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Diffstat (limited to 'lisp/textmodes/pixel-fill.el')
| -rw-r--r-- | lisp/textmodes/pixel-fill.el | 202 |
1 files changed, 202 insertions, 0 deletions
diff --git a/lisp/textmodes/pixel-fill.el b/lisp/textmodes/pixel-fill.el new file mode 100644 index 00000000000..eff09dfca65 --- /dev/null +++ b/lisp/textmodes/pixel-fill.el @@ -0,0 +1,202 @@ +;;; pixel-fill.el --- variable pitch filling functions -*- lexical-binding: t; -*- + +;; Copyright (C) 2021 Free Software Foundation, Inc. + +;; Maintainer: emacs-devel@gnu.org +;; Keywords: filling + +;; This file is part of GNU Emacs. + +;; GNU Emacs 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. + +;; GNU Emacs 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 GNU Emacs. If not, see <https://www.gnu.org/licenses/>. + +;;; Commentary: + +;; The main entry point is `pixel-fill-region', but +;; `pixel-fill-find-fill-point' can also be useful by itself. + +;;; Code: + +(require 'kinsoku) + +(defgroup pixel-fill nil + "Filling based on pixel widths." + :group 'fill + :version "29.1") + +(defcustom pixel-fill-respect-kinsoku t + "If nil, fill even if we can't find a good kinsoku point. +Kinsoku is a Japanese word meaning a rule that should not be violated. +In Emacs, it is a term used for characters, e.g. punctuation marks, +parentheses, and so on, that should not be placed in the beginning +of a line or the end of a line." + :type 'boolean + :version "29.1") + +(defun pixel-fill-region (start end pixel-width) + "Fill the region between START and END. +This will attempt to reformat the text in the region to have no +lines that are visually wider than PIXEL-WIDTH. + +If START isn't at the start of a line, that pixel position will +be used as the indentation prefix on subsequent lines." + (save-excursion + (goto-char start) + (let ((indentation + (car (window-text-pixel-size nil (line-beginning-position) + (point))))) + (when (> indentation pixel-width) + (error "The indentation (%s) is wider than the fill width (%s)" + indentation pixel-width)) + (save-restriction + (narrow-to-region start end) + (goto-char start) + ;; First replace all whitespace with space. + (while (re-search-forward "[ \t\n]+" nil t) + (if (= (match-beginning 0) start) + (delete-region (match-beginning 0) (match-end 0)) + (replace-match " "))) + (goto-char start) + (pixel-fill--fill-line pixel-width indentation))))) + +(defun pixel-fill--goto-pixel (width) + (vertical-motion (cons (/ width (frame-char-width)) 0))) + +(defun pixel-fill--fill-line (width &optional indentation) + (let ((start (point))) + (pixel-fill--goto-pixel width) + (while (not (eolp)) + ;; We have to do some folding. First find the first previous + ;; point suitable for folding. + (if (or (not (pixel-fill-find-fill-point (line-beginning-position))) + (= (point) start)) + ;; We had unbreakable text (for this width), so just go to + ;; the first space and carry on. + (progn + (beginning-of-line) + (skip-chars-forward " ") + (search-forward " " (line-end-position) 'move))) + ;; Success; continue. + (when (= (preceding-char) ?\s) + (delete-char -1)) + (insert ?\n) + (when (> indentation 0) + (insert (propertize " " 'display + (list 'space :align-to (list indentation))))) + (setq start (point)) + (pixel-fill--goto-pixel width)))) + +(define-inline pixel-fill--char-breakable-p (char) + "Return non-nil if a line can be broken before and after CHAR." + (inline-quote (aref fill-find-break-point-function-table ,char))) + +(define-inline pixel-fill--char-nospace-p (char) + "Return non-nil if no space is required before and after CHAR." + (inline-quote (aref fill-nospace-between-words-table ,char))) + +(define-inline pixel-fill--char-kinsoku-bol-p (char) + "Return non-nil if a line ought not to begin with CHAR." + (inline-letevals (char) + (inline-quote (and (not (eq ,char ?')) + (aref (char-category-set ,char) ?>))))) + +(define-inline pixel-fill--char-kinsoku-eol-p (char) + "Return non-nil if a line ought not to end with CHAR." + (inline-quote (aref (char-category-set ,char) ?<))) + +(defun pixel-fill-find-fill-point (start) + "Find a place suitable for breaking the current line. +START should be the earliest buffer position that should be considered +(typically the start of the line), and this function will search +backward in the current buffer from the current position." + (let ((bp (point)) + (end (point)) + failed) + (while (not + (or (setq failed (<= (point) start)) + (eq (preceding-char) ?\s) + (eq (following-char) ?\s) + (pixel-fill--char-breakable-p (preceding-char)) + (pixel-fill--char-breakable-p (following-char)) + (and (pixel-fill--char-kinsoku-bol-p (preceding-char)) + (pixel-fill--char-breakable-p (following-char)) + (not (pixel-fill--char-kinsoku-bol-p (following-char)))) + (pixel-fill--char-kinsoku-eol-p (following-char)) + (bolp))) + (backward-char 1)) + (if failed + ;; There's no breakable point, so we give it up. + (let (found) + (goto-char bp) + ;; Don't overflow the window edge, even if + ;; `pixel-fill-respect-kinsoku' is t. + (when pixel-fill-respect-kinsoku + (while (setq found (re-search-forward + "\\(\\c>\\)\\| \\|\\c<\\|\\c|" + (line-end-position) 'move))) + (if (and found + (not (match-beginning 1))) + (goto-char (match-beginning 0))))) + (or + (eolp) + ;; Don't put kinsoku-bol characters at the beginning of a line, + ;; or kinsoku-eol characters at the end of a line. + (cond + ;; Don't overflow the window edge, even if `pixel-fill-respect-kinsoku' + ;; is t. + ((not pixel-fill-respect-kinsoku) + (while (and (not (eq (preceding-char) ?\s)) + (or (pixel-fill--char-kinsoku-eol-p (preceding-char)) + (pixel-fill--char-kinsoku-bol-p (following-char)))) + (backward-char 1)) + (when (setq failed (<= (point) start)) + ;; There's no breakable point that doesn't violate kinsoku, + ;; so we look for the second best position. + (while (and (progn + (forward-char 1) + (<= (point) end)) + (progn + (setq bp (point)) + (pixel-fill--char-kinsoku-eol-p (following-char))))) + (goto-char bp))) + ((pixel-fill--char-kinsoku-eol-p (preceding-char)) + ;; Find backward the point where kinsoku-eol characters begin. + (let ((count 4)) + (while + (progn + (backward-char 1) + (and (> (setq count (1- count)) 0) + (not (eq (preceding-char) ?\s)) + (or (pixel-fill--char-kinsoku-eol-p (preceding-char)) + (pixel-fill--char-kinsoku-bol-p (following-char))))))) + (when (setq failed (<= (point) start)) + ;; There's no breakable point that doesn't violate kinsoku, + ;; so we go to the second best position. + (if (looking-at "\\(\\c<+\\)\\c<") + (goto-char (match-end 1)) + (forward-char 1)))) + ((pixel-fill--char-kinsoku-bol-p (following-char)) + ;; Find forward the point where kinsoku-bol characters end. + (let ((count 4)) + (while (progn + (forward-char 1) + (and (>= (setq count (1- count)) 0) + (pixel-fill--char-kinsoku-bol-p (following-char)) + (pixel-fill--char-breakable-p (following-char)))))))) + (when (eq (following-char) ?\s) + (forward-char 1)))) + (not failed))) + +(provide 'pixel-fill) + +;;; pixel-fill.el ends here |