spright

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spright is more than a simple sprite sheet packer, it can be used as one though. Its key ideas are:

• Keep all the information about the sprites and tiles, required for being efficiently consumable by the game engine, in a plain text file.
• Instead of forcing one to split each sprite in a separate file and later address them using the filename, it should be possible to keep them in whatever format they are most conveniently to handle.
• It should be possible to give each sprite an ID, group them (e.g. for animations) or further annotate them for game specific purposes.
• The tool should be able to deduce obvious information from the input images and assist with completing the required information.

While any text editor can be used for writing the input definition, the Visual Studio Code Extension can greatly simplify the process.

Also have a look at the spright test suite to get an impression of the functionality.

Introduction:

• Simple sheet packing
• Advanced usage example

Reference:

• Terminology
• Input definition
  • Definition reference
  • Variables
• Output description
  • Additional functions
• Output template engine

Simple sheet packing

To pack your sprites into one or more sheets, create an input definition file spright.conf like the following and run spright:

max-width 1024                 # set some constraints for the sheet
max-height 1024
power-of-two true

output "spright{0-}.png"
description "spright.json"
  template "phaser.inja"       # select the template for your game engine

id "{{ source.filenameBase }}"
glob "characters/**/*.png"     # set the location of the images you want to pack
glob "scenery/**/*.png"

The sample creates a sprite sheet spright0.png along the output description spright.json, consumable by the Phaser game engine. Templates for some other game engines are provided and additional templates can be easily written.

See the input definition section for a description of the available options.

Advanced usage example

Say you got some nice sprites you would like to use in your next game:

"Decorations (32x32).png"	"Old enemies 2.png"	"misc_scenery.png"	"OrcAttack/Frame01.png" to "OrcAttack/Frame04.png"

And your game engine supports efficiently packed sprite sheets like this:

Then you may want to use spright to define the sprites within their original sources and directly pack the sheet from there.

To do so, start by creating a spright.conf containing the essential information:

sheet "sprites"
  padding 1
  output "sheet{0-}.png"

colorkey
crop
crop-pivot

input "Decorations (32x32).png"
  grid 32 32

input "Old enemies 2.png"
  grid 16 16

input "Orc Attack/Frame{01-04}.png"

input "misc_scenery.png"
  atlas

When spright is called without command line arguments, the input definition is read from spright.conf and it writes a spright.json file containing the output description.

Passing the argument -m complete activates the auto-completion, which extends spright.conf with automatically deduced information:

input "Decorations (32x32).png"
  grid 32 32
    sprite
    sprite
    sprite
    sprite
    sprite
  row 1
    sprite
    sprite
    sprite
    sprite
    sprite
...

It detected that Decorations (32x32).png contains five sprites per row and added them below...\ For sheets without grids it adds the sprites' rectangles:

...
input "misc_scenery.png"
  atlas
  sprite
    rect 78 12 6 27
  sprite
    rect 88 12 4 24
  sprite
    rect 97 9 6 34
  sprite
    rect 107 8 7 40
  sprite
    rect 6 17 17 52
...

Now you can complete the definition manually by e.g. giving the sprites IDs and customizing their pivot points:

...
input "Decorations (32x32).png"
  grid 32 32
  pivot left top
    sprite "banner_top"
    sprite "platform_1_left"
    sprite "platform_1_middle"
    sprite "platform_1_right"
    sprite "platform_1_sole"
  row 2
    sprite "banner_middle"
    sprite "platform_2_left"
    sprite "platform_2_middle"
    sprite "platform_2_right"
    sprite "platform_2_sole"
  row 3
    sprite "banner_bottom_1"
...

You can also tag sprites to define animations or other game specific properties and leave sprites you do not want to directly address without ID:

...
input "Old enemies 2.png"
  grid 16 16
    tag anim "blue_enemy_idle"
    sprite
    sprite
    tag anim "blue_enemy_dead"
    sprite
    tag anim "blue_enemy_jump"
    sprite
  row 1
    tag anim "blue_enemy_run"
    sprite
    sprite
    sprite
    sprite
    sprite
    sprite
  row 2
...

See the output template engine section on how to generate a file consumable by your game engine.

Terminology

Since there are quite some terms, an explanation of what they represent in spright might be useful:

• sheet: a collection of sprites which should be arranged on one or more slices, while obeying the defined constraints. Each sprite is part of a single sheet (there is a default sheet "spright").
• slice: a single layer of a sheet where the sprites are arranged.
• sprite bounds: the rectangular space a sprite allocates on the slice.
• pivot point: the coordinate of a point on a sprite used for placing it in the game (a.k.a anchor).
• input: a filename or sequence referring to one or more input images.
• source: a single image file of an input containing the pixel data of one or more sprites.
• output: a filename or sequence referring to one or more output images.
• texture: a single image file of an output containing the pixel data of one slice, possibly with some output transformations applied.
• (output) description: a file generated by spright containing the information about the sprites, like where to find them on which texture.

Input definition

Indentation is relevant in the hierarchical input definition file. There are two scoping rules:

1. A definition affects succeeding items on the same or a sub-level.
2. A definition affects its parent item.

The comments in the following sample should exemplify these:

pivot center middle      # sets default pivot point

input "furniture.png"
  pivot center bottom    # sets pivot point within "furniture.png"
  sprite "chair"
  sprite "lamp"
    pivot center top     # sets pivot point of "lamp"
  sprite "bed"

input "characters.png"
  sprite "player"
  sprite "bird"
    pivot center bottom  # sets pivot point of "bird"
  sprite "wolf"          # "wolf" still gets the default pivot point

Definition reference

The following table contains a list of all definitions, with the item each affects, the expected arguments and a description. Optional arguments are enclosed in square brackets. Unless specified otherwise, optional booleans default to true, numbers default to 1, and an additional value defaults to the first value.

