XVFB on Travis, Gitlab CI: NoAvailablePixelFormat error investigation

xvfb_testing_glutin_on_ci.md

Symptom:

When using XVFB on Travis CI / Gitlab CI for UI testing, creation of a glutin window fails with NoAvailablePixelFormat:

thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: NoAvailablePixelFormat',

Explanation:

This comment is most relevant, but it assumes you know what you're calling Glutin with. If you're using a library, you may not (as was the case with me).

The Travis / Gitlab CI agents do not support multisampling — specifically the GLX_SGI_swap_control GLX extension is not loaded.

In whatever way you're invoking it, you have to turn off multisampling. In Amethyst, you have to set multisamplling: 0 in display_config.ron.

---

Investigation:

Excerpt from Gitlab CI glxinfo:

server glx vendor string: SGI
server glx version string: 1.4
server glx extensions:
    GLX_ARB_create_context, GLX_ARB_create_context_profile, 
    GLX_ARB_fbconfig_float, GLX_ARB_framebuffer_sRGB, GLX_ARB_multisample, 
    GLX_EXT_create_context_es2_profile, GLX_EXT_create_context_es_profile, 
    GLX_EXT_fbconfig_packed_float, GLX_EXT_framebuffer_sRGB, 
    GLX_EXT_import_context, GLX_EXT_libglvnd, GLX_EXT_texture_from_pixmap, 
    GLX_EXT_visual_info, GLX_EXT_visual_rating, GLX_MESA_copy_sub_buffer, 
    GLX_OML_swap_method, GLX_SGIS_multisample, GLX_SGIX_fbconfig, 
    GLX_SGIX_pbuffer, GLX_SGIX_visual_select_group, GLX_SGI_make_current_read
client glx vendor string: Mesa Project and SGI
client glx version string: 1.4
client glx extensions:
    GLX_ARB_create_context, GLX_ARB_create_context_profile, 
    GLX_ARB_create_context_robustness, GLX_ARB_fbconfig_float, 
    GLX_ARB_framebuffer_sRGB, GLX_ARB_get_proc_address, GLX_ARB_multisample, 
    GLX_EXT_buffer_age, GLX_EXT_create_context_es2_profile, 
    GLX_EXT_create_context_es_profile, GLX_EXT_fbconfig_packed_float, 
    GLX_EXT_framebuffer_sRGB, GLX_EXT_import_context, 
    GLX_EXT_texture_from_pixmap, GLX_EXT_visual_info, GLX_EXT_visual_rating, 
    GLX_INTEL_swap_event, GLX_MESA_copy_sub_buffer, 
    GLX_MESA_multithread_makecurrent, GLX_MESA_query_renderer, 
    GLX_MESA_swap_control, GLX_OML_swap_method, GLX_OML_sync_control, 
    GLX_SGIS_multisample, GLX_SGIX_fbconfig, GLX_SGIX_pbuffer, 
    GLX_SGIX_visual_select_group, GLX_SGI_make_current_read, 
    GLX_SGI_swap_control, GLX_SGI_video_sync
GLX version: 1.4
GLX extensions:
    GLX_ARB_create_context, GLX_ARB_create_context_profile, 
    GLX_ARB_fbconfig_float, GLX_ARB_framebuffer_sRGB, 
    GLX_ARB_get_proc_address, GLX_ARB_multisample, 
    GLX_EXT_create_context_es2_profile, GLX_EXT_create_context_es_profile, 
    GLX_EXT_fbconfig_packed_float, GLX_EXT_framebuffer_sRGB, 
    GLX_EXT_import_context, GLX_EXT_texture_from_pixmap, GLX_EXT_visual_info, 
    GLX_EXT_visual_rating, GLX_MESA_copy_sub_buffer, 
    GLX_MESA_multithread_makecurrent, GLX_MESA_query_renderer, 
    GLX_OML_swap_method, GLX_SGIS_multisample, GLX_SGIX_fbconfig, 
    GLX_SGIX_pbuffer, GLX_SGIX_visual_select_group, GLX_SGI_make_current_read

