Wartbed:Design

Overview

At its highest level and end goal WARTBED is a meta-engine for tactical wargaming. More precisely, though, WARTBED is a framework to automate a number of tasks related to this:

• 3D graphic of contemporary standards (implemented through the OGRE middleware)
• Input bindings and input handling (where raw input hardware is accessed through the OIS middleware)
• Flexible camera handling suitable for a wide spectrum of strategy game styles
• A GUI system (currently implemented through the CEGUI middleware)
• Human-readable data file parsing
• Scripting language support (as of yet unimplemented)
• Network support (not yet implemented)

Remaining design decisions

• How game modules (Bright Portents etc) should be implemented:
  • First option: As internal parts of WARTBED framework itself.
  • Second option: Modules are stand-alone applications using WARTBED as a library modules will use.
  • Third option: Modules will be fully implemented in script languages using the WARTBED framework.

"Regimental tactical warfare"

What being a framework for implementing tactical regimental warfare games more specifically means is providing a number of standard formats (and data converter to these formats):

• A unit and regiment ability and statistics set capable of accurately represent most games, periods and battle types.
• A regiment representation system capable of handling several individual units organised into formations (which can consist of other regiments), and formatted movement (manoeuvres) of these.
• Battle arena (battlefield) description
• Campaign definition and flow handling
• Unit and regiment ordering system
• Suitable and flexible AI

Design principles

WARTBED is being designed according to a set of principles and assumptions.

Dependencies

External and third party dependencies are being avoided. Nonetheless, some aspects of a modern game system are impractical or impossible to produce in-house. For such, open-source, free-licensed (Free or LGPL, but not GLP), well testedm stable and actively maintained solutions are acceptable.

• For 3D graphics the open-source 3D API OGRE 3D is being used.
• For input the open-source framework OIS (Open Input System) is being used. It comes with OGRE 3D for easy integration.
• For in-game (in-framework) GUI several frameworks are being considered. OGRE's preferred GUI is CEGUI, which however has proven difficult to initialise and use. See GUI evaluation and GUI widgets for more information.
• Currently full-scale physics support isn't needed. The physics required consists of gravity, wind and trajectories, which can be sufficiently simulated in native code (air/liquid pressure variance, medium drag etc is unnecessary, and still there is no reason for ragdoll animation or fprward kinematics). Candidates would be the Newton framework, ODE (Open Dynamics Engine) or Bullet (preferred due to licencing), all have existing OGRE integration modules.
• For memory management nedmalloc is being evaluated. It is used internally in OGRE and is highly speed- and anti-fragmentation efficient under random usage.
• No system has yet been chosen for networking.
• Boost is currently not included in WARTBED.

Strictness of MVC organisation

Had all code been locally written WARTBED could maintain ideal separation between the components. However, the Controller will have to react to purely cosmetic (user interface) user input and dispatch appropriate orders to View subsystems (f.i. selecting and outlining a particular unit). The controller will thus need knowledge about and access to View objects.

Likewise OGREs built-in functions for line-of-sight, geometry collision and object picking will be utilised, which will validate the separation between Model and View.

We will see how this can be managed.

Coding standard

Though not religious on the topic WARTBED is coded according to a set code style which is an adaptation of the Allman style.

Model-View-Controller

Everything that can interact is a "game object" (or an "entity"). The WARTBED game objects exists in the abstract knows or cares nothing about their representation. In principle, since all game logic takes place in the Model layer, a WARTBED game can run completely in the abstract without any graphical or auditory output at all. Every Entity have one or more corresponding Representations that may read "their" Entity but not change it. Entities CAN communicate with their Representation(s) by sending messages.

 +-----------------------------------+
 |               Model               |
 +------------------------------+--+-+
               ^      The model !  ^
               |      can send  !  |
               |      messages  !  | 
The controller |                !  | The View can
issues orders  |                V  | read the Model
+--------------+-+ +---------------+--+
|   Controller   | |      View        |
+----------------+ +------------------+

Model and View

As example, assume a game class "Ship":

//-------------------------------------------------------------------------
// Basic classes: f.i. in (made-up file) "MVC_base.h" 
//-------------------------------------------------------------------------

typedef shared_ptr<Message> MESSAGE;
typedef std::set<Represenation *> REP_SET;


struct Entity
{
    mutable REP_SET representations;

    virtual ~Entity() {}

    void registerRepresentation( Representation *pRep ) const
    {
        represenations.insert( pRep );
    }
};


struct Representation
{
    virtual void receiveMessage( MESSAGE &msg ) {} = 0;

    Representation( Entity const &rEntity ) { init(rEntity); }
    virtual ~Representation() {}

    void init( Entity const &rEntity )
    { 
        pEntity->registerRepresentation( this );
    }
};

Notice that the Entity interface (abstract base class) doesn't know anything about the specifics of its representations. Also notice that it is required of any Representation to register itself with its Entity.

//-------------------------------------------------------------------------
// Example Entity (model) class, f.i. in "Ship.h"
//-------------------------------------------------------------------------

#include "MVC_base.h"

struct Ship : Entity
{
    VECTOR3 position;      // Example game 
    long    hull_points;  // object data
};

As can be seen, for a Model-layer class, in this instance "Ship", being an Entity is fully non-intrusive. The effect is that it can now send messages to any registered representations.

//-------------------------------------------------------------------------
// Example Representation (view) class, f.i. in "game_display.h"
//-------------------------------------------------------------------------

#incluide "Ship.h"

struct ShipRepresentation : Representation
{
    Ship const *pShip;
    OgreSceneNode *pNode;

    ShipRepresentation( Ship const *pShip ) : Representation(pShip), pShip(pShip) {}
    void receiveMessage( MESSAGE &msg ) {}

    void update() { pNode->setPosition( pShip->position ); }
};   

A specialised representation needs, however, to implement the receiveMessage() function, and must pass an Entity to the superclass constructor. Also note that the ShipRepresentation stores a (const) pointer to its associated Ship object: Representations can see and read its Entity (but not alter it).

Example representations

View objects are similar to the Observer design pattern and hooks a model. Typical representations are

• The graphical model (3D model, each individual unit)
• An iconic representation (regimental banner, attached to formations rather than individuals)
• Audio (a helicopter constantly playing Ride of the Valkyries)

Controller

In real-time tactics games, no units are directly controlled by the player. Instead, all game objects are interacted with through orders. Therefore, the task of the Controller layer is to read input (from players, network or AI) and dispatch orders. In the very simplest terms the Controller is an order-dispatcher that is aware of the Model layer, but cares nothing about the View aspects. (This is however a little to clean to be practical since GUI interfaces bridge the distinction View and Controller).

Strict client/server game architecture

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WARTBED intended to be strictly client server to the extent that even single player games entail the game being a front-end to a local server.

Pros:

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Cons:

• Item

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Graphics specification

Further information: Wartbed:Design/Map_format

• The base measurement unit is 1 meter. All 3D graphics are designed with 1 unit == 1 meter.