Complete pixelwise frame/window resizing, add horizontal scrollbar support.

* frame.el (frame-notice-user-settings): Rewrite using
frame-initial-frame-tool-bar-height.
* menu-bar.el (menu-bar-horizontal-scroll-bar)
(menu-bar-no-horizontal-scroll-bar): New functions.
(menu-bar-showhide-scroll-bar-menu): Add bindings for horizontal
scroll bars.
* scroll-bar.el (scroll-bar-lines)
(set-horizontal-scroll-bar-mode)
(get-horizontal-scroll-bar-mode, horizontal-scroll-bar-mode)
(scroll-bar-horizontal-drag-1, scroll-bar-horizontal-drag)
(scroll-bar-toolkit-horizontal-scroll): New functions.
(horizontal-scroll-bar-mode)
(previous-horizontal-scroll-bar-mode)
(horizontal-scroll-bar-mode-explicit): New variables.
(horizontal-scroll-bar-mode): New option.
(toggle-horizontal-scroll-bar): Do something.
(top-level): Bind horizontal-scroll-bar mouse-1.
* startup.el (tool-bar-originally-present): Remove variable.
(command-line): Don't set tool-bar-originally-present.
* window.el (window-min-height): Update doc-string.
(window--dump-frame): Dump horizontal scroll bar values.
(window--min-size-1): Handle minibuffer window separately.
Count in margins and horizontal scroll bar.  Return safe value
iff IGNORE equals 'safe.
(frame-windows-min-size): New function (used by frame resizing
routines).
(fit-frame-to-buffer, fit-window-to-buffer): Count in horizontal
scroll bars.
(window--sanitize-window-sizes): New function.
(window-split-min-size): Remove.
(split-window): Count divider-width.  Don't use
`window-split-min-size' any more.  Reword error messages.
Sanitize windows sizes after splitting.
* buffer.h (struct buffer): New fields scroll_bar_height and
horizontal_scroll_bar_type.
* buffer.c (bset_scroll_bar_height)
(bset_horizontal_scroll_bar_type): New functions.
(Fbuffer_swap_text): Handle old_pointm field.
(init_buffer_once): Set defaults for scroll_bar_height and
horizontal_scroll_bar_type.
(syms_of_buffer): New variables scroll_bar_height and
horizontal_scroll_bar_type.
* dispextern.h (window_part): Rename ON_SCROLL_BAR to
ON_VERTICAL_SCROLL_BAR.  Add ON_HORIZONTAL_SCROLL_BAR.
(set_vertical_scroll_bar): Remove prototype.
(x_change_tool_bar_height): Add prototype.
* dispnew.c (adjust_frame_glyphs_for_frame_redisplay)
(window_to_frame_vpos, update_frame_1, scrolling, init_display):
Use FRAME_TOTAL_COLS and FRAME_TOTAL_LINES instead of FRAME_COLS
and FRAME_LINES.
(adjust_frame_glyphs_for_window_redisplay): Rearrange lines.
(update_window): Start mode_line_row->y after horizontal scroll
bar.
(change_frame_size_1): Call adjust_frame_size.
(init_display): When changing the size of a tty frame do not
pass height of menu bar.
(Qframe_windows_min_size): New symbol.
* frame.h (struct frame): List tool bar fields after menu bar
fields.  Add official, total_lines, horizontal_scroll_bars,
config_scroll_bar_height and config_scroll_bar_lines fields.
(FRAME_HAS_HORIZONTAL_SCROLL_BARS)
(FRAME_CONFIG_SCROLL_BAR_HEIGHT, FRAME_CONFIG_SCROLL_BAR_LINES)
(FRAME_SCROLL_BAR_AREA_HEIGHT, FRAME_SCROLL_BAR_COLS)
(FRAME_SCROLL_BAR_LINES, FRAME_TOTAL_LINES, SET_FRAME_LINES)
(FRAME_WINDOWS_HEIGHT): New macros.
(SET_FRAME_HEIGHT, FRAME_TEXT_LINES_TO_PIXEL_HEIGHT)
(FRAME_PIXEL_Y_TO_LINE, FRAME_PIXEL_HEIGHT_TO_TEXT_LINES)
(FRAME_TEXT_TO_PIXEL_HEIGHT): Separately count top margin and
horizontal scroll bar.
(frame_inhibit_resize, adjust_frame_size)
(frame_windows_min_size): Add declarations.
(Qscroll_bar_height, Qhorizontal_scroll_bars)
(x_set_scroll_bar_default_height, x_set_left_fringe)
(x_set_right_fringe, x_set_vertical_scroll_bars)
(x_set_horizontal_scroll_bars, x_set_scroll_bar_width)
