lisp/hscroll.el

   1 ;;; hscroll.el: Minor mode to automatically scroll truncated lines horizontally
   2 ;;; Copyright (C) 1992, 1993, 1995, 1996 Free Software Foundation, Inc.
   3
   4 ;; Author: Wayne Mesard <wmesard@esd.sgi.com>
   5 ;; Keywords: display
   6
   7 ;; This file is part of GNU Emacs.
   8
   9 ;; GNU Emacs is free software; you can redistribute it and/or modify
  10 ;; it under the terms of the GNU General Public License as published by
  11 ;; the Free Software Foundation; either version 2, or (at your option)
  12 ;; any later version.
  13
  14 ;; GNU Emacs is distributed in the hope that it will be useful,
  15 ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
  16 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  17 ;; GNU General Public License for more details.
  18
  19 ;; You should have received a copy of the GNU General Public License
  20 ;; along with GNU Emacs; see the file COPYING.  If not, write to the
  21 ;; Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  22 ;; Boston, MA 02111-1307, USA.
  23
  24 ;;; Commentary:a
  25 ;;
  26 ;;    Automatically scroll horizontally when the point moves off the
  27 ;;    left or right edge of the window.
  28 ;;
  29 ;;    - Type "M-x hscroll-mode" to enable it in the current buffer.
  30 ;;    - Type "M-x hscroll-global-mode" to enable it in every buffer.
  31 ;;    - "turn-on-hscroll" is useful in mode hooks as in:
  32 ;;          (add-hook 'text-mode-hook 'turn-on-hscroll)
  33 ;;
  34 ;;    - hscroll-margin controls how close the cursor can get to the edge
  35 ;;      of the window.
  36 ;;    - hscroll-step-percent controls how far to jump once we decide to do so.
  37 ;;
  38 ;;    Most users won't want to mess with the other variables defined
  39 ;;    here.  But they're all documented, and they all start with
  40 ;;    "hscroll-" if you're curious.
  41 ;;
  42 ;;    Oh, you should also know that if you set the hscroll-margin and
  43 ;;    hscroll-step-percent large enough, you can get an interesting, but
  44 ;;    undesired ping-pong effect as the point bounces from one edge to
  45 ;;    the other.
  46 ;;
  47 ;;    wmesard@sgi.com
  48
  49 ;;; Code:
  50
  51 ;;;
  52 ;;; PUBLIC VARIABLES
  53 ;;;
  54
  55 (defvar hscroll-version "2.2")
  56
  57 (defgroup hscroll nil
  58   "Minor mode to automatically scroll truncated lines horizontally."
  59   :group 'editing)
  60
  61 (defcustom hscroll-margin 5
  62   "*How many columns away from the edge of the window point is allowed to get
  63 before HScroll will horizontally scroll the window."
  64   :group 'hscroll
  65   :type 'integer)
  66
  67 (defcustom hscroll-snap-threshold 30
  68   "*When point is this many columns (or less) from the left edge of the document,
  69 don't do any horizontal scrolling.  In other words, be biased towards the left
  70 edge of the document.
  71   Set this variable to zero to disable this bias."
  72   :group 'hscroll
  73   :type 'integer)
  74
  75 (defcustom hscroll-step-percent 25
  76   "*How far away to place the point from the window's edge when scrolling.
  77 Expressed as a percentage of the window's width."
  78   :group 'hscroll
  79   :type 'integer)
  80
  81 (defcustom hscroll-mode-name " Hscr"
  82   "*Horizontal scrolling mode line indicator.
  83 Set this to nil to conserve valuable mode line space."
  84   :group 'hscroll
  85   :type 'string)
  86
  87 (or (assq 'hscroll-mode minor-mode-alist)
  88     (setq minor-mode-alist
  89           (cons '(hscroll-mode hscroll-mode-name) minor-mode-alist)))
  90
  91
  92 ;;;
  93 ;;; PRIVATE VARIABLES
  94 ;;;
  95
  96 (defvar hscroll-mode nil
  97   "Non-nil if HScroll mode is enabled.")
  98 (make-variable-buffer-local 'hscroll-mode)
  99
 100
 101 (defvar hscroll-old-truncate-local nil)
 102 (defvar hscroll-old-truncate-was-global nil)
 103 (make-variable-buffer-local 'hscroll-old-truncate)
 104 (make-variable-buffer-local 'hscroll-old-truncate-was-global)
 105
 106 (defvar hscroll-old-truncate-default nil)
 107
 108 ;;;
 109 ;;; PUBLIC COMMANDS
 110 ;;;
 111
 112 ;;;###autoload
 113 (defun turn-on-hscroll ()
 114   "Unconditionally turn on Hscroll mode in the current buffer."
 115   (hscroll-mode 1))
 116
 117 ;;;###autoload
 118 (defun hscroll-mode (&optional arg)
 119   "Toggle HScroll mode in the current buffer.
 120 With ARG, turn HScroll mode on if ARG is positive, off otherwise.
 121 In HScroll mode, truncated lines will automatically scroll left or
 122 right when point gets near either edge of the window.
