twinkle.cpp

#include <Siv3D.hpp>

struct Twinkle : IEffect
{
	Vec2 pos;
	double angle;
	double scale;

	Twinkle(const Vec2 pos) : pos(pos), angle(RandomSelect({ 0_deg, 45_deg })), scale(Random(0.2, 1.0))
	{
	}

	bool update(double t) override
	{
		scale *= 0.988;

		const double outer = (4 + 25 + 25 * Sin(t * 6_pi)) * scale;
		const double inner = (0.5 + 1 + 1 * Sin(t * 6_pi)) * scale;

		Geometry2D::CreateNStar(4, outer, inner, angle, pos).draw(Alpha(1 + 120 + 120 * Sin(t * 6_pi)));

		return t < 0.50;
	}
};

void Main()
{
	Effect effect;

	while (System::Update())
	{
		if (System::FrameCount() % 2)
			effect.add<Twinkle>(Mouse::Pos() + RandomVec2(Random(80.0)));

		effect.update();
	}
}

Polygon に対する毎フレームの scaled, rotated, movedBy を避けるよう修正（https://twitter.com/Reputeless/status/782582249950617601）