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    <title>Backgrounds and Skyboxes</title>
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        <h1>Backgrounds and Skyboxes</h1>
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      <div class="lesson">
        <div class="lesson-main">
          <p>Most of the articles here use a solid color for a background.</p>
<p>Adding as static background can be as simple as setting some CSS. Taking
an example from <a href="responsive.html">the article on making THREE.js responsive</a>
we only need to change 2 things.</p>
<p>We need to add some CSS to our canvas to set its background to an image</p>
<pre class="prettyprint showlinemods notranslate lang-html" translate="no">&lt;style&gt;
body {
    margin: 0;
}
#c {
    width: 100%;
    height: 100%;
    display: block;
+    background: url(resources/images/daikanyama.jpg) no-repeat center center;
+    background-size: cover;
}
&lt;/style&gt;
</pre>
<p>and we need to tell the <a href="/docs/#api/en/renderers/WebGLRenderer"><code class="notranslate" translate="no">WebGLRenderer</code></a> to use <code class="notranslate" translate="no">alpha</code> so places we are not
drawing anything are transparent.</p>
<pre class="prettyprint showlinemods notranslate lang-js" translate="no">function main() {
  const canvas = document.querySelector('#c');
-  const renderer = new THREE.WebGLRenderer({antialias: true, canvas});
+  const renderer = new THREE.WebGLRenderer({
+    antialias: true,
+    canvas,
+    alpha: true,
+  });
</pre>
<p>And we get a background.</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/background-css.html"></iframe></div>
  <a class="threejs_center" href="/manual/examples/background-css.html" target="_blank">click here to open in a separate window</a>
</div>

<p></p>
<p>If we want the background to be able to be affected by <a href="post-processing.html">post processing
effects</a> then we need to draw the background using
THREE.js.</p>
<p>THREE.js makes this some what simple. We can just set the background of the scene to
a texture.</p>
<pre class="prettyprint showlinemods notranslate lang-js" translate="no">const loader = new THREE.TextureLoader();
const bgTexture = loader.load('resources/images/daikanyama.jpg');
scene.background = bgTexture;
</pre>
<p>which gives us</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/background-scene-background.html"></iframe></div>
  <a class="threejs_center" href="/manual/examples/background-scene-background.html" target="_blank">click here to open in a separate window</a>
</div>

<p></p>
<p>This gets us a background image but its stretched to fit the screen.</p>
<p>We can solve this issue by setting the <code class="notranslate" translate="no">repeat</code> and <code class="notranslate" translate="no">offset</code> properties of
the texture to show only a portion of image.</p>
<pre class="prettyprint showlinemods notranslate lang-js" translate="no">function render(time) {

   ...

+  // Set the repeat and offset properties of the background texture
+  // to keep the image's aspect correct.
+  // Note the image may not have loaded yet.
+  const canvasAspect = canvas.clientWidth / canvas.clientHeight;
+  const imageAspect = bgTexture.image ? bgTexture.image.width / bgTexture.image.height : 1;
+  const aspect = imageAspect / canvasAspect;
+
+  bgTexture.offset.x = aspect &gt; 1 ? (1 - 1 / aspect) / 2 : 0;
+  bgTexture.repeat.x = aspect &gt; 1 ? 1 / aspect : 1;
+
+  bgTexture.offset.y = aspect &gt; 1 ? 0 : (1 - aspect) / 2;
+  bgTexture.repeat.y = aspect &gt; 1 ? 1 : aspect;

  ...

  renderer.render(scene, camera);

  requestAnimationFrame(render);
}
</pre>
<p>and now THREE.js drawing the background. There is no visible difference from
the CSS version at the top but now if we used a <a href="post-processing.html">post processing
effect</a> the background would be affected too.</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/background-scene-background-fixed-aspect.html"></iframe></div>
  <a class="threejs_center" href="/manual/examples/background-scene-background-fixed-aspect.html" target="_blank">click here to open in a separate window</a>
</div>

