rounded

class RoundedRectangleShape : public sf::Shape
{
public:
    explicit RoundedRectangleShape(const sf::Vector2f& size = {})
    : size(size)
    , radius(10.f)
    , pointCount(4)
    , totalPoints(4 * 4)
   {
       update();
   }

    unsigned getPointCount() const
    {
        return totalPoints;
    }

    sf::Vector2f getPoint(unsigned index) const
    {
        static const float deltaAngle = 90.0f/(pointCount-1)* 0.01745329251f;
        static const std::array<sf::Vector2f, 4> centerCorners{{
            {size.x - radius, radius         },
            {radius,          radius         },
            {radius,          size.y - radius},
            {size.x - radius, size.y - radius},
        }};

        if(index >= totalPoints) return {};

        const unsigned centerIndex = index/pointCount;
        const auto center = centerCorners[centerIndex];

        sf::Vector2f point;
        point.x = center.x + radius*std::cos(deltaAngle*(index-centerIndex));
        point.y = center.y - radius*std::sin(deltaAngle*(index-centerIndex));

        return point;
    }

private:
    sf::Vector2f size;
    float radius;
    unsigned pointCount;
    unsigned totalPoints;
};