Aseprite-atlas NPM

🗺️ aseprite-atlas

Aseprite sprite atlas (or sprite sheet) parser and animator for browser and Node.js. See the demo.

Installation

npm i aseprite-atlas. See the changelog for release notes.

Usage

There are two steps: 1) generate the output sprite sheet image and JSON from the Aseprite input files 2) parse and render animations from the sprite sheet outputs.

See the demo source and demo tests!

Generate the Atlas (CLI)

Given a list of Aseprite files, pack all images and animations into a single sprite sheet:

npx aseprite-atlas-pack --sheet atlas.png --data atlas.json *.aseprite

The output is a big image of sprites (atlas.png) and an Aseprite.File (atlas.json) which is ready for parsing.

These outputs should be regenerated any time assets (Aseprite files) change, usually as part of a build step.

Parse and Render (JavaScript)

Once atlas.json and atlas.png are available, a program can parse atlas.json to animate and render animations from atlas.png. A complete but minimal example follows. Subsequent sections detail each step in the example.

Minimal Example

All together, parse the packed sprite sheet and play the frog's idle animation:

import {Animator, Parser} from 'aseprite-atlas'
import * as asepriteJSON from './atlas.json'

const atlas = Parser.parse(asepriteJSON)

const animation = atlas.animations['frog-idle']
let animator = {period: 0, exposure: 0}

animator = Animator.animate(
  animator.period,
  animator.exposure + 16.667,
  animation
)
const index = Animator.index(animator.period, animation.cels)
const {x, y} = animation.cels[index].position
const {w, h} = animation.size
console.log(x, y, w, h)

See the demo for a running example rendered to a canvas.

The following sections only detail this example.

Parsing

Parse the Aseprite.File into an Atlas:

import {Parser} from 'aseprite-atlas'
import * as asepriteJSON from './atlas.json'
// Or:
//   const {Parser} = require('aseprite-atlas')
//   const asepriteJSON = require('./atlas.json')

// Parse the Aseprite.File (atlas.json) into an Atlas.
const atlas = Parser.parse(asepriteJSON)

Retrieve an Animation from the Atlas

Animations are stateless and are retrieved by Aseprite tag:

// Retrieve the Alas.Animation tagged "frog-idle".
const animation = atlas.animations['frog-idle']

Create an Animator and Animate It

import {Animator} from 'aseprite-atlas'
// Or: const {Animator} = require('aseprite-atlas')

// Create a mutable Animator state. Animators keep a record of the cel index
// oscillation period (which is used to derive the active index for the cels
// array) and its exposure timer (which is used to determine when the period
// should be advanced). Animators are just plain data.
let animator = {period: 0, exposure: 0}

// Animate by 1/60th of a second (~16.667 milliseconds). Depending on the cel
// duration specified in Aseprite, this may or may not advance the active cel.
// For a multi-cel forward animation where the first cel has a 10 millisecond
// duration, animator's state would be {period: 1, exposure: 6.667}.
animator = Animator.animate(
  animator.period,
  animator.exposure + 16.667,
  animation
)

Render the Animation

Once the animation has been animated, the current cel should be shown each render loop:

// Print the location of the active cel within the sprite sheet PNG.
const index = Animator.index(animator.period, animation.cels)
const {x, y} = animation.cels[index].position
const {w, h} = animation.size
console.log(x, y, w, h)

Features

aseprite-atlas adds little:

A utility for playing Aseprite animations (forward, reverse, or ping-pong). Mutable and immutable states are kept distinct.
A sparser data structure that includes linking animation cels together in the same array and associating Aseprite slices with their cels. This can be useful for collision detection, for example.
Support (by convention) for infinite durations. When a cel duration is set to 65 535 (hexadecimal ffff) in the Aseprite GUI, it will be parsed in JavaScript as Number.POSITIVE_INFINITY.
TypeScript typings for the Aseprite file format.
Tests for parsing and playback.
Open source.
Easy to replace. If aseprite-atlas doesn't meet your needs, it should be easy to migrate to a solution that does.

You might not need it.

Functionality Not Provided

aseprite-atlas performs light parsing to restructure the standard Aseprite format into a more useful one for animation and slice association. Consumers will likely need to provide additional code for creating and managing sprites, collision detection, etc. It is hoped that by focusing on a small set of responsibilities with a simple API, it will be easy to use (or not use) this library.

Cel durations are allowed to be infinite. This means they are incompatible with JSON (JSON5 supports infinite values).

Assumptions and Conventions

Assumptions

The Aseprite CLI is flexible and can produce a number of different formats. aseprite-atlas an input generated by the options used in aseprite-atlas-pack. Only the current version of Aseprite, v1.2.15-x64, is tested.

Conventions

Some wanted functionality is not modeled in the stock Aseprite format. This section lists conventions used by aseprite-atlas. It's possible to forget to apply these conventions, which can lead to bugs that aseprite-atlas cannot detect. To the extent possible, consumers should add tests for conventions to their code.

A duration of 65 535 (hexadecimal ffff) is considered a special value by aseprite-atlas and parsed as Number.POSITIVE_INFINITY. This value is only permitted in the last cel of a tagged animation but can appear in multiple tagged animations within the same Aseprite file.
Slices are associated to cels by tag name. This is error-prone for artists so consumers may wish to add tests to assure that all slices are associated to a cel tag.

Development

Incomplete work is tracked under todo.

Publishing a New Version

Update the changelog.
Execute npm version <patch|minor|major>.

Known Issues

Sprite sheet dimensions are no longer powers of two when exported. This is observable by re-exporting the demo/ sheet from Aseprite.

License

GPL-3.0-only

This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 3.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program. If not, see https://www.gnu.org/licenses/.