説明

このような波の形の Polygon を作成し描画するサンプルを紹介します。
サンプル

# include <Siv3D.hpp> // OpenSiv3D v0.4.2

class WaveBackground
{
private:

	Polygon m_polygon;

public:

	WaveBackground() = default;

	explicit WaveBackground(const Rect& rect, double distance = 4.0)
	{
		const Vec2 br(rect.x + rect.w, rect.y + rect.h);
		const Vec2 bl(rect.x, rect.y + rect.h);
		const int32 samples = static_cast<int32>(rect.w / distance);

		Array<Vec2> points;

		for (int32 i : Range(0, samples))
		{
			const double x = Math::Lerp(rect.x, rect.x + rect.w, static_cast<double>(i) / samples);
			const double y = rect.y + rect.h * 0.75 - Math::Sin(x * 0.5_deg) * (rect.h * 0.1);
			points.emplace_back(x,  y);
		}

		points << br << bl;

		m_polygon = Polygon(points);
	}

	void draw(const ColorF& color) const
	{
		m_polygon.draw(color);
	}

	void drawWireframe(const ColorF& color) const
	{
		m_polygon.drawWireframe(1.0, color);
	}
};

void Main()
{
	Scene::SetBackground(Palette::White);

	double distance = 5.0;
	bool showWireframe = false;
	WaveBackground waveBackground(Scene::Rect(), distance);

	while (System::Update())
	{
		waveBackground.draw(Palette::Skyblue);

		if (showWireframe)
		{
			waveBackground.drawWireframe(Palette::Blue);
		}

		if (SimpleGUI::Slider(U"Distance: {:.0f}"_fmt(distance), distance, 1.0, 80.0, Vec2(20, 20), 140, 140))
		{
			waveBackground = WaveBackground(Scene::Rect(), distance);
		}

		SimpleGUI::CheckBox(showWireframe, U"Show wireframe", Vec2(20, 60));
	}
}
実行結果