(x_set_scroll_bar_height): Add external declarations.
* frame.c: (frame_inhibit_resize, frame_windows_min_size)
(adjust_frame_size): New functions.
(make_frame): Initial horizontal_scroll_bars field.  Use
SET_FRAME_LINES.  Don't allow horizontal scroll bar in
minibuffer window.
(make_initial_frame, make_terminal_frame): No horizontal scroll
bar in initial and terminal frames.  Use adjust_frame_size.
(Fframe_total_cols): Fix doc-string.
(Fframe_total_lines, Fscroll_bar_height): New Lisp functions.
(Fset_frame_height, Fset_frame_width, Fset_frame_size): Rewrite
using adjust_frame_size.
(Qscroll_bar_height, Qhorizontal_scroll_bars)
(Qframe_windows_min_size): New symbols.
(x_set_frame_parameters): Remove call of check_frame_size.
(x_report_frame_params): Return scroll_bar_height value.
(x_set_left_fringe, x_set_right_fringe): New functions.
(adjust_frame_height, x_set_internal_border_width)
(x_set_fringe_width): Remove.
(x_set_internal_border_width, x_set_vertical_scroll_bars)
(x_set_scroll_bar_width, x_set_right_divider_width)
(x_set_bottom_divider_width): Rewrite using adjust_frame_size.
(x_set_horizontal_scroll_bars, x_set_scroll_bar_height): New
functions.
(x_figure_window_size): Rewrite to make frame display the
expected number of lines.
(Vdefault_frame_scroll_bars): Rewrite doc-string.
(Vdefault_frame_horizontal_scroll_bars)
(Vframe_initial_frame_tool_bar_height)
(frame_inhibit_implied_resize): New variables.
* fringe.c (compute_fringe_widths): Remove.
* gtkutil.h (YG_SB_MIN, YG_SB_MAX, YG_SB_RANGE): Define.
(xg_create_horizontal_scroll_bar)
(xg_update_horizontal_scrollbar_pos)
(xg_set_toolkit_horizontal_scroll_bar_thumb)
(xg_get_default_scrollbar_height)
(xg_clear_under_internal_border): Extern.
* gtkutil.c (xg_frame_resized): Don't call
do_pending_window_change.
(xg_frame_set_char_size): Use adjust_frame_size.
(style_changed_cb): Call update_theme_scrollbar_height and
x_set_scroll_bar_default_height.
(x_wm_set_size_hint): Don't call check_frame_size.
(update_theme_scrollbar_height)
(xg_get_default_scrollbar_height)
(xg_create_horizontal_scroll_bar)
(xg_update_horizontal_scrollbar_pos)
(xg_set_toolkit_horizontal_scroll_bar_thumb): New functions.
(xg_create_scroll_bar): Set horizontal slot of bar.
(xg_initialize): Call update_theme_scrollbar_height.
(xg_clear_under_internal_border): No more static.
* insdel.c (adjust_suspend_auto_hscroll): New function.
(adjust_markers_for_delete, adjust_markers_for_insert)
(adjust_markers_for_replace): Call adjust_suspend_auto_hscroll.
* keyboard.c (readable_events, discard_mouse_events)
(make_lispy_event): Handle horizontal scroll bar click events.
(Fsuspend_emacs): When changing the size of a tty frame do not
pass height of menu bar.
(Qbefore_handle, Qhorizontal_handle, Qafter_handle, Qleft)
(Qright, Qleftmost, Qrightmost): New symbols.
* menu.c (Fx_popup_dialog): Use FRAME_TOTAL_LINES instead of
FRAME_LINES.
* minibuf.c (read_minibuf): Initialize suspend_auto_hscroll.
* nsfns.m (x_set_internal_border_width): New function.
* nsterm.m (ns_draw_fringe_bitmap, ns_set_vertical_scroll_bar):
Remove extended fringe code.
(x_set_window_size, x_new_font): Don't call
compute_fringe_widths.
* term.c (Fresume_tty): When changing the size of a tty frame do
not pass height of menu bar.
(clear_tty_hooks, set_tty_hooks): Clear
horizontal_scroll_bar_hook.
(init_tty): Frame has no horizontal scroll bars.
* termhooks.h (enum scroll_bar_part): Add scroll_bar_move_ratio,
scroll_bar_before_handle, scroll_bar_horizontal_handle,
scroll_bar_after_handle, scroll_bar_left_arrow,
scroll_bar_right_arrow, scroll_bar_to_leftmost and
scroll_bar_to_rightmost entries.
