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- <title>Debugging JavaScript</title>
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- <h1>Debugging JavaScript</h1>
- </div>
- <div class="lesson">
- <div class="lesson-main">
- <p>Most of this article is not directly about THREE.js but is
- rather about debugging JavaScript in general. It seemed important in
- that many people just starting with THREE.js are also just
- starting with JavaScript so I hope this can help them more easily
- solve any issues they run into.</p>
- <p>Debugging is a big topic and I probably can't begin to cover
- everything there is to know but if you're new to JavaScript
- then here's an attempt to give a few pointers. I strongly
- suggest you take some time to learn them. They'll help you
- enormously in your learning.</p>
- <h2 id="learn-your-browser-s-developer-tools">Learn your Browser's Developer Tools</h2>
- <p>All browsers have developer tools.
- <a href="https://developers.google.com/web/tools/chrome-devtools/">Chrome</a>,
- <a href="https://developer.mozilla.org/en-US/docs/Tools">Firefox</a>,
- <a href="https://developer.apple.com/safari/tools/">Safari</a>,
- <a href="https://docs.microsoft.com/en-us/microsoft-edge/devtools-guide">Edge</a>.</p>
- <p>In Chrome you can click the the <code class="notranslate" translate="no">⋮</code> icon, pick More Tools->Developer Tools
- to get to the developer tools. A keyboard shortcut is also shown there.</p>
- <div class="threejs_center"><img class="border" src="../resources/images/devtools-chrome.jpg" style="width: 789px;"></div>
- <p>In Firefox you click the <code class="notranslate" translate="no">☰</code> icon, pick "Web Developer", then pick
- "Toggle Tools"</p>
- <div class="threejs_center"><img class="border" src="../resources/images/devtools-firefox.jpg" style="width: 786px;"></div>
- <p>In Safari you first have to enable the Develop menu from the
- Advanced Safari Preferences.</p>
- <div class="threejs_center"><img class="border" src="../resources/images/devtools-enable-safari.jpg" style="width: 775px;"></div>
- <p>Then in the Develop menu you can pick "Show/Connect Web Inspector".</p>
- <div class="threejs_center"><img class="border" src="../resources/images/devtools-safari.jpg" style="width: 777px;"></div>
- <p>With Chrome you can also <a href="https://developers.google.com/web/tools/chrome-devtools/remote-debugging/">use Chrome on your computer to debug webpages running on Chrome on your Android phone or tablet</a>.
- Similarly with Safari you can
- <a href="https://www.google.com/search?q=safari+remote+debugging+ios">use your computer to debug webpages running on Safari on iPhones and iPads</a>.</p>
- <p>I'm most familiar with Chrome so this guide will be using Chrome
- as an example when referring to tools but most browsers have similar
- features so it should be easy to apply anything here to all browsers.</p>
- <h2 id="turn-off-the-cache">Turn off the cache</h2>
- <p>Browsers try to reuse data they've already downloaded. This is great
- for users so if you visit a website a second time many of the files
- used to display the site will not have be downloaded again.</p>
- <p>On the other hand this can be bad for web development. You change
- a file on your computer, reload the page, and you don't see the changes
- because the browser uses the version it got last time.</p>
- <p>One solution during web development is to turn off the cache. This
- way the browser will always get the newest versions of your files.</p>
- <p>First pick settings from the corner menu</p>
- <div class="threejs_center"><img class="border" src="../resources/images/devtools-chrome-settings.jpg" style="width: 778px"></div>
- <p>Then pick "Disable Cache (while DevTools is open)".</p>
- <div class="threejs_center"><img class="border" src="../resources/images/devtools-chrome-disable-cache.jpg" style="width: 779px"></div>
