用 Three.js 绘制一个基本的三角形

Question

我正在尝试学习three.js 我想绘制一个基本的三角形但是我的代码不起作用。

var scene = new THREE.Scene();
var camera = new THREE.PerspectiveCamera( 70, window.innerWidth/window.innerHeight, 0.1, 1000 );
camera.position.z = 10;


var renderer = new THREE.WebGLRenderer();
renderer.setSize( window.innerWidth, window.innerHeight );
document.body.appendChild( renderer.domElement );

var geometry = new THREE.Geometry();
geometry.vertices= [new THREE.Vector3(2,1,0), new THREE.Vector3(1,3,0), new THREE.Vector3(3,4,0)]; 
geometry.faces = [new THREE.Face3(0,1,2)];
var mesh= new THREE.Mesh( geometry, new THREE.MeshBasicMaterial({ color: 0xffff00 }) );
scene.add(mesh);


renderer.render(scene, camera);

我在哪里做错了？

Answer 1

有趣的是，找到更新的答案是多么困难，因为Geometry在最近版本的 Three.js 中，我发现用原始方法绘制平面三角形的方式已被弃用Shape。

const shape = new THREE.Shape();

const x = 0;
const y = 0;

shape.moveTo(x - 2, y - 2);
shape.lineTo(x + 2, y - 2);
shape.lineTo(x, y + 2);

const TriangleGeometry = new THREE.ShapeGeometry(shape);

基于https://trijs.org/docs/index.html?q=ShapeGeometry#api/en/geometries/ShapeGeometry

Answer 2

您必须小心将顶点添加到面上的顺序。如果顺序遵循顺时针顺序，则表面的法向量将指向下方。由于你的相机是从上方观察的，所以你不会看到三角形。如果顺序是逆时针，则法线将指向您的相机。

如果你改变它就会起作用：
geometry.faces = [new THREE.Face3(0,1,2)];

到：
geometry.faces = [new THREE.Face3(1,0,2)];

您还可以使用参数 side，将其应用于脸部的两侧。
new THREE.MeshBasicMaterial({ color: 0xffff00, side: THREE.DoubleSide };

Answer 3

有脸

var geom = new THREE.Geometry();
var v1 = new THREE.Vector3(0, 0, 0);
var v2 = new THREE.Vector3(30, 0, 0);
var v3 = new THREE.Vector3(30, 30, 0);
var triangle = new THREE.Triangle(v1, v2, v3);
var normal = triangle.normal();
geom.vertices.push(triangle.a);
geom.vertices.push(triangle.b);
geom.vertices.push(triangle.c);
geom.faces.push(new THREE.Face3(0, 1, 2, normal));
var mesh = new THREE.Mesh(geom, new THREE.MeshNormalMaterial());
scene.add(mesh);

只是大纲

 var geometry = new THREE.Geometry();
geometry.vertices.push(new THREE.Vector3(-30, 2, 2));
geometry.vertices.push(new THREE.Vector3(2, 30, 2));
geometry.vertices.push(new THREE.Vector3(30, 2, 2));
geometry.vertices.push(new THREE.Vector3(-30, 2, 2));

var line = new THREE.Line(
  geometry,
  new THREE.LineBasicMaterial({ color: 0x00ff00 })
);
scene.add(line);