Hello,
I am unaware of a straightforward solution to this problem on my
platform, so I am seeking help here.
My attempts to install the ruby-opengl gem yield a bunch of errors along
the lines of:
./…/common/conv.h:146: error: implicit conversion loses integer
precision: ‘long’ tin ‘int’ …
I have googled for solutions and found a few links to this or that
github repo, but I haven’t found anything I could checkout and just
build. (Unless I am mistaken in thinking that invoking ‘rake’ is used to
build a gem from the project root…)
If you don’t have a solution, can you point me in the right direction?
Kind Regards,
Timothy
Hmm, it seems I am having a conversation with myself 
Nevertheless, I am posting my solution here in case it helps anyone
else. There were a gotchas here.
Firstly, I was trying to install ruby-opengl using rvm, but rvm
reportedly breaks
gems with native code extensions on Xcode 4.2. So rvm had to be removed.
Secondly, Apple removed gcc support or something (as far as I can tell)
in Xcode 4.2, meaning gcc 4.2 had to be installed. I did this with
homebrew:
brew update
brew tap homebrew/homebrew-dupes
brew install apple-gcc42
Lastly I used rbenv instead of rvm (optional), and installed ruby 1.8.7,
and finally ‘gem install ruby-opengl’ worked.