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How to implement Entity-Component-System with C?


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#1 Sachs   Members   -  Reputation: 164

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Posted 09 April 2013 - 09:30 AM

Hi.
 
Recently, I read some articles about "Entity-Component-System", one of these is  "What is an entity system framework for game development?" written by Richard Lord.
 
In his article, he mentions that component only contains data which is like C's struct. Entity is a set of components which also don't have any method. All operation are moved to system.
 
This is data-oriented programming rather OOP, so why we still use OOP language rather than the C language? I'm interested  in what it will be when implemented in C.
 
One of the implementation may be like this:

    ecs_component_create("position");
    ecs_component_add_value_int("position", "x");
    ecs_component_add_value_float("position", "y");

    ...

    int id = ecs_entity_create("spaceship");
    ecs_entity_add_component(id, "position");
    ecs_entity_set_value_int(id, "position", "x", 0);
    ecs_entity_set_value_int(id, "position", "y", 0);
    ecs_engine_add_entity(id);

    ...

    ecs_engine_add_system(engine, "RenderSystem", priority);

 
 
I'm not sure whether it is right, can someone give me advises?

 

My English is poor, and thanks for your patient!



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#2 BinaryPhysics   Members   -  Reputation: 294

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Posted 09 April 2013 - 12:58 PM

Are you suggested effectively storing entities and components in giant string tables?

 

I'd have thought that Systems would be better placed to be isolated functions in this case and you just call them all in the game loop.



#3 Sachs   Members   -  Reputation: 164

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Posted 09 April 2013 - 11:35 PM

Are you suggested effectively storing entities and components in giant string tables?

 
Right, as different Component has different "value", e.g. Component "position" has two float value "x" and "y", we may be dynamic generate those values. Because there is no class in C, we couldn't extend from a base class like IComponet. So I store these dynamic generated values into a string hashtable, which key is "variable name", [/size] to describe a Component, just like we "describe" a class is in OOP language.
 
When we create Entity, we can pass the Component name we "described" before, the engine may allocated memory to store the Component's value which just like we create an object in OOP language. 
 

I'd have thought that Systems would be better placed to be isolated functions in this case and you just call them all in the game loop.

 

I agree with you. May be Systems have some function pointer like void (*on_update)(float dt), and we can assign different function for different System, right? But I'm not sure is it a good implemention, I'm still exploring.

 

Anyway, thanks for your replay and  any suggestion is aprreciated!






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