/**
* This is an example of using EntityX.
*
* It is an SFML2 application that spawns 100 random circles on a 2D plane
* moving in random directions. If two circles collide they will explode and
* emit particles.
*
* This illustrates a bunch of EC/EntityX concepts:
*
* - Separation of data via components.
* - Separation of logic via systems.
* - Use of events (colliding bodies trigger a CollisionEvent).
*
* Compile with:
*
* c++ -I.. -O3 -std=c++11 -Wall -lsfml-system -lsfml-window -lsfml-graphics -lentityx example.cc -o example
*/
#include <cmath>
#include <unordered_set>
#include <sstream>
#include <cstdlib>
#include <memory>
#include <string>
#include <vector>
#include <iostream>
#include <SFML/Window.hpp>
#include <SFML/Graphics.hpp>
#include <entityx/entityx.h>
using std::cerr;
using std::cout;
using std::endl;
namespace ex = entityx;
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, float rotationd = 0.0)
: position(position), direction(direction), rotationd(rotationd), alpha(0.0) {}
sf::Vector2f position;
sf::Vector2f direction;
float rotation = 0.0, rotationd, alpha;
};
using Renderable = std::shared_ptr<sf::Shape>;
struct Particle {
explicit Particle(sf::Color colour, float radius, float duration)
: colour(colour), radius(radius), alpha(colour.a), d(colour.a / duration) {}
sf::Color colour;
float radius, alpha, d;
};
struct Collideable {
explicit Collideable(float radius) : radius(radius) {}
float radius;
};
// Emitted when two entities collide.
struct CollisionEvent {
CollisionEvent(ex::Entity left, ex::Entity right) : left(left), right(right) {}
ex::Entity left, right;
};
class SpawnSystem : public ex::System<SpawnSystem> {
public:
explicit SpawnSystem(sf::RenderTarget &target, int count) : size(target.getSize()), count(count) {}
void update(ex::EntityManager &es, ex::EventManager &events, ex::TimeDelta dt) override {
int c = 0;
ex::ComponentHandle<Collideable> collideable;
es.each<Collideable>([&](ex::Entity entity, Collideable&) { ++c; });
for (int i = 0; i < count - c; i++) {
ex::Entity entity = es.create();
// Mark as collideable (explosion particles will not be collideable).
collideable = entity.assign<Collideable>(r(10, 5));
// "Physical" attributes.
entity.assign<Body>(
sf::Vector2f(r(size.x), r(size.y)),
sf::Vector2f(r(100, -50), r(100, -50)));
// Shape to apply to entity.
Renderable shape(new sf::CircleShape(collideable->radius));
shape->setFillColor(sf::Color(r(128, 127), r(128, 127), r(128, 127), 0));
shape->setOrigin(collideable->radius, collideable->radius);
entity.assign<Renderable>(shape);
}
}
private:
sf::Vector2u size;
int count;
};
// Updates a body's position and rotation.
struct BodySystem : public ex::System<BodySystem> {
void update(ex::EntityManager &es, ex::EventManager &events, ex::TimeDelta dt) override {
const float fdt = static_cast<float>(dt);
es.each<Body>([fdt](ex::Entity entity, Body &body) {
body.position += body.direction * fdt;
body.rotation += body.rotationd * fdt;
body.alpha = std::min(1.0f, body.alpha + fdt);
});
};
};
// Bounce bodies off the edge of the screen.
class BounceSystem : public ex::System<BounceSystem> {
public:
explicit BounceSystem(sf::RenderTarget &target) : size(target.getSize()) {}
void update(ex::EntityManager &es, ex::EventManager &events, ex::TimeDelta dt) override {
es.each<Body>([this](ex::Entity entity, Body &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;
};
// Determines if two Collideable bodies have collided. If they have it emits a
// CollisionEvent. This is used by ExplosionSystem to create explosion
// particles, but it could be used by a SoundSystem to play an explosion
// sound, etc..
