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Resourcen:

• Episode 134: Paperclip
• jQuery
• Jcrop
• jsCropperUI
• rjcrop
• Full episode source code

Quellcode:

# models/user.rb
class User < ActiveRecord::Base
  has_attached_file :avatar, :styles => { :small => "100x100#", :large => "500x500>" }, :processors => [:cropper]
  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

  def avatar_geometry(style = :original)
    @geometry ||= {}
    @geometry[style] ||= Paperclip::Geometry.from_file(avatar.path(style))
  end

  private

  def reprocess_avatar
    avatar.reprocess!
  end
end

# users_controller.rb
def create
  @user = User.new(params[:user])
  if @user.save
    if params[:user][:avatar].blank?
      flash[:notice] = "Successfully created user."
      redirect_to @user
    else
      render :action => "crop"
    end
  else
    render :action => 'new'
  end
end

def update
  @user = User.find(params[:id])
  if @user.update_attributes(params[:user])
    if params[:user][:avatar].blank?
      flash[:notice] = "Successfully updated user."
      redirect_to @user
    else
      render :action => "crop"
    end
  else
    render :action => 'edit'
  end
end

# lib/paperclip_processors/cropper.rb
module Paperclip
  class Cropper < 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

<!-- views/users/crop.html.erb -->
<% title "Crop avatar" %>
<% content_for(:head) do %>
<%= stylesheet_link_tag "jquery.Jcrop" %>
<%= javascript_include_tag "jquery.Jcrop.min" %>
<script type="text/javascript" charset="utf-8">
$(function() {
  $('#cropbox').Jcrop({
    onChange: update_crop,
    onSelect: update_crop,
    setSelect: [0, 0, 500, 500],
    aspectRatio: 1
  });
});

function update_crop(coords) {
  var rx = 100/coords.w;
  var ry = 100/coords.h;
  $('#preview').css({
    width: Math.round(rx * <%= @user.avatar_geometry(:large).width %>) + 'px',
    height: Math.round(ry * <%= @user.avatar_geometry(:large).height %>) + 'px',
    marginLeft: '-' + Math.round(rx * coords.x) + 'px',
    marginTop: '-' + Math.round(ry * coords.y) + 'px'
  });
  var ratio = <%= @user.avatar_geometry(:original).width %> / <%= @user.avatar_geometry(:large).width %>;
  $("#crop_x").val(Math.round(coords.x * ratio));
  $("#crop_y").val(Math.round(coords.y * ratio));
  $("#crop_w").val(Math.round(coords.w * ratio));
  $("#crop_h").val(Math.round(coords.h * ratio));
}
</script>
<% end %>

<%= image_tag @user.avatar.url(:large), :id => "cropbox" %>

<h4>Preview:</h4>
<div style="width:100px; height:100px; overflow:hidden">
  <%= image_tag @user.avatar.url(:large), :id => "preview" %>
</div>

<% form_for @user do |f| %>
  <% for attribute in [:crop_x, :crop_y, :crop_w, :crop_h] %>
    <%= f.hidden_field attribute, :id => attribute %>
  <% end %>
  <p><%= f.submit "Crop" %></p>
<% end %>