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235 lines
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235 lines
12 KiB
<!DOCTYPE html><html lang="en"><head>
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<meta charset="utf-8">
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<title>Rendering on Demand</title>
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"three": "../../build/three.module.js"
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</head>
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<body>
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<div class="container">
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<div class="lesson-title">
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<h1>Rendering on Demand</h1>
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</div>
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<div class="lesson">
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<div class="lesson-main">
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<p>The topic might be obvious to many people but just in case ... most Three.js
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examples render continuously. In other words they setup a
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<code class="notranslate" translate="no">requestAnimationFrame</code> loop or "<em>rAF loop</em>" something like this</p>
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<pre class="prettyprint showlinemods notranslate lang-js" translate="no">function render() {
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...
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requestAnimationFrame(render);
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}
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requestAnimationFrame(render);
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</pre>
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<p>For something that animates this makes sense but what about for something that
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does not animate? In that case rendering continuously is a waste of the devices
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power and if the user is on portable device it wastes the user's battery. </p>
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<p>The most obvious way to solve this is to render once at the start and then
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render only when something changes. Changes include textures or models finally
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loading, data arriving from some external source, the user adjusting a setting
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or the camera or giving other relevant input.</p>
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<p>Let's take an example from <a href="responsive.html">the article on responsiveness</a>
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and modify it to render on demand.</p>
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<p>First we'll add in the <a href="/docs/#examples/controls/OrbitControls"><code class="notranslate" translate="no">OrbitControls</code></a> so there is something that could change
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that we can render in response to.</p>
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<pre class="prettyprint showlinemods notranslate lang-js" translate="no">import * as THREE from 'three';
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+import {OrbitControls} from 'three/addons/controls/OrbitControls.js';
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</pre>
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<p>and set them up</p>
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<pre class="prettyprint showlinemods notranslate lang-js" translate="no">const fov = 75;
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const aspect = 2; // the canvas default
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const near = 0.1;
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const far = 5;
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const camera = new THREE.PerspectiveCamera(fov, aspect, near, far);
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camera.position.z = 2;
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+const controls = new OrbitControls(camera, canvas);
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+controls.target.set(0, 0, 0);
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+controls.update();
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</pre>
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<p>Since we won't be animating the cubes anymore we no longer need to keep track of them</p>
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<pre class="prettyprint showlinemods notranslate lang-js" translate="no">-const cubes = [
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- makeInstance(geometry, 0x44aa88, 0),
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- makeInstance(geometry, 0x8844aa, -2),
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- makeInstance(geometry, 0xaa8844, 2),
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-];
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+makeInstance(geometry, 0x44aa88, 0);
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+makeInstance(geometry, 0x8844aa, -2);
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+makeInstance(geometry, 0xaa8844, 2);
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</pre>
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<p>We can remove the code to animate the cubes and the calls to <code class="notranslate" translate="no">requestAnimationFrame</code></p>
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<pre class="prettyprint showlinemods notranslate lang-js" translate="no">-function render(time) {
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- time *= 0.001;
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+function render() {
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if (resizeRendererToDisplaySize(renderer)) {
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const canvas = renderer.domElement;
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camera.aspect = canvas.clientWidth / canvas.clientHeight;
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camera.updateProjectionMatrix();
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}
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- cubes.forEach((cube, ndx) => {
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- const speed = 1 + ndx * .1;
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- const rot = time * speed;
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- cube.rotation.x = rot;
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- cube.rotation.y = rot;
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- });
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renderer.render(scene, camera);
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- requestAnimationFrame(render);
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}
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-requestAnimationFrame(render);
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</pre>
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<p>then we need to render once</p>
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<pre class="prettyprint showlinemods notranslate lang-js" translate="no">render();
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</pre>
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<p>We need to render anytime the <a href="/docs/#examples/controls/OrbitControls"><code class="notranslate" translate="no">OrbitControls</code></a> change the camera settings.
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Fortunately the <a href="/docs/#examples/controls/OrbitControls"><code class="notranslate" translate="no">OrbitControls</code></a> dispatch a <code class="notranslate" translate="no">change</code> event anytime something
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changes.</p>
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<pre class="prettyprint showlinemods notranslate lang-js" translate="no">controls.addEventListener('change', render);
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</pre>
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<p>We also need to handle the case where the user resizes the window. That was
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handled automatically before since we were rendering continuously but now what
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we are not we need to render when the window changes size.</p>
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<pre class="prettyprint showlinemods notranslate lang-js" translate="no">window.addEventListener('resize', render);
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</pre>
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<p>And with that we get something that renders on demand.</p>
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<p></p><div translate="no" class="threejs_example_container notranslate">
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<div><iframe class="threejs_example notranslate" translate="no" style=" " src="/manual/examples/resources/editor.html?url=/manual/examples/render-on-demand.html"></iframe></div>
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<a class="threejs_center" href="/manual/examples/render-on-demand.html" target="_blank">click here to open in a separate window</a>
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</div>
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<p></p>
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<p>The <a href="/docs/#examples/controls/OrbitControls"><code class="notranslate" translate="no">OrbitControls</code></a> have options to add a kind of inertia to make them feel less
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stiff. We can enable this by setting the <code class="notranslate" translate="no">enableDamping</code> property to true.</p>
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<pre class="prettyprint showlinemods notranslate lang-js" translate="no">controls.enableDamping = true;
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</pre>
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<p>With <code class="notranslate" translate="no">enableDamping</code> on we need to call <code class="notranslate" translate="no">controls.update</code> in our render function
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so that the <a href="/docs/#examples/controls/OrbitControls"><code class="notranslate" translate="no">OrbitControls</code></a> can continue to give us new camera settings as they
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smooth out the movement. But, that means we can't call <code class="notranslate" translate="no">render</code> directly from
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the <code class="notranslate" translate="no">change</code> event because we'll end up in an infinite loop. The controls will
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send us a <code class="notranslate" translate="no">change</code> event and call <code class="notranslate" translate="no">render</code>, <code class="notranslate" translate="no">render</code> will call <code class="notranslate" translate="no">controls.update</code>.
