[Adonthell-commits] CVS: doc/architecture inventory.fig,NONE,1.1 inventory.pdf,NONE,1.1 items.fig,NONE,1.1 items.pdf,NONE,1.1 items.tex,NONE,1.1 Makefile,1.2,1.3 architecture.tex,1.3,1.4

[Kai Sterker <address@hidden>]

Update of /cvsroot/adonthell/doc/architecture
In directory subversions:/tmp/cvs-serv3462

Modified Files:
        Makefile architecture.tex 
Added Files:
        inventory.fig inventory.pdf items.fig items.pdf items.tex 
Log Message:
ADDED description of item/inventory system

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--- NEW FILE ---
\subsection{Items and Inventories}

In this section, we will explore how items are modelled and kept. The main goal 
was to allow for all kinds of items, with many different abilities. Creation of 
new items should be fast and simple, without having to modify the engine. And 
last but not least, the item system as a whole should be efficient and 
convenient for both designers and players. \\

Therefore, items have been splitted into three layers.

\begin{enumerate}
\item{\bf Engine layer.} Functionality required to manage items is implemented 
by the engine. This includes item instantiation, inventory handling and access 
to advanced item functionality.

\item{\bf Game extension layer.} The item system itself -- that is properties 
and abilities as well as game rules concerning items -- is implemented as a 
game extension on top of these basic functions. That way, different games can 
have totally different item systems.

\item{\bf Data layer.} On top of the item system sits the item data, i.e. all 
the individual items actually available in a game.
\end{enumerate}

\begin{figure}[hb]
\center
\includegraphics{items.pdf}
\caption{Item hierarchy}
\end{figure}

The figure shows the relation between game extension, data and engine layer. 
For each ``class" of items\footnote{Like weapons, armour, potions, lightsources 
and so on. Subclassing is also possible, of course. Imagine ranged weapons, 
healing potions, etc.}, a {\it template} needs to be written in Python. By 
initialising attributes of the same template with different values, different 
{\it items} can be defined. At runtime, multiple {\it instances} of every such 
item can be created and used by the engine. \\

For efficiency reasons, the engine distinguishes between two different kinds of 
items: {\it mutable} items require an actual physical instance for every 
occurrence in the game. As a result, they can be easily changed throughout the 
game. {\it Immutable} items on the other hand are instantiated only once. They 
are kept in a central repository, and reference counts are used to allow 
multiple occurrences in the game. \\

Despite the fact that large parts of the item system are not implemented by the 
game engine, items are always stored on engine level, in so called {\it slots}. 
A slot may contain several items of the same kind, if the item allows that. 
Immutable items are considered to be of a kind when their instance pointers are 
equal. For mutable items, item names have to match. 

\begin{figure}[h]
\center
\includegraphics{inventory.pdf}
\caption{Inventory, slots and stacks}
\end{figure}

With the above in mind, an {\it inventory} is easily implemented. It is little 
more than a list of slots. To remain flexible, only the most basic inventory 
operations have been implemented on engine level, like adding new items. For 
convenience, the inventory tries to group items of same kind together in a {\it 
stack}. Furthermore, removal of items happens automatically as they are moved 
from one slot or inventory to the other.

Inventories are not limited to a certain number of slots. If desired, they can 
even grow or shrink at runtime. Therefore, inventories can be used whenever 
large quantities of items need to be stored, not only to represent a 
character's backpack. 


Index: Makefile
===================================================================
RCS file: /cvsroot/adonthell/doc/architecture/Makefile,v
retrieving revision 1.2
retrieving revision 1.3
diff -C2 -r1.2 -r1.3
*** Makefile    2 Jan 2003 23:07:07 -0000       1.2
--- Makefile    3 Mar 2003 23:26:54 -0000       1.3
***************
*** 1,5 ****
! IMAGES = layers.pdf \
!         arch.pdf \
!               mapview.pdf
          
  all: pdf
--- 1,7 ----
! IMAGES = arch.pdf \
!         inventory.pdf \
!         items.pdf \
!         layers.pdf \
!       mapview.pdf
          
  all: pdf

Index: architecture.tex
===================================================================
RCS file: /cvsroot/adonthell/doc/architecture/architecture.tex,v
retrieving revision 1.3
retrieving revision 1.4
diff -C2 -r1.3 -r1.4
*** architecture.tex    22 Feb 2003 11:27:05 -0000      1.3
--- architecture.tex    3 Mar 2003 23:26:54 -0000       1.4
***************
*** 72,74 ****
--- 72,75 ----
  \include{overview}          % Overview
  \include{edesign}           % Engine design
+ \include{items}
  \end{document}