Three.js CRT Effect with DotScreen and RGB Shift

This article explains how to recreate a retro CRT monitor aesthetic in a 3D scene using Three.js post-processing. By combining the EffectComposer, DotScreenPass to simulate phosphor screen pixels, and a custom ShaderPass with RGBShiftShader to create chromatic aberration, you can easily achieve a nostalgic, analog television screen distortion.

1. Import the Required Modules

To implement post-processing, you need to import the core Three.js library along with the specific post-processing passes and shaders. Ensure you import the EffectComposer, RenderPass, DotScreenPass, ShaderPass, and RGBShiftShader.

import * as THREE from 'three';
import { EffectComposer } from 'three/examples/jsm/postprocessing/EffectComposer.js';
import { RenderPass } from 'three/examples/jsm/postprocessing/RenderPass.js';
import { DotScreenPass } from 'three/examples/jsm/postprocessing/DotScreenPass.js';
import { ShaderPass } from 'three/examples/jsm/postprocessing/ShaderPass.js';
import { RGBShiftShader } from 'three/examples/jsm/shaders/RGBShiftShader.js';

2. Initialize the Effect Composer

First, set up your standard Three.js scene, camera, and WebGL renderer. Once those are established, initialize the EffectComposer by passing your renderer to it. Add a standard RenderPass so the composer renders your original 3D scene before applying any effects.

// Set up the composer
const composer = new EffectComposer(renderer);

// Add the base render pass
const renderPass = new RenderPass(scene, camera);
composer.addPass(renderPass);

3. Add the DotScreenPass for the Pixel Grid

The DotScreenPass simulates the shadow mask or aperture grille of a classic CRT monitor by overlaying a dot pattern. You can control the angle and scale of the pattern. A high scale value creates a fine, subtle pixel grid.

// Parameters: (center, angle, scale)
const dotScreenPass = new DotScreenPass(new THREE.Vector2(0.5, 0.5), 0.5, 0.8);
composer.addPass(dotScreenPass);

Center: The focus point of the dot pattern.
Angle: The rotation of the dot pattern grid.
Scale: The density of the dots. Lower numbers make the dots larger and more obvious; higher numbers simulate a higher-resolution screen grid.

4. Add the RGBShiftShader for Color Bleeding

CRT monitors often suffer from convergence issues, causing color channels (Red, Green, and Blue) to misalign at the edges of the screen. You can replicate this using the RGBShiftShader wrapped in a ShaderPass.

const rgbShiftPass = new ShaderPass(RGBShiftShader);

// Adjust the amount of color separation
rgbShiftPass.uniforms['amount'].value = 0.0035;

composer.addPass(rgbShiftPass);

amount: Controls the distance of the color channel separation. Keep this value small (between 0.001 and 0.005) for a subtle, realistic analog glitch, or increase it for a heavily distorted look.

5. Update the Render Loop

To apply the effects, you must replace your standard renderer call in the animation loop. Instead of calling renderer.render(scene, camera), call composer.render().

function animate() {
    requestAnimationFrame(animate);

    // Update animations or controls here
    
    // Render the scene through the post-processing pipeline
    composer.render();
}

animate();

6. Handle Window Resizing

Because post-processing relies on render targets that match the screen dimensions, you must update the EffectComposer size whenever the browser window is resized.

```window.addEventListener(‘resize’, onWindowResize);

function onWindowResize() { const width = window.innerWidth; const height = window.innerHeight;

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

renderer.setSize(width, height);
composer.setSize(width, height);

} ```