<p></p>
<p>Of course a static background is not usually what we want in a 3D scene. Instead
we usually want some kind of <em>skybox</em>. A skybox is just that, box with the sky
draw on it. We put the camera inside the box and it looks like there is a sky in
the background.</p>
<p>The most common way to implement a skybox is to make a cube, apply a texture to
it, draw it from the inside. On each side of the cube put a texture (using
texture coordinates) that looks like some image of the horizon. It's also often
common to use a sky sphere or a sky dome with a texture drawn on it. You can
probably figure that one out on your own. Just make a cube or sphere, 
<a href="textures.html">apply a texture</a>, mark it as <code class="notranslate" translate="no">THREE.BackSide</code> so we 
render the inside instead of the outside, and either put it in your scene directly 
or like above, or, make 2 scenes, a special one to draw the skybox/sphere/dome and the
normal one to draw everything else. You'd use your normal <a href="/docs/#api/en/cameras/PerspectiveCamera"><code class="notranslate" translate="no">PerspectiveCamera</code></a> to
draw. No need for the <a href="/docs/#api/en/cameras/OrthographicCamera"><code class="notranslate" translate="no">OrthographicCamera</code></a>.</p>
<p>Another solution is to use a <em>Cubemap</em>. A Cubemap is a special kind of texture
that has 6 sides, the sides of a cube. Instead of using standard texture
coordinates it uses a direction from the center pointing outward to decide where
to get a color.</p>
<p>Here are the 6 images of a cubemap from the computer history museum in Mountain
View, California.</p>
<div class="threejs_center">
  <img src="../examples/resources/images/cubemaps/computer-history-museum/pos-x.jpg" style="width: 200px" class="border">
  <img src="../examples/resources/images/cubemaps/computer-history-museum/neg-x.jpg" style="width: 200px" class="border">
  <img src="../examples/resources/images/cubemaps/computer-history-museum/pos-y.jpg" style="width: 200px" class="border">
</div>
<div class="threejs_center">
  <img src="../examples/resources/images/cubemaps/computer-history-museum/neg-y.jpg" style="width: 200px" class="border">
  <img src="../examples/resources/images/cubemaps/computer-history-museum/pos-z.jpg" style="width: 200px" class="border">
  <img src="../examples/resources/images/cubemaps/computer-history-museum/neg-z.jpg" style="width: 200px" class="border">
</div>

<p>To use them we use <a href="/docs/#api/en/loaders/CubeTextureLoader"><code class="notranslate" translate="no">CubeTextureLoader</code></a> to load them and then use that as a the
scene's background.</p>
<pre class="prettyprint showlinemods notranslate lang-js" translate="no">{
  const loader = new THREE.CubeTextureLoader();
  const texture = loader.load([
    'resources/images/cubemaps/computer-history-museum/pos-x.jpg',
    'resources/images/cubemaps/computer-history-museum/neg-x.jpg',
    'resources/images/cubemaps/computer-history-museum/pos-y.jpg',
    'resources/images/cubemaps/computer-history-museum/neg-y.jpg',
    'resources/images/cubemaps/computer-history-museum/pos-z.jpg',
    'resources/images/cubemaps/computer-history-museum/neg-z.jpg',
  ]);
  scene.background = texture;
}
</pre>
<p>At render time we don't need to adjust the texture like we did above</p>
<pre class="prettyprint showlinemods notranslate lang-js" translate="no">function render(time) {

   ...

