Scruffy gem that uses rmagick has a bug that caused me a lot of troubles since I am new to Ruby programming language. I am using windows environment.
Anyway, I was trying an example from Ruby in Practice by Jeremy McAnally and Assaf Arkin when I encountered a strange bug with Scruffy (now I know that it is its bug but it took me a while :).
This bug causes that any graph you try to render, renders only partially, similarly to the picture below:
The problem (with solution) is described here: http://rubyforge.org/tracker/index.php?func=detail&aid=27102&group_id=2030&atid=7929.
The cause of this problem is incorrect generation of viewbox by the base renderer. When you incorporate changes mentioned in the link above to RUBY_INSTALL\lib\ruby\gems\1.8\gems\scruffy-0.2.6\lib\scruffy\renderers\base.rb you should be able to render correct graphs.