I don't think you mean GL_EXT_abgr, I don't see Weston using that.
Weston is using GL_BGRA_EXT format, when GL_EXT_texture_format_BGRA8888 extension is available. Weston's GL-renderer refuses to start without this extension.
I believe this is because GL_BGRA_EXT, GL_UNSIGNED_BYTE matches the WL_SHM_FORMAT_XRGB8888 and WL_SHM_FORMAT_ARGB8888 layouts, so we can avoid a conversion.
I don't think you mean GL_EXT_abgr, I don't see Weston using that.
Weston is using GL_BGRA_EXT format, when GL_EXT_ texture_ format_ BGRA8888 extension is available. Weston's GL-renderer refuses to start without this extension.
I believe this is because GL_BGRA_EXT, GL_UNSIGNED_BYTE matches the WL_SHM_ FORMAT_ XRGB8888 and WL_SHM_ FORMAT_ ARGB8888 layouts, so we can avoid a conversion.