Attractor and Repeller with OpenSiv3D library.

Main.cpp

# include <Siv3D.hpp>

#include <iostream>
#include <string>
#include <random>

using namespace std;

inline double myrand(double min, double max)
{
	// 以下2行は一回だけでよいのでは?
	std::random_device rnd;
	std::mt19937 mt(rnd());

	std::uniform_real_distribution<> dist(min, max);
	return dist(mt);
}
inline double constrain(double n, double low, double high) {
	return std::max(std::min(n, high), low);
}

class Mover {
public:
	Mover()
		: m_position(Vec2::Zero()),
		m_velocity(Vec2::Zero()), 
		m_acceleration (Vec2::Zero()),
		m_lifespan(255),
		m_mass(1),
		m_r(5)
	{
		double offx = myrand(-50.0, 50.0);
		double offy = myrand(-50.0, 50.0);
		//m_position = Vec2(Window::Center().x + offx, Window::Center().y + offy);
		m_position = Vec2(Window::Center().x, 100);
		m_velocity = Vec2(myrand(-1.0,1.0), myrand(-1.0,1.0));
		std::cout << "Mover constructor" << std::endl;
	}

	void ApplyForce(Vec2 f)
	{
		Vec2 a = f / this->m_mass; // F=MA, A=F/M
		m_acceleration += a;
	}
	void Update()
	{
		m_velocity += m_acceleration;
		m_position += m_velocity;
		m_acceleration *= 0;

		this->m_lifespan += -1;
	}
	void Display()
	{
		//Print << m_position;
		double r = m_r;
		Circle(m_position, r)
			.draw(Color(175,175,175, this->m_lifespan))
			.drawFrame(1, 0, Color(0, 0, 0, this->m_lifespan));
	}
	void Run()
	{
		Update();
		Display();
	}
	bool IsDead() {
		return (m_lifespan <= 0);
	}
	Vec2 m_position;
private:
	Vec2 m_velocity;
	Vec2 m_acceleration;
	int32_t m_lifespan;
	int32_t m_mass;
	int32_t m_r;
};

class Attractor {
public:
	Attractor()
		:
		m_position(Vec2::Zero())
	{
	}
	Attractor(const Vec2 pos)
		:
		m_position(pos)
	{
	}
	Vec2 Attract(Mover &m)
	{
		Vec2 dir = m_position - m.m_position;
		double len = dir.length();
		len = constrain(len, 20, 110);
		// limit
		dir.normalize();

		double force = 1.0 * 100.0 / (len*len);
		dir *= force;
		return dir;
	}
	void Display() {
		double r = 10;
		Circle(m_position, r)
			.draw(Color(175, 125, 125, 200))
			.drawFrame(1, 0, Color(0, 0, 0, 200));
	}
private:
	Vec2 m_position;
};

class Repeller {
public:
	Repeller()
		:
		m_position(Vec2::Zero())
	{
	}
	Repeller(const Vec2 pos)
		:
		m_position(pos)
	{
	}
	Vec2 Repel(Mover &m)
	{
		Vec2 dir = m_position - m.m_position;
		double len = dir.length();
		len = constrain(len, 10, 110);
		// limit
		dir.normalize();

		double force = -1.0 * 100.0 / (len*len);
		dir *= force;
		return dir;
	}
	void Display() {
		double r = 10;
		Circle(m_position, r)
			.draw(Color(175, 175, 175, 200))
			.drawFrame(1, 0, Color(0, 0, 0, 200));
	}
private:
	Vec2 m_position;
};

class ParticleSystem {
public:
	ParticleSystem() {
	}
	void AddParticle() {
		//if (Random() < 0.5) {}
		m_data.emplace_back(); // 引数なしMoverコンストラクター呼び出し
	}
	void ApplyForce(Vec2 force)	{
		for (Mover &e : m_data) {
			e.ApplyForce(force);
		}
	}
	void ApplyRepeller(Repeller & repeller)
	{
		for (Mover &m : m_data) {
			Vec2 force = repeller.Repel(m);
			m.ApplyForce(force);
		}
	}
	void ApplyAttract(Attractor & attractor)
	{
		for (Mover &m : m_data) {
			Vec2 force = attractor.Attract(m);
			m.ApplyForce(force);
		}
	}
	void Run() {
		for (Mover &e : m_data) {
			e.Run();
		}
	}
	void Remove() {
		auto n = std::remove_if(m_data.begin(), m_data.end(),
			[](Mover &m)->bool { return m.IsDead(); });
		m_data.erase(n, m_data.end());
	}
	size_t Size() {
		return m_data.size();
	}
private:
	vector<Mover> m_data;
};

void Main()
{
	Graphics::SetBackground(Color(240, 240, 240, 255));

	const Font font(30);

	const Vec2 gravity(0.00, 0.03);
	//vector<Mover> movers(100);
	ParticleSystem ps;

	const Vec2 pos(Window::Center().x - 120, Window::Center().y);
	Repeller repeller1(pos);
	const Vec2 pos2(Window::Center().x + 90, Window::Center().y+130);
	Repeller repeller2(pos2);
	const Vec2 pos3(Window::Center().x + 150, Window::Center().y + 0);
	Attractor attractor1(pos3);

	double t = 0.0;
	while (System::Update())
	{
		font(L"Attractor Repeller(りぺらー)🐣").drawAt(Window::Center().x, 30, Palette::Black);

		for (int i = 0; i < 10; i++) ps.AddParticle();

		ps.ApplyForce(gravity);
		ps.ApplyRepeller(repeller1);
		ps.ApplyRepeller(repeller2);
		ps.ApplyAttract(attractor1);
		ps.Run();
		ps.Remove();
		repeller1.Display();
		repeller2.Display();
		attractor1.Display();

		font(ps.Size()).draw(20, 200, Palette::Black);

		t += System::DeltaTime();
	}
}