-  // Set the repeat and offset properties of the background texture
-  // to keep the image's aspect correct.
-  // Note the image may not have loaded yet.
-  const canvasAspect = canvas.clientWidth / canvas.clientHeight;
-  const imageAspect = bgTexture.image ? bgTexture.image.width / bgTexture.image.height : 1;
-  const aspect = imageAspect / canvasAspect;
-
-  bgTexture.offset.x = aspect &gt; 1 ? (1 - 1 / aspect) / 2 : 0;
-  bgTexture.repeat.x = aspect &gt; 1 ? 1 / aspect : 1;
-
-  bgTexture.offset.y = aspect &gt; 1 ? 0 : (1 - aspect) / 2;
-  bgTexture.repeat.y = aspect &gt; 1 ? 1 : aspect;

  ...

  renderer.render(scene, camera);

  requestAnimationFrame(render);
}
</pre>
<p>Let's add some controls in so we can rotate the camera.</p>
<pre class="prettyprint showlinemods notranslate lang-js" translate="no">import {OrbitControls} from 'three/addons/controls/OrbitControls.js';
</pre>
<pre class="prettyprint showlinemods notranslate lang-js" translate="no">const fov = 75;
const aspect = 2;  // the canvas default
const near = 0.1;
-const far = 5;
+const far = 100;
const camera = new THREE.PerspectiveCamera(fov, aspect, near, far);
-camera.position.z = 2;
+camera.position.z = 3;

+const controls = new OrbitControls(camera, canvas);
+controls.target.set(0, 0, 0);
+controls.update();
</pre>
<p>and try it out. Drag on the example to rotate the camera and see the cubemap
surrounds us.</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/background-cubemap.html"></iframe></div>
  <a class="threejs_center" href="/manual/examples/background-cubemap.html" target="_blank">click here to open in a separate window</a>
</div>

<p></p>
<p>Another option is to use an Equirectangular map. This is the kind of picture a
<a href="https://google.com/search?q=360+camera">360 camera</a> takes.</p>
<p><a href="https://hdrihaven.com/hdri/?h=tears_of_steel_bridge">Here's one</a> I found from
<a href="https://hdrihaven.com">this site</a>.</p>
<div class="threejs_center"><img src="../examples/resources/images/equirectangularmaps/tears_of_steel_bridge_2k.jpg" style="width: 600px"></div>

<p>It's not much different. First we load the equirectangular image as a texture
and then, in the callback after it has loaded, we can call <a href="/docs/#api/en/renderers/WebGLCubeRenderTarget.fromEquirectangularTexture"><code class="notranslate" translate="no">WebGLCubeRenderTarget.fromEquirectangularTexture</code></a>
which will generate a cubemap from the equirectangular texture for us.
We pass in the size we want the cubemap to be to <a href="/docs/#api/en/renderers/WebGLCubeRenderTarget"><code class="notranslate" translate="no">WebGLCubeRenderTarget</code></a>.
Passing in the height of the equirectangular image seems like a good bet.</p>
<pre class="prettyprint showlinemods notranslate lang-js" translate="no">{
-  const loader = new THREE.CubeTextureLoader();
-  const texture = loader.load([
-    'resources/images/cubemaps/computer-history-museum/pos-x.jpg',
-    'resources/images/cubemaps/computer-history-museum/neg-x.jpg',
-    'resources/images/cubemaps/computer-history-museum/pos-y.jpg',
-    'resources/images/cubemaps/computer-history-museum/neg-y.jpg',
-    'resources/images/cubemaps/computer-history-museum/pos-z.jpg',
-    'resources/images/cubemaps/computer-history-museum/neg-z.jpg',
-  ]);
-  scene.background = texture;
+  const loader = new THREE.TextureLoader();
+  const texture = loader.load(
+    'resources/images/equirectangularmaps/tears_of_steel_bridge_2k.jpg',
+    () =&gt; {
+      const rt = new THREE.WebGLCubeRenderTarget(texture.image.height);
+      rt.fromEquirectangularTexture(renderer, texture);
+      scene.background = rt.texture;
+    });
}
</pre>
<p>And that's all there is to it.</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/background-equirectangularmap.html"></iframe></div>
  <a class="threejs_center" href="/manual/examples/background-equirectangularmap.html" target="_blank">click here to open in a separate window</a>
</div>

<p></p>
<p>Rather than do it at load time you can also convert an equirectangular image
to a cubemap beforehand. <a href="https://matheowis.github.io/HDRI-to-CubeMap/">Here's a site that will do it for you</a>.</p>

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