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Asked: 2026-06-16T13:09:39+00:00

How do I create two SFML windows, and then draw to both of them

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How do I create two SFML windows, and then draw to both of them using OpenGL?

If you ever wondered how to create and use two or more SFML windows with OpenGL, then here is the solution. I was not able to find the information on how to do this anywhere else on the internet, so here it is. I hope this will be useful to someone, someday.

As an aside, you might want to know why this might be a useful thing to do:

It is a very useful thing for physicists to be able to show animations of systems to other people, because we often want to program a demonstration of something to help us explain it. A trivial example would be the behaviour of gas particles in a box. In on window, particles would be drawn and move about as they do in the real world thanks to our fancy physics calculations, and in the other window, graphs might be drawn to show the total energy inside the box or average particle velocity (temperature) and other such things. Another good example would be a simulation of the solar system. Data about planets can be drawn to one window, and a view of the solar system can be drawn to another.

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1 Answer

  1. Editorial Team

    There are several steps required to make this work. The subtly with multiple windows lies with the fact that you have to resize each window before drawing to it, or at least this is the easiest way of doing things. With one window, you would only resize after the window was created, and every time it was resized or reshaped. You might argue that there are better ways of doing this by pushing and popping from the matrix stack, in which case, please comment and leave other answers.

    Firstly you need to declare two sfml windows, as you would expect: sf::Window window, window2; (Probably you should check that they are both closed at end of program execution too!)

    Secondly, implement a resize method for both. Something like this will do.

    /// Window
glViewport(0, 0, window.GetWidth(), window.GetHeight());
// Set matrix mode back again
glMatrixMode(GL_PROJECTION);
// Reset matrix stack
glLoadIdentity();
// Set drawing surface properties - either Perspective or Orthographic
///gluPerspective(45.0, (double)w / (double)h, 1.0d, 100.0d);
glOrtho(-50.0d, 50.0d, -50.0d, 50.0d, -10.0d, 10.0d);
// Put matrix mode back
glMatrixMode(GL_MODELVIEW);

    And now the other:

    /// Window2, which can be different to window!
glViewport(0, 0, window.GetWidth(), window.GetHeight());
// Set matrix mode back again
glMatrixMode(GL_PROJECTION);
// Reset matrix stack
glLoadIdentity();
// Set drawing surface properties - either Perspective or Orthographic
///gluPerspective(45.0, (double)w / (double)h, 1.0d, 100.0d);
glOrtho(-50.0d, 50.0d, -50.0d, 50.0d, -10.0d, 10.0d);
// Put matrix mode back
glMatrixMode(GL_MODELVIEW);

    You might want to put these two blocks of code in two different functions, and perhaps implement a camera class of your choice. The reason for this is that you will need to call the resize function for each window before drawing to it using the various OpenGL drawing methods.

    Now for the fun part. Before drawing call the resize method for the window you are going to draw to. Then if you need to call glMatrixMode(GL_MODELVIEW); (just in case!), glLoadIdentity();, and glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);. Obviously, if you dont want to clear the screen, don’t call glClear or glLoadIdentity, if you dont want to reset the matrix transformation stack…

    Now do your drawing: glBegin() and glEnd() and all the other things you need to do.

    Finally, call window.Display() or window2.Display(), depending on which one you were just drawing stuff to. Now go back to the fun part above, and call the resize method for the other window, and continue doing everything you need to do for this second window, exactly as for the first!

    Now enjoy OpenGL SFML programming with multiple windows. You might like to plonk a load of windows into a vector or other fancy container too.

    [EDIT] For some reason sf::Windows are non-copyable, which means you cannot push_back() them into a container like a deque or vector. This is probably due to some OpenGL specific things, which would “go wrong” if you tried to copy all the bits from one window class to another. (Perhaps?) Instead, a sf::Window* = new sf::Window[number_of_windows] and unsigned int number_of_windows = 2 will suffice, although it is not as nice…

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