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1 | ;;; scroll-lock.el --- Scroll lock scrolling. |
2 | ||
ba318903 | 3 | ;; Copyright (C) 2005-2014 Free Software Foundation, Inc. |
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4 | |
5 | ;; Author: Ralf Angeli <angeli@iwi.uni-sb.de> | |
34dc21db | 6 | ;; Maintainer: emacs-devel@gnu.org |
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7 | ;; Created: 2005-06-18 |
8 | ||
9 | ;; This file is part of GNU Emacs. | |
10 | ||
eb3fa2cf | 11 | ;; GNU Emacs is free software: you can redistribute it and/or modify |
94396ace | 12 | ;; it under the terms of the GNU General Public License as published by |
eb3fa2cf GM |
13 | ;; the Free Software Foundation, either version 3 of the License, or |
14 | ;; (at your option) any later version. | |
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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 | |
eb3fa2cf | 22 | ;; along with GNU Emacs. If not, see <http://www.gnu.org/licenses/>. |
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23 | |
24 | ;;; Commentary: | |
25 | ||
26 | ;; By activating Scroll Lock mode, keys for moving point by line or | |
27 | ;; paragraph will scroll the buffer by the respective amount of lines | |
28 | ;; instead. Point will be kept vertically fixed relative to window | |
29 | ;; boundaries. | |
30 | ||
31 | ;;; Code: | |
32 | ||
33 | (defvar scroll-lock-mode-map | |
34 | (let ((map (make-sparse-keymap))) | |
35 | (define-key map [remap next-line] 'scroll-lock-next-line) | |
36 | (define-key map [remap previous-line] 'scroll-lock-previous-line) | |
a0aeeaa7 KS |
37 | (define-key map [remap forward-paragraph] 'scroll-lock-forward-paragraph) |
38 | (define-key map [remap backward-paragraph] 'scroll-lock-backward-paragraph) | |
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39 | map) |
40 | "Keymap for Scroll Lock mode.") | |
41 | ||
42 | (defvar scroll-lock-preserve-screen-pos-save scroll-preserve-screen-position | |
43 | "Used for saving the state of `scroll-preserve-screen-position'.") | |
44 | (make-variable-buffer-local 'scroll-lock-preserve-screen-pos-save) | |
45 | ||
46 | (defvar scroll-lock-temporary-goal-column 0 | |
47 | "Like `temporary-goal-column' but for scroll-lock-* commands.") | |
48 | ||
49 | ;;;###autoload | |
50 | (define-minor-mode scroll-lock-mode | |
c44a951a | 51 | "Buffer-local minor mode for pager-like scrolling. |
e1ac4066 GM |
52 | With a prefix argument ARG, enable the mode if ARG is positive, |
53 | and disable it otherwise. If called from Lisp, enable the mode | |
54 | if ARG is omitted or nil. When enabled, keys that normally move | |
55 | point by line or paragraph will scroll the buffer by the | |
56 | respective amount of lines instead and point will be kept | |
57 | vertically fixed relative to window boundaries during scrolling." | |
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58 | :lighter " ScrLck" |
59 | :keymap scroll-lock-mode-map | |
60 | (if scroll-lock-mode | |
61 | (progn | |
62 | (setq scroll-lock-preserve-screen-pos-save | |
63 | scroll-preserve-screen-position) | |
64 | (set (make-local-variable 'scroll-preserve-screen-position) 'always)) | |
65 | (setq scroll-preserve-screen-position | |
66 | scroll-lock-preserve-screen-pos-save))) | |
67 | ||
68 | (defun scroll-lock-update-goal-column () | |
69 | "Update `scroll-lock-temporary-goal-column' if necessary." | |
70 | (unless (memq last-command '(scroll-lock-next-line | |
71 | scroll-lock-previous-line | |
72 | scroll-lock-forward-paragraph | |
73 | scroll-lock-backward-paragraph)) | |
74 | (setq scroll-lock-temporary-goal-column (current-column)))) | |
75 | ||
76 | (defun scroll-lock-move-to-column (column) | |
77 | "Like `move-to-column' but cater for wrapped lines." | |
78 | (if (or (bolp) | |
79 | ;; Start of a screen line. | |
80 | (not (zerop (mod (- (point) (line-beginning-position)) | |
81 | (window-width))))) | |
82 | (move-to-column column) | |
83 | (forward-char (min column (- (line-end-position) (point)))))) | |
84 | ||
85 | (defun scroll-lock-next-line (&optional arg) | |
86 | "Scroll up ARG lines keeping point fixed." | |
87 | (interactive "p") | |
88 | (or arg (setq arg 1)) | |
89 | (scroll-lock-update-goal-column) | |
90 | (if (pos-visible-in-window-p (point-max)) | |
97546017 | 91 | (forward-line arg) |
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92 | (scroll-up arg)) |
93 | (scroll-lock-move-to-column scroll-lock-temporary-goal-column)) | |
94 | ||
95 | (defun scroll-lock-previous-line (&optional arg) | |
96 | "Scroll up ARG lines keeping point fixed." | |
97 | (interactive "p") | |
98 | (or arg (setq arg 1)) | |
99 | (scroll-lock-update-goal-column) | |
100 | (condition-case nil | |
101 | (scroll-down arg) | |
97546017 | 102 | (beginning-of-buffer (forward-line (- arg)))) |
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103 | (scroll-lock-move-to-column scroll-lock-temporary-goal-column)) |
104 | ||
105 | (defun scroll-lock-forward-paragraph (&optional arg) | |
106 | "Scroll down ARG paragraphs keeping point fixed." | |
107 | (interactive "p") | |
108 | (or arg (setq arg 1)) | |
109 | (scroll-lock-update-goal-column) | |
110 | (scroll-up (count-screen-lines (point) (save-excursion | |
111 | (forward-paragraph arg) | |
112 | (point)))) | |
113 | (scroll-lock-move-to-column scroll-lock-temporary-goal-column)) | |
114 | ||
115 | (defun scroll-lock-backward-paragraph (&optional arg) | |
116 | "Scroll up ARG paragraphs keeping point fixed." | |
117 | (interactive "p") | |
118 | (or arg (setq arg 1)) | |
119 | (scroll-lock-update-goal-column) | |
120 | (let ((goal (save-excursion (backward-paragraph arg) (point)))) | |
121 | (condition-case nil | |
122 | (scroll-down (count-screen-lines goal (point))) | |
123 | (beginning-of-buffer (goto-char goal)))) | |
124 | (scroll-lock-move-to-column scroll-lock-temporary-goal-column)) | |
125 | ||
126 | (provide 'scroll-lock) | |
127 | ||
128 | ;;; scroll-lock.el ends here |