(enum event_kind): Add HORIZONTAL_SCROLL_BAR_CLICK_EVENT
(struct terminal): Add set_horizontal_scroll_bar_hook.
* w32console.c (initialize_w32_display): Clear
horizontal_scroll_bar_hook.
* w32fns.c (x_set_mouse_color): Use FRAME_W32_DISPLAY instead of
FRAME_X_DISPLAY.
(x_clear_under_internal_border, x_set_internal_border_width):
New functions.
(x_set_menu_bar_lines): Rewrite using frame_inhibit_resize.  Set
windows_or_buffers_changed when adding the menu bar.
(x_set_tool_bar_lines): Rewrite using adjust_frame_size.
(x_change_tool_bar_height, x_set_scroll_bar_default_height)
(w32_createhscrollbar): New functions.
(w32_createscrollbar): Rename to w32_createvscrollbar.
(w32_createwindow): Init WND_HSCROLLBAR_INDEX.
(w32_name_of_message): Replace WM_EMACS_CREATESCROLLBAR by
WM_EMACS_CREATEVSCROLLBAR and WM_EMACS_CREATEHSCROLLBAR.  Add
WM_EMACS_SHOWCURSOR.
(w32_wnd_proc): Handle WM_HSCROLL case.  In WM_WINDOWPOSCHANGING
case do not artificially impose WM size hints.  Handle
WM_EMACS_SHOWCURSOR case.  Replace WM_EMACS_CREATESCROLLBAR case
by WM_EMACS_CREATEVSCROLLBAR and WM_EMACS_CREATEHSCROLLBAR
cases.
(my_create_tip_window): Replace WND_SCROLLBAR_INDEX by
WND_VSCROLLBAR_INDEX and WND_HSCROLLBAR_INDEX.
(unwind_create_frame_1): Remove.
(Fx_create_frame): Make both scrollbars the system standard
width and height.  Use official field of frame structure to
inhibit running window-configuration-change-hook.
(x_create_tip_frame): Call SET_FRAME_LINES and change_frame_size
pixelwise.  Handle frame's official field.
(w32_frame_parm_handlers): Remove x_set_fringe_width
entries. Add x_set_scroll_bar_height,
x_set_horizontal_scroll_bars, x_set_left_fringe and
x_set_right_fringe.
* w32inevt.c (resize_event, maybe_generate_resize_event): Do not
pass height of menu bar to change_frame_size.
* w32menu.c (set_frame_menubar): Rewrite using
frame_inhibit_resize.
* w32term.h (struct w32_display_info): Add
horizontal_scroll_bar_cursor and cursor_display_counter.
(struct scroll_bar): Add horizontal.
(HORIZONTAL_SCROLL_BAR_INSIDE_HEIGHT)
(HORIZONTAL_SCROLL_BAR_LEFT_RANGE)
(HORIZONTAL_SCROLL_BAR_INSIDE_WIDTH)
(HORIZONTAL_SCROLL_BAR_LEFT_BORDER)
(HORIZONTAL_SCROLL_BAR_RIGHT_BORDER)
(HORIZONTAL_SCROLL_BAR_TOP_BORDER)
(HORIZONTAL_SCROLL_BAR_BOTTOM_BORDER)
(HORIZONTAL_SCROLL_BAR_MIN_HANDLE): New macros.
(WM_EMACS_CREATEVSCROLLBAR, WM_EMACS_CREATEHSCROLLBAR): Define
instead of WM_EMACS_CREATESCROLLBAR.
(WND_VSCROLLBAR_INDEX, WND_HSCROLLBAR_INDEX): Define instead of
WND_SCROLLBAR_INDEX.
* w32term.c (horizontal_scroll_bar_min_handle)
(horizontal_scroll_bar_left_border)
(horizontal_scroll_bar_right_border): New integers.
(x_set_frame_alpha): Replace x_highlight_frame by
w32_focus_frame.
(x_window_to_scroll_bar): New argument "type".  Update callers
accordingly.
(w32_set_horizontal_scroll_bar_thumb)
(x_horizontal_scroll_bar_report_motion)
(w32_set_horizontal_scroll_bar)
(w32_horizontal_scroll_bar_handle_click)
(x_horizontal_scroll_bar_report_motion): New functions.
(w32_mouse_position): Discriminate horizontal and vertical
scrollbar cases.
(my_create_scrollbar): Replace with two new functions
my_create_vscrollbar and my_create_hscrollbar.
(x_scroll_bar_create): New argument "horizontal".  Update
callers accordingly.
(x_scroll_bar_remove, w32_condemn_scroll_bars)
(w32_redeem_scroll_bar, x_scroll_bar_clear): Handle horizontal
scroll bar case.
(w32_read_socket): Handle WM_HSCROLL cae.
(x_new_font): Don't recompute fringe widths.  Use
frame_inhibit_resize.  Calculate new menu bar height iff we
build without toolkit.  Always clear under internal border.
(x_set_window_size): Don't check frame size or recompute
