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Entity System

Started by InFerN0 Oct 26, 2000 at 5:13 AM 3 replies 250+ views

Original Post

Oct 26, 2000 at 5:13 AM

Hey, I am trying to work out an entity system for my engine. I created a base class CEntity which all other entities would be derived from.

//Base entity class
class CEntity
{
public:

        char *name;//entities name 
	virtual void UpdateEntState();// This will usually be overridden by the derived class
	void LoadModel(char *modelname);//load the model
	bool drawable;//entity can be drawn to screen
	vec3_t position;
	vec3_t facing;
	
	CEntity *next;//next entity
	//model
	

private:

};

I figured the best way to store them was in a linked list so I could just go throught the list updating as necessary. My questions are should the linked list be made from CEntity and if I do will I be able to call UpdateEntState() in the derived class. Thanks. InFerN0 Not all who wander are lost...

Oct 26, 2000 at 9:40 PM

Hi InFerN0. I''m not sure if this helps, but here goes anyway.

Making a linked list directly from the entity has the advantage of being just slightly marginally quicker, but I think using a template is much more convinient, and worth the tiny performance hit. This way, you have a general list of pointers to entity objects. As to calling and accessing the derived functions, this isn''t a problem if you make a list of POINTERS to entities (which is where the performance hit comes in), but I don''t think you can do it if you place the entity itself in the list.

Hope this helps-- SH

Zipster

511

Zipster

Oct 26, 2000 at 10:52 PM

Take a look at the HL source code. They have a nice class system set up.

revolver

Oct 26, 2000 at 10:59 PM

IMHO, that can get pretty messy (linked list inside the entity class). Best option is to have a linked list of entities OUTSIDE of the class itself (via STL, or custom code), perhaps in a CEntityManager class...

Another thing which you might consider is seperating entity type from entity instance. This would allow you to just have the model data (and other data) loaded just once, and shared among every instance of the entity. Basically you have (no it doesn't work, it's just on the spot stuff):

    
CEntityClass {
  ModelData* Model;
  std::string Name;
  void LoadModel(std::string filename);
  void Draw();
  void ProcessAI(SituationalData* SD);
};


CEntity {
  CEntity(CEntityClass* UseEC) { 
    EC = UseEC;
  }
  CEntityClass* EC;
  void Render() { 
    ApplyTransforms(); 
    ED->ProcessAI(SituationalData);
    ED->Draw(); 
  }  
};


CEntityManager {
  void Create(std::string name, std::string ModelFile) {
    EC = new CEntityClass; 
    ED->Name = name;
    EC->LoadModel(ModelFile) 
  }
  void Spawn(std::string name) {
    CEntity* Ent = new(FindClass(name)) CEntity;
    AddEntityToList(Ent);
  }
};


void main() {
  EntManager->Create("HiigaranShip", "mdls/hiigaranship.mdl");
  for (int i = 0; i < 11; i++) {
    EntManager->Spawn("HiigaranShip");
  }
};

The late Seumas discussed in pretty easy to understand terms how Treadmark's entity system works over here:

http://www.longbowdigitalarts.com/ubb/Forum3/HTML/000018.html

Edited by - revolver on October 26, 2000 12:20:06 AM

InFerN0

Author

InFerN0

Oct 31, 2000 at 3:03 PM

I have a quick question. How do I make a Linked List with derived classes? When I use the base class as the type the derived classes have base class functionality. Thanks

InFerN0

Not all who wander are lost...

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