Three.js基础探寻九——网格
在学习了几何形状和材质之后，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。
本篇将介绍创建较为常用的物体：网格，然后介绍如何修改物体的属性。
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>
整理自张雯莉《Three.js入门指南》
