Created attachment 294807 [details]
Patch

When you request an OpenGL 3.2 core profile context using gtk_gl_area_set_profile with GDK_GL_PROFILE_3_2_CORE, the profile you get is not core profile when using the X11 backend.

In gdk/x11/gdkglcontext-x11.c, function create_gl3_context, begins with this comment:
>  /* There are no profiles before OpenGL 3.2.
>   *
>   * The GLX_ARB_create_context_profile spec says:
>   *
>   *   If the requested OpenGL version is less than 3.2,
>   *   GLX_CONTEXT_PROFILE_MASK_ARB is ignored and the functionality
>   *   of the context is determined solely by the requested version.
>   *
>   * Which means we can ask for the CORE_PROFILE_BIT without asking for
>   * a 3.2 version.
>   */

This conclusion is incorrect. The default value for GLX_CONTEXT_MAJOR_VERSION_ARB is 1 and the default for GLX_CONTEXT_MINOR_VERSION_ARB is 0, which is less than 3.2, so the value of GLX_CONTEXT_PROFILE_MASK_ARB which the function sets to GLX_CONTEXT_CORE_PROFILE_BIT_ARB is ignored as per the quoted part of the spec. The created context therefore has to be compatible with OpenGL 1.0. A 3.2 core profile context is not compatible with GL 1.0, as some deprecated functionality is removed, so at best, when using mesa, a GL 3.0 context is created.

create_gl3_context should request the desired GL version explicitly. See the attached patch.

However, when the patch is applied, I get this error from libepoxy when using a core profile:
> No provider of glBindRenderbufferEXT found.  Requires one of:
>     GL extension "GL_EXT_framebuffer_object"
it then aborts. This is a different bug. Mesa does not provide GL_EXT_framebuffer_object in core profile contexts. It should use GL_ARB_framebuffer_object instead, which is present in OpenGL 3.0.

Gtk+ version: git cf277fabb5bb28f0a31b281f068250603c3900d6 built with jhbuild
System: Fedora 21 x86_64