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129 lines
4.7 KiB
EmacsLisp
129 lines
4.7 KiB
EmacsLisp
;;; scroll-lock.el --- Scroll lock scrolling.
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;; Copyright (C) 2005-2017 Free Software Foundation, Inc.
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;; Author: Ralf Angeli <angeli@iwi.uni-sb.de>
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;; Maintainer: emacs-devel@gnu.org
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;; Created: 2005-06-18
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;; This file is part of GNU Emacs.
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;; GNU Emacs is free software: you can redistribute it and/or modify
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;; it under the terms of the GNU General Public License as published by
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;; the Free Software Foundation, either version 3 of the License, or
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;; (at your option) any later version.
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;; GNU Emacs is distributed in the hope that it will be useful,
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;; but WITHOUT ANY WARRANTY; without even the implied warranty of
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;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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;; GNU General Public License for more details.
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;; You should have received a copy of the GNU General Public License
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;; along with GNU Emacs. If not, see <http://www.gnu.org/licenses/>.
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;;; Commentary:
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;; By activating Scroll Lock mode, keys for moving point by line or
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;; paragraph will scroll the buffer by the respective amount of lines
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;; instead. Point will be kept vertically fixed relative to window
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;; boundaries.
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;;; Code:
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(defvar scroll-lock-mode-map
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(let ((map (make-sparse-keymap)))
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(define-key map [remap next-line] 'scroll-lock-next-line)
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(define-key map [remap previous-line] 'scroll-lock-previous-line)
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(define-key map [remap forward-paragraph] 'scroll-lock-forward-paragraph)
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(define-key map [remap backward-paragraph] 'scroll-lock-backward-paragraph)
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map)
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"Keymap for Scroll Lock mode.")
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(defvar scroll-lock-preserve-screen-pos-save scroll-preserve-screen-position
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"Used for saving the state of `scroll-preserve-screen-position'.")
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(make-variable-buffer-local 'scroll-lock-preserve-screen-pos-save)
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(defvar scroll-lock-temporary-goal-column 0
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"Like `temporary-goal-column' but for scroll-lock-* commands.")
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;;;###autoload
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(define-minor-mode scroll-lock-mode
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"Buffer-local minor mode for pager-like scrolling.
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With a prefix argument ARG, enable the mode if ARG is positive,
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and disable it otherwise. If called from Lisp, enable the mode
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if ARG is omitted or nil. When enabled, keys that normally move
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point by line or paragraph will scroll the buffer by the
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respective amount of lines instead and point will be kept
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vertically fixed relative to window boundaries during scrolling."
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:lighter " ScrLck"
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:keymap scroll-lock-mode-map
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(if scroll-lock-mode
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(progn
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(setq scroll-lock-preserve-screen-pos-save
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scroll-preserve-screen-position)
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(set (make-local-variable 'scroll-preserve-screen-position) 'always))
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(setq scroll-preserve-screen-position
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scroll-lock-preserve-screen-pos-save)))
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(defun scroll-lock-update-goal-column ()
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"Update `scroll-lock-temporary-goal-column' if necessary."
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(unless (memq last-command '(scroll-lock-next-line
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scroll-lock-previous-line
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scroll-lock-forward-paragraph
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scroll-lock-backward-paragraph))
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(setq scroll-lock-temporary-goal-column (current-column))))
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(defun scroll-lock-move-to-column (column)
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"Like `move-to-column' but cater for wrapped lines."
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(if (or (bolp)
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;; Start of a screen line.
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(not (zerop (mod (- (point) (line-beginning-position))
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(window-width)))))
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(move-to-column column)
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(forward-char (min column (- (line-end-position) (point))))))
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(defun scroll-lock-next-line (&optional arg)
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"Scroll up ARG lines keeping point fixed."
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(interactive "p")
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(or arg (setq arg 1))
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(scroll-lock-update-goal-column)
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(if (pos-visible-in-window-p (point-max))
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(forward-line arg)
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(scroll-up arg))
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(scroll-lock-move-to-column scroll-lock-temporary-goal-column))
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(defun scroll-lock-previous-line (&optional arg)
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"Scroll up ARG lines keeping point fixed."
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(interactive "p")
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(or arg (setq arg 1))
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(scroll-lock-update-goal-column)
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(condition-case nil
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(scroll-down arg)
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(beginning-of-buffer (forward-line (- arg))))
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(scroll-lock-move-to-column scroll-lock-temporary-goal-column))
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(defun scroll-lock-forward-paragraph (&optional arg)
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"Scroll down ARG paragraphs keeping point fixed."
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(interactive "p")
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(or arg (setq arg 1))
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(scroll-lock-update-goal-column)
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(scroll-up (count-screen-lines (point) (save-excursion
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(forward-paragraph arg)
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(point))))
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(scroll-lock-move-to-column scroll-lock-temporary-goal-column))
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(defun scroll-lock-backward-paragraph (&optional arg)
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"Scroll up ARG paragraphs keeping point fixed."
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(interactive "p")
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(or arg (setq arg 1))
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(scroll-lock-update-goal-column)
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(let ((goal (save-excursion (backward-paragraph arg) (point))))
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(condition-case nil
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(scroll-down (count-screen-lines goal (point)))
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(beginning-of-buffer (goto-char goal))))
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(scroll-lock-move-to-column scroll-lock-temporary-goal-column))
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(provide 'scroll-lock)
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;;; scroll-lock.el ends here
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