does not work

ui::GLArea glwidget_new(bool zbuffer)
{
    auto self = ui::GLArea::from(GTK_GL_AREA(gtk_gl_area_new()));
    gtk_gl_area_set_has_depth_buffer(self, zbuffer);
    gtk_gl_area_set_auto_render(self, true); // FIXME

    if ( g_shared )
    {
        GdkGLContext *context = gtk_gl_area_get_context(GTK_GL_AREA(self));

        GdkGLContext *shared = gtk_gl_area_get_context(GTK_GL_AREA(g_shared));
//      GdkGLContext *sharedshared = gdk_gl_context_get_shared_context(shared);

        GValue gvalue = G_VALUE_INIT;
        g_value_init(&gvalue, G_TYPE_OBJECT);
        g_value_set_object(&gvalue, G_OBJECT(shared));

        g_object_set_property(G_OBJECT(context), "shared-context", &gvalue);
//      g_object_set(G_OBJECT(context), "shared-context", G_OBJECT(shared), NULL);
    }

    self.connect("realize", G_CALLBACK(glwidget_context_created), nullptr);
}