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, 3 insertions, 1 deletions

diff --git a/src/xterm.h b/src/xterm.h
index 65349834c9b..80b57137981 100644
--- a/src/xterm.h
+++ b/src/xterm.h
@@ -1025,13 +1025,15 @@ extern void x_mark_frame_dirty (struct frame *f);
    code after any drawing command, but we can run code whenever
    someone asks for the handle necessary to draw.  */
 #define FRAME_X_DRAWABLE(f)                             \
-  (x_mark_frame_dirty((f)), FRAME_X_RAW_DRAWABLE ((f)))
+  (x_mark_frame_dirty ((f)), FRAME_X_RAW_DRAWABLE ((f)))
 
+#ifdef HAVE_XDBE
 #define FRAME_X_DOUBLE_BUFFERED_P(f)            \
   (FRAME_X_WINDOW (f) != FRAME_X_RAW_DRAWABLE (f))
 
 /* Return the need-buffer-flip flag for frame F.  */
 #define FRAME_X_NEED_BUFFER_FLIP(f) ((f)->output_data.x->need_buffer_flip)
+#endif
 
 /* Return the outermost X window associated with the frame F.  */
 #ifdef USE_X_TOOLKIT