class ActiveStorage::Variant

  • {ruby-vips reference}[http://www.rubydoc.info/gems/ruby-vips/Vips/Image]
    * {ImageProcessing::Vips}[https://github.com/janko-m/image_processing/blob/master/doc/vips.md#methods]
    * {ImageMagick reference}[https://www.imagemagick.org/script/mogrify.php]
    * {ImageProcessing::MiniMagick}[https://github.com/janko-m/image_processing/blob/master/doc/minimagick.md#methods]

    Visit the following links for a list of available ImageProcessing commands and ImageMagick/libvips operations:
    avatar.variant(resize_to_limit: [800, 800], monochrome: true, rotate: “-90”)
    ImageProcessing gem (such as resize_to_limit):
    You can combine any number of ImageMagick/libvips operations into a variant, as well as any macros provided by the
    Then it’ll upload said variant to the service according to a derivative key of the blob and the transformations.
    This will create and process a variant of the avatar blob that’s constrained to a height and width of 100.
    avatar.variant(resize_to_limit: [100, 100]).processed.service_url
    the transformations, upload the variant to the service, and return itself again. Example:
    has already been processed and uploaded to the service, and, if so, just return that. Otherwise it will perform
    When you do want to actually produce the variant needed, call processed. This will check that the variant
    can then produce on-demand.
    This will create a URL for that specific blob with that specific variant, which the ActiveStorage::RepresentationsController
    <%= image_tag Current.user.avatar.variant(resize_to_limit: [100, 100]) %>
    by Active Storage like so:
    To refer to such a delayed on-demand variant, simply link to the variant through the resolved route provided
    ActiveStorage::RepresentationsController.
    in a template, for example. Delay the processing to an on-demand controller, like the one provided in
    you also want to be considerate about when the variant is actually processed. You shouldn’t be processing variants inline
    Note that to create a variant it’s necessary to download the entire blob file from the service. Because of this process,
    # => :vips
    Rails.application.config.active_storage.variant_processor = :vips
    # => :mini_magick
    Rails.application.config.active_storage.variant_processor
    gem).
    processor operated by the ruby-vips}[https://github.com/jcupitt/ruby-vips]<br>{MiniMagick gem, but you can also switch to the
    default, images will be processed with ImageMagick using the
    of the file, so you must add gem "image_processing" to your Gemfile if you wish to use variants. By
    Variants rely on ImageProcessing gem for the actual transformations
    original.
    These variants are used to create thumbnails, fixed-size avatars, or any other derivative image from the
    Image blobs can have variants that are the result of a set of transformations applied to the original.

def image

Returns the receiving variant. Allows ActiveStorage::Variant and ActiveStorage::Preview instances to be used interchangeably. 
def image
  self
end

def initialize(blob, variation_or_variation_key) 

def initialize(blob, variation_or_variation_key)
  @blob, @variation = blob, ActiveStorage::Variation.wrap(variation_or_variation_key)
end

def key

Returns a combination key of the blob and the variation that together identifies a specific variant. 
def key
  "variants/#{blob.key}/#{Digest::SHA256.hexdigest(variation.key)}"
end

def process 

def process
  blob.open do |image|
    transform(image) { |output| upload(output) }
  end
end

def processed

Returns the variant instance itself after it's been processed or an existing processing has been found on the service. 
def processed
  process unless processed?
  self
end

def processed? 

def processed?
  service.exist?(key)
end

def service_url(expires_in: ActiveStorage.service_urls_expire_in, disposition: :inline)

for its redirection.
for a variant that points to the ActiveStorage::RepresentationsController, which in turn will use this +service_call+ method
Use url_for(variant) (or the implied form, like +link_to variant+ or +redirect_to variant+) to get the stable URL

it allows permanent URLs that redirect to the +service_url+ to be cached in the view.
Hiding the +service_url+ behind a redirect also gives you the power to change services without updating all URLs. And
with users. Instead, the +service_url+ should only be exposed as a redirect from a stable, possibly authenticated URL.
Returns the URL of the variant on the service. This URL is intended to be short-lived for security and not used directly 
def service_url(expires_in: ActiveStorage.service_urls_expire_in, disposition: :inline)
  service.url key, expires_in: expires_in, disposition: disposition, filename: filename, content_type: content_type
end

def specification 

def specification
  @specification ||=
    if WEB_IMAGE_CONTENT_TYPES.include?(blob.content_type)
      Specification.new \
        filename: blob.filename,
        content_type: blob.content_type,
        format: nil
    else
      Specification.new \
        filename: ActiveStorage::Filename.new("#{blob.filename.base}.png"),
        content_type: "image/png",
        format: "png"
    end
end

def transform(image, &block) 

def transform(image, &block)
  variation.transform(image, format: format, &block)
end

def upload(file) 

def upload(file)
  service.upload(key, file)
end