SFML massive performance loss when sf::Window is not created - c++

Question

I am writing an app drawing multiple figures and comparing images (counting pixels values). Drawing and counting thread doesn't display any image. Gui is implemented in another thread.
Currently, I have found very strange anomaly. My drawing and comparing thread works very slow, but when I add before main loop sf::Window
I have x70 performance increase, but adding these lines breaks my GUI (probably because I create a window in another thread)*.
I am looking for a way of increasing performance without using sf::Window::create(...).
Full example:
int main()
{
// sf::Window window(sf::VideoMode(200, 200), "SFML");
std::vector<sf::CircleShape> circles_;
for (int i = 0; i < 200; i++)
{
sf::CircleShape circle(rand() % 50 + 10, 20);
circle.setFillColor(sf::Color(rand() % 256, rand() % 256, rand() % 256, 128));
circle.setPosition(rand() % (100), rand() % (100));
circles_.push_back(circle);
}
sf::RenderTexture generated_texture;
generated_texture.create(100, 100);
sf::Clock clock;
uint i = 0;
while (i < 10)
{
for (auto &shape : circles_)
{
generated_texture.draw(shape);
}
i++;
}
double result = double(i) / clock.getElapsedTime().asSeconds();
cout << "Result: " << result << " loops/sec";
return 0;
}
*For simplification let's assume that I don't have any gui (in my app it is optional). I just wanna run my app from commandline.

Answer 1

I have opened an issue on SFML github and found out that it was caused by activating and deactivating context, so in this case instead of:
sf::Window window(sf::VideoMode(200, 200), "SFML");
should be
sf::Context some_context;.
Original issue link:
https://github.com/SFML/SFML/issues/1672
Full answer:
"When sf::RenderTexture is done drawing it tries to restore the state to how it was before the draw call. Since this was the "no context" state it will repeatedly activate and deactivate the context every iteration. This is standard behaviour for any OpenGL resource that can live on its own without necessarily having a window.
If you want to do anything rendering related it is recommended to always have some kind of context-owning-thing lying around. If you don't want a full sf::Window then an sf::Context will have to do.
Due to the nature of OpenGL, you will never get around the limitation of having some kind of window (whether it's visible or not) that itself owns a context. That's just the way the API designers designed it 25 years ago."