Clean up X11 double buffering code

This fixes several latent bugs where code went down the path
with double buffering enabled when it wasn't, and vice versa.

* src/xfns.c (x_set_inhibit_double_buffering): Improve
commentary and only define when HAVE_XDBE.
(x_mark_frame_dirty): Only set buffer flip flag when HAVE_XDBE.
(initial_set_up_x_back_buffer): Clean up coding style and remove
unnecessary block_input pair.
(Fx_double_buffered_p): Always return nil if !HAVE_XDBE.
(x_frame_parm_handlers): Don't set double buffering handler if
!HAVE_XDBE.

* src/xftfont.c (xftfont_drop_xrender_surfaces, xftfont_driver):
Only define when XDBE is available.

* src/xterm.c (x_drop_xrender_surfaces): Likewise.
(x_clear_window): Don't test double buffering flags when
!HAVE_XDBE.
(show_back_buffer): Only define when HAVE_XDBE.
(x_flip_and_flush): Don't try to flip when !HAVE_XDBE.
(XTframe_up_to_date): Likewise.
(XTbuffer_flipping_unblocked_hook): Only define when Xdbe is
available.
(x_clear_area): Don't test double buffering flags when Xdbe is
not available.
(flush_dirty_back_buffer_on): Don't define if there's no DBE.
(handle_one_xevent, x_create_terminal): Likewise.

* src/xterm.h (FRAME_X_DRAWABLE): Fix coding style.

1 files changed, 35 insertions, 28 deletions

diff --git a/src/xftfont.c b/src/xftfont.c
index e27c6cf3146..31fb877c35b 100644
--- a/src/xftfont.c
+++ b/src/xftfont.c
@@ -643,18 +643,23 @@ xftfont_end_for_frame (struct frame *f)
   return 0;
 }
 
-/* When using X double buffering, the XftDraw structure we build
-   seems to be useless once a frame is resized, so recreate it on
+/* When using X double buffering, the XRender surfaces we create seem
+   to become useless once the window acting as the front buffer is
+   resized for an unknown reason (X server bug?), so recreate it on
    ConfigureNotify and in some other cases.  */
 
+#ifdef HAVE_XDBE
 static void
 xftfont_drop_xrender_surfaces (struct frame *f)
 {
-  block_input ();
   if (FRAME_X_DOUBLE_BUFFERED_P (f))
-    xftfont_end_for_frame (f);
-  unblock_input ();
+    {
+      block_input ();
+      xftfont_end_for_frame (f);
+      unblock_input ();
+    }
 }
+#endif
 
 static bool
 xftfont_cached_font_ok (struct frame *f, Lisp_Object font_object,
@@ -741,35 +746,37 @@ static void syms_of_xftfont_for_pdumper (void);
 struct font_driver const xftfont_driver =
   {
     /* We can't draw a text without device dependent functions.  */
-  .type = LISPSYM_INITIALLY (Qxft),
-  .get_cache = xfont_get_cache,
-  .list = xftfont_list,
-  .match = xftfont_match,
-  .list_family = ftfont_list_family,
-  .open_font = xftfont_open,
-  .close_font = xftfont_close,
-  .prepare_face = xftfont_prepare_face,
-  .done_face = xftfont_done_face,
-  .has_char = xftfont_has_char,
-  .encode_char = xftfont_encode_char,
-  .text_extents = xftfont_text_extents,
-  .draw = xftfont_draw,
-  .get_bitmap = ftfont_get_bitmap,
-  .anchor_point = ftfont_anchor_point,
+    .type = LISPSYM_INITIALLY (Qxft),
+    .get_cache = xfont_get_cache,
+    .list = xftfont_list,
+    .match = xftfont_match,
+    .list_family = ftfont_list_family,
+    .open_font = xftfont_open,
+    .close_font = xftfont_close,
+    .prepare_face = xftfont_prepare_face,
+    .done_face = xftfont_done_face,
+    .has_char = xftfont_has_char,
+    .encode_char = xftfont_encode_char,
+    .text_extents = xftfont_text_extents,
+    .draw = xftfont_draw,
+    .get_bitmap = ftfont_get_bitmap,
+    .anchor_point = ftfont_anchor_point,
 #ifdef HAVE_LIBOTF
-  .otf_capability = ftfont_otf_capability,
+    .otf_capability = ftfont_otf_capability,
 #endif
-  .end_for_frame = xftfont_end_for_frame,
+    .end_for_frame = xftfont_end_for_frame,
 #if defined HAVE_M17N_FLT && defined HAVE_LIBOTF
-  .shape = xftfont_shape,
+    .shape = xftfont_shape,
 #endif
 #if defined HAVE_OTF_GET_VARIATION_GLYPHS || defined HAVE_FT_FACE_GETCHARVARIANTINDEX
-  .get_variation_glyphs = ftfont_variation_glyphs,
+    .get_variation_glyphs = ftfont_variation_glyphs,
+#endif
+    .filter_properties = ftfont_filter_properties,
+    .cached_font_ok = xftfont_cached_font_ok,
+    .combining_capability = ftfont_combining_capability,
+#ifdef HAVE_XDBE
+    .drop_xrender_surfaces = xftfont_drop_xrender_surfaces,
 #endif
-  .filter_properties = ftfont_filter_properties,
-  .cached_font_ok = xftfont_cached_font_ok,
-  .combining_capability = ftfont_combining_capability,
-  .drop_xrender_surfaces = xftfont_drop_xrender_surfaces,
   };
 #ifdef HAVE_HARFBUZZ
 struct font_driver xfthbfont_driver;