This is a sample application that shows how to implement image cropping using the popular Paperclip Rails plugin and the Jcrop jQuery plugin for selecting the cropping area.
Paperclip project page: github.com/thoughtbot/paperclip/tree/master Jcrop home page: deepliquid.com/content/Jcrop.html
Most of the inspiration for this application was taken from this thread: groups.google.com/group/paperclip-plugin/browse_thread/thread/817266ea5b37580c and especially this helpful piece of code: groups.google.com/group/paperclip-plugin/msg/5b6dd7ade3ba6b87?hl=en
git clone git://github.com/jschwindt/rjcrop.git cd rjcrop rake db:migrate git submodule init git submodule update ./script/server
After that you can point your browser to localhost:3000, upload an image and see how easy is to create a cropped image that can be used as an avatar.
This application was featured by Ryan Bates on his Railscast #182 railscasts.com/episodes/182-cropping-images
The tricky part creating this application was to find a simple way of interacting with Paperclip in order to create the cropped images after the model was saved. In fact it was necessary to reprocess the attachments after they were initially loaded by the plugin.
class User < ActiveRecord::Base
has_attached_file :avatar,
:styles => { :normal => "240x240>",
:small = > "55x55#" },
:processors => [:jcropper]
attr_accessor :crop_x, :crop_y, :crop_w, :crop_h
after_update :reprocess_avatar, :if => :cropping?
def cropping?
!crop_x.blank? && !crop_y.blank? && !crop_w.blank? && !crop_h.blank?
end
# helper method used by the cropper view to get the real image geometry
def avatar_geometry(style = :original)
@geometry ||= {}
@geometry[style] ||= Paperclip::Geometry.from_file avatar.path(style)
end
private
def reprocess_avatar
avatar.reprocess!
end
end
The model includes the has_attached_file as usual but it specifies a custom processor jcropper that is slightly different from the original thumbnail.rb processor provided by Paperclip.
The process of creating the avatar works like this:
-
The user uploads an image and Paperclip creates the :normal and the :small version and because none of the :crop_x, :crop_y, :crop_w, :crop_h are defined
cropping?returns false. This way thejcropperprocessor works just like the originalthumbnailprocessor. -
Then the user is presented with the
normalthumbnail that is used to choose the cropping rectangle. -
Finally when the user model is updated and
cropping?returns true, the Paperclip reprocess! method is invoked and thejcropperprocessor crop the original image according to the cropping rectangle.
Because now the cropping rectangle parameters are provided by the view, then the crop_command specifies how to crop the original image. The string looks like: “-crop 500x500+125+450” that in the ImageMagick convert command means “crop the original image at offset 125,450 with a size of 500x500”. Finally the images are resized using :normal => “240x240>” and :small = > “55x55” parameters.
# Jcropper paperclip processor # # This processor very slightly changes the default thumbnail processor in order to work properly with Jcrop # the jQuery cropper plugin. module Paperclip # Handles thumbnailing images that are uploaded. class Jcropper < Thumbnail def transformation_command if crop_command crop_command + super.sub(/ -crop \S+/, '') else super end end def crop_command target = @attachment.instance if target.cropping? " -crop '#{target.crop_w.to_i}x#{target.crop_h.to_i}+#{target.crop_x.to_i}+#{target.crop_y.to_i}'" end end end end
The jcropper processor inherits from the original Thumbnail processor but redefines the transformation_command in order to get the cropping rectangle from the model if it is defined. Otherwise it works just like the original thumbnail processor.
All the magic happens in cropping.html.erb view and it should be easy to understand it by reading the Jcrop documentation. One important thing to remark is how the ratio between the original image and the normal thumbnail is computed using the avatar_geometry helper method from the model:
function showPreview(coords)
{
:
var ratio = <%= @user.avatar_geometry(:original).width %> / <%= @user.avatar_geometry(:normal).width %>;
:
}
Juan Schwindt juan(at)schwindt.org