Polygonの形状に沿って軌跡を描く

https://scrapbox.io/files/64e4c4cdc79a2d001bfe806e.mp4

code:siv_trail_polygon_highlight.cpp

# include <Siv3D.hpp> // OpenSiv3D v0.6.11

struct PolygonHighlightEffect : IEffect

{

Array<TrailMotion> trails;

Polygon polygon;

PolygonHighlightEffect(const Polygon& targetPolygon)

: polygon{ targetPolygon }

{

constexpr std::array<ColorF, 3> colors = { Palette::White, Palette::Magenta, Palette::Cyan };

for (int iTrail : step(3))

{

trails << TrailMotion{}

.setLifeTime(DisplayTime + 0.5 * iTrail)

const double size = 2 + 3 * iTrail;

const double sizeScale1 = timeSec < LifeTime ? 1 : 0;

const double sizeScale2 = timeSec < 0.1 ? timeSec / 0.1 : 1;

const double displayTimeScaled = DisplayTime * 0.7;

const double sizeScale3 = timeSec < displayTimeScaled ? 1 : EaseInExpo(1 - ((timeSec - displayTimeScaled) / (LifeTime - displayTimeScaled)));

return size * sizeScale1 * sizeScale2 * sizeScale3;

})

const double t = Min(timeSec, DisplayTime);

const double t0_1 = t / (DisplayTime * 0.8);

const auto& vertices = polygon.outer();

const int index1 = ((int)(t0_1 * vertices.size())) % vertices.size();

const int index2 = (index1 + 1) % vertices.size();

double tmp;

const double lerpFactor = modf(t0_1 * vertices.size(), &tmp);

return v;

});

}

}

bool update(double timeSec) override

{

for (auto& trail : trails)

{

trail.update();

}

{

const ScopedRenderStates2D blend{ BlendState::Additive };

for (const auto& trail : trails)

{

trail.draw();

}

}

return timeSec < 3.0;

}

private:

inline static constexpr double DisplayTime = 0.3;

inline static constexpr double LifeTime = 1.0;

};

void Main()

{

Scene::SetBackground(ColorF{ 0 });

const RectF rect{ Arg::center = Scene::CenterF().movedBy(-160, -140), SizeF{ 200, 180 }};

const Circle circle{ Scene::CenterF().movedBy(160, 140), 100 };

const Polygon star = Shape2D::Star(128, Scene::CenterF().movedBy(-160, 140));

const Polygon nstar = Shape2D::NStar(12, 128, 96, Scene::CenterF().movedBy(160, -140));

Effect effect;

while (System::Update())

{

rect.drawFrame(1, 0, Palette::Silver);

circle.drawFrame(1, 0, Palette::Silver);

star.drawFrame(1, Palette::Silver);

nstar.drawFrame(1, Palette::Silver);

if (rect.leftClicked())

{

effect.add<PolygonHighlightEffect>(rect.asPolygon());

}

else if (circle.leftClicked())

{

effect.add<PolygonHighlightEffect>(circle.asPolygon());

}

else if (star.leftClicked())

{

effect.add<PolygonHighlightEffect>(star);

}

else if (nstar.leftClicked())

{

effect.add<PolygonHighlightEffect>(nstar);

}

else if (Scene::Rect().leftClicked())

{

effect.add<PolygonHighlightEffect>(Scene::Rect().stretched(-1).asPolygon());

}

effect.update();

}

}