Tag Archives: engine

My game development demons

It’s been now a long time, since I decided to write a certain game and talked a lot about it with friends. However I must confess, now after a few years, I still haven’t managed to finish a game. I wrote a lot of code and both bugs and documentation is so far not the problem. Instead there are a couple of demons that  slow down the process that I would like to introduce to you (you probably know them already):

Efficiency Demon: This one is always in the back of my head. It tries to convince me not to use virtual functions as they are somewhat slower than normal function calls. However this approach makes things a lot more complicated and I spent time to circumvent the usage of “the single most important feature of C++” by using probably less efficient detours. Additionally following strictly the rule: first make it run, then optimize would encourage me to take a deeper look in profilers, which would be definitely a knowledge I wish to possess. There are a couple of nice quotes to this one on the Wikipedia page on program optimization – I guess I am not the only one having this demon.

Engine Demon: Instead of tackling simply completing the game logic/event managing/input handling part, I try to generalize what I just coded and put it into a part that I call “engine”. This “engine” is some kind of container of reusable code that I will most certainly need in the future. The catch is just: I do not yet know what exactly I will be needing in the future. Actually neither whether I need the generalized case nor the specialized I wrote in the first place. There is a very well written article (write-games-not-engines) from Josh Petrie which talks about this one. This demon is sometimes called Premature Generalization.

Beauty Demon: The Beauty Demon is related to the Engine Demon. It makes you want to clean up your mess (a.k.a. code). You just hacked in some features and now you want to polish it a little. So you polish. Then you realize you should add documentation. So you add it (and look at the beautiful caller graphs that Doxygen creates automatically for you). Then you realize that you could create of this feature set a library against which you can link dynamically – oh yeah, this is great, because then you can do this for all the other games you will write and reuse it. Oh, and the build system it got a little messy. How about … Yeah, you get it. You do a lot of things which are actually very useful. However they do not complete your game.

Just-that-feature-and-then-I’m-done Demon: I coded hard. The prototype works. And I am very happy. So I relax and think: Awesome, I’ll be done soon with the whole game and I can finish the rest tomorrow. There is a huge difference between a prototype and putting it into your game. I had a few nice parts, such as an event system and entity management system and so on which worked very well on them selves. But when I actually tried to make a simple game with it, I had to rewrite a lot of it and it was a lot harder than I expected. So unless the code is not in your game don’t think anything is done! (Please note that this is not an argument against writing prototypes – they are very important because you realize what the actual problem is and what kind of difficulties you run into!)

A long time ago, I read this very inspiring article ‘How do I make games?’ A Path to Game Development.When I look back, I must admit, I skipped quite a few steps suggested there. So last week I started to abuse my “engine” to create an Asteroids clone. So far controlling the ship, destroying asteroids and getting killed works, but there are still some areas untouched (menu, game-over screen, etc.). It took me a lot longer than I expected and I currently have a lot of quirks on making things work.

So far it is not efficient, not an engine, not beautiful and there is still a lot of work to be done. But I’ll stay on that rocky road and bring it home.

Thought game development is fun? It is – but getting it done is actually quite hard!

What has been happening so far…

It seems as if there haven’t been too many updates here lately. I’ve been quite distracted with studying and getting the simulation of multi body systems into my head. And by doing so I stumbled over a few quite amazing papers and dissertations that seem to cope pretty much everything you need to know for a fully fledged physics engine (assuming you have some spare time).

For example the dissertation of Brian Mirtich (which you should be able to download here or here) covers just about everything from advanced collision detection to collision response. Even the calculation of inertia tensors in 3D is contained and the appendix covers all the math basics such as quaternion arithmacy and a rigid body primer. The whole thing wheighs a bit over 250 pages and is freely available. It still requires a lot of math knowledge, but as a math major I hope I have enough knowledge.

The method he describes in his thesis is the so called impulse based simulation which is stated in contrast to analytical methods as they are used in David Baraffs papers (as far as I understand). Instead of trying to fulfill all constraints simultaneously, instead if a constraint is violated it applies an impulse to the constrained bodies so that the constraint stays fulfilled within the next integration time horizon.

A more recent version of Mirtich’ aproach can be found at the site of Jan Bender (www.impulse-based.de). He also wrote a dissertation over impulse based simulation (however in German) which has less math in it. The best is: his code is available under the zlib license! There is also a lot of documentation in English available, so go check it out!

Oh, and of course I have not just been doing multi body simulation stuff. I was playing around with Blender already for a while to have a nice visualization for my thesis. And I finally made a model for a character in a game I have been planning already for ages. Now I added a little movement to the model. Here you have it:

Be nice, she is a little older (and my first animation). You can get the full resolution version here.

Cheers,

Martin