aseprite-atlas

Aseprite sprite atlas (or sprite atlas) parser and animator for browser and Node.js.

Installation

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

Usage

CLI

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

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

The contents of atlas.json are an Aseprite.File and ready for parsing.

JavaScript

Parse the packed sprite sheet and play a frog's idle animation:

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

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

// Retrieve the Alas.Animation tagged "frog-idle". Animations are stateless.
const frogAnimation = atlas.animations['frog-idle']

// 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). animator's state is now {period: 0, exposure: 0}.
let frogAnimator = Animator.animate(0, 0, frogAnimation)

// 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}.
frogAnimator = Animator.animate(
  frogAnimator.period,
  frogAnimator.exposure + 16.667,
  frogAnimation
)

// Print the location of the active cel within the sprite sheet PNG.
const frogCelIndex = Animator.index(frogAnimator.period, frogAnimation.cels)
const {x, y} = frogAnimation.cels[frogCelIndex].position
const {w, h} = frogAnimation.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's 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.

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 asepriteExportAtlas. 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

Publishing a New Version

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

License

© Stephen Niedzielski.

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/.