emacs/lisp/fringe.el

;;; fringe.el --- fringe setup and control  -*- coding: utf-8 -*-

;; Copyright (C) 2002-2012 Free Software Foundation, Inc.

;; Author: Simon Josefsson <simon@josefsson.org>
;; Maintainer: FSF
;; Keywords: frames
;; Package: emacs

;; 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 <http://www.gnu.org/licenses/>.

;;; Commentary:

;; This file contains code to initialize the built-in fringe bitmaps
;; as well as helpful functions for customizing the appearance of the
;; fringe.

;; The code is influenced by scroll-bar.el and avoid.el.  The author
;; gratefully acknowledge comments and suggestions made by Miles
;; Bader, Eli Zaretskii, Richard Stallman, Pavel Janík and others which
;; improved this package.

;;; Code:

(defgroup fringe nil
  "Window fringes."
  :version "22.1"
  :group 'frames)

;; Define the built-in fringe bitmaps and setup default mappings

(when (boundp 'fringe-bitmaps)
  (let ((bitmaps '(question-mark
		   left-arrow right-arrow up-arrow down-arrow
		   left-curly-arrow right-curly-arrow
		   left-triangle right-triangle
		   top-left-angle top-right-angle
		   bottom-left-angle bottom-right-angle
		   left-bracket right-bracket
		   filled-rectangle hollow-rectangle
		   filled-square hollow-square
		   vertical-bar horizontal-bar
		   empty-line))
	(bn 1))
    (while bitmaps
      (push (car bitmaps) fringe-bitmaps)
      (put (car bitmaps) 'fringe bn)
      (setq bitmaps (cdr bitmaps)
	    bn (1+ bn))))

  (setq-default fringe-indicator-alist
		'((truncation . (left-arrow right-arrow))
		  (continuation . (left-curly-arrow right-curly-arrow))
		  (overlay-arrow . right-triangle)
		  (up . up-arrow)
		  (down . down-arrow)
		  (top . (top-left-angle top-right-angle))
		  (bottom . (bottom-left-angle bottom-right-angle
			     top-right-angle top-left-angle))
		  (top-bottom . (left-bracket right-bracket
				 top-right-angle top-left-angle))
		  (empty-line . empty-line)
		  (unknown . question-mark)))

  (setq-default fringe-cursor-alist
		'((box . filled-rectangle)
		  (hollow . hollow-rectangle)
		  (bar . vertical-bar)
		  (hbar . horizontal-bar)
		  (hollow-small . hollow-square))))


(defmacro fringe-bitmap-p (symbol)
  "Return non-nil if SYMBOL is a fringe bitmap."
  `(get ,symbol 'fringe))


;; Control presence of fringes

(defvar fringe-mode)

(defvar fringe-mode-explicit nil
  "Non-nil means `set-fringe-mode' should really do something.
This is nil while loading `fringe.el', and t afterward.")

(defun set-fringe-mode-1 (_ignore value)
  "Call `set-fringe-mode' with VALUE.
See `fringe-mode' for valid values and their effect.
This is usually invoked when setting `fringe-mode' via customize."
  (set-fringe-mode value))

(defun set-fringe-mode (value)
  "Set `fringe-mode' to VALUE and put the new value into effect.
See `fringe-mode' for possible values and their effect."
  (setq fringe-mode value)

  (when fringe-mode-explicit
    (modify-all-frames-parameters
     (list (cons 'left-fringe (if (consp fringe-mode)
				  (car fringe-mode)
				fringe-mode))
	   (cons 'right-fringe (if (consp fringe-mode)
				   (cdr fringe-mode)
				 fringe-mode))))))

;; For initialization of fringe-mode, take account of changes
;; made explicitly to default-frame-alist.
(defun fringe-mode-initialize (symbol value)
  (let* ((left-pair (assq 'left-fringe default-frame-alist))
	 (right-pair (assq 'right-fringe default-frame-alist))
	 (left (cdr left-pair))
	 (right (cdr right-pair)))
    (if (or left-pair right-pair)
	;; If there's something in default-frame-alist for fringes,
	;; don't change it, but reflect that into the value of fringe-mode.
	(progn
	  (setq fringe-mode (cons left right))
	  (if (equal fringe-mode '(nil . nil))
	      (setq fringe-mode nil))
	  (if (equal fringe-mode '(0 . 0))
	      (setq fringe-mode 0)))
      ;; Otherwise impose the user-specified value of fringe-mode.
      (custom-initialize-reset symbol value))))

(defconst fringe-styles
  '(("default" . nil)
    ("no-fringes" . 0)
    ("right-only" . (0 . nil))
    ("left-only" . (nil . 0))
    ("half-width" . (4 . 4))
    ("minimal" . (1 . 1))))