fringes.  Reset fullscreen status before applying sizes.  Always
resize as requested by pixelwise argument.  Don't call
do_pending_window_change.
(x_wm_set_size_hint): Add call for FRAME_SCROLL_BAR_AREA_HEIGHT.
(w32_initialize_display_info): Initialize dpyinfo's
horizontal_scroll_bar_cursor entry.
(w32_create_terminal): Add set_horizontal_scroll_bar_hook.
(w32_initialize): Init horizontal_scroll_bar_min_handle and
horizontal_scroll_bar_left_border.
(w32fullscreen_hook): Intermittently resize window to normal
when switching from fullscreen to maximized state.
(run_window_configuration_change_hook): Don't run it if frame is
not official yet.
(unwind_change_frame): Remove.
(Fset_window_configuration): Rewrite using frame's official field.
* widget.c (set_frame_size): Don't call compute_fringe_widths.
(EmacsFrameSetCharSize): Obey frame_inhibit_resize.
* window.h (struct window): New fields old_pointm,
horizontal_scroll_bar, horizontal_scroll_bar_type, hscroll_whole,
scroll_bar_height and suspend_auto_hscroll.
(wset_horizontal_scroll_bar, wset_horizontal_scroll_bar_type):
New functions.
(sanitize_window_sizes): Extern.
(MINI_NON_ONLY_WINDOW_P, MINI_ONLY_WINDOW_P, WINDOW_PSEUDO_P)
(WINDOW_TOPMOST_P, WINDOW_HAS_HORIZONTAL_SCROLL_BAR)
(WINDOW_CONFIG_SCROLL_BAR_HEIGHT)
(WINDOW_CONFIG_SCROLL_BAR_LINES)
(WINDOW_SCROLL_BAR_LINES, WINDOW_SCROLL_BAR_AREA_HEIGHT): New
macros.
(WINDOW_LEFT_FRINGE_COLS, WINDOW_RIGHT_FRINGE_COLS)
(WINDOW_FRINGE_COLS, WINDOW_FRINGE_EXTENDED_P): Remove macros.
(WINDOW_VERTICAL_SCROLL_BAR_TYPE)
(WINDOW_HAS_VERTICAL_SCROLL_BAR_ON_LEFT)
(WINDOW_HAS_VERTICAL_SCROLL_BAR_ON_RIGHT)
(WINDOW_HAS_VERTICAL_SCROLL_BAR): Minor rewrite.
(WINDOW_BOX_HEIGHT_NO_MODE_LINE, WINDOW_BOX_TEXT_HEIGHT)
(WINDOW_SCROLL_BAR_AREA_Y): Count in scroll bar height.
* window.c (wset_old_pointm, Fwindow_scroll_bar_height)
(Fwindow_old_point, sanitize_window_sizes): New functions.
(Qwindow_sanitize_window_sizes): New symbol.
(window_body_height): Count in horizontal scroll bar.
(set_window_hscroll, Fscroll_left, Fscroll_right): Set
suspend_auto_hscroll slot.
(Fwindow_inside_edges): Count fringes pixelwise.
(coordinates_in_window, Fcoordinates_in_window_p): Consider
horizontal scroll bar.
(check_frame_size, adjust_window_margins): Remove functions and
corresponding calls.
(set_window_buffer): Initialize old_pointm and horizontal scroll
bars.
(temp_output_buffer_show): Reset hscroll related fields.
Initialize old_pointm.
(make_parent_window): Initialize old_pointm.
(make_window): Initialize old_pointm, horizontal scroll bar type,
and scroll bar height.
(resize_frame_windows): Don't count top margin in new sizes.
Don't use safe sizes when shrinking a frame; let the window
manager do the clipping.
(Fsplit_window_internal): Inherit horizontal scroll bar type and
height.
(Fdelete_window_internal): Unchain old_pointm marker.
(window_scroll_pixel_based, Fscroll_other_window): Adjust
old_pointm.
(Fwindow_text_width, Fwindow_text_height): New argument
"pixelwise".
(struct saved_window): New fields, old_pointm, hscroll_whole,
suspend_auto_hscroll, scroll_bar_height and
horizontal_scroll_bar_type.
(Fset_window_configuration, save_window_save): Set new fields of
saved_window.
(apply_window_adjustment): Don't call adjust_window_margins.
(set_window_margins): Don't change margins if new sizes don't
fit into window.
(set_window_scroll_bars): New argument "horizontal_type".
Handle horizontal scroll bars.  Don't change scroll bars if they
don't fit into window.
(Fset_window_scroll_bars): New argument "horizontal_type".
(Fwindow_scroll_bars): Return values for horizontal scroll bars.
