> /usr/local/src/ruby-gtkglarea-0.9.0/examples/gtkglarea_demo.rb:3:in
`require': No such file to load -- opengl (LoadError)
>         from
/usr/local/src/ruby-gtkglarea-0.9.0/examples/gtkglarea_demo.rb:3

You need the OpenGL extensions for Ruby. The latest version can be
downloaded from this link:

    http://www2.giganet.net/~yoshi/rbogl-0.32.tgz

There are no English-language instructions in the distribution, but
fortunately it's just the standard sequence for building extensions:

    ruby extconf.rb
    make
    make install

For more information, check the "Library/Graphics/OpenGL Interface" entry in
the Ruby Application Archive:

    http://www.ruby-lang.org/en/raa.html

Hope this helps,

Lyle