[gtk/fix-glx-slowness] Fix glx slowness

[Matthias Clasen <matthiasc src gnome org>]

commit bc29114ce6f3b1811caee14111e121f9cc71869e
Author: Matthias Clasen <mclasen redhat com>
Date:   Thu Sep 10 17:53:24 2020 -0400

    Fix glx slowness
    
    Without this glFinish() call, I see glxMakeCurrent
    block for up to one second. No idea why.

 gdk/x11/gdkglcontext-x11.c | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/gdk/x11/gdkglcontext-x11.c b/gdk/x11/gdkglcontext-x11.c
index ec0bb2f454..ae5c7f73a7 100644
--- a/gdk/x11/gdkglcontext-x11.c
+++ b/gdk/x11/gdkglcontext-x11.c
@@ -1483,6 +1483,7 @@ gdk_x11_display_make_gl_context_current (GdkDisplay   *display,
             g_message ("Making GLX context %p current to drawable %lu",
                        context, (unsigned long) drawable));
 
+  glFinish ();
   if (!glXMakeContextCurrent (dpy, drawable, drawable,
                               context_x11->glx_context))
     {