@c -*-texinfo-*- @node Introduction, Building, Top, Top @chapter Introduction @cindex Introduction @menu * What Is CEL:: What Is Crystal Entity Layer? * Concepts:: * How To Read:: How To Read This Manual * Current Status:: * Using CEL For Your Project:: Using Crystal Entity Layer For Your Project * Guide:: A Guide To This Documentation * Features:: Feature List * Where To Get CEL:: Where to Get Crystal Entity Layer * Mailing Lists:: * Licence:: GNU Library General Public License @end menu @node What Is CEL, Concepts, Introduction, Introduction @section What Is Crystal Entity Layer? Crystal Entity Layer is a plugin developed to be used in conjunction with Crystal Space. It is designed to make it easier for game developers to create games based on Crystal Space by providing such concepts as entities, properties and behaviours. Crystal Space is a portable modular 3D SDK, including many components for building various applications and games. For more information on Crystal Space please see the @uref{http://www.crystalspace3d.org/,Crystal Space web page}. It is assumed here that you know the basic ideas behind Crystal Space. More specifically you should have a notion about @sc{scf} and @sc{vfs} as those are used a lot in @sc{cel} too. Crystal Entity Layer is still in development. It's development efforts are currently hosted by SourceForge. Anybody wishing to contribute should visit the @uref{http://cel.crystalspace3d.org/,Crystal Entity Layer} project page and @uref{http://www.sourceforge.net/,SourceForge}. Crystal Entity Layer is free and should remain free. Crystal Entity Layer falls under the GNU copyleft license for libraries (LGPL). A copy of of the LGPL is included in this manual for your perusal. In short, the LGPL allows you to use CrystalSpace as a library in your products, even commercial products, but modifications to the library or derivative works incorporating parts of the library must be made freely available to everyone, under the LGPL's terms. @node Concepts, How To Read, What Is CEL, Introduction @section Concepts Every object within the game world is represented by an entity. This includes the world itself and all the objects within it, such as players, non-player characters, items and cameras. The base Crystal Entity Layer Entities are managed within the Physical Layer. These basic Entities cannot do very much at all as they are. In order to add functionality one, or usually more, Physical Layer Property Classes are added to the Entity. Property Classes are used to provide specific attributes, functionality and constraints to Entities and also provide the interface with the Crystal Space library. This may be a simple attribute, such as allowing an entity to store it's weight, or it may provide more complex functionality such as receiving input from the keyboard or drawing a 3D object such as a mesh. The set of properties provides by all the property classes together defines what the entity really is, and what functionality is provided. Property Classes are added to Entities at run-time. What this means for the developer is that if required Property Classes can be added, or removed, from Entities on-the-fly. Property Classes are generated by Property Class Factories. These are usually implemented as a Crystal Space plugin. This means that you load the plugin, and then invoke the plugin as required to create property classes. The Physical Layer is also responsible for providing the Persistence Layer. This is a system that is responsible for being able to save and load the state of each and every Entity. This may be a file on a disk, or to some form of database. Single-player games would use this to provide save-game functionality for example. The Behaviour Layer handles things such as game logic. It is this layer that dictates how an Entity will behave within the constraints placed upon it by the Physical Layer. The Physical Layer is able to generate events, which are passed to the Behaviour Layer in order to be acted upon. Examples of such events are when an Entity is clicked on by the mouse pointer, when a particular key is hit or when an item is added to an inventory. Such events are usually generated from within the Property Classes when a predetermined set of conditions is achieved. The majority of the Behaviour Layer may be implemented in a scripting language such as Python if this is suitable for the project. This allows the behavior of Entities to be easily scripted without having to recompile the entire project, and also for new behaviours to be added in the same manner. In summary, Crystal Entity Layer is made up itself of two layers, these being the Physical Layer and the Behaviour Layer. The Physical Layer is responsible for all managing base Entities, providing the Property Class system to manage attributes, functionality and constraints to Entities, to prove a system for the Property Classes to communicate with the Behaviour Layer and to provide a Persistence Layer in order to be able to load and save Entities to some form of storage. The Behaviour Layer is responsible for managing how Entities behave within the restrictions placed up on by the Physical Layer. This may be implemented in C++, or it may be implemented in some form of scripting language. @node How To Read, Current Status, Concepts, Introduction @section How To Read This Manual This manual was written and is currently maintained by Daniel Thoroughgood. Constructive feedback, suggestions and contributions are always welcome. If you find something in this manual which you beleive is not correct please notify the mailing list in