2016-10-27  Daniel Colascione  <dancol@dancol.org>

	* src/xterm.h (struct x_display_info): New member supports_xdbe.
	(struct x_output): New member draw_desc.
	(FRAME_X_DRAWABLE, FRAME_X_DOUBLE_BUFFERED_P)
	(FRAME_X_NEED_BUFFER_FLIP): New macros.
	(set_up_x_back_buffer, tear_down_x_back_buffer)
	(initial_set_up_x_back_buffer): Declare.

	* src/xterm.c: Include Xdbe.h.
	(x_begin_cr_clip, x_fill_rectangle, x_draw_rectangle)
	(x_draw_vertical_window_border, x_update_end)
	(x_setup_relief_color, x_draw_relief_rect)
	(x_draw_fringe_bitmap, x_shift_glyphs_for_insert)
	(x_scroll_run, x_draw_hollow_cursor, x_draw_bar_cursor): Use
	FRAME_X_DRAWABLE instead of FRAME_X_WINDOW; rename local
	variables appropriately; substitute calls to XClearArea with
	x_clear_area, which DTRT for double buffering.
	(x_clear_window, x_clear_area): In double-buffering mode, use
	rect-drawing X functions instead of XClearWindow and
	XClearArea, which always operate on the front buffer.
	(show_back_buffer): New function.
	(XTframe_up_to_date): Call show_back_buffer when done.
	(x_clear_frame, x_clear_frame_area): Remove obsolete calls to
	gtk_widget_queue_draw to refresh scroll bars; scroll bars are
	now independent X windows.
	(handle_one_xevent): Call font_drop_xrender_surfaces when XftDraw
	might need regenerating; perform buffer flip when responding
	to Expose events; issue front-buffer clearing commands as
	stopgap while we wait for redisplay.
	(x_make_frame_visible): Un-bitrot comment; move XSETFRAME
	earlier in function.
	(x_free_frame_resources): Call tear_down_x_back_buffer when
	destroying frame.
	(x_term_init): Attempt to initialize double buffer extension.
	(x_flip_and_flush): New function.
	(x_redisplay_interface): Point to x_flip_and_flush instead of
	x_flip directly.

	* src/xftfont.c (xftfont_drop_xrender_surfaces): Use
	FRAME_X_DRAWABLE instead of FRAME_X_WINDOW.
	(xftfont_drop_xrender_surfaces): New function.
	(syms_of_xftfont): Register it.

	* src/xfont.c (xfont_draw): Use FRAME_X_DRAWABLE instead of
	FRAME_X_WINDOW.

	* src/xfns.c: Include Xdbe.h.
	(x_set_inhibit_double_buffering, set_up_x_back_buffer)
	(Fx_double_buffered_p): New functions.
	(x_window): Call initial_set_up_x_back_buffer.
	(x_make_gc): Use FRAME_X_DRAWABLE instead of FRAME_X_WINDOW.
	(Fx_create_frame): Configure `inhibit-double-buffering'
	frame parameter.
	(x_create_tip_frame): Call initial_set_up_x_back_buffer.
	(x_frame_parm_handlers): Register
	x_set_inhibit_double_buffering.
	(syms_of_xfns): Register Sx_double_buffered_p.

	* src/xfaces.c (x_create_gc): Use FRAME_X_DRAWABLE instead of
	FRAME_X_WINDOW.

	* src/xdisp.c (remember_mouse_glyph, init_glyph_string): Use
	FRAME_X_DRAWABLE instead of FRAME_X_WINDOW.
	(redisplay_internal): Restart redisplay if a frame is garbaged
	during updating; explain why.
	(redisplay_preserve_echo_area): Call flush_frame
	conditionally, depending on `double_buffered'.
	(show_mouse_face): In the `double_buffered' case, queue frame
	for redisplay (and thus buffer flip), because immediate
	drawing will have no effect.

	* src/w32fns.c (w32_frame_parm_handlers): Add placeholder for
	x_set_inhibit_double_buffering.

	* src/termhooks.h (struct terminal): Explain why calling
	`frame_up_to_date_hook' is important.

	* src/nsfns.m (ns_frame_parm_handlers): Add placeholder for
	x_set_inhibit_double_buffering.

	* src/image.c (x_create_bitmap_from_data)
	(x_create_bitmap_from_file, x_create_x_image_and_pixmap)
	(Create_Pixmap_From_Bitmap_Data)
	(x_create_bitmap_from_xpm_data, xpm_load, gs_load): Use
	FRAME_X_DRAWABLE instead of FRAME_X_WINDOW; rename local
	variables appropriately.

	* src/gtkutil.c: Include Xdbe.h.
	(xg_get_widget_from_map): Forward declare.
	(xg_clear_under_internal_border): Remove obsolete calls to
	refresh scroll bars.
	(xg_create_frame_widgets): Call initial_set_up_x_back_buffer.
	(xg_free_frame_widgets): Call tear_down_x_back_buffer; reset
	FRAME_X_DRAWABLE as well as FRAME_X_WINDOW and for the
	same reason.
	(xg_set_background_color): Set scroll bar background colors.
	(xg_finish_scroll_bar_creation): New function with common
	logic of xg_create_scroll_bar, xg_create_horizontal_scroll_bar. Force
	scroll bars to be real X11 windows.
	(xg_create_scroll_bar, xg_create_horizontal_scroll_bar): Call
	xg_finish_scroll_bar_creation.
	(xg_update_scrollbar_pos, xg_update_horizontal_scrollbar_pos):
	Remove obsolete calls to refresh scroll bars; fix comments.

	* src/ftxfont.c (ftxfont_get_gcs, ftxfont_draw_bitmap,
	(ftxfont_draw_background): Use FRAME_X_DRAWABLE instead of
	FRAME_X_WINDOW.

	* src/frame.h (struct frame): Add double_buffered bitfield.

	* src/frame.c (frame_parms): Add table entry for new
	`inhibit-double-buffering' frame parameter
	(syms_of_frame): Register Qinhibit_double_buffering.

	* src/font.h (struct font_driver): Add new
	`flush_frame_caches' hook.
	(font_drop_xrender_surfaces): Declare.

	* src/font.c (font_drop_xrender_surfaces): New function.

	* src/dispnew.c (redraw_frame): Call font_drop_xrender_surfaces.

	* src/Makefile.in (XDBE_LIBS, XDBE_CFLAGS): Substitute.

	* etc/NEWS: Mention use of double buffering

	* doc/lispref/frames.texi (Management Parameters): Document
	`inhibit-double-buffering' frame parameters.
	(Visibility of Frames): Document `x-double-buffered-p'.

	* configure.ac: Check for the X double buffer extension