Reactive Streams in Scala meet a Game Engine - Part 1

Mikołaj Koziarkiewicz

Series' Table of Contents

Intro

It’s always interesting to see a new (or newly fashionable) technique being applied to new and unexpected areas, and see whether it makes sense (and what makes or breaks it).

Such is the case with Scala (reactive) streaming and computer game creation. A while ago, I stumbled upon a talk by Aleksandar Prokopec, which planted the seed of inspiration for this blog series. And what set that seed on a path of growth was another presentation, this time by Michał Płachta [1].

So, why another thing on this?

Well, of course it wouldn’t be fun if the blog series was just a same-scenario rehash. Here’s what’s going to be different - while the aforementioned talks were more-or-less "from-scratch" affairs, creating a game engine and/or a streaming platform along the way - I will be going the "lazy" route, and attempting to join together a ready-made game engine with a ready-made streaming framework.

The primary advantage of this kind-of-unique[2] setup is that the focus almost by definition falls on the paradigm mismatch problem, and thus it’s easy to see what one must solve to make the whole shebang work.

And there’s a related blessing in disguise - because we’re operating between two rigid boundaries of stable libraries, any domain-related idiosyncrasies will be easily identifiable, and have a reduced chance of rising up later on to bite is in the hind parts.

Now, let’s talk framework choices.

Decisions, decisions

Game Engine

It may come as a surprise to some of the readers, but JVM game programming is not exactly a barren field, despite the infamous "Java is slow" stereotype. Probably the greatest influence in recent years has been the rise of Android, hence why a high proportion of JVM game engines provide support for both "mobile" and "desktop" targets[3].

In any case, two engines seem to be the strongest contenders at the moment: libGDX and jMonkeyEngine. Both have been present on the scene for several years, and offer comprehensive game development feature sets[4].

The choice, however, falls on libGDX, for two reasons: it has explicit support for 2D rendering, and it’s the one I’m actually familiar with.

I’m going to expand on libGDX in upcoming installments. Right now, let’s roll over to the other side for the…​

Streaming Implementation

Apart from the obvious choice of Akka Streams, I was also monitoring the progress of Swave.

I recommend following its development closely. It is, in implementation and design, significantly less complex than Akka Streams. Swave can therefore serve as a convenient stepping stone in beating the learning curve, when adapting to the streaming paradigm.

However, Swave is still shaping up, its documentation is somewhat lacking[5], and I have a sneaking suspicion that some unique features of its "competitor" (like blueprinting) might come in handy, so we’re sticking with Akka Streams.

OK, so the tech base is decided now. All that remains is one tiny detail - just what is the end goal and how to achieve it?

Some ground rules

Let’s start with the goal itself, since it’s pretty obvious - a natural way to verify whether something works (or doesn’t), is through a practical proof-of-concept. Therefore, during this series, I’m going to work towards a fully-playable simple game, that uses streaming as its core operational model.

This leads nicely to the preferred form of the series, i.e. a development blog - meaning:

  • installments will be posted (hopefully) regularly,

  • with a soft word-length cutoff,

  • mistakes will be made prominent (and prominently made), including potentially avoidable ones, in order to showcase them and their solutions[6].

Finally, to spice things up a bit, I’m going to deliberately forgo gathering "technical" inspiration from the aforementioned related talks and projects (like the additional abstractions introduced by Dr. Prokopec), in order to see where the problem domain lends toward convergent solution creation.

Up Next

In the next installment, we’re going to cover defining the scope of the PoC game. Stay tuned!

1. Source code here.
2. There are at least two similar projects. One went in the direction of providing an Rx* translation layer. It seems to be inactive for about two years now. Another, implemented in Kotlin, seems to be under active development. Both use the Rx* family of libraries.
3. Be aware 'though that since Android supports "native applications", a lot of Android games are written in C/C++ instead.
4. To answer a - perhaps - lingering question: Minecraft, the poster child of JVM games, uses neither. It has a proprietary engine, with several native bridges for OpenGL support etc.
5. Do see the presentations 'though for a good feel of what it offers.
6. Also making for a nice excuse in case of eggregious blunders.