WatchfulEye

# include <Siv3D.hpp> // OpenSiv3D v0.2.7

class WatchfulEye
{
	Vec2	m_position;
	Vec2	m_aimed;
	Vec2	m_target;
	double	m_degree;
	double	m_timer;
	double	m_size;

public:
	WatchfulEye(const Vec2& position, double size)
		: m_size(size)
		, m_position(position)
		, m_degree(0.5)
		, m_aimed(0.0, 0.0)
		, m_target(0.0, 0.0)
		, m_timer(0.0)
	{}

	void update()
	{
		auto base = Circle(m_position, m_size / 2.0).asPolygon();

		m_degree += Min(Max(m_timer - m_degree, -0.025), 0.025);

		if (m_degree == m_timer)
		{
			if (RandomBool(0.005)) { m_timer = 0.5; }
			if (RandomBool(0.0025)) { m_timer = 0.0; }
			if (RandomBool(0.00125)) { m_timer = 0.75; }
		}

		if (RandomBool(0.01)) { m_target = RandomVec2(Random(m_size / 12.0)); }
		if ((m_target - m_aimed).length() > 1.0) { m_aimed += (m_target - m_aimed).setLength(m_size / 128.0); }

		base.draw(Palette::White);

		{
			Array<Vec2> points;
			for (double t = 0.0; t < Math::TwoPi; t += 0.1)
			{
				points.emplace_back((Vec2(cos(t), sin(t) * m_degree) * m_size / 8.0).movedBy(-m_size / 4.0, 0.0).movedBy(m_position));
			}
			base.addHole(points);

			points.clear();
			for (double t = 0.0; t < Math::TwoPi; t += 0.1)
			{
				points.emplace_back((Vec2(cos(t), sin(t) * m_degree) * m_size / 8.0).movedBy(+m_size / 4.0, 0.0).movedBy(m_position));
			}
			base.addHole(points);
		}

		Circle(m_position, m_size / 12.0).movedBy(m_aimed).movedBy(-m_size / 4.0, 0.0).draw(Palette::Darkred);
		Circle(m_position, m_size / 18.0).movedBy(m_aimed).movedBy(-m_size / 4.0, 0.0).draw(Palette::Red);
		Circle(m_position, m_size / 12.0).movedBy(m_aimed).movedBy(+m_size / 4.0, 0.0).draw(Palette::Darkred);
		Circle(m_position, m_size / 18.0).movedBy(m_aimed).movedBy(+m_size / 4.0, 0.0).draw(Palette::Red);

		base.draw(Color(11, 22, 33));
	}

	bool	intersects(const Circle& circle) const { return Circle(m_position, m_size / 2.0).intersects(circle); }
};

void Main()
{
	Graphics::SetBackground(Color(11, 22, 33));

	Array<WatchfulEye> eyes;

	for (int i = 0; i < 128; i++)
	{
		auto p = RandomVec2(Window::ClientRect());
		auto s = Random(64, 128);

		if (!eyes.any([&p, &s](const WatchfulEye& e) { return e.intersects(Circle(p, s)); })) { eyes.emplace_back(p, s); }
	}

	while (System::Update())
	{
		for (auto& e : eyes) { e.update(); }
	}
}