My Emacs configuration.
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;;; page-break-lines.el --- Display ^L page breaks as tidy horizontal lines -*- lexical-binding: t -*-
;; Copyright (C) 2012-2015 Steve Purcell
;; Author: Steve Purcell <steve@sanityinc.com>
;; URL: https://github.com/purcell/page-break-lines
;; Package-Commit: 69caea070379f3324c530e96e06625c3cd097cb9
;; Package-Version: 0.14
;; Package-X-Original-Version: 0
;; Package-Requires: ((emacs "24.4"))
;; Keywords: convenience, faces
;; This program is free software; you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation, either version 3 of the License, or
;; (at your option) any later version.
;; This program is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
;; GNU General Public License for more details.
;; You should have received a copy of the GNU General Public License
;; along with this program. If not, see <http://www.gnu.org/licenses/>.
;;; Commentary:
;; This library provides a global mode which displays form feed
;; characters as horizontal rules.
;; Install from Melpa or Marmalade, or add to `load-path' and use
;; (require 'page-break-lines).
;; Use `page-break-lines-mode' to enable the mode in specific buffers,
;; or customize `page-break-lines-modes' and enable the mode globally with
;; `global-page-break-lines-mode'.
;; Issues and limitations:
;; If `page-break-lines-char' is displayed at a different width to
;; regular characters, the rule may be either too short or too long:
;; rules may then wrap if `truncate-lines' is nil. On some systems,
;; Emacs may erroneously choose a different font for the page break
;; symbol, which choice can be overridden using code such as:
;; (set-fontset-font "fontset-default"
;; (cons page-break-lines-char page-break-lines-char)
;; (face-attribute 'default :family))
;; Use `describe-char' on a page break char to determine whether this
;; is the case.
;; Additionally, the use of `text-scale-increase' or
;; `text-scale-decrease' will cause the rule width to be incorrect,
;; because the reported window width (in characters) will continue to
;; be the width in the frame's default font, not the scaled font used to
;; display the rule.
;; Adapted from code http://www.emacswiki.org/emacs/PageBreaks
;;; Code:
(defgroup page-break-lines nil
"Display ugly ^L page breaks as tidy horizontal lines."
:prefix "page-break-lines-"
:group 'faces)
(defcustom page-break-lines-char ?─
"Character used to render page break lines."
:type 'character
:group 'page-break-lines)
(defcustom page-break-lines-lighter " PgLn"
"Mode-line indicator for `page-break-lines-mode'."
:type '(choice (const :tag "No lighter" "") string)
:group 'page-break-lines)
(defcustom page-break-lines-max-width nil
"If non-nil, maximum width (in characters) of page break indicator.
If nil, indicator will span the width of the frame."
:type '(choice integer (const :tag "Full width" nil))
:group 'page-break-lines)
(defcustom page-break-lines-modes
'(emacs-lisp-mode lisp-mode scheme-mode compilation-mode outline-mode help-mode)
"Modes in which to enable `page-break-lines-mode'."
:type '(repeat symbol)
:group 'page-break-lines)
(defface page-break-lines
'((t :inherit font-lock-comment-face :bold nil :italic nil))
"Face used to colorize page break lines.
If using :bold or :italic, please ensure `page-break-lines-char'
is available in that variant of your font, otherwise it may be
displayed as a junk character."
:group 'page-break-lines)
;;;###autoload
(define-minor-mode page-break-lines-mode
"Toggle Page Break Lines mode.
In Page Break mode, page breaks (^L characters) are displayed as a
horizontal line of `page-break-lines-char' characters."
:lighter page-break-lines-lighter
:group 'page-break-lines
(page-break-lines--update-display-tables))
(dolist (hook '(window-configuration-change-hook
window-size-change-functions
after-setting-font-hook
display-line-numbers-mode-hook))
(add-hook hook 'page-break-lines--update-display-tables))
(defun page-break-lines--update-display-table (window)
"Modify a display-table that displays page-breaks prettily.
If the buffer inside WINDOW has `page-break-lines-mode' enabled,
its display table will be modified as necessary."
(with-current-buffer (window-buffer window)
(with-selected-window window
(if page-break-lines-mode
(progn
(unless buffer-display-table
(setq buffer-display-table (make-display-table)))
(let ((default-height (face-attribute 'default :height nil 'default)))
(set-face-attribute 'page-break-lines nil :height default-height)
(let* ((cwidth (char-width page-break-lines-char))
(wwidth-pix (- (window-width nil t)
(if (and (bound-and-true-p display-line-numbers)
(fboundp 'line-number-display-width))
(line-number-display-width t)
0)))
(width (- (/ wwidth-pix (frame-char-width) cwidth)
(if (display-graphic-p) 0 1)))
(width (if page-break-lines-max-width
(min width page-break-lines-max-width)
width))
(glyph (make-glyph-code page-break-lines-char 'page-break-lines))
(new-display-entry (vconcat (make-list width glyph))))
(unless (equal new-display-entry (elt buffer-display-table ?\^L))
(aset buffer-display-table ?\^L new-display-entry)))))
(when (and (apply 'derived-mode-p page-break-lines-modes)
buffer-display-table)
(aset buffer-display-table ?\^L nil))))))
(defun page-break-lines--update-display-tables (&optional frame)
"Function called for updating display table in windows of FRAME."
(unless (minibufferp)
(mapc 'page-break-lines--update-display-table (window-list frame 'no-minibuffer))))
;;;###autoload
(defun page-break-lines-mode-maybe ()
"Enable `page-break-lines-mode' in the current buffer if desired.
When `major-mode' is listed in `page-break-lines-modes', then
`page-break-lines-mode' will be enabled."
(if (and (not (minibufferp))
(apply 'derived-mode-p page-break-lines-modes))
(page-break-lines-mode 1)))
;;;###autoload
(define-global-minor-mode global-page-break-lines-mode
page-break-lines-mode page-break-lines-mode-maybe
:require 'page-break-lines
:group 'page-break-lines)
(provide 'page-break-lines)
;; Local Variables:
;; coding: utf-8
;; checkdoc-minor-mode: t
;; End:
;;; page-break-lines.el ends here