テクスチャに残像をつける

https://gyazo.com/7d3f31317301f502f125af9bec10a689

code:trail.cpp

// 徐々に消えるテクスチャ（残像）

struct Afterimage : IEffect

{

TexturedQuad m_texture;

Vec2 m_pos;

double m_fadeoutTime;

Afterimage(const TexturedQuad& texture, const Vec2& pos, double fadeoutTime = 1.0)

: m_texture(texture), m_pos(pos), m_fadeoutTime(fadeoutTime)

{

}

bool update(double t) override

{

m_texture.drawAt(m_pos, AlphaF(1.0 - t / m_fadeoutTime));

return t < m_fadeoutTime;

}

};

void Main()

{

Scene::SetBackground(Palette::White);

const Texture dolphin(Emoji(U"🐬"));

Effect effect;

Stopwatch interval{ StartImmediately::Yes };

while (System::Update())

{

const double t = Scene::Time();

const auto texture = dolphin.scaled(1.0 + 0.4 * Sin(t * 3.0)).rotated(t * -6.0);

const Vec2 pos = Scene::CenterF().movedBy(200 * Cos(t * 5.0), 200 * Sin(t * 4.0));

texture.drawAt(pos);

// 0.1秒ごとに残像を生成

if (interval.elapsed() >= 0.1s)

{

effect.add<Afterimage>(texture, pos, 0.7); //0.7秒かけて消える

interval.restart();

}

effect.update();

}

}