//
// Uses a fairly rudimentary 2D partition system, but performs reasonably well.
class CollisionSystem : public ex::System<CollisionSystem> {
static const int PARTITIONS = 200;
struct Candidate {
sf::Vector2f position;
float radius;
ex::Entity entity;
};
public:
explicit CollisionSystem(sf::RenderTarget &target) : size(target.getSize()) {
size.x = size.x / PARTITIONS + 1;
size.y = size.y / PARTITIONS + 1;
}
void update(ex::EntityManager &es, ex::EventManager &events, ex::TimeDelta dt) override {
reset();
collect(es);
collide(events);
};
private:
std::vector<std::vector<Candidate>> grid;
sf::Vector2u size;
void reset() {
grid.clear();
grid.resize(size.x * size.y);
}
void collect(ex::EntityManager &entities) {
entities.each<Body, Collideable>([this](ex::Entity entity, Body &body, Collideable &collideable) {
unsigned int
left = static_cast<int>(body.position.x - collideable.radius) / PARTITIONS,
top = static_cast<int>(body.position.y - collideable.radius) / PARTITIONS,
right = static_cast<int>(body.position.x + collideable.radius) / PARTITIONS,
bottom = static_cast<int>(body.position.y + collideable.radius) / PARTITIONS;
Candidate candidate {body.position, collideable.radius, entity};
unsigned int slots[4] = {
left + top * size.x,
right + top * size.x,
left + bottom * size.x,
right + bottom * size.x,
};
grid[slots[0]].push_back(candidate);
if (slots[0] != slots[1]) grid[slots[1]].push_back(candidate);
if (slots[1] != slots[2]) grid[slots[2]].push_back(candidate);
if (slots[2] != slots[3]) grid[slots[3]].push_back(candidate);
});
}
void collide(ex::EventManager &events) {
for (const std::vector<Candidate> &candidates : grid) {
for (const Candidate &left : candidates) {
for (const Candidate &right : candidates) {
if (left.entity == right.entity) continue;
if (collided(left, right))
events.emit<CollisionEvent>(left.entity, right.entity);
}
}
}
}
float length(const sf::Vector2f &v) {
return std::sqrt(v.x * v.x + v.y * v.y);
}
bool collided(const Candidate &left, const Candidate &right) {
return length(left.position - right.position) < left.radius + right.radius;
}
};
// Fade out and then remove particles.
class ParticleSystem : public ex::System<ParticleSystem> {
public:
void update(ex::EntityManager &es, ex::EventManager &events, ex::TimeDelta dt) override {
es.each<Particle>([dt](ex::Entity entity, Particle &particle) {
particle.alpha -= particle.d * dt;
if (particle.alpha <= 0) {
entity.destroy();
} else {
particle.colour.a = particle.alpha;
}
});
}
};
// Renders all explosion particles efficiently as a quad vertex array.
class ParticleRenderSystem : public ex::System<ParticleRenderSystem> {
public:
explicit ParticleRenderSystem(sf::RenderTarget &target) : target(target) {}
void update(ex::EntityManager &es, ex::EventManager &events, ex::TimeDelta dt) override {
sf::VertexArray vertices(sf::Quads);
es.each<Particle, Body>([&vertices](ex::Entity entity, Particle &particle, Body &body) {
const float r = particle.radius;
// Spin the particles.
sf::Transform transform;
transform.rotate(body.rotation);
vertices.append(sf::Vertex(body.position + transform.transformPoint(sf::Vector2f(-r, -r)), particle.colour));
vertices.append(sf::Vertex(body.position + transform.transformPoint(sf::Vector2f(r, -r)), particle.colour));
vertices.append(sf::Vertex(body.position + transform.transformPoint(sf::Vector2f(r, r)), particle.colour));
vertices.append(sf::Vertex(body.position + transform.transformPoint(sf::Vector2f(-r, r)), particle.colour));
});
target.draw(vertices);
}
private:
sf::RenderTarget ⌖
};
// For any two colliding bodies, destroys the bodies and emits a bunch of bodgy explosion particles.
