ecs-test/main-entt.cpp at master · cjuniet/ecs-test · GitHub

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#include <SFML/Graphics.hpp>
#include <entt/entity/registry.hpp>
#include <cstdlib>
#include <iostream>
#include <sstream>

inline float r(int a, float b = 0) { return static_cast<float>(std::rand() % (a * 1000) + b * 1000) / 1000.0; }

////////////////////////////////////////////////////////////////

struct Body {
  Body(const sf::Vector2f& position, const sf::Vector2f& direction)
    : position(position), direction(direction)
  {}

  sf::Vector2f position;
  sf::Vector2f direction;
};

struct BodySystem {
  void update(entt::DefaultRegistry &registry, double dt)
  {
    const auto fdt = static_cast<float>(dt);
    registry.view<Body>().each([fdt](auto entity, auto& body) { body.position += body.direction * fdt; });
  };
};

class BounceSystem
{
public:
  explicit BounceSystem(sf::Vector2u size) : size(size) {}

  void update(entt::DefaultRegistry &registry, double dt)
  {
    registry.view<Body>().each([this](auto entity, auto& body) {
      if (body.position.x + body.direction.x < 0 || body.position.x + body.direction.x >= size.x) {
        body.direction.x = -body.direction.x;
      }
      if (body.position.y + body.direction.y < 0 || body.position.y + body.direction.y >= size.y) {
        body.direction.y = -body.direction.y;
      }
    });
  }

private:
  sf::Vector2u size;
};

////////////////////////////////////////////////////////////////

using Renderable = std::shared_ptr<sf::Shape>;

class RenderSystem
{
public:
  explicit RenderSystem(sf::RenderTarget& target, sf::Font& font) : target(target)
  {
    text.setFont(font);
    text.setPosition(sf::Vector2f(32, 2));
  }

  void update(entt::DefaultRegistry &registry, double dt)
  {
    int count = 0;
    registry.view<Body, Renderable>().each([this, &count](auto entity, auto& body, auto& renderable) {
      renderable->setPosition(body.position);
      target.draw(*renderable);
      ++count;
    });

    print_fps(dt, count);
  }

private:
  void print_fps(double dt, size_t nb_entities)
  {
    last_update += dt;
    ++frame_count;
    if (last_update >= 0.5) {
      const double fps = frame_count / last_update;
      oss.seekp(0);
      oss << nb_entities << " entities (" << static_cast<int>(fps) << " fps) ";
      text.setString(oss.str());
      last_update = 0.0;
      frame_count = 0.0;
    }
    target.draw(text);
  }

private:
  sf::RenderTarget& target;
  sf::Text text;
  double last_update = 0;
  double frame_count = 0;
  std::ostringstream oss;
};

////////////////////////////////////////////////////////////////

class GameEngine
{
  entt::DefaultRegistry registry;
  BodySystem body_system;
  BounceSystem bounce_system;
  RenderSystem render_system;

public:
  GameEngine(sf::RenderTarget& target, sf::Font& font)
    : bounce_system(target.getSize()), render_system(target, font)
  {}

  void update(double dt) {
    body_system.update(registry, dt);
    bounce_system.update(registry, dt);
    render_system.update(registry, dt);
  }

  void create_bodies(sf::Vector2u size, int count)
  {
    for (int i = 0; i < count; i++) {
      auto entity = registry.create();

      registry.assign<Body>(entity, sf::Vector2f(r(size.x), r(size.y)), sf::Vector2f(r(200, -200), r(200, -200)));

      Renderable shape(new sf::CircleShape(20));
      shape->setOrigin(10, 10);
      shape->setFillColor(sf::Color(r(128, 127), r(128, 127), r(128, 127)));
      registry.assign<Renderable>(entity, shape);
    }
  }
};


////////////////////////////////////////////////////////////////

int main()
{
  std::srand(std::time(nullptr));

  sf::Font font;
  if (!font.loadFromFile("Roboto.ttf")) {
    std::cerr << "error: failed to load Roboto.ttf" << std::endl;
    return 1;
  }

  sf::RenderWindow window(sf::VideoMode::getDesktopMode(), "ECS Test", sf::Style::Fullscreen);
  window.setVerticalSyncEnabled(true);

  GameEngine engine(window, font);
  engine.create_bodies(window.getSize(), 100);

  sf::Clock clock;
  while (window.isOpen()) {
    sf::Event event;
    while (window.pollEvent(event)) {
      switch (event.type) {
        case sf::Event::Closed:
        case sf::Event::KeyPressed:
          window.close();
          break;
        default:
          break;
      }
    }

    window.clear();
    auto elapsed = clock.restart();
    engine.update(elapsed.asSeconds());
    window.display();
  }

  return 0;
}