(compare_window_configurations): Compare horizontal scroll bar
settings.
* xdisp.c (window_text_bottom_y, window_box_height): Count in
horizontal scroll bar height.
(pixel_to_glyph_coords, init_xdisp): Use FRAME_TOTAL_LINES
instead of FRAME_LINES.
(remember_mouse_glyph): Case ON_SCROLL_BAR changed to
ON_VERTICAL_SCROLL_BAR.
(with_echo_area_buffer): Initialize old_pointm.
(with_echo_area_buffer_unwind_data): Store old_pointm values in
vector.
(unwind_with_echo_area_buffer): Handle old_pointm.
(update_tool_bar): Set do_update when the tool bar window has at
least one line (since this is what the user sets).
(MAX_FRAME_TOOL_BAR_HEIGHT): Remove macro.
(redisplay_tool_bar): Return early when toolbar has zero lines.
Call x_change_tool_bar_height.  Don't use max_tool_bar_height.
(hscroll_window_tree): Handle suspension of auto_hscroll and
old_pointm.
(set_horizontal_scroll_bar): New function.
(redisplay_window): Set ignore_mouse_drag_p when tool bar has
more than one line.  Handle horizontal scroll bars.
(note_mouse_highlight): Handle horizontal scrol bars.
(expose_frame): Set dimensions of XRectangle from frame's text
sizes.
(Vvoid_text_area_pointer): Update doc-string.
* xfns.c (x_set_menu_bar_lines): Use adjust_frame_size.
(x_change_tool_bar_height, x_set_scroll_bar_default_height)
(x_set_internal_border_width): New functions.
(x_set_tool_bar_lines): Call x_change_tool_bar_height.
(unwind_create_frame_1): Remove.
(Fx_create_frame): Handle horizontal scroll bars.  Use official
field of frame structure to inhibit running
window-configuration-change-hook.
(x_create_tip_frame): Call SET_FRAME_LINES and change_frame_size
pixelwise.  Handle frame's official field.
(x_frame_parm_handlers): Add x_set_scroll_bar_height,
x_set_horizontal_scroll_bars, x_set_left_fringe,
x_set_right_fringe.
* xmenu.c (update_frame_menubar, free_frame_menubar): Use
adjust_frame_size.
* xterm.h (struct x_display_info): Add
horizontal_scroll_bar_cursor and Xatom_Horizontal_Scrollbar
slots.
(struct scroll_bar): Add horizontal slot.
(HORIZONTAL_SCROLL_BAR_INSIDE_HEIGHT)
(HORIZONTAL_SCROLL_BAR_LEFT_RANGE)
(HORIZONTAL_SCROLL_BAR_INSIDE_WIDTH): New macros.
(HORIZONTAL_SCROLL_BAR_LEFT_BORDER)
(HORIZONTAL_SCROLL_BAR_RIGHT_BORDER)
(HORIZONTAL_SCROLL_BAR_TOP_BORDER)
(HORIZONTAL_SCROLL_BAR_BOTTOM_BORDER)
(HORIZONTAL_SCROLL_BAR_MIN_HANDLE): Define.
(x_clear_under_internal_border): Remove.
* xterm.c (XTmouse_position): Handle horizontal scroll bars.
(x_window_to_scroll_bar): New argument TYPE.  Update callers.
(x_send_scroll_bar_event, x_scroll_bar_create): New arguments
HORIZONTAL.  Update callers.
(horizontal_action_hook_id): New action hook id.
(x_horizontal_scroll_bar_to_input_event)
(x_create_horizontal_toolkit_scroll_bar)
(xt_horizontal_action_hook)
(x_set_toolkit_horizontal_scroll_bar_thumb)
(XTset_horizontal_scroll_bar, x_net_wm_state)
(x_horizontal_scroll_bar_report_motion): New functions.
(xg_scroll_callback, x_scroll_bar_handle_click): Handle
horizontal scroll bars.
(SCROLL_BAR_HORIZONTAL_NAME): Define.
(XTset_vertical_scroll_bar): Attempt to clear areas not covered
by scroll bar.
(XTcondemn_scroll_bars, XTredeem_scroll_bar): Rewrite.  Handle
horizontal scroll bars.
(handle_one_xevent): Handle horizontal scroll bar events.  Call
x_net_wm_state.
(x_set_window_size_1, x_wm_set_size_hint): Don't call
check_frame_size.
(x_set_window_size): Don't call check_frame_size and
do_pending_window_change.
(x_term_init): Init horizontal_scroll_bar_cursor display info.
(x_create_terminal): Add set_horizontal_scroll_bar_hook.
(x_scroll_bar_set_handle): Add some checks when calling
x_clear_area.

