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Bunto Assets

Bunto assets is an asset pipeline using Sprockets (v3) to build especially for Bunto. It utilizes new features of both Sprockets and Bunto to achieve a clean and extensible assets platform for Bunto.

Using Bunto Assets with Bunto

Add gem "bunto-assets" to your Gemfile and add bunto-assets to your _config.yml like the following:

  - bunto-assets


A lot of our configuration transforms based on the BUNTO_ENV variable set in your environment. Such as digesting and whether or not to enable the CDN. Some of them can be explicitly overridden but a few cannot right now. You should set your BUNTO_ENV=development on your development machine and BUNTO_ENV=production when building to push.

    css: false | true | default - development: false, production: true
    js: false | true | default - development: false, production: true
  cache: false | directory | default: .asset-cache
  skip_baseurl_with_cdn: false
  skip_prefix_with_cdn: false
  prefix: "/assets"
    - "*.png"
    - "bundle.css"
  digest: true
    - _assets/css
    - _assets/images
    - _assets/javascripts
    - _assets/stylesheets
    - _assets/fonts
    - _assets/img
    - _assets/js
    liquid: true | false | default: false
    automatic_img_size: true | false | default: true
    automatic_img_alt : true | false | default: true

Liquid Processing with your Bunto context

By default (whether features.liquid is true or false) we will process all files with the extension ".liquid", so if you give us ".scss.liquid" we will parse the liquid and then we will parse the SCSS and finally output your ".css" file.

When features.liquid is set to true, we will process ALL files through Liquid, regardless of whether they have the ".liquid" extension. Use this at your own risk.

Cache Folder

If you plan to change the cache folder, please make sure to add that folder to your exclude list in Bunto or you will generate over and over and over again, . folders are not ignored by default.


The listed resources in the example are all defaults. It should be noted that we append your sources instead of replace our resources with yours. So if you add _assets/folder then we will append that to our sources and both will work.

NOTE: if you use our _assets base folder container as a base folder for your sprockets, we will not append our sources, we will only use that folder as the sole source (base folder.)


  • Disable digesting by default in development.
  • Digest by default in production.

You can force digesting with digest: true in your _config.yml


  • Requires sass and uglifier.
  • Disable compression by default in development.
  • Enable by default in production.

Bower Components

Modify your .bowerrc file and add:

  "directory": "_assets/bower"

And then add _assets/bower to your sources list and Sprockets will do the the rest for you... you can even //= require bower_asset.js. We will even compress them for you per normal if Sprockets supports it and allows us to.

You do not need to modify your .bowerrc file, you can optionally just add it to your sources list and it will work that way too! As long as it's in your Bunto folder.


  • image, img
  • javascript, js
  • stylesheet, css, style
  • asset, asset_source
  • asset_path

Tag Example:

{% img src magick:2x alt:'This is my alt' %}
{% img src magick:2x alt:'This is my alt' sprockets:accept:image/gif %}

What do the colons mean? Proxies/Tags

  • argument is a boolean HTML argument.
  • key:value is an HTML key="value" if no proxy exists.
  • proxy:key:value will set a proxy key with the given value.
  • proxy:key is a boolean argument if the proxy and key exists.
  • unknown:key:value will raise DoubleColonError, escape it.
  • proxy:unknown:value will raise a UnknownProxyError.

Lets say we have sprockets proxies and sprockets allows you to proxy accept, if you send {% img src sprockets:accept:image/gif } then Sprockets find_asset will get { :accept => "image/gif" } but if you try to proxy "unknown" on sprockets we will raise a Proxy error. For more information then look at parser_spec.rb in the spec folder because it literally lays out the ground rules for our tags as a specification.

Current Proxies:

  • sprockets:accept:<value>
  • sprockets:write_to:<value>

Liquid Variables

We support liquid arguments for tag values (but not tag keys), and we also support Liquid pre-processing (with your Bunto context) sass/less/css files you need do nothing special for the preprocessing an entire file, it's always done.

An example of using Liquid in your tags:

{% img '{{ image_path }}' %}
{% img '{{ image_path }}' proxy:key:'{{ value }}' %}
{% img {{\ image_path\ }} %}

An example of using Liquid in your SCSS:

.bg {
  background: url(asset_path("{{ site.background_image }}"));

You have full access to your entire Bunto context from any liquid processing we do, so you can do whatever you like and be as dynamic as you like, including full loops and conditional Liquid based CSS since we pre-process your text files.

Getting a list of your assets and basic info from Liquid

We provide all your assets as a hash of Liquid Drops so you can get basic info that we wish you to have access to without having to prepare the class.

{{ assets["bundle.css"].content_type }} => "text/css"
{{ assets["images.jpg"].width  }} => 62
{{ assets["images.jpg"].height }} => 62

The current list of available accessors:

  • logical_path
  • content_type -> type
  • filename
  • basename
  • width
  • height

If you would like more, please feel free to add a pull request, at this time we will reject all pull requests that wish to add any digested paths as those are dynamically created when a proxy is ran so we can never predict it reliably unless we proxy and that would be a performance problem.

ERB Support

ERB Support is removed in favor of trying to get this included on Github Pages eventually (if I can.) Having ERB presents a security risk to Github because it would allow you to use Ruby in ways they don't want you to.


There is a full suite of filters, actually, any tag and any proxy can be a filter by way of filter arguments, take the following example:

{{ src | img : "magick:2x magick:quality:92" }}


  • :env => [:init]

You can register and trigger hooks like so:

Bunto::Assets::Hook.register :env, :init do
  # Your Work

Sass Helpers

Our currently supported helpers are:

  • asset_path
  • image_path
  • font_path


  • CSS Auto Prefixer - add "autoprefixer-rails" to your Gemfile.
  • ES6 Transpiler (through Babel) - add "sprockets-es6" to your Gemfile.
  • Image Magick - add "mini_magick" to your Gemfile, only works with img, image.
  • Bootstrap - add "bootstrap-sass" to your Gemfile and "@import 'bootstrap'"
  • Font Awesome - add "font-awesome-sass" to your Gemfile.

Please note that some of these (if not all) have trouble with Rhino -- therubyrhino so you would probably be best to just use Node.js or io.js at that point rather than trying to fight it.

Image Magick Proxy arguments:

  • magick:resize:<value>
  • magick:format:<value>
  • magick:quality:<value>
  • magick:rotate:<value>
  • magick:gravity:<value>
  • magick:crop:<value>
  • magick:flip:<value>
  • magick:quadruple, magick:4x
  • magick:one-third, magick:1/3
  • magick:three-fourths, magick:3/4
  • magick:two-fourths, magick:2/4
  • magick:two-thirds, magick:2/3
  • magick:one-fourth, magick:1/4
  • magick:half, magick:1/2

Having trouble with our documentation?

If you do not understand something in our documentation please feel free to file a ticket and it will be explained and the documentation updated, however... if you have already figured out the problem please feel free to submit a pull request with clarification in the documentation and we'll happily work with you on updating it.