SDL3 feature request: create OpenGL contexts detached from windows

[vittorioromeo]

Somewhat related to #12787. In order to share some OpenGL resources across multiple GL contexts, I create a hidden base shared OpenGL context like this:

// Create a hidden window for the context
m_window = SDL_CreateWindow("", 1, 1, SDL_WINDOW_OPENGL | SDL_WINDOW_HIDDEN);
if (m_window == nullptr) { /* ...error handling... */ }

// Create the OpenGL context
m_context = SDL_GL_CreateContext(m_window);
if (!m_context) { /* ...error handling... */ }

Note that, despite not needing event handling or any other window functionality, I am forced to create a hidden window just to create the the OpenGL context. This also complicates my code as I now have to manage the lifetime of the window as well as the one for the context.

It would be nice if I could pass nullptr as an argument to SDL_GL_CreateContext to create a context detached from any window, e.g.:

m_sharedContext = SDL_GL_CreateContext(nullptr); // detached context

Similarly, it would also be nice if I could pass nullptr as the first argument of SDL_GL_MakeCurrent to set a detached context as active:

SDL_GL_MakeCurrent(nullptr, m_sharedContext); // set detached context as active

How difficult would it be to implement these changes? What is the fundamental reason why OpenGL contexts are architecturally tied to windows in SDL3?

[Semphriss]

Is it possible at all to use OpenGL without a window, even outside the scope of SDL? I always thought OpenGL required a window, and that offscreen rendering was traditionally done with hidden windows...

I did a quick research, and I've found sparse references to an extension (ARB_create_context, OpenGL 3+ only) on 15+ years old forum threads, with discussions about how it was then not widely supported. Everything else seems to state that OpenGL requires a window to work at all, but I can't find any modern information on this so my sources could be outdated.

Is anything known to work with OpenGL without any (hidden) window?

---

The stuff I read, not sure what it's worth in 2025:

• Khronos source stating OpenGL requires a window: https://www.khronos.org/opengl/wiki/FAQ#What_is_an_OpenGL_context_and_why_do_you_need_a_window_to_do_GL_rendering?
• A Khronos forum thread discussing the extension: https://community.khronos.org/t/using-opengl-without-creating-window/65020/3
• A blog (?) giving instructions on how to use the extension, and hacks to do it on Windows and Linux for OpenGL < 3: https://sidvind.com/wiki/Opengl/windowless
• A StackOverflow answer discussing methods to do offscreen rendering, which partially rely on using hidden windows: https://stackoverflow.com/a/12482274

[vittorioromeo]

Is it possible at all to use OpenGL without a window, even outside the scope of SDL? I always thought OpenGL required a window, and that offscreen rendering was traditionally done with hidden windows...

I did a quick research, and I've found sparse references to an extension (ARB_create_context, OpenGL 3+ only) on 15+ years old forum threads, with discussions about how it was then not widely supported. Everything else seems to state that OpenGL requires a window to work at all, but I can't find any modern information on this so my sources could be outdated.

Is anything known to work with OpenGL without any (hidden) window?

The stuff I read, not sure what it's worth in 2025:

• Khronos source stating OpenGL requires a window: https://www.khronos.org/opengl/wiki/FAQ#What_is_an_OpenGL_context_and_why_do_you_need_a_window_to_do_GL_rendering?
• A Khronos forum thread discussing the extension: https://community.khronos.org/t/using-opengl-without-creating-window/65020/3
• A blog (?) giving instructions on how to use the extension, and hacks to do it on Windows and Linux for OpenGL < 3: https://sidvind.com/wiki/Opengl/windowless
• A StackOverflow answer discussing methods to do offscreen rendering, which partially rely on using hidden windows: https://stackoverflow.com/a/12482274

SFML is able to provide a windowless context for many platforms, e.g.:

• https://github.com/SFML/SFML/blob/master/src/SFML/Window/Win32/WglContext.cpp#L126-L139
• https://github.com/vittorioromeo/VRSFML/blob/bubble_idle/src/SFML/GLUtils/EGL/EGLContext.cpp#L248-L274
• https://github.com/vittorioromeo/VRSFML/blob/bubble_idle/src/SFML/GLUtils/EGL/EGLContext.cpp#L248-L274

There are platform-specific workarounds, but it would be nice to have a somewhat portable API to use them in SDL.

[cher-nov]

What is the fundamental reason why OpenGL contexts are architecturally tied to windows in SDL3?

They always were, both in SDL 1.x and in SDL2. I believe this is due to a popular misconception that an OpenGL context is bound to a specific window upon creation. As far as I know, this originally arose in the Windows world, where WGL requires to obtain the pixel format from an existing "window" or "bitmap" to create a context. Traces of this misconception can be found in many older codebases.