1 files changed, 196 insertions, 40 deletions

diff --git a/lisp/scroll-bar.el b/lisp/scroll-bar.el
index 2990e8e5ffa..09f30d5d3f0 100644
--- a/lisp/scroll-bar.el
+++ b/lisp/scroll-bar.el
@@ -70,16 +70,36 @@ SIDE must be the symbol `left' or `right'."
                (frame-char-width)))
      (0))))
 
+(defun scroll-bar-lines ()
+  "Return the height, measured in lines, of the horizontal scrollbar."
+  (let* ((wsb   (window-scroll-bars))
+         (htype (nth 5 wsb))
+         (lines  (nth 4 wsb)))
+    (cond
+     (htype lines)
+     ((frame-parameter nil 'horizontal-scroll-bars)
+      ;; nil means it's a non-toolkit scroll bar (which is currently
+      ;; impossible), and its width in columns is 14 pixels rounded up.
+      (ceiling (or (frame-parameter nil 'scroll-bar-height) 14)
+               (frame-char-width)))
+     (0))))
+
 
 ;;;; Helpful functions for enabling and disabling scroll bars.
 
 (defvar scroll-bar-mode)
+(defvar horizontal-scroll-bar-mode)
 (defvar previous-scroll-bar-mode nil)
+(defvar previous-horizontal-scroll-bar-mode nil)
 
 (defvar scroll-bar-mode-explicit nil
   "Non-nil means `set-scroll-bar-mode' should really do something.
 This is nil while loading `scroll-bar.el', and t afterward.")
 
+(defvar horizontal-scroll-bar-mode-explicit nil
+  "Non-nil means `set-horizontal-scroll-bar-mode' should really do something.
+This is nil while loading `scroll-bar.el', and t afterward.")
+
 (defun set-scroll-bar-mode (value)
   "Set the scroll bar mode to VALUE and put the new value into effect.
 See the `scroll-bar-mode' variable for possible values to use."
@@ -92,6 +112,18 @@ See the `scroll-bar-mode' variable for possible values to use."
     (modify-all-frames-parameters (list (cons 'vertical-scroll-bars
 					      scroll-bar-mode)))))
 
+(defun set-horizontal-scroll-bar-mode (value)
+  "Set the horizontal scroll bar mode to VALUE and put the new value into effect.
+See the `horizontal-scroll-bar-mode' variable for possible values to use."
+  (if horizontal-scroll-bar-mode
+      (setq previous-horizontal-scroll-bar-mode horizontal-scroll-bar-mode))
+
+  (setq horizontal-scroll-bar-mode value)
+
+  (when horizontal-scroll-bar-mode-explicit
+    (modify-all-frames-parameters (list (cons 'horizontal-scroll-bars
+					      horizontal-scroll-bar-mode)))))
+
 (defcustom scroll-bar-mode default-frame-scroll-bars
   "Specify whether to have vertical scroll bars, and on which side.
 Possible values are nil (no scroll bars), `left' (scroll bars on left)
@@ -108,14 +140,32 @@ Setting the variable with a customization buffer also takes effect."
   :initialize 'custom-initialize-default
   :set (lambda (_sym val) (set-scroll-bar-mode val)))
 
+(defcustom horizontal-scroll-bar-mode default-frame-horizontal-scroll-bars
+  "Specify whether to have horizontal scroll bars, and on which side.
+To set this variable in a Lisp program, use `set-horizontal-scroll-bar-mode'
+to make it take real effect.
+Setting the variable with a customization buffer also takes effect."
+  :type '(choice (const :tag "none (nil)" nil)
+		 (const t))
+  :group 'frames
+  ;; The default value for :initialize would try to use :set
+  ;; when processing the file in cus-dep.el.
+  :initialize 'custom-initialize-default
+  :set (lambda (_sym val) (set-horizontal-scroll-bar-mode val)))
+
 ;; We just set scroll-bar-mode, but that was the default.
 ;; If it is set again, that is for real.
 (setq scroll-bar-mode-explicit t)
+(setq horizontal-scroll-bar-mode-explicit t)
 
 (defun get-scroll-bar-mode ()
   (declare (gv-setter set-scroll-bar-mode))
   scroll-bar-mode)
 
