Categories: CS at a glance, 513 wordsSend feedback • Permalink
So, what is Crystal Space and what can it do for you?
Crystal Space is, centrally, a realtime 3D engine. In addition to that it includes everything that one needs to make a game or application; sound, keyboard, mouse and tons of other stuff. CS is event-driven, which means that once you've set up the map for playing, your code gets called each time something relevant happens.
To make juggling all that data easier, the Crystal Entity Layer (CEL) has been introduced. It adds the concepts of entities, property classes and messages. An entity is a "thing" in your game, the properties of which are determined by the property classes given to it. Property classes are, for example, pcmesh (which keeps the entities reference to a mesh), pctimer (which you can use to get a message either after a set delay or every frame), pccommandinput (keyboard and mouse input), pcmeshselect (which sends you a message when the user clicks on the pcmesh that the entity having this class also has) and so on.
Messages, lastly, are CELs mode of inter-entity communication. Property classes send messages to their entities when something relevant happens, and you can make your entities send messages to each other, too. Messages have a name and parameters, which are keys and values.
A somewhat deprecated concept is that entities also have behaviours. Those are the part of code that "receives" the messages, that is, gets called when a message with a name which is also the methods name in the code (I'm specifiaclly talking about writing behaviours in Python, but you can also do it in HTML) comes in, and is given the messages parameters. This concept is outdated only insofar as these message handlers now are encapsulated into "regular" property classes. So instead of having one and only one behaviour script per entity, you can now load and unload behaviour script property classes as you like.
Last, but not least, I also should mention entity templates. If you have multiple entities with are rather similar to each other, you can create a template from which those entities then are created.
To make things even easier (yes, that paragraph just now really was about how things get easier, not more complicated ;) ), CELstart was written. While all the defining templates, entities, meshes etc. can be done in map files, there still has to be a program that actually loads and runs those files. CELstart is that program. All it needs is a .zip file that includes your map files, artwork, whatever code you may have written and configuration files. It'll take those and start up the engine, load or create whatever you mentioned in celstart.cfg in your .zip, and off you go: Your game is running.
Well, that's the theory. All you have to do now is to think of a game or application that you want to write, then you find out what your entities are, then you assign property classes, model, texture and animate the models you want to use, write behaviour property classes and... Voila. Presto game.
Categories: CS at a glance, 246 wordsSend feedback • Permalink
Hi. My name is Sebastian, and if you visit the IRC channel #crystalspace on irc.freenode.net, you may know me as Baribal.
Somewhen around 2002 I heard of Crystal Space (CS) took a look. On my first try, the build process was frustrating enough for me to become discouraged. Every now and then I checked back and found new, shiny features. Also, each time I tried, I got a bit farther than before.
This time around I managed to set up everything that I need to get developing for real. Less than a month ago, I decided to create a chessboard with it; three years ago, I nearly managed to create a Go game using nothing but hand-edited XML and Python scripts. Now, three weeks after I looked at the first cube I made, I have both gathered a fundamental understanding of how to work with CS and wrote most of my chessboard. Considering that despite the hurdles I encountered on the way, I got quite far in a short time, I am wondering why not more people are developing games using CS, especially as nearly all the tools one could need are provided.
Then again building CS, then making the game are not trivial tasks, either, and most of the documentation meant to help along newcomers consists of the explained code of small applications. Personally, I can think of easier ways by which CS could be explained.
And that's why I asked for this blog.