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<title>How to use Post Processing</title>
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<div class="lesson-title">
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<h1>How to use Post Processing</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>
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Many three.js applications render their 3D objects directly to the screen. Sometimes, however, you want to apply one or more graphical
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effects like Depth-Of-Field, Bloom, Film Grain or various types of Anti-aliasing. Post-processing is a widely used approach
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to implement such effects. First, the scene is rendered to a render target which represents a buffer in the video card's memory.
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In the next step one or more post-processing passes apply filters and effects to the image buffer before it is eventually rendered to
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the screen.
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</p>
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<p>
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three.js provides a complete post-processing solution via `EffectComposer` to implement such a workflow.
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</p>
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<h2>Workflow</h2>
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<p>
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The first step in the process is to import all necessary files from the examples directory. The guide assumes you are using the official
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[link:https://www.npmjs.com/package/three npm package] of three.js. For our basic demo in this guide we need the following files.
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</p>
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<pre class="prettyprint notranslate lang-js" translate="no">
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import { EffectComposer } from 'three/addons/postprocessing/EffectComposer.js';
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import { RenderPass } from 'three/addons/postprocessing/RenderPass.js';
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import { GlitchPass } from 'three/addons/postprocessing/GlitchPass.js';
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import { OutputPass } from 'three/addons/postprocessing/OutputPass.js';
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</pre>
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<p>
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After all files are successfully imported, we can create our composer by passing in an instance of `WebGLRenderer`.
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</p>
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<pre class="prettyprint notranslate lang-js" translate="no">
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const composer = new EffectComposer( renderer );
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</pre>
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<p>
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When using a composer, it's necessary to change the application's animation loop. Instead of calling the render method of
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`WebGLRenderer`, we now use the respective counterpart of `EffectComposer`.
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</p>
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<pre class="prettyprint notranslate lang-js" translate="no">
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function animate() {
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requestAnimationFrame( animate );
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composer.render();
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}
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</pre>
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<p>
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Our composer is now ready so it's possible to configure the chain of post-processing passes. These passes are responsible for creating
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the final visual output of the application. They are processed in order of their addition/insertion. In our example, the instance of `RenderPass`
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is executed first, then the instance of `GlitchPass` and finally `OutputPass`. The last enabled pass in the chain is automatically rendered to the screen.
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The setup of the passes looks like so:
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</p>
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<pre class="prettyprint notranslate lang-js" translate="no">
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const renderPass = new RenderPass( scene, camera );
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composer.addPass( renderPass );
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const glitchPass = new GlitchPass();
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composer.addPass( glitchPass );
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const outputPass = new OutputPass();
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composer.addPass( outputPass );
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</pre>
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<p>
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`RenderPass` is normally placed at the beginning of the chain in order to provide the rendered scene as an input for the next post-processing step. In our case,
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`GlitchPass` is going to use these image data to apply a wild glitch effect. `OutputPass` is usually the last pass in the chain which performs sRGB color space conversion and tone mapping.
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Check out this [link:https://threejs.org/examples/webgl_postprocessing_glitch live example] to see it in action.
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</p>
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<h2>Built-in Passes</h2>
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<p>
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You can use a wide range of pre-defined post-processing passes provided by the engine. They are located in the
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[link:https://github.com/mrdoob/three.js/tree/dev/examples/jsm/postprocessing postprocessing] directory.
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</p>
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<h2>Custom Passes</h2>
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<p>
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Sometimes you want to write a custom post-processing shader and include it into the chain of post-processing passes. For this scenario,
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you can utilize `ShaderPass`. After importing the file and your custom shader, you can use the following code to setup the pass.
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</p>
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<pre class="prettyprint notranslate lang-js" translate="no">
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import { ShaderPass } from 'three/addons/postprocessing/ShaderPass.js';
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import { LuminosityShader } from 'three/addons/shaders/LuminosityShader.js';
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// later in your init routine
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const luminosityPass = new ShaderPass( LuminosityShader );
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composer.addPass( luminosityPass );
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</pre>
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<p>
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The repository provides a file called [link:https://github.com/mrdoob/three.js/blob/master/examples/jsm/shaders/CopyShader.js CopyShader] which is a
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good starting code for your own custom shader. `CopyShader` just copies the image contents of the `EffectComposer`'s read buffer
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to its write buffer without applying any effects.
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</p>
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</div>
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</div>
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