Programming language: Go
Tags: Tools    
Latest version: v0.0.9

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Automatically build and rebuild Xcode image catalogs for app icons, universal images, and more.

  • Use in existing projects to generate image catalogs with no extra work. Blade will automagically refresh your image catalogs based on given master images.
  • Use templates of image catalogs to generate new catalogs (see [templates](templates/)).

See blade-sample for a preconfigured project.


Because most of the time your image catalogs are the same image, resized to various sizes.

Here is how people solve this usually:

The problem with these solutions is:

  • Some times the various slices are not up to date with Xcode (new devices, new sizes)
  • It Almost always require extra work from you (placing each image manually in the catalog, fixing mismatches etc.)
  • You can't control the quality of the resize
  • You can't integrate the tooling into your build workflow or CI

Blade is an open source tool which will replace the PSD template and/or online services for you, and has a goal to satisfy the above requirements in the best way possible.

Quick start

You have 2 ways to install:


Using Homebrew:

 $ brew tap jondot/tap
 $ brew install blade

Download one of the binaries in releases, and put in your PATH or just include in each Xcode project's root.

This should be a typical run of blade:

Use a Bladefile

Here's how a project setup with a Bladefile feels like (more in the Blade Sample repo):


The best way to use Blade, is to set up a local Bladefile for your entire project. Within it, specify all of your resources. Blade will pick it up automatically.

See blade-sample for a preconfigured project.

$ blade --init
Wrote Bladefile.

Here is how your Bladefile would look like:

  - source: [email protected]
    mount: foobar/Assets.xcassets/AppIcon.appiconset
  - source: Spaceship_1024.png
    mount: foobar/Assets.xcassets/Spaceship.imageset

It was made for this project structure:

โ”œโ”€โ”€ Bladefile
โ”œโ”€โ”€ images
โ”‚ย ย  โ”œโ”€โ”€ [email protected]
โ”‚ย ย  โ””โ”€โ”€ Spaceship_1024.png
โ”œโ”€โ”€ foobar
โ”‚ย ย  โ”œโ”€โ”€ AppDelegate.swift
โ”‚ย ย  โ”œโ”€โ”€ Assets.xcassets
โ”‚ย ย  โ”‚ย ย  โ”œโ”€โ”€ AppIcon.appiconset
โ”‚ย ย  โ”‚ย ย  โ”‚ย ย  โ””โ”€โ”€ Contents.json
โ”‚ย ย  โ”‚ย ย  โ””โ”€โ”€ Spaceship.imageset
โ”‚ย ย  โ”‚ย ย      โ”œโ”€โ”€ Contents.json

Then use Blade (use --verbose if you want logs) within the same folder where your Bladefile lives:

$ blade --verbose
INFO[0000] Found a local Bladefile.
INFO[0000] Bladefile contains 2 blade defs.

And it will generate all of the images needed within each image catalog.

To make this happen before each build see how to run a script while building a product

Use directly


$ blade [email protected] --template=templates/watch.json --out=out/watch --catalog

Here's what we did:

  • Use a source image (--source)
  • Make a brand new image catalog (--catalog), from a template (templates/watch.json)
  • Put everything in out/watch
$ blade -s [email protected] -t existing.imageset -o existing.imageset

Here's what we did:

  • Use a source image (-s)
  • Point to an existing image catalog (-t)
  • Output to that same existing image catalog (-o)
  • In other words, Blade will refresh the images in this catalog

How does it work?

Blade parses the same Xcode image catalog configuration file as its own configuration source - no new concept introduced. This allows it to be future-proof with Xcode updates for new image sizes and catalog types.

Supported workflows:

  • Prototyping ad-hoc, while prototyping projects
  • Development build with Build Steps, transforming all of your source image assets to image catalogs
  • CI in your CI servers, either on OSX or Linux (though Linux can't compile code in this case, you can still use it to do image processing)

Supported resize algorithms (-i or --interpolation flag):

See here for live samples.

Hacking on Blade

Pull requests are happily accepted.

Here's what you should know if you want to improve Blade:

  • Your workflow starting point is the Makefile. There you should see how to setup the development tooling, run builds, tests and coverage.
  • The architecture splits out the runner from the converter, so that we could swap to other, faster, converters (vips) if needed.
  • The other concerns are the Contents.json ([contents.go](contents.go)) parsing and dimension ([dimensions.go](dimensions.go)) computation logic.
  • Finally, you're left with the Bladefile ([bladefile.go](bladefile.go)) and CLI ([main.go](main.go)) logic to handle.

Also, check out [fixtures](fixtures) for quick image catalog configuration to work with.

Here is a typical flow:

  1. Clone project
  2. Branch off for your changes
  3. Edit code
  4. Test your changes, submit PR
  5. (release) make bump
  6. (release) make release
  7. (release) use hub to upload release binaries
  8. (release) make brew_sha ver=<current version>
  9. (release) update jondot/homebrew-tap version and sha to point to new binary

(* 'release' flows are done by core committers)


Fork, implement, add tests, pull request, get my everlasting thanks and a respectable place here :).


Copyright (c) 2015 Dotan Nahum @jondot. See MIT-LICENSE for further details.

*Note that all licence references and agreements mentioned in the Blade README section above are relevant to that project's source code only.