15パズル

イラスト提供: 古古米 さん

# include <Siv3D.hpp>

bool Swappable(int32 a, int32 b)
{
    return (a / 4 == b / 4 && Abs(a - b) == 1) || (a % 4 == b % 4 && Abs(a - b) == 4);
}

void Main()
{
    const Texture texture = Dialog::OpenTexture(TextureDesc::Mipped);
    const int32 pieceSize = 100;
    Optional<int32> grabbed;
    std::array<Optional<int32>, 16> pieces = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 };

    for (int32 i = 0; i < 10000; ++i)
    {
        const int32 a = Random(0, 15);
        const int32 b = a + RandomSelect({ -4, -1, 1, 4 });

        if (pieces[a] && InRange(b, 0, 15) && !pieces[b] && Swappable(a, b))
        {
            std::swap(pieces[a], pieces[b]);
        }
    }

    while (System::Update())
    {
        if (!Input::MouseL.pressed)
        {
            grabbed = none;
        }

        for (auto i : step(16))
        {
            const Rect pieceRect(i % 4 * pieceSize, i / 4 * pieceSize, pieceSize, pieceSize);

            if (!pieces[i])
            {
                if (grabbed && pieceRect.mouseOver && Swappable(i, grabbed.value()))
                {
                    std::swap(pieces[i], pieces[grabbed.value()]);
                    grabbed = none;
                }

                continue;
            }

            const int32 offset = pieces[i].value();
            pieceRect(texture.uv(offset % 4 * 0.25, offset / 4 * 0.25, 0.25, 0.25)).draw();

            if (pieceRect.leftPressed)
            {
                grabbed = i;
                pieceRect.draw({ 255, 0, 0, 80 });
            }

            pieceRect.drawFrame();
        }

        texture.resize(200, 200).draw(440, 200);
    }
}