three.js多场景绘制代码示例

新闻页面或者商品详情页，可能需要展示多个3D对象，webgl的一个问题是浏览器对webgl context的个数有限制，大概是8个，另外context之间不能共享数据（这意味着图片、模型可能会被重复加载），所以使用多个context来实现这个目标不太合适。解决方法是使用“虚拟画布virtual canvas”，使用一个真实的canvas来做背景，然后使用不同的scene来在页面各个位置模拟virtual canvas。

three, multiple scene, context

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JavaScript

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CSS

HTML

<canvas id="c"></canvas>
<p>
  <span id="box" class="diagram left"></span>
  this is a box...i love box.
</p>
<p>
  <span id="pyramid" class="diagram right"></span>
  this is a pyramid...i hate pyramid.
</p>
  
<script type="module">
import * as THREE from '//techbrood.com/threejs/build/three.module.js';

function main() {
  const canvas = document.querySelector('#c');
  const renderer = new THREE.WebGLRenderer({canvas, alpha: true});

function makeScene(elem) {
    const scene = new THREE.Scene();

const fov = 45;
    const aspect = 2;  // the canvas default
    const near = 0.1;
    const far = 5;
    const camera = new THREE.PerspectiveCamera(fov, aspect, near, far);
    camera.position.set(0, 1, 2);
    camera.lookAt(0, 0, 0);

{
      const color = 0xFFFFFF;
      const intensity = 1;
      const light = new THREE.DirectionalLight(color, intensity);
      light.position.set(-1, 2, 4);
      scene.add(light);
    }

return {scene, camera, elem};
  }

function setupScene1() {
    const sceneInfo = makeScene(document.querySelector('#box'));
    const geometry = new THREE.BoxBufferGeometry(1, 1, 1);
    const material = new THREE.MeshPhongMaterial({color: 'red'});
    const mesh = new THREE.Mesh(geometry, material);
    sceneInfo.scene.add(mesh);
    sceneInfo.mesh = mesh;
    return sceneInfo;
  }

function setupScene2() {
    const sceneInfo = makeScene(document.querySelector('#pyramid'));
    const radius = .8;
    const widthSegments = 4;
    const heightSegments = 2;
    const geometry = new THREE.SphereBufferGeometry(radius, widthSegments, heightSegments);
    const material = new THREE.MeshPhongMaterial({
      color: 'blue',
      flatShading: true,
    });
    const mesh = new THREE.Mesh(geometry, material);
    sceneInfo.scene.add(mesh);
    sceneInfo.mesh = mesh;
    return sceneInfo;
  }

const sceneInfo1 = setupScene1();
  const sceneInfo2 = setupScene2();

function resizeRendererToDisplaySize(renderer) {
    const canvas = renderer.domElement;
    const width = canvas.clientWidth;
    const height = canvas.clientHeight;
    const needResize = canvas.width !== width || canvas.height !== height;
    if (needResize) {
      renderer.setSize(width, height, false);
    }
    return needResize;
  }

function renderSceneInfo(sceneInfo) {
    const {scene, camera, elem} = sceneInfo;

// get the viewport relative position opf this element
    const {left, right, top, bottom, width, height} =
        elem.getBoundingClientRect();

const isOffscreen =
        bottom < 0 ||
        top > renderer.domElement.clientHeight ||
        right < 0 ||
        left > renderer.domElement.clientWidth;

if (isOffscreen) {
      return;
    }

camera.aspect = width / height;
    camera.updateProjectionMatrix();

const positiveYUpBottom = renderer.domElement.clientHeight - bottom;
    renderer.setScissor(left, positiveYUpBottom, width, height);
    renderer.setViewport(left, positiveYUpBottom, width, height);

renderer.render(scene, camera);
  }

function render(time) {
    time *= 0.001;

resizeRendererToDisplaySize(renderer);

renderer.setScissorTest(false);
    renderer.clear(true, true);
    renderer.setScissorTest(true);

sceneInfo1.mesh.rotation.y = time * .1;
    sceneInfo2.mesh.rotation.y = time * .1;

renderSceneInfo(sceneInfo1);
    renderSceneInfo(sceneInfo2);

requestAnimationFrame(render);
  }

requestAnimationFrame(render);
}

main();

</script>

three, multiple scene, context

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