+(defun get-horizontal-scroll-bar-mode ()
+  (declare (gv-setter set-horizontal-scroll-bar-mode))
+  horizontal-scroll-bar-mode)
+
 (define-minor-mode scroll-bar-mode
   "Toggle vertical scroll bars on all frames (Scroll Bar mode).
 With a prefix argument ARG, enable Scroll Bar mode if ARG is
@@ -126,8 +176,21 @@ This command applies to all frames that exist and frames to be
 created in the future."
   :variable ((get-scroll-bar-mode)
              . (lambda (v) (set-scroll-bar-mode
-                       (if v (or previous-scroll-bar-mode
-                                 default-frame-scroll-bars))))))
+			    (if v (or previous-scroll-bar-mode
+				      default-frame-scroll-bars))))))
+
+(define-minor-mode horizontal-scroll-bar-mode
+  "Toggle horizontal scroll bars on all frames (Horizontal Scroll Bar mode).
+With a prefix argument ARG, enable Horizontal Scroll Bar mode if
+ARG is positive, and disable it otherwise.  If called from Lisp,
+enable the mode if ARG is omitted or nil.
+
+This command applies to all frames that exist and frames to be
+created in the future."
+  :variable ((get-horizontal-scroll-bar-mode)
+             . (lambda (v) (set-horizontal-scroll-bar-mode
+			    (if v (or previous-scroll-bar-mode
+				      default-frame-horizontal-scroll-bars))))))
 
 (defun toggle-scroll-bar (arg)
   "Toggle whether or not the selected frame has vertical scroll bars.
@@ -147,12 +210,21 @@ when they are turned on; if it is nil, they go on the left."
 	       (if (> arg 0)
 		   (or scroll-bar-mode default-frame-scroll-bars))))))
 
-(defun toggle-horizontal-scroll-bar (_arg)
+(defun toggle-horizontal-scroll-bar (arg)
   "Toggle whether or not the selected frame has horizontal scroll bars.
-With arg, turn horizontal scroll bars on if and only if arg is positive.
-Horizontal scroll bars aren't implemented yet."
+With arg, turn horizontal scroll bars on if and only if arg is positive."
   (interactive "P")
-  (error "Horizontal scroll bars aren't implemented yet"))
+  (if (null arg)
+      (setq arg
+	    (if (cdr (assq 'horizontal-scroll-bars
+			   (frame-parameters (selected-frame))))
+		-1 1))
+    (setq arg (prefix-numeric-value arg)))
+  (modify-frame-parameters
+   (selected-frame)
+   (list (cons 'horizontal-scroll-bars
+	       (if (> arg 0)
+		   (or horizontal-scroll-bar-mode default-frame-horizontal-scroll-bars))))))
 
 ;;;; Buffer navigation using the scroll bar.
 
@@ -249,6 +321,45 @@ If you click outside the slider, the window scrolls to bring the slider there."
     (with-current-buffer (window-buffer window)
       (setq point-before-scroll before-scroll))))
 
