sfmlNoShapeGL

#include <SFML/Graphics.hpp>
#include <SFML/Window.hpp>
#include <GL/gl.h>

int main(int argc, char* argv[])
{
    sf::RenderWindow window(sf::VideoMode(800, 600), sf::String("SFML noShapeGL"), sf::Style::Default, sf::ContextSettings(32,0,8,4,2));
    window.setFramerateLimit(60);

    sf::RectangleShape shape(sf::Vector2f(50, 50));
    shape.setPosition(100, 100);

    while(window.isOpen())
    {
        sf::Event event;
        while(window.pollEvent(event))
        {
            switch(event.type)
            {
                case sf::Event::Closed:
                    window.close();
                    break;
            }
        }

        window.setActive();
        window.clear(sf::Color(0, 0, 0));


        //////////////////////////////////////////////////////////////////////////
        // With the line below it's working fine, without it nothing is drawed. //
        //////////////////////////////////////////////////////////////////////////
        //window.draw(shape);

        // custom GL-Rendering
        glPushAttrib(GL_TRANSFORM_BIT);
        glLoadIdentity();

        glPushAttrib(GL_CURRENT_BIT | GL_LINE_BIT);
        glColor4f(1.0, 0, 0, 1.0);
        glLineWidth(5);

        glBegin(GL_LINES);
        {
            glVertex2d(10, 50);
            glVertex2d(50, 10);
        }
        glEnd();

        glPopAttrib();

        glPopAttrib();

        window.display();
    }
}