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Well...I have learned a lot

Posted by adam4813, 11 December 2011 · 235 views

engine C++ componet based entity system CBES modular
Some time about I posted about systems, and their respective managers. I still have used parts of that system, but at the same time I have evolved beyond the system approach and moved into using distinct and operate modules.

Let's define a few things first:
  • Module: any system or system-like representation that is loaded externally, and controls a specific system and/or certain types of components.
  • Component: any self-contained unit of code that is used to make up an entity. Entities are made up of many components ranging from 3d models, to sound effects, and even physics objects. They are extremely encapsulated, and they are never transferred beyond the barrier of the module.
  • Entity: the basic game object. All things inside the game that the player can interact with in some way is an entity. Entity are just a position, rotation, and scale structure to describe the root of the components that are linked to that entity. Entities also have a unique id used to link the components that make up that entity inside each module.
Those 3 things make up the core idea for the engine I (and another classmate) are currently working on. The concept is simple: create a different style of game engine that is modern, clean and encapsulated, and can be added to very easily.

The high-level design of the engine provides a generic interface through which all modules are accessed.
#pragma once
/*
	Author: Adam Martin
	Date: July 20 2011
	Description ModuleInterface class used as a common base for all modules.
*/

// Standard Includes
#include <string>
#include <map>

// Library Includes
#include <boost/any.hpp>

// Local Includes

// Forward Declarations
class GlobalProperties;
class ComponentInterface;
class MessageRouter;
class Envelope;
class EntityManager;
struct Entity;

// Typedefs

class ModuleInterface { // All systems derive from this
public:
	ModuleInterface() : { };
	~ModuleInterface(void) { }

	virtual void Update(double dt) = 0; // Called each game update with change in time (dt) in milliseconds since last update
    virtual void CreateComponent(std::string type, std::map< std::string, boost::any > &attributes, Entity* e) = 0; // Called to create a component of type (type), with the set of attributes (attributes), and with parent entity (e)

protected:
	double deltaAccumulator; // Accumulator for the change in time between each call to update
	std::map< int, ComponentInterface* > components; // Map components with a given Entity ID
};


Of course this isn't very useful on its own, so a few other class pointers are include to provide some communication and basic global data sharing. *Note the forward declarations were left in the original code block for the following.

The constructor becomes:
ModuleInterface(GlobalProperties* gprops, MessageRouter* msgrouter, EntityManager* emgr = nullptr) : msgrouter(msgrouter), gprops(gprops), emgr(emgr) { };

The actual message handling function:
virtual void Message(Envelope* e) = 0; // Handle message ID (msg). Messages are such as mouse click, keyboard, or os events. Envelope is a container to store the arguments of the message.
Some additional member variables:
MessageRouter* msgrouter;
 GlobalProperties* gprops;
 EntityManager* emgr;

The code for the engine code named NLS Engine (as the in Next Logical Step in engine development) is online and open sourced here NLS Engine on Bitbucket




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