Making 'The Matrix' Effect in Javascript
Tags: javascript, codepen, frontend, html
Published: 2019-09-20 08:49:17

---
title: Making 'The Matrix' Effect in Javascript
published: true
tags: javascript, codepen, frontend, html
description: How to make the falling green text on black terminal effect from the Matrix movie series using vanilla JS and HTML5 canvas API.  
cover_image: https://thepracticaldev.s3.amazonaws.com/i/n9b2p3j0h1mdqvms3ogc.gif
---

I have always been a big fan of the movie series 'The Matrix Trilogy'. In this article we will make the following visual effect from the matrix series in vanilla Javascript.

![Matrix Terminal](https://thepracticaldev.s3.amazonaws.com/i/n9b2p3j0h1mdqvms3ogc.gif)

This GIF here is optimized for size, so it's rather low quality and it janks. But our end result will be smooth. Let's get started.

We will render this visual effect on a HTML5 `canvas`. For this article, we don't need any other elements on our page than a `canvas`. Initially we can give it just any valid size (width and height), because we will be setting the actual width and height of the canvas from our JS code. And we will give it an ID to reference it easily from the JS code.

```html
<canvas width="500" height="200" id="canv" />
```

Now we can get the DOM Node for this `canvas` and set its width and height to fill the `body`. We will also get the 2D drawing context for this canvas. The screen will be black for this effect, so we will fill the canvas with black by drawing a black rectangle with width and height same as that of the canvas.

```js
// Get the canvas node and the drawing context
const canvas = document.getElementById('canv');
const ctx = canvas.getContext('2d');

// set the width and height of the canvas
const w = canvas.width = document.body.offsetWidth;
const h = canvas.height = document.body.offsetHeight;

// draw a black rectangle of width and height same as that of the canvas
ctx.fillStyle = '#000';
ctx.fillRect(0, 0, w, h);
```

We want to make the text fall in columns. Each column will be 20px wide. And in each frame of the animation, we will put a single character at the end of each column. Initially the end (y coordinate) of each column is at 0.

```js
const cols = Math.floor(w / 20) + 1;
const ypos = Array(cols).fill(0);
```

In each frame, we need to render a semi transparent black rectangle on top of the previous frame, so that the characters rendered in previous frames can look progressively dimmed. Then we need to render the new characters at the end of each column for the current frame.

The y coordinates for each column is stored in the `ypos` array. In each frame we want to randomly reset some columns to start from the top again, so that it seems like columns of varying heights are falling from the top. For the rest of the columns we will simply move the y coordinate 20px down, so that in next frame a new character appears below the current one.

```js
function matrix () {
  // Draw a semitransparent black rectangle on top of previous drawing
  ctx.fillStyle = '#0001';
  ctx.fillRect(0, 0, w, h);
  
  // Set color to green and font to 15pt monospace in the drawing context
  ctx.fillStyle = '#0f0';
  ctx.font = '15pt monospace';
  
  // for each column put a random character at the end
  ypos.forEach((y, ind) => {
    // generate a random character
    const text = String.fromCharCode(Math.random() * 128);
    
    // x coordinate of the column, y coordinate is already given
    const x = ind * 20;
    // render the character at (x, y)
    ctx.fillText(text, x, y);

    // randomly reset the end of the column if it's at least 100px high
    if (y > 100 + Math.random() * 10000) ypos[ind] = 0;
    // otherwise just move the y coordinate for the column 20px down,
    else ypos[ind] = y + 20;
  });
}

// render the animation at 20 FPS.
setInterval(matrix, 50);
```

That's all we need to render a matrix effect in vanilla JS. The code for this article is given in the pen below for reference.

{% codepen https://codepen.io/gnsp/pen/vYBQZJm %}

Hoping you enjoyed reading this article and learned a few things from it. 
You can find more about me at [gnsp.in](https://gnsp.in).

**Thanks for reading !**