The brave new object model
project components data driven
A few years ago when I was reaching the end of my multi-threaded game engine project I ran across the following article:
I had never heard of the component approach to designing objects but it fascinated me and made total sense. After all I had all of the problems that came from the traditional deep hierarchies. I had big base classes with too much functionality, I was constantly dealing with keeping objects from having cyclical dependencies and it seemed like I wasn't gaining a lot from some of my different abstractions. Being near the end of development I didn't want to do anything as drastic as reworking my object model so I filed the article away and planned to revisit the component notion again in the future. Flash forward a few years and at the start of this project I dug up that article to refresh things in my mind and then I set it as a goal to try and implement a similar approach.
I'm definitely one who would rather take an iterative approach to development and design rather than attempting to sketch out a complete object model before writing a single line of code. Add in the fact that I'm only about a month into my current project and you'll understand when I say that I'm not 100% sure where the full object model is going to end up but I am 99% sure that it's going in a way better direction thanks to the component model approach. Not only does the approach really allow you to better partition specific functionality into specific objects but it almost does it for you. Add in the fact that it also lends itself extremely well to being completely data driven and you'd understand why I'm so happy with things so far.
To give you a high level view of my object model I have five main buckets of objects:
1. Base objects - very general objects like a scene and the empty game object which will hold the components
2. Managers - things like the renderer, resource manager, input manager, etc.
3. Components - renderable, positionable, scriptable, etc.able...
4. Resources - mesh, texture, shader, scripts....
5. Bindings - the odd ducks. They really aren't separate objects per se but the binding glue allowing everything else to be used through scripting
It just becomes so natural to think that you have a game object that is made up of components that happen to use some resources. Being able to easily put those together in your head means that it's even easier to put them together in a nice XML file. While I was working on getting the first components coded up it became almost necessary to write a quick parser because it seemed like so much fun. Now with a little snippet like this:
<gameobject name="TestObject 1">
<renderable wire="0" ortho="0">
<location x="-1" y="0" z="3"></location>
<rotation x="0" y="90" z="0"></rotation>
<scale x="1" y="1" z="1"></scale>
I can load some resources, attach them to a renderable component and get it rendering on my screen without having to change a line of code. Talk about sweetness! Of course I'm not going to give all the credit to the component approach as I had data driven design high on my goal list as well but it really just seems to dove tail so well together that instead of dreading writing boring parsing code I was actually super excited about it because the iterative bonuses just were so appealing.
Alright enough of the love fest for now. In short though if you're looking to try something new in your OO approach and also have a desire to get your game more data driven so you're not spending so much time waiting around for your compiler while you move a sprite five pixels to the right you need to check components out. Yes the link at the top of this post is four years old but if it's still that exciting to me then it might be for you as well.