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1 | ;;; scroll-lock.el --- Scroll lock scrolling. |
2 | ||
3 | ;; Copyright (C) 2005 Free Software Foundation, Inc. | |
4 | ||
5 | ;; Author: Ralf Angeli <angeli@iwi.uni-sb.de> | |
6 | ;; Maintainer: FSF | |
7 | ;; Created: 2005-06-18 | |
8 | ||
9 | ;; This file is part of GNU Emacs. | |
10 | ||
11 | ;; GNU Emacs is free software; you can redistribute it and/or modify | |
12 | ;; it under the terms of the GNU General Public License as published by | |
13 | ;; the Free Software Foundation; either version 2, or (at your option) | |
14 | ;; any later version. | |
15 | ||
16 | ;; GNU Emacs is distributed in the hope that it will be useful, | |
17 | ;; but WITHOUT ANY WARRANTY; without even the implied warranty of | |
18 | ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
19 | ;; GNU General Public License for more details. | |
20 | ||
21 | ;; You should have received a copy of the GNU General Public License | |
22 | ;; along with this program; see the file COPYING. If not, write to | |
23 | ;; the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, | |
24 | ;; Boston, MA 02110-1301, USA. | |
25 | ||
26 | ;;; Commentary: | |
27 | ||
28 | ;; By activating Scroll Lock mode, keys for moving point by line or | |
29 | ;; paragraph will scroll the buffer by the respective amount of lines | |
30 | ;; instead. Point will be kept vertically fixed relative to window | |
31 | ;; boundaries. | |
32 | ||
33 | ;;; Code: | |
34 | ||
35 | (defvar scroll-lock-mode-map | |
36 | (let ((map (make-sparse-keymap))) | |
37 | (define-key map [remap next-line] 'scroll-lock-next-line) | |
38 | (define-key map [remap previous-line] 'scroll-lock-previous-line) | |
39 | (define-key map [remap forward-paragraph] 'scroll-lock-forward-paragrap= | |
40 | h) | |
41 | (define-key map [remap backward-paragraph] 'scroll-lock-backward-paragr= | |
42 | aph) | |
43 | map) | |
44 | "Keymap for Scroll Lock mode.") | |
45 | ||
46 | (defvar scroll-lock-preserve-screen-pos-save scroll-preserve-screen-position | |
47 | "Used for saving the state of `scroll-preserve-screen-position'.") | |
48 | (make-variable-buffer-local 'scroll-lock-preserve-screen-pos-save) | |
49 | ||
50 | (defvar scroll-lock-temporary-goal-column 0 | |
51 | "Like `temporary-goal-column' but for scroll-lock-* commands.") | |
52 | ||
53 | ;;;###autoload | |
54 | (define-minor-mode scroll-lock-mode | |
55 | "Minor mode for pager-like scrolling. | |
56 | Keys which normally move point by line or paragraph will scroll | |
57 | the buffer by the respective amount of lines instead and point | |
58 | will be kept vertically fixed relative to window boundaries | |
59 | during scrolling." | |
60 | :lighter " ScrLck" | |
61 | :keymap scroll-lock-mode-map | |
62 | (if scroll-lock-mode | |
63 | (progn | |
64 | (setq scroll-lock-preserve-screen-pos-save | |
65 | scroll-preserve-screen-position) | |
66 | (set (make-local-variable 'scroll-preserve-screen-position) 'always)) | |
67 | (setq scroll-preserve-screen-position | |
68 | scroll-lock-preserve-screen-pos-save))) | |
69 | ||
70 | (defun scroll-lock-update-goal-column () | |
71 | "Update `scroll-lock-temporary-goal-column' if necessary." | |
72 | (unless (memq last-command '(scroll-lock-next-line | |
73 | scroll-lock-previous-line | |
74 | scroll-lock-forward-paragraph | |
75 | scroll-lock-backward-paragraph)) | |
76 | (setq scroll-lock-temporary-goal-column (current-column)))) | |
77 | ||
78 | (defun scroll-lock-move-to-column (column) | |
79 | "Like `move-to-column' but cater for wrapped lines." | |
80 | (if (or (bolp) | |
81 | ;; Start of a screen line. | |
82 | (not (zerop (mod (- (point) (line-beginning-position)) | |
83 | (window-width))))) | |
84 | (move-to-column column) | |
85 | (forward-char (min column (- (line-end-position) (point)))))) | |
86 | ||
87 | (defun scroll-lock-next-line (&optional arg) | |
88 | "Scroll up ARG lines keeping point fixed." | |
89 | (interactive "p") | |
90 | (or arg (setq arg 1)) | |
91 | (scroll-lock-update-goal-column) | |
92 | (if (pos-visible-in-window-p (point-max)) | |
93 | (next-line arg) | |
94 | (scroll-up arg)) | |
95 | (scroll-lock-move-to-column scroll-lock-temporary-goal-column)) | |
96 | ||
97 | (defun scroll-lock-previous-line (&optional arg) | |
98 | "Scroll up ARG lines keeping point fixed." | |
99 | (interactive "p") | |
100 | (or arg (setq arg 1)) | |
101 | (scroll-lock-update-goal-column) | |
102 | (condition-case nil | |
103 | (scroll-down arg) | |
104 | (beginning-of-buffer (previous-line arg))) | |
105 | (scroll-lock-move-to-column scroll-lock-temporary-goal-column)) | |
106 | ||
107 | (defun scroll-lock-forward-paragraph (&optional arg) | |
108 | "Scroll down ARG paragraphs keeping point fixed." | |
109 | (interactive "p") | |
110 | (or arg (setq arg 1)) | |
111 | (scroll-lock-update-goal-column) | |
112 | (scroll-up (count-screen-lines (point) (save-excursion | |
113 | (forward-paragraph arg) | |
114 | (point)))) | |
115 | (scroll-lock-move-to-column scroll-lock-temporary-goal-column)) | |
116 | ||
117 | (defun scroll-lock-backward-paragraph (&optional arg) | |
118 | "Scroll up ARG paragraphs keeping point fixed." | |
119 | (interactive "p") | |
120 | (or arg (setq arg 1)) | |
121 | (scroll-lock-update-goal-column) | |
122 | (let ((goal (save-excursion (backward-paragraph arg) (point)))) | |
123 | (condition-case nil | |
124 | (scroll-down (count-screen-lines goal (point))) | |
125 | (beginning-of-buffer (goto-char goal)))) | |
126 | (scroll-lock-move-to-column scroll-lock-temporary-goal-column)) | |
127 | ||
128 | (provide 'scroll-lock) | |
129 | ||
130 | ;;; scroll-lock.el ends here |