Archive for April, 2013

David Henningsson

I ported my game to Ubuntu

If you just want to play the game, here’s where you find it. Or, in a terminal window write:

sudo add-apt-repository ppa:diwic/theblobgame
sudo apt-get update
sudo apt-get install theblobgame

Then just search for “blob” in the Dash.

The rest of this blog post is mostly directed towards game developers. Screenshot

Background and motivation

Ten years ago I finished a game called “The Blob Game”. It was a 2D platform style game, more cute than violent. My cousin had made the graphics, a level editor, and part of the game engine. I made seven levels, music, and completed the code. Back then, I was still working for a company doing closed source software for Windows, so naturally this game was a Windows game.

A while ago I decided to try to port this game to Ubuntu. My main motivations were:

  • To see how easy (or hard) it was, given my current level of experience. Also because we currently have some undergoing efforts to make Ubuntu a better gaming platform, and what better way to do that, than to become a game developer yourself?
  • People complain that there are not enough games available in Ubuntu – I wanted to make my small contribution to help even that out.
  • Nostalgia purposes – after all, most of the work with the game was to make the levels and the artwork, rather than actual code. All of this can be reused, and it would be nice if this game could entertain a new audience.

Overall, the experience has been good. Sure, there has been some work to do and new things to learn and conquer, but there has been very little of frustration. A fun side project!

One of the strength and weaknesses of the Linux ecosystem is all the choices you can, and have to, make. What components do you choose to build your software on? That can be bewildering, especially if you’re new to Linux and unfamiliar what components are suboptimal for one reason or another. I would therefore like to talk you through the choices I made and why I made them. As usual, these are my own opinions, not my employer’s.

Language: C

To give some background, my cousin and I started programming twenty years ago. Back then, my father introduced me to Turbo Pascal, which was more powerful than the QBasic that came with DOS 5.0. Ten years later, I was using Delphi (the Windows continuation of Pascal) at my work. So the game was written in Delphi, mixed with some hand written assembly code (!).

Was it possible to reuse the code written? I looked at the available compilers:

  • GNU Pascal. This project seems mostly abandoned, so not a stable choice for the future.
  • FreePascal. This was the main alternative, but it has its own code generator (not integrated with GCC or LLVM), so chances are it won’t keep up in the future. Also, if you need to link to a library, chances are you have to translate headers yourself.

So; rewrite the code. In what language? My choice fell on C, for the following reasons:

  • It is a very popular language, maybe even the most popular one. It is likely to be around for a long time, and have support for new processors and architectures as they come to market.
  • It is compatible with everything. In fact, it’s what every other language tries to be compatible with (Java has JNI, Python has C extensions, etc).
  • It is what I use at work, so I know the language very well. (Both Linux and PulseAudio are written in C.)
  • I like the low memory footprint and predictability of C – you want a game to run fluently, the audio to run at a reasonably low latency, and so on. With the exception of calling functions you don’t know about, you can almost see how quick your code executes. I’m not sure how well Java, Python, and the other garbage collecting languages do in this area; so my fear might be unfounded, but at least I know C does well.

Gaming library: libSDL

Fortunately, the cross-platform toolkit libSDL is very well supported under Linux. I have almost only positive experiences of this library: it seems very stable. It handles graphics (window setup, fullscreen etc), input events (keyboard, mouse, gamepads just work), audio, and more. The documentation is extensive and there are plenty of examples out there. And because libSDL is already used by so many games already, most distributions make sure libSDL works on their software and hardware.

What about OpenGL? Well, this is a 2D game, so I don’t need 3D. It is possible I could use some hardware acceleration for the scaling (the frame is rendered in 320×200, then upscaled to the screen’s resolution), but my very simple scaler seems to perform well enough. As such, there was no real need to bring in a dependency on OpenGL.

Music library: FluidSynth

First I’m a more than a bit biased on this dependency, as I’m one of the FluidSynth developers. However, the reason I first got involved with FluidSynth was that I wanted to use it in a game, and needed to fix something in the library…

FluidSynth is a softsynth – it takes MIDI data and a soundfont, and gives you rendered audio as a result. This has the drawback that you need to download a soundfont too, and the only one available in the Ubuntu archive is > 100 MB. The good thing is that FluidSynth is very embeddable into many different kinds of applications, so taking the audio output, mixing it with sound effects, and then send it to the sound card (with libSDL) was easy. It is also easy to manipulate the MIDI in real-time – in this game I’ve used it to pitch down the audio when you die.

GUI toolkit library: glib and GTK3

Let’s first admit it; in the Linux world we don’t have anything as stable as the Win32 API for creating windows. The two main contesters, GTK and QT, are both rewritten every five years or so. So if I, ten years from now, need to run this game again, chances are that I have to rewrite this part. The GUI is just used in the beginning though (to setup the game), so it shouldn’t be too much work.

