| 1 | ;;; scroll-lock.el --- Scroll lock scrolling. |
| 2 | |
| 3 | ;; Copyright (C) 2005-2014 Free Software Foundation, Inc. |
| 4 | |
| 5 | ;; Author: Ralf Angeli <angeli@iwi.uni-sb.de> |
| 6 | ;; Maintainer: emacs-devel@gnu.org |
| 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 3 of the License, or |
| 14 | ;; (at your option) 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 GNU Emacs. If not, see <http://www.gnu.org/licenses/>. |
| 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) |
| 37 | (define-key map [remap forward-paragraph] 'scroll-lock-forward-paragraph) |
| 38 | (define-key map [remap backward-paragraph] 'scroll-lock-backward-paragraph) |
| 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 |
| 51 | "Buffer-local minor mode for pager-like scrolling. |
| 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." |
| 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)) |
| 91 | (forward-line arg) |
| 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) |
| 102 | (beginning-of-buffer (forward-line (- arg)))) |
| 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 |