Clojure + Processing + Live-coding at the REPL

If you are familiar with Scheme and Common Lisp, I would say not hard. Much easier than if you were a Java-only guy coming to Clojure I would imagine. (disclaimer: I'm only really a dabbler in any of them, but I found starting out in Clojure very comfortable after learning the crippled Scheme from SICP and enough Common Lisp from Practical Common Lisp, ANSI Common Lisp, and Land of Lisp...)

I don't think it would be that difficult. The one big change I can think of is Clojure's pervasive immutability (a la Haskell). But even if you've never played with Haskell, I don't think it would take you too long to get comfortable with it.

If you want straight-up OpenGL bindings for clojure, there's Penumbra:

https://github.com/ztellman/penumbra

I am a CL guy, I find the Java stuff in Clojure quite frustrating. This is not because of any deficiencies in Clojure (it is much better than writing straight Java code).

The problem is that it is (comparatively) so hard to do anything in Java, and a lot of the object hierarchies and interfaces in the Java libraries are overly complex. But you can write macros and end up with a pretty nice DSL out of even an ugly Java library.

You also have to know all of the basic Java stuff, knowing about how to configure the classpath and how classes basically work in Java are key. It is good to know the various Java build tools as well.

There's a new OpenGL output being developed for Processing in the latest 192 pre-release of Processing. It is very performant.