Yeeeeh, I figured it out :D,
I can manipulate the view. With this codesnippet my View goes from (0.0, 0.0) to (1.0, aspectRatio), which is even better than that what I wanted. Now I don't need to bother because of the resolution anymore. Very simple. The more I work with SFML, the more I like it.
sf::View view = m_Window.getDefaultView();
view.setSize(sf::Vector2f{ 1.0f, static_cast<float>(m_Window.getSize().y) / static_cast<float>(m_Window.getSize().x) });
view.setCenter(view.getSize() / 2.0f);
m_Window.setView(view);
Thank you for this great library.
Best regards,
Stefan
In case you actually wanted to use the -1 to 1 method, the view is really simple:
sf::View view;
view.setCenter(0.f, 0.f);
view.setSize(2.f, 2.f);
or, more succinctly:
sf::View view(sf::Vector2f(0.f, 0.f), sf::Vector2f(2.f, 2.f));