- <h2 id="use-the-javascript-console">Use the JavaScript console</h2>
- <p>Inside all devtools is a <em>console</em>. It shows warnings and error messages.</p>
- <p><strong> READ THE MESSAGES!! </strong></p>
- <p>Typically there should be only 1 or 2 messages.</p>
- <div class="threejs_center"><img class="border" src="../resources/images/devtools-no-errors.jpg" style="width: 779px"></div>
- <p>If you see any others <strong>READ THEM</strong>. For example:</p>
- <div class="threejs_center"><img class="border" src="../resources/images/devtools-errors.jpg" style="width: 779px"></div>
- <p>I mis-spelled "three" as "threee"</p>
- <p>You can also print your own info to the console with with <code class="notranslate" translate="no">console.log</code> as in</p>
- <pre class="prettyprint showlinemods notranslate lang-js" translate="no">console.log(someObject.position.x, someObject.position.y, someObject.position.z);
- </pre>
- <p>Even cooler, if you log an object you can inspect it. For example if we log
- the root scene object from <a href="load-gltf.html">the gLTF article</a></p>
- <pre class="prettyprint showlinemods notranslate lang-js" translate="no"> {
- const gltfLoader = new GLTFLoader();
- gltfLoader.load('resources/models/cartoon_lowpoly_small_city_free_pack/scene.gltf', (gltf) => {
- const root = gltf.scene;
- scene.add(root);
- + console.log(root);
- </pre>
- <p>Then we can expand that object in the JavaScript console</p>
- <div class="threejs_center"><img class="border" src="../resources/images/devtools-console-object.gif"></div>
- <p>You can also use <code class="notranslate" translate="no">console.error</code> which reports the message in red
- in includes a stack trace.</p>
- <h2 id="put-data-on-screen">Put data on screen</h2>
- <p>Another obvious but often overlooked way is to add <code class="notranslate" translate="no"><div></code> or <code class="notranslate" translate="no"><pre></code> tags
- and put data in them.</p>
- <p>The most obvious way is to make some HTML elements</p>
- <pre class="prettyprint showlinemods notranslate lang-html" translate="no"><canvas id="c"></canvas>
- +<div id="debug">
- + <div>x:<span id="x"></span></div>
- + <div>y:<span id="y"></span></div>
- + <div>z:<span id="z"></span></div>
- +</div>
- </pre>
- <p>Style them so they stay on top of the canvas. (assuming your canvas
- fills the page)</p>
- <pre class="prettyprint showlinemods notranslate lang-html" translate="no"><style>
- #debug {
- position: absolute;
- left: 1em;
- top: 1em;
- padding: 1em;
- background: rgba(0, 0, 0, 0.8);
- color: white;
- font-family: monospace;
- }
- </style>
- </pre>
- <p>And then looking the elements up and setting their content.</p>
- <pre class="prettyprint showlinemods notranslate lang-js" translate="no">// at init time
- const xElem = document.querySelector('#x');
- const yElem = document.querySelector('#y');
- const zElem = document.querySelector('#z');
- // at render or update time
- xElem.textContent = someObject.position.x.toFixed(3);
- yElem.textContent = someObject.position.y.toFixed(3);
- zElem.textContent = someObject.position.z.toFixed(3);
- </pre>
- <p>This is more useful for real time values</p>
- <p></p><div translate="no" class="threejs_example_container notranslate">
- <div><iframe class="threejs_example notranslate" translate="no" style=" " src="/manual/examples/resources/editor.html?url=/manual/examples/debug-js-html-elements.html"></iframe></div>
- <a class="threejs_center" href="/manual/examples/debug-js-html-elements.html" target="_blank">click here to open in a separate window</a>
- </div>
- <p></p>
- <p>Another way to put data on the screen is to make a clearing logger.
- I just made that term up but lots of games I've worked on have used this solution. The idea
- is you have a buffer that displays messages for only one frame.
