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A 100% api compliant, low clutter, near-zero overhead way to add image size dimensions to a paperclip database record.
Ruby
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README.rdoc

Paperclip Autosizer

Paperclip Autosizer is a simple system to save “WxH” information to the database. The system works entirely in concert with the Paperclip API and makes no additional calls to imagemagick. This allows the programmer to use a stock paperclip gem or plugin and take advantage of upgrades to the most current version. It also runs without significant changes to performance or memory footprint. Compatibility problems should therefore be low and I hope this will be a useful safe solution for forward looking projects. These were at least my specific concerns with other well written but forked solutions and what drove me to write this.

The system operates by sending the original image dimensions from a slight subclass of the standard thumbnail processor to the model. Final images sizes are obtained through pure calculation. It sounds strange to calculate and resize an image in IM and then calculate that again in the model, but it's actually the best solution I found to this problem. Using a few lines of already preloaded code to allocate space for a few integers and floats, do two or three multiplications and divisions and retain a single non-destroyed variable to save to the database is not high overhead. This is much faster than calling out to identify, more compatible across server environments and easy. Furthermore thanks to the elegant and little used paperclip api options, the autosizer only runs after a post_processing event has succeeded and the sizes are written to the database during the normal rails model save method. Columns are auto-detected allowing for optional autosizing of each attached_file or specific style of attachment completely at the programmers discretion.

This is my first public software so please feel free to criticize. I know the syntax is pretty fast and I will make it human friendly when I get the chance.

Author

Andrew Eisberg

Copyright

Copyright © 2009 Andrew Eisberg

License

MIT License (www.opensource.org/licenses/mit-license.php)

Limitations

Currently only the '>' geometry flag is written as that's what I use 99% of the time when I also want a size. It would be quite easy to write in additional methods to support other IM geometries. These things are really just a few lines and not the rocket science part of IM.

Usage

To use Autosizer, simply copy the paperclip_autosizer.rb file to the models folder and the paperclip_processors folder to the lib folder. Make the model you wish to autosize a subclass of the PaperclipAutosizer class. Tell paperclip to use the autosize processor (a 100% compatible subclass of the default thumbnail processor) and add the line +after_post_process :autosize_attached_files+ after the has_attached_file declarations:

class User < PaperclipAutosizer
  has_attached_file :avatar, :styles => { :thumb => "100x100>" },
                             :processors => [:autosize]
  has_attached_file :center, :styles => { :large => "500x500>" },
                             :processors => [:autosize]
  after_post_process :autosize_attached_files
end

This is sufficient to handle multiple attached_files. If only one attachment of many is being autosized, the stricter callback +after_<attachment>_post_process+ can be used instead for greater efficiency.

In the migration for the model, simply add columns for each attached_file/style combination you wish to retain sizes for. PaperclipAutosizer will see them and ignore any saved attachments it doesn't see columns for. Columns must conform to the format +t.string :(attachment)_(style)_size+ to be recognized by the model.

t.string   :avatar_thumb_size
t.string   :center_large_size

The sizes can then be easily called in the view.

image_tag(@user.avatar.url(:thumb), :size => @user.avatar_thumb_size)
image_tag(@user.center.url(:large), :size => @user.center_large_size)

TextMate

Here is a textmate snippet you can use if you want. If you're not used to hacking stuff into your TM, here's how to do it. Make a new bundle with your name. Then a new snippet and paste this in. Give it a tab trigger of 'autosizer' or what you want and a scope selector of 'source.ruby.rails'. Then just type autosizer and tab in a model.

# Paperclip Method for ${1/[[:alpha:]]+|(_)/(?1::u$0)/g} Attachment with Autosizing has_attached_file :${1:attachment_name}, :styles => { :${2:large} => “${3:750}x${4:750}>”, :${5:thumb} => “${6:150}x${7:150}>” }, :processors => [:autosize], :url => “/system/auto_load/${1}s/:id/:style/:basename.:extension”, :path => “:rails_root/public/system/auto_load/:attachment/:id/:style/:basename.:extension”, :default_url => “/system/auto_load/defaults/default_:style.png”

validates_attachment_size :${1}, :less_than => 1.megabytes validates_attachment_content_type :${1}, :content_type => ['image/jpeg', 'image/png'] after_${1}_post_process :autosize_attached_files

$0

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