 123   See also \\[hscroll-global-mode]."
 124   (interactive "P")
 125   (make-local-hook 'post-command-hook)
 126   (let ((newmode (if (null arg)
 127                       (not hscroll-mode)
 128                     (> (prefix-numeric-value arg) 0))))
 129
 130     (if newmode
 131         ;; turn it on
 132         (if (not hscroll-mode)
 133             ;; it was off
 134             (let ((localp (local-variable-p 'truncate-lines)))
 135               (if localp
 136                   (setq hscroll-old-truncate-local truncate-lines))
 137               (setq hscroll-old-truncate-was-global (not localp))
 138               (setq truncate-lines t)
 139               (add-hook 'post-command-hook
 140                         (function hscroll-window-maybe) nil t)
 141               ))
 142       ;; turn it off
 143       (if hscroll-mode
 144           ;; it was on
 145           (progn
 146             (if hscroll-old-truncate-was-global
 147                 (kill-local-variable 'truncate-lines)
 148               (setq truncate-lines hscroll-old-truncate-local))
 149             (if (not truncate-lines)
 150                 (set-window-hscroll (selected-window) 0))
 151             (remove-hook 'post-command-hook
 152                          (function hscroll-window-maybe) t)
 153             ))
 154       )
 155
 156     (setq hscroll-mode newmode)
 157     (force-mode-line-update nil)
 158     ))
 159
 160
 161 ;;;###autoload
 162 (defun hscroll-global-mode  (&optional arg)
 163   "Toggle HScroll mode in all buffers.
 164 With ARG, turn HScroll mode on if ARG is positive, off otherwise.
 165 If a buffer ever has HScroll mode set locally (via \\[hscroll-mode]),
 166 it will forever use the local value (i.e., \\[hscroll-global-mode]
 167 will have no effect on it).
 168   See also \\[hscroll-mode]."
 169   (interactive "P")
 170   (let* ((oldmode (default-value 'hscroll-mode))
 171          (newmode (if (null arg)
 172                       (not oldmode)
 173                     (> (prefix-numeric-value arg) 0))))
 174
 175     (if newmode
 176         ;; turn it on
 177         (if (not hscroll-mode)
 178             ;; it was off
 179             (progn
 180               (setq hscroll-old-truncate-default (default-value truncate-lines))
 181               (setq hscroll-old-truncate-was-global t)
 182               (setq-default truncate-lines t)
 183               (add-hook 'post-command-hook (function hscroll-window-maybe))
 184               ))
 185       ;; turn it off
 186       (if hscroll-mode
 187           ;; it was on
 188           (progn
 189             (setq-default truncate-lines hscroll-old-truncate-default)
 190             (remove-hook 'post-command-hook (function hscroll-window-maybe))
 191             ))
 192       )
 193
 194     (setq-default hscroll-mode newmode)
 195     (force-mode-line-update t)
 196     ))
 197
 198 (defun hscroll-window-maybe ()
 199   "Scroll horizontally if point is off or nearly off the edge of the window.
 200 This is called automatically when in HScroll mode, but it can be explicitly
 201 invoked as well (i.e., it can be bound to a key)."
 202   (interactive)
 203   ;; Only consider scrolling if truncate-lines is true,
 204   ;; the window is already scrolled or partial-widths is true and this is
 205   ;; a partial width window.  See display_text_line() in xdisp.c.
 206   (if (and hscroll-mode
 207            (or truncate-lines
 208                (not (zerop (window-hscroll)))
 209                (and truncate-partial-width-windows
 210                     (< (window-width) (frame-width)))))
 211       (let ((linelen (save-excursion (end-of-line) (current-column)))
 212             (rightmost-char (+ (window-width) (window-hscroll)))
 213             )
 214         (if (< (current-column) hscroll-snap-threshold)
 215             (set-window-hscroll
 216              (selected-window)
 217              (- (window-hscroll)))
 218           (if (>= (current-column)
 219                 (- rightmost-char hscroll-margin
 220                    ;; Off-by-one if the left edge is scrolled
 221                    (if (not (zerop (window-hscroll))) 1 0)
 222                    ;; Off by one if the right edge is scrolled
 223                    (if (> linelen rightmost-char) 1 0)
 224                    ))
 225             ;; Scroll to the left a proportion of the window's width.
 226             (set-window-hscroll
 227              (selected-window)
 228              (- (+ (current-column)
 229                    (/ (* (window-width) hscroll-step-percent) 100))
 230                 (window-width)))
 231           (if (< (current-column) (+ (window-hscroll) hscroll-margin))
 232               ;; Scroll to the right a proportion of the window's width.
 233               (set-window-hscroll
 234                (selected-window)
 235                (- (current-column) (/ (* (window-width) hscroll-step-percent) 100)))
 236             )))
 237         )))
 238
 239 ;;;
 240 ;;; It's not a bug, it's a *feature*
 241 ;;;
 242
 243 (provide 'hscroll)
 244
 245 ;;; hscroll.el ends here