- Any part of your code that wants to display data calls some function
- to add data to that buffer every frame. This is much less work
- than making an element per piece of data above.</p>
- <p>For example let's change the HTML from above to just this</p>
- <pre class="prettyprint showlinemods notranslate lang-html" translate="no"><canvas id="c"></canvas>
- <div id="debug">
- <pre></pre>
- </div>
- </pre>
- <p>And let's make simple class to manage this <em>clear back buffer</em>.</p>
- <pre class="prettyprint showlinemods notranslate lang-js" translate="no">class ClearingLogger {
- constructor(elem) {
- this.elem = elem;
- this.lines = [];
- }
- log(...args) {
- this.lines.push([...args].join(' '));
- }
- render() {
- this.elem.textContent = this.lines.join('\n');
- this.lines = [];
- }
- }
- </pre>
- <p>Then let's make a simple example that every time we click the mouse makes a mesh
- that moves in a random direction for 2 seconds. We'll start with one of the
- examples from the article on <a href="responsive.html">making things responsive</a></p>
- <p>Here's the code that adds a new <a href="/docs/#api/en/objects/Mesh"><code class="notranslate" translate="no">Mesh</code></a> every time we click the mouse</p>
- <pre class="prettyprint showlinemods notranslate lang-js" translate="no">const geometry = new THREE.SphereGeometry();
- const material = new THREE.MeshBasicMaterial({color: 'red'});
- const things = [];
- function rand(min, max) {
- if (max === undefined) {
- max = min;
- min = 0;
- }
- return Math.random() * (max - min) + min;
- }
- function createThing() {
- const mesh = new THREE.Mesh(geometry, material);
- scene.add(mesh);
- things.push({
- mesh,
- timer: 2,
- velocity: new THREE.Vector3(rand(-5, 5), rand(-5, 5), rand(-5, 5)),
- });
- }
- canvas.addEventListener('click', createThing);
- </pre>
- <p>And here's the code that moves the meshes we created, logs them,
- and removes them when their timer has run out</p>
- <pre class="prettyprint showlinemods notranslate lang-js" translate="no">const logger = new ClearingLogger(document.querySelector('#debug pre'));
- let then = 0;
- function render(now) {
- now *= 0.001; // convert to seconds
- const deltaTime = now - then;
- then = now;
- ...
- logger.log('fps:', (1 / deltaTime).toFixed(1));
- logger.log('num things:', things.length);
- for (let i = 0; i < things.length;) {
- const thing = things[i];
- const mesh = thing.mesh;
- const pos = mesh.position;
- logger.log(
- 'timer:', thing.timer.toFixed(3),
- 'pos:', pos.x.toFixed(3), pos.y.toFixed(3), pos.z.toFixed(3));
- thing.timer -= deltaTime;
- if (thing.timer <= 0) {
- // remove this thing. Note we don't advance `i`
- things.splice(i, 1);
- scene.remove(mesh);
- } else {
- mesh.position.addScaledVector(thing.velocity, deltaTime);
- ++i;
- }
- }
- renderer.render(scene, camera);
- logger.render();
- requestAnimationFrame(render);
- }
- </pre>
- <p>Now click the mouse a bunch in the example below</p>
- <p></p><div translate="no" class="threejs_example_container notranslate">
- <div><iframe class="threejs_example notranslate" translate="no" style=" " src="/manual/examples/resources/editor.html?url=/manual/examples/debug-js-clearing-logger.html"></iframe></div>
- <a class="threejs_center" href="/manual/examples/debug-js-clearing-logger.html" target="_blank">click here to open in a separate window</a>
- </div>
- <p></p>
- <h2 id="query-parameters">Query Parameters</h2>
- <p>Another thing to remember is that webpages can have data passed
- into them either via query parameters or the anchor, sometimes called
- the search and the hash.</p>
- <pre class="prettyprint showlinemods notranslate notranslate" translate="no">https://domain/path/?query#anchor
- </pre><p>You can use this to make features optional or pass in parameters.</p>
- <p>For example let's take the previous example and make it so
- the debug stuff only shows up if we put <code class="notranslate" translate="no">?debug=true</code> in the URL.</p>
- <p>First we need some code to parse the query string</p>
- <pre class="prettyprint showlinemods notranslate lang-js" translate="no">/**
- * Returns the query parameters as a key/value object.
