如何围绕边缘旋转三角形？答案

【问题标题】：How do I rotate a triangle around an edge?如何围绕边缘旋转三角形？
【发布时间】：2018-06-08 04:28:04
【问题描述】：

用three.js 制作的三角形如何围绕其边缘之一旋转？当我尝试旋转它时，它看起来像它的中心一样。

三角形由以下组成：

var triangleMesh; 
var triangleGeometry = new THREE.Geometry(); 
    triangleGeometry.vertices.push( new THREE.Vector3( 0.0, 1.0, 0.0 ) ); 
    triangleGeometry.vertices.push( new THREE.Vector3( -1.0, -1.0, 0.0 ) ); 
    triangleGeometry.vertices.push( new THREE.Vector3( 1.0, -1.0, 0.0 ) ); 

    triangleGeometry.faces.push( new THREE.Face3( 0, 1, 2 ) ); 

    triangleGeometry.faces[0].vertexColors[0] = new THREE.Color(0xFF0000); 
    triangleGeometry.faces[0].vertexColors[1] = new THREE.Color(0x00FF00); 
    triangleGeometry.faces[0].vertexColors[2] = new THREE.Color(0x0000FF); 

var triangleMaterial = new THREE.MeshBasicMaterial({ vertexColors:THREE.VertexColors, side:THREE.DoubleSide }); 

    triangleMesh = new THREE.Mesh( triangleGeometry, triangleMaterial ); 
    triangleMesh.position.set(-1.5, 0.0, 4.0 ); 

    triangleMesh.position.z     -=  5;
    triangleMesh.rotation.z     +=  angle * Math.PI / 180; // angle is from outer for loop

    parent.add( triangleMesh );

我需要围绕一个边缘旋转它来构建棱镜/六边形。

【问题讨论】：

您能否说明一下您的意思是 “我需要围绕一个边缘旋转它来构建棱镜/六边形。”？
当三角形在屏幕上时，你可以看到它的整个平面，一个边向上，我想把三角形旋转60度，比如说顺时针旋转60度，围绕这个上边，把它进入父对象，所以我可以旋转下一个三角形，围绕其上边缘旋转 120 度，依此类推，直到六边形在 6 次运行后存在（因此每个图块 60 度）。
我想，你的意思是你想围绕它的顶部顶点旋转那个三角形[0.0, 1.0, 0.0]？如果不是，那么最好显示所需结果的解释性图片。

标签： javascript object three.js rotation

【解决方案1】：

要围绕其中一个角旋转三角形，该角必须位于坐标中心。为此，您可以使用THREE.Geometry() 的.translate ( x, y, z ) 方法。

看一下代码sn-p。

var scene = new THREE.Scene();
var camera = new THREE.PerspectiveCamera(60, window.innerWidth / window.innerHeight, 1, 1000);
camera.position.set(0, 0, 5);
var renderer = new THREE.WebGLRenderer({
  antialias: true
});
renderer.setSize(window.innerWidth, window.innerHeight);
document.body.appendChild(renderer.domElement);

var ngon = 11;
var radius = 2;
var angle = Math.PI / ngon;
var triHeight = Math.cos(angle) * radius;
var triWidth = Math.sin(angle) * radius;

var triangleMesh;
var triangleGeometry = new THREE.Geometry();
triangleGeometry.vertices.push(new THREE.Vector3(0.0, triHeight, 0.0));
triangleGeometry.vertices.push(new THREE.Vector3(-triWidth, 0, 0.0));
triangleGeometry.vertices.push(new THREE.Vector3(triWidth, 0, 0.0));

triangleGeometry.faces.push(new THREE.Face3(0, 1, 2));

triangleGeometry.faces[0].vertexColors[0] = new THREE.Color(0xFF0000);
triangleGeometry.faces[0].vertexColors[1] = new THREE.Color(0x00FF00);
triangleGeometry.faces[0].vertexColors[2] = new THREE.Color(0x0000FF);

triangleGeometry.translate(0, -triHeight, 0); // the upper vertex is at the center  now

var triangleMaterial = new THREE.MeshBasicMaterial({
  vertexColors: THREE.VertexColors,
  side: THREE.DoubleSide
});

triangleMesh = new THREE.Mesh(triangleGeometry, triangleMaterial);

for (var i = 1; i < ngon; i++) {
  var newTri = triangleMesh.clone();
  newTri.rotation.z = i * angle * 2;
  scene.add(newTri);
}

scene.add(triangleMesh);

render();

function render() {
  requestAnimationFrame(render);
  renderer.render(scene, camera);
}

body {
  overflow: hidden;
  margin: 0;
}

&lt;script src="https://threejs.org/build/three.min.js"&gt;&lt;/script&gt;

【讨论】：