class ExplosionSystem : public ex::System<ExplosionSystem>, public ex::Receiver<ExplosionSystem> {
public:
void configure(ex::EventManager &events) override {
events.subscribe<CollisionEvent>(*this);
}
void update(ex::EntityManager &es, ex::EventManager &events, ex::TimeDelta dt) override {
for (ex::Entity entity : collided) {
emit_particles(es, entity);
entity.destroy();
}
collided.clear();
}
void emit_particles(ex::EntityManager &es, ex::Entity entity) {
ex::ComponentHandle<Body> body = entity.component<Body>();
ex::ComponentHandle<Renderable> renderable = entity.component<Renderable>();
ex::ComponentHandle<Collideable> collideable = entity.component<Collideable>();
sf::Color colour = (*renderable)->getFillColor();
colour.a = 200;
float area = (M_PI * collideable->radius * collideable->radius) / 3.0;
for (int i = 0; i < area; i++) {
ex::Entity particle = es.create();
float rotationd = r(720, 180);
if (std::rand() % 2 == 0) rotationd = -rotationd;
float offset = r(collideable->radius, 1);
float angle = r(360) * M_PI / 180.0;
particle.assign<Body>(
body->position + sf::Vector2f(offset * cos(angle), offset * sin(angle)),
body->direction + sf::Vector2f(offset * 2 * cos(angle), offset * 2 * sin(angle)),
rotationd);
float radius = r(3, 1);
particle.assign<Particle>(colour, radius, radius / 2);
}
}
void receive(const CollisionEvent &collision) {
// Events are immutable, so we can't destroy the entities here. We defer
// the work until the update loop.
collided.insert(collision.left);
collided.insert(collision.right);
}
private:
std::unordered_set<ex::Entity> collided;
};
// Render all Renderable entities and draw some informational text.
class RenderSystem :public ex::System<RenderSystem> {
public:
explicit RenderSystem(sf::RenderTarget &target, sf::Font &font) : target(target) {
text.setFont(font);
text.setPosition(sf::Vector2f(2, 2));
text.setCharacterSize(18);
text.setColor(sf::Color::White);
}
void update(ex::EntityManager &es, ex::EventManager &events, ex::TimeDelta dt) override {
es.each<Body, Renderable>([this](ex::Entity entity, Body &body, Renderable &renderable) {
sf::Color fillColor = renderable->getFillColor();
fillColor.a = sf::Uint8(body.alpha * 255);
renderable->setFillColor(fillColor);
renderable->setPosition(body.position);
renderable->setRotation(body.rotation);
target.draw(*renderable.get());
});
last_update += dt;
frame_count++;
if (last_update >= 0.5) {
std::ostringstream out;
const double fps = frame_count / last_update;
out << es.size() << " entities (" << static_cast<int>(fps) << " fps)";
text.setString(out.str());
last_update = 0.0;
frame_count = 0.0;
}
target.draw(text);
}
private:
double last_update = 0.0;
double frame_count = 0.0;
sf::RenderTarget ⌖
sf::Text text;
};
class Application : public ex::EntityX {
public:
explicit Application(sf::RenderTarget &target, sf::Font &font) {
systems.add<SpawnSystem>(target, 500);
systems.add<BodySystem>();
systems.add<BounceSystem>(target);
systems.add<CollisionSystem>(target);
systems.add<ExplosionSystem>();
systems.add<ParticleSystem>();
systems.add<RenderSystem>(target, font);
systems.add<ParticleRenderSystem>(target);
systems.configure();
}
void update(ex::TimeDelta dt) {
systems.update_all(dt);
}
};
int main() {
std::srand(std::time(nullptr));
sf::RenderWindow window(sf::VideoMode::getDesktopMode(), "EntityX Example", sf::Style::Fullscreen);
sf::Font font;
if (!font.loadFromFile("LiberationSans-Regular.ttf")) {
cerr << "error: failed to load LiberationSans-Regular.ttf" << endl;
return 1;
}
Application app(window, font);
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();
sf::Time elapsed = clock.restart();
app.update(elapsed.asSeconds());
window.display();
}
}