- * Example: If the query parameters are
- *
- * abc=123&def=456&name=gman
- *
- * Then `getQuery()` will return an object like
- *
- * {
- * abc: '123',
- * def: '456',
- * name: 'gman',
- * }
- */
- function getQuery() {
- return Object.fromEntries(new URLSearchParams(window.location.search).entries());
- }
- </pre>
- <p>Then we might make the debug element not show by default</p>
- <pre class="prettyprint showlinemods notranslate lang-html" translate="no"><canvas id="c"></canvas>
- +<div id="debug" style="display: none;">
- <pre></pre>
- </div>
- </pre>
- <p>Then in the code we read the params and choose to un-hide the
- debug info if and only if <code class="notranslate" translate="no">?debug=true</code> is passed in</p>
- <pre class="prettyprint showlinemods notranslate lang-js" translate="no">const query = getQuery();
- const debug = query.debug === 'true';
- const logger = debug
- ? new ClearingLogger(document.querySelector('#debug pre'))
- : new DummyLogger();
- if (debug) {
- document.querySelector('#debug').style.display = '';
- }
- </pre>
- <p>We also made a <code class="notranslate" translate="no">DummyLogger</code> that does nothing and chose to use it if <code class="notranslate" translate="no">?debug=true</code> has not been passed in.</p>
- <pre class="prettyprint showlinemods notranslate lang-js" translate="no">class DummyLogger {
- log() {}
- render() {}
- }
- </pre>
- <p>You can see if we use this url:</p>
- <p><a target="_blank" href="../examples/debug-js-params.html">debug-js-params.html</a></p>
- <p>there is no debug info but if we use this url:</p>
- <p><a target="_blank" href="../examples/debug-js-params.html?debug=true">debug-js-params.html?debug=true</a></p>
- <p>there is debug info.</p>
- <p>Multiple parameters can be passed in by separating with '&' as in <code class="notranslate" translate="no">somepage.html?someparam=somevalue&someotherparam=someothervalue</code>.
- Using parameters like this we can pass in all kinds of options. Maybe <code class="notranslate" translate="no">speed=0.01</code> to slow down our app for making it easier to understand something or <code class="notranslate" translate="no">showHelpers=true</code> for whether or not to add helpers
- that show the lights, shadow, or camera frustum seen in other lessons.</p>
- <h2 id="learn-to-use-the-debugger">Learn to use the Debugger</h2>
- <p>Every browser has a debugger where you can pause your program
- step through line by line and inspect all the variables.</p>
- <p>Teaching you how to use a debugger is too big a topic for this
- article but here's a few links</p>
- <ul>
- <li><a href="https://developers.google.com/web/tools/chrome-devtools/javascript/">Get Started with Debugging JavaScript in Chrome DevTools</a></li>
- <li><a href="https://javascript.info/debugging-chrome">Debugging in Chrome</a></li>
- <li><a href="https://hackernoon.com/tips-and-tricks-for-debugging-in-chrome-developer-tools-458ade27c7ab">Tips and Tricks for Debugging in Chrome Developer Tools</a></li>
- </ul>
- <h2 id="check-for-nan-in-the-debugger-or-elsewhere">Check for <code class="notranslate" translate="no">NaN</code> in the debugger or elsewhere</h2>
- <p><code class="notranslate" translate="no">NaN</code> is short for Not A Number. It's what JavaScript will assign
- as a value when you do something that doesn't make sense mathwise.</p>
- <p>As a simple example</p>
- <div class="threejs_center"><img class="border" src="../resources/images/nan-banana.png" style="width: 180px;"></div>
- <p>Often when I'm making something and nothing appears on the screen
- I'll check some values and if I see <code class="notranslate" translate="no">NaN</code> I will instantly have a
- place to start looking.</p>
- <p>As an example when I first started making the path for the
- <a href="load-gltf.html">article about loading gLTF files</a> I made
- a curve using the <a href="/docs/#api/en/extras/curves/SplineCurve"><code class="notranslate" translate="no">SplineCurve</code></a> class which makes a 2D curve.</p>
- <p>I then used that curve to move the cars like this</p>
- <pre class="prettyprint showlinemods notranslate lang-js" translate="no">curve.getPointAt(zeroToOnePointOnCurve, car.position);
