ecs.hpp
C++17 Entity Component System
Requirements
Installation
ecs.hpp is a header-only library. All you need to do is copy the headers files from headers directory into your project and include them:
#include "ecs.hpp/ecs.hpp"
Also, you can add the root repository directory to your cmake project:
add_subdirectory(external/ecs.hpp)
target_link_libraries(your_project_target PUBLIC ecs.hpp::ecs.hpp)
Basic usage
#include <ecs.hpp/ecs.hpp>
namespace ecs = ecs_hpp;
// events
struct update_event {
float dt{};
};
struct render_event {
std::string camera;
};
// components
struct movable {};
struct disabled {};
struct sprite {
std::string name;
};
struct position {
float x{};
float y{};
};
struct velocity {
float x{};
float y{};
};
// systems
class gravity_system : public ecs::system<update_event> {
public:
gravity_system(float gravity)
: gravity_(gravity) {}
void process(ecs::registry& world, const update_event& evt) override {
world.for_each_component<velocity>(
[this, &evt](ecs::entity, velocity& vel) {
vel.x += gravity_ * evt.dt;
vel.y += gravity_ * evt.dt;
}, ecs::exists<movable>{} && !ecs::exists<disabled>{});
}
private:
float gravity_{};
};
class movement_system : public ecs::system<update_event> {
public:
void process(ecs::registry& world, const update_event& evt) override {
world.for_joined_components<position, velocity>(
[&evt](ecs::entity, position& pos, const velocity& vel) {
pos.x += vel.x * evt.dt;
pos.y += vel.y * evt.dt;
}, ecs::exists<movable>{} && !ecs::exists<disabled>{});
}
};
class render_system : public ecs::system<render_event> {
public:
void process(ecs::registry& world, const render_event& evt) override {
world.for_joined_components<sprite, position>(
[&evt](ecs::entity, const sprite& s, const position& p) {
std::cout << "Render sprite:" << std::endl;
std::cout << "--> pos: " << p.x << "," << p.y << std::endl;
std::cout << "--> sprite: " << s.name << std::endl;
std::cout << "--> camera: " << evt.camera << std::endl;
}, !ecs::exists<disabled>{});
}
};
// world
ecs::registry world;
struct physics_feature {};
world.assign_feature<physics_feature>()
.add_system<movement_system>()
.add_system<gravity_system>(9.8f);
struct rendering_feature {};
world.assign_feature<rendering_feature>()
.add_system<render_system>();
// entities
auto entity_one = world.create_entity();
ecs::entity_filler(entity_one)
.component<movable>()
.component<sprite>("ship")
.component<position>(4.f, 2.f)
.component<velocity>(10.f, 20.f);
auto entity_two = world.create_entity();
ecs::entity_filler(entity_two)
.component<movable>()
.component<sprite>("player")
.component<position>(4.f, 2.f)
.component<velocity>(10.f, 20.f);
// processing
world.process_event(update_event{0.1f});
world.process_event(render_event{"main"});