How to use OpenGL in a background thread?

[ArtjomP]

I tried to create window in a background thread and got exception that the Create can be called only from the MainThread. Is it possbile to use OpenGL in a background thread? Thank you in advance!

//... background thread worker
var opts = WindowOptions.Default with
        {
            Size = new Vector2D<int>(_width, _height),
            IsVisible = false,
            VSync = false,
            API = new GraphicsAPI(
                ContextAPI.OpenGL,
                ContextProfile.Core,
                ContextFlags.ForwardCompatible,
                new APIVersion(4, 1))
        };

 var win = Window.Create(opts);

[poglad-ds]

Well, there catch - you cannot run window in any different than main thread. But you can run context on different thread. In WindowOptions you need to specify flag IsContextControlDisabled as true. Then, when Load event is triggered, you create new thread in it and inside new thread create context. Then call glMakeCurrent, and do default renderloop afterwards. But do not forget to glSwapBuffers inside that custom render loop! And do anything related to OpenGL only and only inside that thread. And switch back to main, to do anything to glfw window.

So, from my perspective in kinda pointless?

[ArtjomP]

Thank you!
I'll try that and let you know.
I need to do rendering in background without window, then readpixels, process them and send via network. I don't need to bother the MainThread as far as its the only one and it has other jobs to do. Also even if the MainThread will be busy handling some big collections rendering my OpenGl should not be affect and should go on without any delays.

[ArtjomP]

Thank you!
Looks like it can help. And works on Windows but on MacOS it throws exception on MacOS:

Unable to load shared library 'libEGL.dll' or one of its dependencies. In order to help diagnose loading problems, consider setting the DYLD_PRINT_LIBRARIES environment variable: dlopen(liblibEGL.dll, 0x0001): tried: 'liblibEGL.dll' (no such file), '/System/Volumes/Preboot/Cryptexes/OSliblibEGL.dll' (no such file), '/usr/lib/liblibEGL.dll' (no such file, not in dyld cache), 'liblibEGL.dll' (no such file), '/usr/local/lib/liblibEGL.dll' (no such file), '/usr/lib/liblibEGL.dll' (no such file, not in dyld cache)

Should I use any nuget package to fix that?

[poglad-ds]

Well, MacOS support only up to OpenGL 4.1. If you try to link to any newer version, there just none of it. If you intended to use compute pipeline, yeah...

If that not and issue, then i can't help. Just don't know any more details.

[ArtjomP]

I added Silk.NET.Windowing.Glfw Nuget package & it does not throw the exception it silently swallows something and does not after the Window.Create

 private IWindow? _win;
 ///...

var opts = WindowOptions.Default with
{
            Size = new Vector2D<int>(_width, _height),
            IsVisible = false,
            IsContextControlDisabled = true,
            VSync = false,
            API = new GraphicsAPI(
                ContextAPI.OpenGL,
                ContextProfile.Core,
                ContextFlags.Debug,
                new APIVersion(4, 1))
 };


Debug.WriteLine("Creating window Silk.Net");
 _win = Window.Create(opts);
// It never gets here on MacOS
 _win.Load += OnLoad;
 _win.Render += OnRender;
 _win.Closing += OnClosing;
 _win.Initialize();
while (!ct.IsCancellationRequested)
{
      _win.DoRender();
      Thread.Sleep(AppConstraints.UpdateIntervalMillisecondsFor60Fps);
}