I chose GTK over QT here because

  • I had previous experience with GTK
  • QT adds complexities to your build system, as you need not only a C++ compiler, but also a special preprocessor to turn some special QT constructs into valid C++ code.

Build system: simple Makefile

In my case, my application takes a few seconds to compile. For really simple applications like this one, I find build systems such as autotools or CMake to be more trouble than what they solve. In both cases, you’ll have to learn an additional language just to specify your build dependencies. (Autotools also has a few nuisances, such as requiring some extra files to be present, and in all upper-case, such as AUTHORS or NEWS.)

For larger projects, they make more sense though as they might help you create libraries for different platforms, give nice error messages when build dependencies can not be found, etc.

Licensing: LGPL-2 + CC-BY-SA

This is always a tricky and controversial subject, and I’d like to reiterate that this a layman’s thoughts on the topic and nothing else.

  • GPL is the strongest license when it comes to free software. But that also makes it a very incompatible license, it is essentially impossible to link GPL code with everything that’s not extremely weak (e g BSD) or explicitly made to fit with GPL (e g LGPL). One example of an incompatible license is MPL 1.1 – this was a quite popular license in the Delphi community, and the incompatibility with GPL was a real pain.
  • It is not obvious where the boundaries between GPL and non-GPL code can be, causing confusion in court from time to time. FSF might offer some advice on how to interpret the license; but they’re not a neutral party. In this case, I find the LGPL, the second strongest license, more clear.
  • So LGPL-2, LGPL-3 or LGPL2+? Well, to me, any “at your option, any later version” clause is out of the question; for me, that’s essentially the same as giving your code away to the FSF as they can relicense your code any way they wish. And LGPL-2 is shorter than LGPL-3 because LGPL-3 includes the full GPL-3 license code, too.
  • LGPL-2 is suitable for code, but not for data. So music, graphics and levels are licensed under CC-BY-SA. I was considering adding “non-commercial”; but the border between commercial and non-commercial can be fluid, and might also be a problem with the DFSG, so I skipped that part.

Update: Seems I didn’t read closely enough – LGPL-2 has a GPL-2+ clause, now making it possible for the FSF to relicense my code by making a new GPL version.

I also downloaded new sound effects (which is the only part not completely made by myself or my cousin), to make sure there was no licensing problems with those.

Getting it into the Ubuntu Software Center

Unfortunately, this does not currently work for free applications. While adapting my packaging to fit the requirements was relatively straight-forward, and also walking through the dialogs for app submission, when all this work was done, I was met by the following message:
Thank you for submitting a gratis Free Software application through MyApps. At this time we are unable to process this request, as we are working on the implementation of a new app upload process.
Bummer. Disappointing message.

A packaging tip

While we’re on the topic of packaging, let me just share a quick tip. If you’re new to Debian packaging (the system used in Ubuntu), and just want to package your own app, one thing to think about is that the packaging system was designed for having coders and packagers belong to separate organisations. So that means, that if you during packaging find a bug in your code, you’re meant to make a temporary patch, send that the coder, who will then make another release of the non-packaged software, which you will then package. In practice, this is a bit heavy-weight if you’re just one person and don’t keep packaging and code apart, so I used the following shortcut:
tar -cjf theblobgame_0.20130202.orig.tar.bz2 --exclude=debian theblobgame-0.20130202
If you fixed something in the code and want to work on the packaging, the command above will create a new “code release” from the packaging system’s point of view.

…and finally, it’s free software!

This means you’re allowed not only download and run this game, but also look at the code, copy-paste parts into your own game (under the terms of the LGPL-2!) or just use for inspiration. You can fix a bug or a feature and send me patches (or publish the modified code yourself), etc. Enjoy!

Update: Someone asked me how to get the source, so here’s a quick howto:
If you have executed the lines in the top of this blog post, just change into a suitable directory and execute “apt-get source theblobgame”. Before you build, you can use “sudo apt-get build-dep theblobgame” to automatically install all build dependencies. Building can be done with “dpkg-buildpackage -b” (from the source code directory). Then install the resulting .deb package (“sudo dpkg -i theblobgame_version.deb”) to test.

If you’re not running Ubuntu/Debian, you can get the source from going to the PPA page, click “View package details”, click one of the arrows on the left side in the table, and download the file ending with “orig.tar.bz2”.

Disclaimer: This does not mean that the source is written by the book, with lots of helpful comments, etc. The game engine is mostly a quick translation of the code as it looked like ten years ago, with new glue code added for interfacing with the libraries I now depend on.