Automatically generate sprite sheet atlas files for your Phaser JS game with a Node.js script

Written in June 22, 2021 - 🕒 2 min. read

In one of my first game devlogs, I explained how to automate the sprite sheet generation for Phaser 3 using Webpack, but I think it would be more helpful if I had an external script to do that, so anyone can use it.

But why not simply use those websites that mesh together PNG files into a sprite sheet? Well because Phaser not only needs the PNG sprite sheet, but also an atlas JSON file with all the sprite sheet details like frame name and dimensions.

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For this I’m going to use the free-tex-packer-core package made by odrick. The basic usage in its documentation looks like the following:

const { packAsync } = require('free-tex-packer-core');

const images = [
    { path: "img1.png", contents: fs.readFileSync("./img1.png") },
    { path: "img2.png", contents: fs.readFileSync("./img2.png") },
    { path: "img3.png", contents: fs.readFileSync("./img3.png") }

const options = { allowRotation: false };

async function packImages() {
    try {
        const files = await packAsync(images, options);
        for (let item of files) {
            console.log(, item.buffer);
    } catch (error) {

That by itself is already super helpful, but I want to take the extra step and be able to generate sprite sheets for all my sprites, and the way I have my files and folder is:

- original-files
  - sprites
    - hero
      - hero_walking_1.png
      - hero_walking_2.png
      - hero_walking_3.png
      - hero_jumping_1.png
      - hero_jumping_2.png
    - enemy
      - enemy_walking_1.png
      - enemy_walking_2.png

With a directories structure like the one above, I can have the following script that will loop through all directories in my sprite directory and get all the images inside each one of them:

const { packAsync } = require('free-tex-packer-core');
const path = require('path');
const { readFileSync, readdirSync, writeFileSync } = require('fs');

const SOURCE_SPRITES_PATH = path.resolve(__dirname, 'original-files', 'sprites');
const SPRITES_PATH = path.resolve(__dirname, 'assets', 'sprites');

async function generateAtlasFiles(assetName) {
    let spritesFolders;

    // use the parameter or get all folders from a directory
    if (assetName) {
        spritesFolders = [assetName];
    } else {
        spritesFolders = readdirSync(SOURCE_SPRITES_PATH);

    for (const spritesFolder of spritesFolders) {
        const spritesFiles = readdirSync(path.resolve(__dirname, SOURCE_SPRITES_PATH, spritesFolder));
        const images = [];
        spritesFiles.forEach((spritesFile) => {
                path: spritesFile,
                contents: readFileSync(
                    path.resolve(__dirname, SOURCE_SPRITES_PATH, spritesFolder, spritesFile)

        await packImages(images, spritesFolder);

async function packImages(images, spriteName) {
    try {
        const files = await packAsync(images, { allowRotation: false });

        // let's save the png and json files
        for (const item of files) {
            // get the file extension
            const fileExt ='.').pop();
            // save the file in the sprites directory
            await writeFileSync(
                path.resolve(__dirname, SPRITES_PATH, `${spriteName}.${fileExt}`),
    } catch (error) {

// process.argv[2] is the argument from the command when you run `node script.js arg`

This script will create the files my-sprite.png and my-sprite.json for each of your sprites in your sprite folder when running node generate-sprites.js, or node generate-sprites.js hero to generate sprites sheets for only one sprite, in this case, the hero sprite.

I hope this blog post was useful for you, have a good one!


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mettli on 6/19/22

This is very helpful! Thank you a lot!