- </pre>
- <p>Internally <code class="notranslate" translate="no">curve.getPointAt</code> calls the <code class="notranslate" translate="no">set</code> function
- on the object passed as the second argument. In this case that
- second argument is <code class="notranslate" translate="no">car.position</code> which is a <a href="/docs/#api/en/math/Vector3"><code class="notranslate" translate="no">Vector3</code></a>. <a href="/docs/#api/en/math/Vector3"><code class="notranslate" translate="no">Vector3</code></a>'s
- <code class="notranslate" translate="no">set</code> function requires 3 arguments, x, y, and z but <a href="/docs/#api/en/extras/curves/SplineCurve"><code class="notranslate" translate="no">SplineCurve</code></a> is a 2D curve
- and so it calls <code class="notranslate" translate="no">car.position.set</code> with just x and y.</p>
- <p>The result is that <code class="notranslate" translate="no">car.position.set</code> sets x to x, y to y, and z to <code class="notranslate" translate="no">undefined</code>.</p>
- <p>A quick glance in the debugger looking at the car's <code class="notranslate" translate="no">matrixWorld</code>
- showed a bunch of <code class="notranslate" translate="no">NaN</code> values.</p>
- <div class="threejs_center"><img class="border" src="../resources/images/debugging-nan.gif" style="width: 476px;"></div>
- <p>Seeing the matrix had <code class="notranslate" translate="no">NaN</code>s in it suggested something like <code class="notranslate" translate="no">position</code>,
- <code class="notranslate" translate="no">rotation</code>, <code class="notranslate" translate="no">scale</code> or some other function that affects that matrix had bad
- data. Working backward from their it was easy to track down the issue.</p>
- <p>In top of <code class="notranslate" translate="no">NaN</code> there's also <code class="notranslate" translate="no">Infinity</code> which is a similar sign there
- is a math bug somewhere.</p>
- <h2 id="look-in-the-code-">Look In the Code!</h2>
- <p>THREE.js is Open Source. Don't be afraid to look inside the code!
- You can look inside on <a href="https://github.com/mrdoob/three.js">github</a>.
- You can also look inside by stepping into functions in the debugger.</p>
- <h2 id="put-requestanimationframe-at-bottom-of-your-render-function-">Put <code class="notranslate" translate="no">requestAnimationFrame</code> at bottom of your render function.</h2>
- <p>I see this pattern often</p>
- <pre class="prettyprint showlinemods notranslate lang-js" translate="no">function render() {
- requestAnimationFrame(render);
- // -- do stuff --
- renderer.render(scene, camera);
- }
- requestAnimationFrame(render);
- </pre>
- <p>I'd suggest that putting the call to <code class="notranslate" translate="no">requestAnimationFrame</code> at
- the bottom as in</p>
- <pre class="prettyprint showlinemods notranslate lang-js" translate="no">function render() {
- // -- do stuff --
- renderer.render(scene, camera);
- requestAnimationFrame(render);
- }
- requestAnimationFrame(render);
- </pre>
- <p>The biggest reason is it means your code will stop if you have an error. Putting
- <code class="notranslate" translate="no">requestAnimationFrame</code> at the top means your code will keep running even if you
- have an error since you already requested another frame. IMO it's better to find
- those errors than to ignore them. They could easily be the reason something is
- not appearing as you expect it to but unless your code stops you might not even
- notice.</p>
- <h2 id="check-your-units-">Check your units!</h2>
- <p>This basically means knowing for example when to use degrees vs
- when to use radians. It's unfortunate that THREE.js does not
- consistently use the same units everywhere. Off the top of my head
- the camera's field of view is in degrees. All other angles are in
- radians.</p>
- <p>The other place to look out is your world unit size. Until
- recently 3D apps could choose any unit size they wanted. One app might choose
- 1 unit = 1cm. Another might choose 1 unit = 1 foot. It's actually still
- true that you can chose any units you want for certain applications.