(defcustom fringe-mode nil
  "Specify appearance of fringes on all frames.
This variable can be nil (the default) meaning the fringes should have
the default width (8 pixels), it can be an integer value specifying
the width of both left and right fringe (where 0 means no fringe), or
a cons cell where car indicates width of left fringe and cdr indicates
width of right fringe (where again 0 can be used to indicate no
fringe).
Note that the actual width may be rounded up to ensure that the sum of
the width of the left and right fringes is a multiple of the frame's
character width.  However, a fringe width of 0 is never rounded.
To set this variable in a Lisp program, use `set-fringe-mode' to make
it take real effect.
Setting the variable with a customization buffer also takes effect.
If you only want to modify the appearance of the fringe in one frame,
you can use the interactive function `set-fringe-style'."
  :type `(choice
          ,@ (mapcar (lambda (style)
                      (let ((name
                             (replace-regexp-in-string "-" " " (car style))))
                        `(const :tag
                                ,(concat (capitalize (substring name 0 1))
                                         (substring name 1))
                                ,(cdr style))))
                    fringe-styles)
          (integer :tag "Specific width")
          (cons :tag "Different left/right sizes"
                (integer :tag "Left width")
                (integer :tag "Right width")))
  :group 'fringe
  :require 'fringe
  :initialize 'fringe-mode-initialize
  :set 'set-fringe-mode-1)

;; We just set fringe-mode, but that was the default.
;; If it is set again, that is for real.
(setq fringe-mode-explicit t)

(defun fringe-query-style (&optional all-frames)
  "Query user for fringe style.
Returns values suitable for left-fringe and right-fringe frame parameters.
If ALL-FRAMES, the negation of the fringe values in
`default-frame-alist' is used when user enters the empty string.
Otherwise the negation of the fringe value in the currently selected
frame parameter is used."
  (let* ((mode (completing-read
                (concat
                 "Select fringe mode for "
                 (if all-frames "all frames" "selected frame")
                 ": ")
                fringe-styles nil t))
         (style (assoc (downcase mode) fringe-styles)))
    (if style (cdr style)
      (if (eq 0 (cdr (assq 'left-fringe
                           (if all-frames
                               default-frame-alist
                             (frame-parameters (selected-frame))))))
          nil
        0))))

(defun fringe-mode (&optional mode)
  "Set the default appearance of fringes on all frames.

When called interactively, query the user for MODE.  Valid values
for MODE include `none', `default', `left-only', `right-only',
`minimal' and `half'.

When used in a Lisp program, MODE can be a cons cell where the
integer in car specifies the left fringe width and the integer in
cdr specifies the right fringe width.  MODE can also be a single
integer that specifies both the left and the right fringe width.
If a fringe width specification is nil, that means to use the
default width (8 pixels).  This command may round up the left and
right width specifications to ensure that their sum is a multiple
of the character width of a frame.  It never rounds up a fringe
width of 0.

Fringe widths set by `set-window-fringes' override the default
fringe widths set by this command.  This command applies to all
frames that exist and frames to be created in the future.  If you
want to set the default appearance of fringes on the selected
frame only, see the command `set-fringe-style'."
  (interactive (list (fringe-query-style 'all-frames)))
  (set-fringe-mode mode))

(defun set-fringe-style (&optional mode)
  "Set the default appearance of fringes on the selected frame.

When called interactively, query the user for MODE.  Valid values
for MODE include `none', `default', `left-only', `right-only',
`minimal' and `half'.

When used in a Lisp program, MODE can be a cons cell where the
integer in car specifies the left fringe width and the integer in
cdr specifies the right fringe width.  MODE can also be a single
integer that specifies both the left and the right fringe width.
If a fringe width specification is nil, that means to use the
default width (8 pixels).  This command may round up the left and
right width specifications to ensure that their sum is a multiple
of the character width of a frame.  It never rounds up a fringe
width of 0.

Fringe widths set by `set-window-fringes' override the default
fringe widths set by this command.  If you want to set the
default appearance of fringes on all frames, see the command
`fringe-mode'."
  (interactive (list (fringe-query-style)))
  (modify-frame-parameters
   (selected-frame)
   (list (cons 'left-fringe (if (consp mode) (car mode) mode))
	 (cons 'right-fringe (if (consp mode) (cdr mode) mode)))))

(defsubst fringe-columns (side &optional real)
  "Return the width, measured in columns, of the fringe area on SIDE.
If optional argument REAL is non-nil, return a real floating point
number instead of a rounded integer value.
SIDE must be the symbol `left' or `right'."
  (funcall (if real '/ 'ceiling)
	   (or (funcall (if (eq side 'left) 'car 'cadr)
			(window-fringes))
	       0)
           (float (frame-char-width))))

(provide 'fringe)

;;; fringe.el ends here