Carrierwave on the fly resize - ruby-on-rails

Question

I'm using carrierwave and I have this problem:
Suppose once the project has been delivered you need to add a section where the images in the system need to be displayed with a different size. I don' t want to regenerate the new dimension for each one of the images already in the system. I want to be able to generate (and cache it) whenever a view demands. Something like: " /> . If the new size 500x150 already exists, then returns the cached url, else generate it and return the cached url
I like pretty much Carrierwave but unfortunately doesn't have any on the fly resize feature out of the box. Everyone says it should be pretty simple add this feature but I found almost nothing. The only thing which goes pretty close is this uploader https://gist.github.com/DAddYE/1541912
I had to modify it to make it work so here is my version
class ImageUploader < FileUploader
include CarrierWave::RMagick
#version :thumb do
# process :resize_to_fill => [100,100]
#end
#
#version :thumb_square do
# process :resize_to_fill => [100,100]
#end
#
#version :full do
# process :resize_to_fit => [550, 550]
#end
def re_size(string_size)
if self.file.nil?
return self
end
begun_at = Time.now
string_size.gsub!(/#/, '!')
uploader = Class.new(self.class)
uploader.versions.clear
uploader.version_names = [string_size]
img = uploader.new(model, mounted_as)
img.retrieve_from_store!(self.file.identifier)
cached = File.join(CarrierWave.root, img.url)
unless File.exist?(cached)
img.cache!(self)
img.send(:original_filename=, self.file.original_filename)
size = string_size.split(/x|!/).map(&:to_i)
resizer = case string_size
when /[!]/ then :resize_to_fit
# add more like when />/ then ...
else :resize_to_fill
end
img.send(resizer, *size)
FileUtils.mv(img.file.file, cached)
#img.store!
end
img
end
def extension_white_list
%w[jpg jpeg gif png]
end
def filename
Digest::MD5.hexdigest(original_filename) << File.extname(original_filename) if original_filename
end
def cache_dir
"#{Rails.root}/tmp/uploads"
end
def default_url
'/general/no-image.png'
end
end
The problem with this version is that apparently when calling re_size("100x100").url, the url gets generated and returned before the actual resized image is created resulting in a page with broken links which displays good on any subsequent refresh.
Anyone achieved better results willing to share? :)
Please don't tell me to switch to Dragonfly. I'm using Carrierwave and i really like it. Also it seamlessly integrates with RailsAdmin which is part of my projects too.

Answer 1

Why don't you just generate a different version of the image, such as a thumbnail? In your image_uploader.rb
# Create different versions of your uploaded files:
include CarrierWave::RMagick
version :thumb do
process :resize_to_limit => [100, 100]
end
Then in your view just call
<%= image_tag nameofimage.image_url(:thumb).to_s %>
You could create multiple versions of our original image without resizing the original image. The processing is done by RMagick which you'll need to install.
RMagick requires you to have ImageMagick, so you'll need to install that as well. These can be a little tricky to get installed and working but well worth it. Plus the stackoverflow community has provided a lot of help with this issue.
Error installing Rmagick on Mountain Lion
rmagick gem install "Can't find Magick-config"