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<code class="notranslate" translate="no">controls.update</code> will send another <code class="notranslate" translate="no">change</code> event.</p>
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<p>We can fix that by using <code class="notranslate" translate="no">requestAnimationFrame</code> to call <code class="notranslate" translate="no">render</code> but we need to
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make sure we only ask for a new frame if one has not already been requested
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which we can do by keeping a variable that tracks if we've already requested a frame.</p>
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<pre class="prettyprint showlinemods notranslate lang-js" translate="no">+let renderRequested = false;
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function render() {
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+ renderRequested = false;
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if (resizeRendererToDisplaySize(renderer)) {
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const canvas = renderer.domElement;
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camera.aspect = canvas.clientWidth / canvas.clientHeight;
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camera.updateProjectionMatrix();
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}
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renderer.render(scene, camera);
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}
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render();
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+function requestRenderIfNotRequested() {
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+ if (!renderRequested) {
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+ renderRequested = true;
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+ requestAnimationFrame(render);
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+ }
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+}
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-controls.addEventListener('change', render);
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+controls.addEventListener('change', requestRenderIfNotRequested);
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</pre>
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<p>We should probably also use <code class="notranslate" translate="no">requestRenderIfNotRequested</code> for resizing as well</p>
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<pre class="prettyprint showlinemods notranslate lang-js" translate="no">-window.addEventListener('resize', render);
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+window.addEventListener('resize', requestRenderIfNotRequested);
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</pre>
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<p>It might be hard to see the difference. Try clicking on the example below and
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use the arrow keys to move around or dragging to spin. Then try clicking on the
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example above and do the same thing and you should be able to tell the
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difference. The one above snaps when you press an arrow key or drag, the one
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below slides.</p>
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<p></p><div translate="no" class="threejs_example_container notranslate">
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<div><iframe class="threejs_example notranslate" translate="no" style=" " src="/manual/examples/resources/editor.html?url=/manual/examples/render-on-demand-w-damping.html"></iframe></div>
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<a class="threejs_center" href="/manual/examples/render-on-demand-w-damping.html" target="_blank">click here to open in a separate window</a>
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</div>
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<p></p>
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<p>Let's also add a simple lil-gui GUI and make its changes render on demand.</p>
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<pre class="prettyprint showlinemods notranslate lang-js" translate="no">import * as THREE from 'three';
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import {OrbitControls} from 'three/addons/controls/OrbitControls.js';
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+import {GUI} from 'three/addons/libs/lil-gui.module.min.js';
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</pre>
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<p>Let's allow setting the color and x scale of each cube. To be able to set the
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color we'll use the <code class="notranslate" translate="no">ColorGUIHelper</code> we created in the <a href="lights.html">article on
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lights</a>.</p>
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<p>First we need to create a GUI</p>
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<pre class="prettyprint showlinemods notranslate lang-js" translate="no">const gui = new GUI();
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</pre>
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<p>and then for each cube we'll create a folder and add 2 controls, one for
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<code class="notranslate" translate="no">material.color</code> and another for <code class="notranslate" translate="no">cube.scale.x</code>.</p>
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<pre class="prettyprint showlinemods notranslate lang-js" translate="no">function makeInstance(geometry, color, x) {
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const material = new THREE.MeshPhongMaterial({color});
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const cube = new THREE.Mesh(geometry, material);
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scene.add(cube);
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cube.position.x = x;
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+ const folder = gui.addFolder(`Cube${x}`);
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+ folder.addColor(new ColorGUIHelper(material, 'color'), 'value')
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+ .name('color')
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+ .onChange(requestRenderIfNotRequested);
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+ folder.add(cube.scale, 'x', .1, 1.5)
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+ .name('scale x')
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+ .onChange(requestRenderIfNotRequested);
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+ folder.open();
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return cube;
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}
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</pre>
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<p>You can see above lil-gui controls have an <code class="notranslate" translate="no">onChange</code> method that you can pass a
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callback to be called when the GUI changes a value. In our case we just need it
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to call <code class="notranslate" translate="no">requestRenderIfNotRequested</code>. The call to <code class="notranslate" translate="no">folder.open</code> makes the
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folder start expanded.</p>
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<p></p><div translate="no" class="threejs_example_container notranslate">
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<div><iframe class="threejs_example notranslate" translate="no" style=" " src="/manual/examples/resources/editor.html?url=/manual/examples/render-on-demand-w-gui.html"></iframe></div>
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<a class="threejs_center" href="/manual/examples/render-on-demand-w-gui.html" target="_blank">click here to open in a separate window</a>
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</div>
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<p></p>
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<p>I hope this gives some idea of how to make three.js render on demand instead of
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continuously. Apps/pages that render three.js on demand are not as common as
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most pages using three.js are either games or 3D animated art but examples of
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pages that might be better rendering on demand would be say a map viewer, a 3d
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editor, a 3d graph generator, a product catalog, etc...</p>
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</div>
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