github から直接読み込むことは難しいと思います。
質問文に記載の通りに書いていて THREE が読み込めているならば、ConvexGeometry は下記の要領で読み込めるはずです。
js
1 import { ConvexGeometry } from 'https://unpkg.com/three@0.120.0/examples/jsm/geometries/ConvexGeometry.js';
例:
html
1<!DOCTYPE html>
2<html>
3
4<head>
5 <meta charset="utf-8">
6 <title>sample</title>
7</head>
8
9<body>
10 <canvas id="canvas"></canvas>
11 <script async src="https://unpkg.com/es-module-shims@1.3.6/dist/es-module-shims.js"></script>
12 <script type="module">
13 import * as THREE from 'https://unpkg.com/three@0.120.0/build/three.module.js';
14 import { ConvexGeometry } from 'https://unpkg.com/three@0.120.0/examples/jsm/geometries/ConvexGeometry.js';
15
16
17 window.onload = function () {
18 const renderer = new THREE.WebGLRenderer({ 'canvas': document.getElementById('canvas') });
19 renderer.setSize(300, 300);
20 const camera = new THREE.PerspectiveCamera();
21 camera.position.z = 400;
22
23 const scene = new THREE.Scene();
24 scene.add(camera);
25 const points = [
26 new THREE.Vector3(0, -100, 100),
27 new THREE.Vector3(0, 100, 100),
28 new THREE.Vector3(100, -100, -100),
29 new THREE.Vector3(-100, -100, -100)
30 ];
31 const material = new THREE.MeshLambertMaterial({ color: 0x00eeaa });
32 const mesh = new THREE.Mesh(new ConvexGeometry(points), material);
33 scene.add(mesh)
34
35 const light = new THREE.DirectionalLight( 0xffffff, 1 );
36 light.position.set(0.2, 0.5, 1).normalize();
37 scene.add(light);
38 scene.add(new THREE.AmbientLight( 0x404040 ));
39 renderer.render(scene, camera);
40 }
41 </script>
42
43</body>