order to have this investigated and corrected. This manual is intended to also serve the purpose of a reference and as such the order in which it is read is not important for the experienced developer. People that are new to Crystal Entity Layer however should read the manual front to back. @node Current Status, Using CEL For Your Project, How To Read, Introduction @section Current Status Crystal Entity Layer is still in Beta status, and is likely to be for the foreseeable future. Crystal Space, on which this work is based, is still under very active development and from time to time changes may be made to the Crystal Space sources which will cause Crystal Entity Layer not to work as expected, or not to work at all. Likewise Crystal Entity Layer is still in development and you may find that some features do not work as expected, or may not work at all. Some features may be only partially implemented and there may be both known and unknown bugs. Please do not let this discourage you from using Crystal Entity Layer. Most of the core functions are implemented and working correctly. Any bugs which are reported will be investigated as soon as possible and contributions are always welcome. @node Using CEL For Your Project, Guide, Current Status, Introduction @section Using Crystal Entity Layer For Your Project If you wish to use Crystal Entity Layer for your project you should obtain and build sources of both Crystal Space and Crystal Entity Layer. Read the Crystal Space documentation and take a look through the samples and examples to become familiar with how it works. You should also join the appropriate Crystal Space and Crystal Entity Layer mailing lists in order to watch how things develop. You also need to agree to the LGPL (GNU Library General Public Licence). If you are using Crystal Entity Layer for a project please let us know as we are very interested in hearing what people are doing with both Crystal Space and Crystal Entity Layer. @node Guide, Features, Using CEL For Your Project, Introduction @section A Guide To This Documentation TODO: Complete this section when the layout of the manual is solid and cross refernces are all in place. @node Features, Where To Get CEL, Guide, Introduction @section Feature List @node Where To Get CEL, Mailing Lists, Features, Introduction @section Where to Get Crystal Entity Layer The Crystal Entity Layer homepage contains information on obtaining both the official releases of Crystal Entity Layer and the current development version. Please keep in mind that both types of releases are still Beta. The main difference being that release versions should be well tested and generally stable. With the development version your milage may vary. Sometimes it may not compile easily on all platforms, or may not compile at all. There may be features that are only partially implemented and these probably will not be very well documented. However, the development version will always have all the most recent features and will probably contain features that are not available in the release version. You will also need Crystal Space in order to use Crystal Entity Layer. Like Crystal Entity Layer this is also available in both official release and development status. For more information on the two of these please see the Crystal Space documentation. Crystal Entity Layer is available at:@* @uref{http://cel.crystalspace3d.org/} Crystal Space is available at:@* @uref{http://www.crystalspace3d.org/} Generally a release version of Crystal Entity Layer should be built against the matching release of Crystal Space. Likewise development versions should be build against a development version of Crystal Space from the same date. Mixing and matching of versions is not guaranteed to work, and in fact quite likely will not. @subheading CVS As Crystal Entity Layer is being actively developed changes are quite often made to the sources on a daily basis. The latest sources to Crystal Entity Layer may be downloaded from SourceForge's Anonymous CVS Servers. TODO: Add instructions for downloading from SourceForge CVS Please keep in mind that currently SourceForge's Anonymous CVS servers are running approximately 5 hours behind the developer's CVS servers. This means that bugfix's, new features, etc. which are updated by developers may not become available on the public servers immediatelly. @node Mailing Lists, Licence, Where To Get CEL, Introduction @section Mailing Lists There are currently two Crystal Entity Layer mailing lists that may be of interest to to users and developers. The main list is for general discussion, questions and bug reports. You may subscribe to this list by visiting:@* @uref{http://lists.sourceforge.net/mailman/listinfo/cel-main} You may also view an archive of prior posts to this list at:@* @uref{http://sourceforge.net/mailarchive/forum.php?forum_id=1108} The CVS update list is for notification of changes to the CVS source repository. All users subscribed to this list will receive an e-mail every time a developer updates the source. You may subscribe to this list at:@* @uref{http://lists.sourceforge.net/mailman/listinfo/cel-cvs-update} You may also view an archive of prior posts to this list at:@* @uref{http://sourceforge.net/mailarchive/forum.php?forum_id=33225} @node Licence, , Mailing Lists, Introduction @section GNU Library General Public License @noindent Version 2, June 1991 Copyright @copyright{} 1991 Free Software Foundation, Inc. 675 Mass Ave, Cambridge, @sc{ma} 02139, @sc{usa} Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed. 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