i wrote some helper methods for my application like this
module Magick
class Draw
def qrcode(qrcode, left_corner, top_corner, right_corner, bottom_corner)
size = qrcode.modules.length
width = right_corner - left_corner
height = bottom_corner - top_corner
wset = width.to_f / size
hset = height.to_f / size
...............
Where to place such code in rails ?
A common and easy way to load those patches is to create a file inside your ./config/initializers directory (ie: rmagick.rb) and put your code in this file.
All files in this directory are loaded and executed on environment startup.
You could also create a new file with your code in the lib/ directory (ie: rmagick_draw.rb) and add this line in ./config/application.rb:
config.autoload_paths += %W(#{config.root}/lib)
And then require the file anywhere you need it.