torsdag 8 april 2010

Scala and JMonkeEngine 2

I've started a small game development project for funsies. Getting JME2 to work properly on my linux box was a bit of a hassel initally since I wanted to have it work with maven. After a bit of tinkering and following the slightly dated tutorial (most of it is still correct as of March 2010) I got everything running smothly with a Hello3D sample in Java. However, since I wanted to use Scala 2.8, I realized I had to update Netbeans to 6.8 and get the new Scala plugin for it. So to get going a little faster I skipped the maven part for now. Setup is always easier the second time around I have noticed.

With my environment setup I created a Scala project. Included the lwjgl-, jinput- and the jme-2.0 jar and added the native bindings to the VM options. And I was ready to go!

So I quickly ran into a problem that is due to (I believe) the scala-netbeans plugin, a import error "jme is not a member of com". It seems that the issue is that the plugin had not realized that I had included the libraries. When I restarted Netbeans the following generated no errors:

A few nice features in Scala can be seen here. First, importing using a wildcard i.e. "somepackage._". In the case above I imported "com.jme._" because of that I dont have to write the entire package name for all the things I import from a subpackage of jme. Instead I can write, for instance, "app.SimpleGame" to import that class from "". Not the greatest thing in the world, but a good thing to know when looking at Scala code, and it does clean the import statements up.

The object keyword in Scala defines a "singleton object". What this means is that there will only ever be a single instance of that object. It's kind of like a Java class with only static methods. So why is this useful? Well, for starters Scala doesn't allow static methods so it's needed to create the entry point for the program. But, there is also something called companion objects (I'll talk about them another time) and that is when objects shine :)

The rest of the code is very similar to Java code. However, we can notice that the val "box" has no declared type. "box" still has a type of course, which is inferred by the scala compiler from the assignment to it. This cuts down on a bunch of boiler-plate. Oh, and "val" is a variable which can only be assigned to once (like a variable marked with the final keyword in Java). There is also "var" which is mutable.

I expect to see more Scala power once I get things rolling, for instance a DSL for the core game rules would be nice. I'll have to come back to that...

- Emil H

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