Image to Polygon

# include <Siv3D.hpp>

void Main()
{
    double max_distance = 4.0;

    GUI gui(GUIStyle::Default);
    gui.addln(L"max_distance", GUISlider::Create(0.5, 40.0, max_distance, 300));
    gui.addln(L"vertices", GUIText::Create(L""));
    gui.addln(L"original", GUIText::Create(L""));
    gui.setPos(280, 20);

    const Image image(L"Example/siv3d-kun.png");

    // アルファ値を使うか、白黒を使うか
    const bool useAlpha = true;

    const Polygon polygon = Imaging::FindExternalContour(image, useAlpha);

    Polygon simplifiedPolygon = polygon.simplified(gui.slider(L"max_distance").value);

    const Texture texture(image);

    const Circle circle(350, 250, 15);

    while (System::Update())
    {
        if (gui.slider(L"max_distance").hasChanged)
        {
            max_distance = gui.slider(L"max_distance").value;

            simplifiedPolygon = polygon.simplified(max_distance);
        }

        texture.draw(Alpha(120));

        gui.text(L"vertices").text = Format(simplifiedPolygon.num_vertices, L" 頂点\tmax_distance : ", max_distance);

        gui.text(L"original").text = Format(L"オリジナル : ", polygon.num_vertices, L" 頂点");

        simplifiedPolygon.drawWireframe(1.0, Palette::Yellowgreen);

        const Polygon movedPolygon = simplifiedPolygon.movedBy(Mouse::Pos() - simplifiedPolygon.boundingRect.center);

        const Color color = Alpha(movedPolygon.intersects(circle) ? 150 : 50);

        circle.draw(Palette::Red);

        movedPolygon.draw(color);
    }
}