Excerpt from Travis CI glxinfo, using trusty:

server glx vendor string: SGI
server glx version string: 1.4
server glx extensions:
    GLX_ARB_multisample, GLX_EXT_import_context, GLX_EXT_texture_from_pixmap, 
    GLX_EXT_visual_info, GLX_EXT_visual_rating, GLX_MESA_copy_sub_buffer, 
    GLX_OML_swap_method, GLX_SGIS_multisample, GLX_SGIX_fbconfig, 
    GLX_SGIX_pbuffer, GLX_SGI_make_current_read
client glx vendor string: Mesa Project and SGI
client glx version string: 1.4
client glx extensions:
    GLX_ARB_create_context, GLX_ARB_create_context_profile, 
    GLX_ARB_create_context_robustness, GLX_ARB_fbconfig_float, 
    GLX_ARB_framebuffer_sRGB, GLX_ARB_get_proc_address, GLX_ARB_multisample, 
    GLX_EXT_create_context_es2_profile, GLX_EXT_fbconfig_packed_float, 
    GLX_EXT_framebuffer_sRGB, GLX_EXT_import_context, 
    GLX_EXT_texture_from_pixmap, GLX_EXT_visual_info, GLX_EXT_visual_rating, 
    GLX_INTEL_swap_event, GLX_MESA_copy_sub_buffer, 
    GLX_MESA_multithread_makecurrent, GLX_MESA_query_renderer, 
    GLX_MESA_swap_control, GLX_OML_swap_method, GLX_OML_sync_control, 
    GLX_SGIS_multisample, GLX_SGIX_fbconfig, GLX_SGIX_pbuffer, 
    GLX_SGIX_visual_select_group, GLX_SGI_make_current_read, 
    GLX_SGI_swap_control, GLX_SGI_video_sync
GLX version: 1.4
GLX extensions:
    GLX_ARB_get_proc_address, GLX_ARB_multisample, GLX_EXT_import_context, 
    GLX_EXT_texture_from_pixmap, GLX_EXT_visual_info, GLX_EXT_visual_rating, 
    GLX_MESA_copy_sub_buffer, GLX_MESA_multithread_makecurrent, 
    GLX_OML_swap_method, GLX_SGIS_multisample, GLX_SGIX_fbconfig, 
    GLX_SGIX_pbuffer, GLX_SGI_make_current_read

See these commit messages and the build statuses next to them to see what I tried. The bottom two green builds are failures — I just read the logs to see if certain GLX extensions were loaded but they weren't.

1. gfx_window_glutin failed to create a GlWindow, on this unwrap():

2. Tracing code path:

   • GlWindow::new
   • platform::Context::new

   Potential Err locations:

   • match events_loop.get_xlib_xconnection()

   • match gl_attr.version

     What is the gl_attr

     It's definitely GlRequest::Latest:

     $ rg -F 'GlRequest'             
     amethyst_renderer/src/renderer.rs
     278:    use glutin::{self, GlProfile, GlRequest};
     284:        .with_gl(GlRequest::Latest);
     

     • creation of GlxContext

       Looks like it's down to the choose_fbconfig function, which uses the following strings in the extensions:

       • GLX_ARB_create_context
       • GLX_ARB_create_context_robustness
       • GLX_ARB_fbconfig_float
       • GLX_ARB_multisample
       • GLX_ARB_framebuffer_sRGB
       • GLX_EXT_framebuffer_sRGB
       • GLX_ARB_context_flush_control
       • GLX_EXT_swap_control or GLX_SGI_swap_control

       My personal computer has all of them, except GLX_ARB_context_flush_control and GLX_EXT_swap_control in all 3 sections

       CI runner's differences from my computer, it only has the following in the Client section (missing from Server and GLX_Extensions sections):

       • GLX_SGI_swap_control
       • GLX_ARB_create_context_robustness

       So it's looks very likely that one or both extensions need to be in GLX_Extensions.

   • finish creating the OpenGL context — ignore, we've determined it's one of the extensions in the earlier point.

From the top answer in What is the relationship between OpenGL, GLX, DRI, and Mesa3D?:

• X provides a windowing system
• GLX is an X extension that provides OpenGL API functions to draw on the window
• There's a server side to GLX, and a client side
• The client side must only call functions that the server side supports (otherwise it doesn't work).
• Mesa is an implementation of the OpenGL standard.

XVFB is the X server. Our XVFB setup has not loaded / does not support GLX_SGI_swap_control or GLX_ARB_create_context_robustness extensions.

• From source code, it looks like the GL context creation won't fail if GLX_ARB_create_context_robustness is not available.

• Can we load the GLX_SGI_swap_control extension?

  This may be updating the Mesa library. -> No. I've updated to Debian Sid which uses Mesa 17.3, and it fails in the same way.

  Not sure how else the extensions can be loaded. Maybe it's to do with the underlying OS.

• If not, we may have to disable vsync as it needs GLX_SGI_swap_control.

  Tried setting vsync: false in display_config.ron, it still failed.

  Tried setting multisamplling: 0 in display_config.ron. This worked. orz

Okay that didn't fully solve the problem, but at least I can test my app in CI.