- That said, THREE.js assumes 1 unit = 1 meter. This is important for
- things like physically based rendering which uses meters to compute
- lighting effects. It's also important for AR and VR which need to
- deal with real world units like where your phone is or where the VR
- controllers are.</p>
- <h2 id="making-a-minimal-complete-verifiable-example-for-stack-overflow">Making a <em>Minimal, Complete, Verifiable, Example</em> for Stack Overflow</h2>
- <p>If you decide to ask a question about THREE.js it's almost always
- required for you to provide an MCVE which stands for Minimal, Complete,
- Verifiable, Example.</p>
- <p>The <strong>Minimal</strong> part is important. Let's say you where having an issue with the
- path movement in the last example of the <a href="load-gltf.html">loading a gLTF
- article</a>. That example has many parts. Listing them out
- it has</p>
- <ol>
- <li>A bunch of HTML</li>
- <li>Some CSS</li>
- <li>Lights</li>
- <li>Shadows</li>
- <li>lil-gui code to manipulate shadows</li>
- <li>Code to load a .GLTF file</li>
- <li>Code to resize the canvas.</li>
- <li>Code to move the cars along paths</li>
- </ol>
- <p>That's pretty huge. If your question is only about the path following part you
- can remove most of the HTML as you only need a <code class="notranslate" translate="no"><canvas></code> and a <code class="notranslate" translate="no"><script></code> tag
- for THREE.js. You can remove the CSS and the resizing code. You can remove .GLTF
- code because you only care about the path. You can remove the lights and the
- shadows by using a <a href="/docs/#api/en/materials/MeshBasicMaterial"><code class="notranslate" translate="no">MeshBasicMaterial</code></a>. You can certainly remove the lil-gui
- code. The code makes a ground plane with a texture. It would be easier to use a
- <a href="/docs/#api/en/helpers/GridHelper"><code class="notranslate" translate="no">GridHelper</code></a>. Finally if our question is about moving things on a path we could
- just use cubes on the path instead of loaded car models.</p>
- <p>Here's a more minimal example taking all the above into account. It
- shrunk from 271 lines to 135. We might consider shrinking it even
- more by simplifying our path. Maybe a path with 3 or 4 points would
- work just as well as our path with 21 points.</p>
- <p></p><div translate="no" class="threejs_example_container notranslate">
- <div><iframe class="threejs_example notranslate" translate="no" style=" " src="/manual/examples/resources/editor.html?url=/manual/examples/debugging-mcve.html"></iframe></div>
- <a class="threejs_center" href="/manual/examples/debugging-mcve.html" target="_blank">click here to open in a separate window</a>
- </div>
- <p></p>
- <p>I kept the <code class="notranslate" translate="no">OrbitController</code> just because it's useful for others
- to move the camera and figure out what's going on but depending
- on your issue you might be able to remove that as well.</p>
- <p>The best thing about making an MCVE is we'll often solve our own
- problem. The process of removing everything that's not needed and
- making the smallest example we can that reproduces the issue more
- often than not leads us to our bug.</p>
- <p>On top of that it's respectful of all the people's time who you are
- asking to look at your code on Stack Overflow. By making the minimal
- example you make it much easier for them to help you. You'll also
- learn in the process.</p>
- <p>Also important, when you go to Stack Overflow to post your question <strong>put your
- code <a href="https://stackoverflow.blog/2014/09/16/introducing-runnable-javascript-css-and-html-code-snippets/">in a snippet</a>.</strong>
- Of course you are welcome to use JSFiddle or Codepen or similar site to test out
- your MCVE but once you actually get to posting your question on Stack Overflow
- you're required to put the code to reproduce your issue <strong>in the question itself</strong>.
