OpenSiv3Dで縞模様を描く

DrawStripe.cpp

#include <Siv3D.hpp>

void DrawStripe(const Rect& rect, double angle, double barWidth, const Array<ColorF>& pattern = { Palette::Yellow, Palette::Black })
{
	// 傾けたときの描画範囲を計算
	const auto renderRect =
		RectF{ 0, 0, rect.size }.asQuad()
		.rotatedAt(0, 0, -angle)
		.boundingRect();

	// 切り抜き
	ScopedViewport2D view(rect);

	// angle分だけ傾ける
	Transformer2D t(Mat3x2::Rotate(angle));

	// 縞模様を描画
	for (int32 i = 0;
		i * barWidth < renderRect.w;
		i++)
	{
		const auto color = pattern[i % pattern.size()];
		RectF{ renderRect.x + i * barWidth, renderRect.y, barWidth, renderRect.h }
			.draw(color);
	}
}

void Main()
{
	double angle = 45_deg;
	double barWidth = 20;

	while (System::Update())
	{
		Rect rect = Scene::Rect().stretched(-100);

		DrawStripe(rect, angle, barWidth);
		rect.drawFrame(2, 0, Palette::Red);

		SimpleGUI::Slider(U"Angle", angle, 0_deg, 360_deg, { 0, 0 }, 100);
		SimpleGUI::Slider(U"BarWidth", barWidth, 10.0, 100.0, { 0, 36 }, 100);
	}
}