Variables

Beside variables defined by set the following variables can be accessed in string parameters using {{variable}}:

In sprite definitions:

• index - the sprite`s index.
• inputIndex - the input`s index.
• inputSpriteIndex - the sprite's index in the input.
• sheet.id - the sheet id.
• source.filename - the source filename (e.g. "dir/file 01.png").
• source.filenameBase - the source filename without extension (e.g. "dir/file 01").
• source.filenameStem - the source filename without directory and extension (e.g. "file 01").
• source.filenameId - the source filename without extension and special characters replaced by '_' (e.g. "dir_file_01").
• source.dirname - the directory part of the source filename (e.g. "dir").

In output definitions:

• index - the output`s index.
• sheet.id - the sheet`s id.
• sprite.id - the first sprite's id.

The variables are substituted before the description is output. Custom transformations can be applied afterwards using the template engine functions.

Output description

By default a JSON file containing all the information about the sprites is written to spright.json. It has the following structure:

{
  "sprites": [
    {
      "id": "sprite_0",
      "index": 0,
      "inputIndex": 0,
      "inputSpriteIndex": 0,
      "pivot": { "x": 8.0, "y": 8.0 },
      "rect": { "x": 0, "y": 0, "w": 16, "h": 16 },
      "trimmedRect": { "x": 0, "y": 0, "w": 16, "h": 16 },
      "rotated": false,
      "sourceIndex": 0,
      "sourceRect": { "x": 0, "y": 0, "w": 16, "h": 16 },
      "trimmedSourceRect": { "x": 0, "y": 0, "w": 16, "h": 16 },
      "sliceIndex": 0,
      "sliceSpriteIndex": 0,
      "data": { "key": "value" },
      "tags": { "key": "value" },
      "vertices": [ 0.0, 0.0,  16.0, 0.0,  16.0, 16.0,  0.0, 16.0 ]
    }
  ],
  "slices": [
    {
      "spriteIndices": [0]
    }
  ],
  "sources": [
    {
      "filename": "dir/source.png",
      "path": "root",
      "width": 256,
      "height": 256,
    }
  ],
  "inputs": [
    {
      "filename": "dir/source.png",
      "sources": [
        {
          "index": 0,
          "spriteIndices": [0]
        }
      ]
    }
  ],
  "tags": {
    "key": {
      "value": [0]
    }
  },
  "textures": [
    {
      "sliceIndex": 0,
      "spriteIndices": [0],
      "path": "root",
      "filename": "dir/spright-0.png",
      "width": 256,
      "height": 256,
      "scale": 1.0,
      "map": ""
    }
  ]
}

This spright.json was generated from the sample above. As you can see, it is very verbose and only intended as an intermediate file, which should be transformed using the template engine.

Output template engine

With the power of the inja template engine it should be possible to transform the output description to a text file consumable by your game engine.\ A template is selected with the -t or --template and the output filename with the -o or --output parameter:

spright -t cpp.inja -o spright.h

This is what a simple template, that transforms the IDs of the output description's sprites into a JavaScript array initialization, looks like:

let sprite_ids = [
{% for sprite in sprites %}
"{{ sprite.id }}",
{% endfor %}
];

For information about the functionality of the template engine, please see the inja reference and the provided templates:

Additional functions

Beside the functions provided by inja the following functions are available:

• ceil(number): Returns the lowest integer which is bigger or equal than the passed number.
• floor(number): Returns the biggest integer which is less or equal than the passed number.
• makeId(string): Returns the string with all special characters replaced by _.
• removeExtension(filename): Returns the filename without the extension.
• removeDirectories(filename, [keep]): Returns the filename without the directories, with an optional number of directories to keep.
• joinPaths(path, ...): Returns a filename by joining the passed paths with directory separators.
• base64(filename): Returns the base64 encoded content of the file.

Templates

The following templates are already available:

Please share templates you come up with in the Discussions section.

The C++ template is just an example for how the sprite description can be directly embedded in code. This spright.h was generated from the sample, using the cpp.inja template.

Command line arguments

Usage: spright [-options]
  -m, --mode <mode>       sets the run mode:
     'update'             the default run mode.
     'rebuild'            regenerate output even when input did not change.
     'describe'           only output description, no texture files.
     'describe-input'     only output description of input, do not pack.
     'complete' [pattern] autocomplete inputs (matching optional pattern).
  -i, --input <file>      input definition file (default: spright.conf).
  -o, --output <file>     output file containing either the output
                     description (default: spright.json) or the
                     autocompleted input definition (defaults to --input).
  -t, --template <file>   template for the output description.
  -p, --path <path>       path to prepend to all output files.
  -v, --verbose           enable verbose messages.
  -h, --help              print this help.

The special identifiers stdin and stdout can be passed to --input and --output to enable console redirection.

Installation

Linux / MacOS

Pre-built packages can be downloaded from the latest release page.

A Homebrew formula is provided for building and installing spright:

brew tap houmain/tap
brew install --HEAD spright

Arch Linux users can install an up to date build from the AUR.

Windows

Pre-built packages can be downloaded from the latest release page.

Most conveniently but possibly not always the very latest version can be installed using a package manager:

# install using winget
winget install spright

# install using Chocolatey
choco install spright

Building

A C++17 conforming compiler is required. A script for the CMake build system is provided.

Installing dependencies on Debian Linux and derivatives:

sudo apt install build-essential git cmake

Checking out the source:

git clone --recurse-submodules https://github.com/houmain/spright

Building:

cd spright
cmake -B build
cmake --build build

License

spright is released under the GNU GPLv3. It comes with absolutely no warranty. Please see LICENSE for license details.

All image files are derived from files released as CC0 on OpenGameArt.