+;; Scroll the window to the proper position for EVENT.
+(defun scroll-bar-horizontal-drag-1 (event)
+  (let* ((start-position (event-start event))
+	 (window (nth 0 start-position))
+	 (portion-whole (nth 2 start-position))
+	 (unit (frame-char-width (window-frame window))))
+    (set-window-hscroll
+     window (/ (1- (+ (car portion-whole) unit)) unit))))
+
+(defun scroll-bar-horizontal-drag (event)
+  "Scroll the window horizontally by dragging the scroll bar slider.
+If you click outside the slider, the window scrolls to bring the slider there."
+  (interactive "e")
+  (let* (done
+	 (echo-keystrokes 0)
+	 (end-position (event-end event))
+	 (window (nth 0 end-position))
+	 (before-scroll))
+    (with-current-buffer (window-buffer window)
+      (setq before-scroll point-before-scroll))
+    (save-selected-window
+      (select-window window)
+      (setq before-scroll
+	    (or before-scroll (point))))
+    (scroll-bar-horizontal-drag-1 event)
+    (track-mouse
+      (while (not done)
+	(setq event (read-event))
+	(if (eq (car-safe event) 'mouse-movement)
+	    (setq event (read-event)))
+	(cond ((eq (car-safe event) 'scroll-bar-movement)
+	       (scroll-bar-horizontal-drag-1 event))
+	      (t
+	       ;; Exit when we get the drag event; ignore that event.
+	       (setq done t)))))
+    (sit-for 0)
+    (with-current-buffer (window-buffer window)
+      (setq point-before-scroll before-scroll))))
+
 (defun scroll-bar-scroll-down (event)
   "Scroll the window's top line down to the location of the scroll bar click.
 EVENT should be a scroll bar click."
@@ -300,47 +411,92 @@ EVENT should be a scroll bar click."
 	 (window (nth 0 end-position))
 	 (part (nth 4 end-position))
 	 before-scroll)
-    (cond ((eq part 'end-scroll))
-	  (t
-	   (with-current-buffer (window-buffer window)
-	     (setq before-scroll point-before-scroll))
-	   (save-selected-window
-	     (select-window window)
-	     (setq before-scroll (or before-scroll (point)))
-	     (cond ((eq part 'above-handle)
-		    (scroll-up '-))
-		   ((eq part 'below-handle)
-		    (scroll-up nil))
-		   ((eq part 'ratio)
-		    (let* ((portion-whole (nth 2 end-position))
-			   (lines (scroll-bar-scale portion-whole
-						    (1- (window-height)))))
-		      (scroll-up (cond ((not (zerop lines)) lines)
-				       ((< (car portion-whole) 0) -1)
-				       (t 1)))))
-		   ((eq part 'up)
-		    (scroll-up -1))
-		   ((eq part 'down)
-		    (scroll-up 1))
-		   ((eq part 'top)
-		    (set-window-start window (point-min)))
-		   ((eq part 'bottom)
-		    (goto-char (point-max))
-		    (recenter))
-		   ((eq part 'handle)
-		    (scroll-bar-drag-1 event))))
-	   (sit-for 0)
-	   (with-current-buffer (window-buffer window)
-	     (setq point-before-scroll before-scroll))))))
-
+    (cond
+     ((eq part 'end-scroll))
+     (t
+      (with-current-buffer (window-buffer window)
+	(setq before-scroll point-before-scroll))
+      (save-selected-window
+	(select-window window)
+	(setq before-scroll (or before-scroll (point)))
+	(cond
+	 ((eq part 'above-handle)
+	  (scroll-up '-))
+	 ((eq part 'below-handle)
+	  (scroll-up nil))
+	 ((eq part 'ratio)
+	  (let* ((portion-whole (nth 2 end-position))
+		 (lines (scroll-bar-scale portion-whole
+					  (1- (window-height)))))
+	    (scroll-up (cond ((not (zerop lines)) lines)
+			     ((< (car portion-whole) 0) -1)
+			     (t 1)))))
+	 ((eq part 'up)
+	  (scroll-up -1))
+	 ((eq part 'down)
+	  (scroll-up 1))
+	 ((eq part 'top)
+	  (set-window-start window (point-min)))
+	 ((eq part 'bottom)
+	  (goto-char (point-max))
+	  (recenter))
+	 ((eq part 'handle)
+	  (scroll-bar-drag-1 event))))
+      (sit-for 0)
+      (with-current-buffer (window-buffer window)
+	(setq point-before-scroll before-scroll))))))
 
+(defun scroll-bar-toolkit-horizontal-scroll (event)
+  (interactive "e")
+  (let* ((end-position (event-end event))
+	 (window (nth 0 end-position))
+	 (part (nth 4 end-position))
+	 before-scroll)
+    (cond
+     ((eq part 'end-scroll))
+     (t
+      (with-current-buffer (window-buffer window)
+	(setq before-scroll point-before-scroll))
+      (save-selected-window
+	(select-window window)
+	(setq before-scroll (or before-scroll (point)))
+	(cond
+	 ((eq part 'before-handle)
+	  (scroll-right 4))
+	 ((eq part 'after-handle)
+	  (scroll-left 4))
+	 ((eq part 'ratio)
+	  (let* ((portion-whole (nth 2 end-position))
+		 (columns (scroll-bar-scale portion-whole
+					    (1- (window-width)))))
+	    (scroll-right
+	     (cond
+	      ((not (zerop columns))
+	       columns)
+	      ((< (car portion-whole) 0) -1)
+	      (t 1)))))
+	 ((eq part 'left)
+	  (scroll-right 1))
+	 ((eq part 'right)
+	  (scroll-left 1))
+	 ((eq part 'leftmost)
+	  (goto-char (line-beginning-position)))
+	 ((eq part 'rightmost)
+	  (goto-char (line-end-position)))
+	 ((eq part 'horizontal-handle)
+	  (scroll-bar-horizontal-drag-1 event))))
+      (sit-for 0)
+      (with-current-buffer (window-buffer window)
+	(setq point-before-scroll before-scroll))))))
 
 ;;;; Bindings.
 
 ;; For now, we'll set things up to work like xterm.
 (cond ((and (boundp 'x-toolkit-scroll-bars) x-toolkit-scroll-bars)
        (global-set-key [vertical-scroll-bar mouse-1]
-		       'scroll-bar-toolkit-scroll))
+		       'scroll-bar-toolkit-scroll)
+       (global-set-key [horizontal-scroll-bar mouse-1]
+		       'scroll-bar-toolkit-horizontal-scroll))
       (t
        (global-set-key [vertical-scroll-bar mouse-1]
 		       'scroll-bar-scroll-up)