- By making a snippet you satisfy that requirement.</p>
- <p>Also note all the live examples on this site should run as snippets.
- Just copy the HTML, CSS, and JavaScript parts to their respective
- parts of the <a href="https://stackoverflow.blog/2014/09/16/introducing-runnable-javascript-css-and-html-code-snippets/">snippet editor</a>.
- Just remember to try to remove the parts that are not relevant to
- your issue and try to make your code the minimal amount needed.</p>
- <p>Follow these suggestions and you're far more likely to get help
- with your issue.</p>
- <h2 id="use-a-meshbasicmaterial-">Use a <a href="/docs/#api/en/materials/MeshBasicMaterial"><code class="notranslate" translate="no">MeshBasicMaterial</code></a></h2>
- <p>Because the <a href="/docs/#api/en/materials/MeshBasicMaterial"><code class="notranslate" translate="no">MeshBasicMaterial</code></a> uses no lights this is one way to
- remove reasons something might not be showing up. If your objects
- show up using <a href="/docs/#api/en/materials/MeshBasicMaterial"><code class="notranslate" translate="no">MeshBasicMaterial</code></a> but not with whatever materials
- you were using then you know the issue is likely with the materials
- or the lights and not some other part of the code.</p>
- <h2 id="check-your-near-and-far-settings-for-your-camera">Check your <code class="notranslate" translate="no">near</code> and <code class="notranslate" translate="no">far</code> settings for your camera</h2>
- <p>A <a href="/docs/#api/en/cameras/PerspectiveCamera"><code class="notranslate" translate="no">PerspectiveCamera</code></a> has <code class="notranslate" translate="no">near</code> and <code class="notranslate" translate="no">far</code> settings which are covered in the
- <a href="cameras.html">article on cameras</a>. Make sure they are set to fit the
- space that contains your objects. Maybe even just <strong>temporarily</strong> set them to
- something large like <code class="notranslate" translate="no">near</code> = 0.001 and <code class="notranslate" translate="no">far</code> = 1000000. You will likely run
- into depth resolution issues but you'll at least be able to see your objects
- provided they are in front of the camera.</p>
- <h2 id="check-your-scene-is-in-front-of-the-camera">Check your scene is in front of the camera</h2>
- <p>Sometimes things don't appear because they are not in front of the camera. If
- your camera is not controllable try adding camera control like the
- <code class="notranslate" translate="no">OrbitController</code> so you can look around and find your scene. Or, try framing
- the scene using code which is covered in <a href="load-obj.html">this article</a>.
- That code finds the size of part of the scene and then moves the camera and
- adjusts the <code class="notranslate" translate="no">near</code> and <code class="notranslate" translate="no">far</code> settings to make it visible. You can then look in
- the debugger or add some <code class="notranslate" translate="no">console.log</code> messages to print the size and center of
- the scene.</p>
- <h2 id="put-something-in-front-of-the-camera">Put something in front of the camera</h2>
- <p>This is just another way of saying if all else fails start with
- something that works and then slowly add stuff back in. If you get
- a screen with nothing on it then try putting something directly in
- front of the camera. Make a sphere or box, give it a simple material
- like the <a href="/docs/#api/en/materials/MeshBasicMaterial"><code class="notranslate" translate="no">MeshBasicMaterial</code></a> and make sure you can get that on the screen.
- Then start adding things back a little at time and testing. Eventually
- you'll either reproduce your bug or you'll find it on the way.</p>
- <hr>
- <p>These were a few tips for debugging JavaScript. Let's also go
- over <a href="debugging-glsl.html">some tips for debugging GLSL</a>.</p>
- </div>
- </div>
- </div>
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- <script src="../resources/lesson.js"></script>
- </body></html>
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