
   scene.add(zAxis);
  }
 </script>
</html>

本文的内容到这就结束了，文章通过详细实例及图片介绍了Three.js中的网格，希望本文对大家学习Three.js有所帮助。

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