Using Filament with shared context exits with BadMatch on Linux

[roxlu]

Describe the bug

I'm embedding Filament into an GLFW based application on Linux (Linux arch680 5.2.1-arch1-1-ARCH #1 SMP PREEMPT Sun Jul 14 14:52:52 UTC 2019 x86_64 GNU/Linux). When sharing the GL context that's created by GLFW the application exists with a BadMatch error, see this output.

To Reproduce

I should create a test repository... hopefully I've got time to do that, but for now:

1. Compile filament as described in the readme.
2. Create a simple GLFW app.
3. Initialize filament like in this test app.
4. Run the application.

Expected behavior

A GLFW app that renders a triangle via Filament. I'm still diving into the code / documentation on how to correctly initialize and use filament in GLFW. I based my code on this example.

Desktop (please complete the following information):

• OS: Arch Linux
• GPU: NVIDIA GTX 960
• Backend: OpenGL

Additional Info

I think the BadMatch is caused because the GL context is created with a GLXFBConfig that doesn't match with the GLXFBConfig of the shared GL context. I've updated PlatformGLX.cpp in such a way that it uses the GLXFBConfig from the shared GL context when it was given by the user.

[prideout]

Hi @roxlu, this isn't an issue specific to GLFW, it's more of a feature request for our context creation strategy on X to be more flexible. Your tentative modifications to PlatformGLX.cpp seem reasonable to me; by querying the shared context, we can create a matching one.

Curious what others on the team will think. Can you make a pull request? That way it will be easier for my colleagues to look over your changes.

[romainguy]

This is tricky because arbitrary user configs may not work. We could document what Filament expects.

[prideout]

Good point, Filament doesn't really care if they have stencil or depth but we do require an OpenGL 4.1 context.

@roxlu, with GLFW you should be able to set up context-related window creation hints to create a compatible context. Check it out:

https://www.glfw.org/docs/latest/window_guide.html#window_hints_ctx

Try setting GLFW_CONTEXT_VERSION_MAJOR to 4 and GLFW_CONTEXT_VERSION_MINOR to 1.

[prideout]

Note that GLFW_SAMPLES should be 1, (Filament does AA in an offscreen buffer.)

[roxlu]

@prideout

Thanks for your feedback. I created this pull request, please let me know if I'm doing this correctly.

Try setting GLFW_CONTEXT_VERSION_MAJOR to 4 and GLFW_CONTEXT_VERSION_MINOR to 1.
Note that GLFW_SAMPLES should be 1, (Filament does AA in an offscreen buffer.)

Yes I was using those indeed:

  glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 4);
  glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 1);
  glfwWindowHint(GLFW_SAMPLES, 1);

When I use these glfwWindowHints I'm getting the same issue.

@romainguy and @prideout thanks, I indeed think that having a list with the required context attributes would be very useful. Also having some super tiny examples would probably make it a lot easier to get a general idea how Filament works. The current documentation is amazing, but I'm talking more about guides/styles that speed up the process of learning how to use Filament.