olafvisker / mnes

A minimal entity component system focused on efficiency and readable code.

mnes

A minimal c++11 entity component system focused on efficiency and readable code.

example

includes

#include  "entity.h"
#include  "component.h"
#include  "system.h"

using  namespace  mnes;

components

struct Position : Component {
    float x, y, z = 0.0f;
    Position(float x, float y, float z) : x(x), y(y), z(z) { }
};

struct Velocity : Component {
    float v1, v2, v3 = 0.0f;
    Velocity(float v1, float v2, float v3) : v1(v1), v2(v2), v3(v3) { }
};

system

class MovementSystem : public System {
    void Init() {
        Require<Position>();
        Require<Velocity>();
    }

    void Update() {
        for (auto e : GetEntities()) {
            Position* pos = e.GetComponent<Position>();
            Velocity* vel = e.GetComponent<Velocity>();

            pos->x += vel->v1;
            pos->y += vel->v2;
            pos->z += vel->v3;
        }
    }
};

main

EntityManager entity_manager;
SystemManager system_manager(&entity_manager);

system_manager.Register<MovementSystem>();  	//register a new system to the system manager
system_manager.Init();                      	//initialize all systems

Entity e = entity_manager.Create();         	//create a new entity
e.AddComponent<Position>(10.0f, 12.0f, 4.0f)	//add a position components
 .AddComponent<Velocity>(1.0f, 0.0f, 0.5f)	//add a velocity component using chaining
 .Bind();					//bind entity to relevant systems next update

for (int i = 0; i < 10; i++) {
	system_manager.Update();		//update all systems
	Position pos = *e.GetComponent<Position>();
	std::cout << pos.x << " " << pos.y << " " << pos.z << std::endl;
}

system sets

Sometimes systems require access to multiple sets of components. In order to solve this problem mnes makes use of so called system sets. This allows a single system to work with multiple combinations (entities) of components. You can find an example below.

class RenderSystem : public System {
    enum Sets {                                       //define your entity sets
        CAMERAS,
        OBJECTS,
    };

    void Init() {
        Require<Viewport>(Sets::CAMERAS);             //define camera entity
        Require<Camera>(Sets::CAMERAS);

        Require<Transform>(Sets::OBJECTS);            //define object entity
        Require<MeshRenderer>(Sets::OBJECTS);
    }

    void Update() {
        for (auto c : GetEntities(Sets::CAMERAS)) {     //get all cameras entities
            ...  		        
            for (auto e : GetEntities(Sets::OBJECTS)) { //get all objects entities
                ...
            }
        }
    }
};

enjoy!