emacs/lisp/image-file.el

;;; image-file.el --- support for visiting image files
;;
;; Copyright (C) 2000-2019 Free Software Foundation, Inc.
;;
;; Author: Miles Bader <miles@gnu.org>
;; Keywords: multimedia

;; 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:

;; Defines a file-name-handler hook that transforms visited (or
;; inserted) image files so that they are displayed by Emacs as
;; images.  This is done by putting a `display' text-property on the
;; image data, with the image-data still present underneath; if the
;; resulting buffer file is saved to another name it will correctly save
;; the image data to the new file.

;;; Code:

(require 'image)


;;;###autoload
(defcustom image-file-name-extensions
  (purecopy '("png" "jpeg" "jpg" "gif" "tiff" "tif" "xbm" "xpm" "pbm" "pgm" "ppm" "pnm" "svg"))
  "A list of image-file filename extensions.
Filenames having one of these extensions are considered image files,
in addition to those matching `image-file-name-regexps'.

See `auto-image-file-mode'; if `auto-image-file-mode' is enabled,
setting this variable directly does not take effect unless
`auto-image-file-mode' is re-enabled; this happens automatically when
the variable is set using \\[customize]."
  :type '(repeat string)
  :set (lambda (sym val)
	 (set-default sym val)
	 (when auto-image-file-mode
	   ;; Re-initialize the image-file handler
	   (auto-image-file-mode t)))
  :initialize 'custom-initialize-default
  :group 'image)

;;;###autoload
(defcustom image-file-name-regexps nil
  "List of regexps matching image-file filenames.
Filenames matching one of these regexps are considered image files,
in addition to those with an extension in `image-file-name-extensions'.

See function `auto-image-file-mode'; if `auto-image-file-mode' is
enabled, setting this variable directly does not take effect unless
`auto-image-file-mode' is re-enabled; this happens automatically when
the variable is set using \\[customize]."
  :type '(repeat regexp)
  :set (lambda (sym val)
	 (set-default sym val)
	 (when auto-image-file-mode
	   ;; Re-initialize the image-file handler
	   (auto-image-file-mode t)))
  :initialize 'custom-initialize-default
  :group 'image)


;;;###autoload
(defun image-file-name-regexp ()
  "Return a regular expression matching image-file filenames."
  (let ((exts-regexp
	 (and image-file-name-extensions
	      (concat "\\."
		      (regexp-opt (nconc (mapcar #'upcase
						 image-file-name-extensions)
					 image-file-name-extensions)
				  t)
		      "\\'"))))
    (mapconcat
     'identity
     (delq nil (list exts-regexp
		     image-file-name-regexps
		     (car (rassq 'imagemagick image-type-file-name-regexps))))
     "\\|")))


;;;###autoload
(defun insert-image-file (file &optional visit beg end replace)
  "Insert the image file FILE into the current buffer.
Optional arguments VISIT, BEG, END, and REPLACE are interpreted
as for the command `insert-file-contents'.  Return list of
absolute file name and number of characters inserted."
  (let ((rval
	 (image-file-call-underlying #'insert-file-contents-literally
				     'insert-file-contents
				     file visit beg end replace)))
    ;; Turn the image data into a real image, but only if the whole file
    ;; was inserted
    (when (and (or (null beg) (zerop beg)) (null end))
      (let* ((ibeg (point))
	     (iend (+ (point) (cadr rval)))
	     (visitingp (and visit (= ibeg (point-min)) (= iend (point-max))))
             (image (create-image (encode-coding-region ibeg iend 'binary t)
                                  nil t))
	     (props
	      `(display ,image
			yank-handler
			(image-file-yank-handler nil t)
			intangible ,image
			rear-nonsticky (display intangible)
			;; This a cheap attempt to make the whole buffer
			;; read-only when we're visiting the file (as
			;; opposed to just inserting it).
			,@(and visitingp
			       '(read-only t front-sticky (read-only))))))
	(add-text-properties ibeg iend props)
	(when visitingp
	  ;; Inhibit the cursor when the buffer contains only an image,
	  ;; because cursors look very strange on top of images.
	  (setq cursor-type nil)
	  ;; This just makes the arrow displayed in the right fringe
	  ;; area look correct when the image is wider than the window.
	  (setq truncate-lines t))))
    rval))

;; We use a yank-handler to make yanked images unique, so that
;; yanking two copies of the same image next to each other are
;; recognized as two different images.
(defun image-file-yank-handler (string)
  "Yank handler for inserting an image into a buffer."
  (let ((len (length string))
	(image (get-text-property 0 'display string)))
    (if (eq yank-excluded-properties t)
        (set-text-properties 0 len () string)
      (remove-list-of-text-properties 0 len yank-excluded-properties string))
    (if (consp image)
	(add-text-properties 0
			     (or (next-single-property-change 0 'image-counter string)
				 (length string))
			     `(display
			       ,(cons (car image) (cdr image))
			       yank-handler
			       ,(cons 'image-file-yank-handler '(nil t)))
			     string))
    (insert string)))

(put 'image-file-handler 'safe-magic t)
(defun image-file-handler (operation &rest args)
  "Filename handler for inserting image files.
OPERATION is the operation to perform, on ARGS.
See `file-name-handler-alist' for details."
  (if (and (eq operation 'insert-file-contents)
	   auto-image-file-mode)
      (apply #'insert-image-file args)
    ;; We don't handle OPERATION, use another handler or the default
    (apply #'image-file-call-underlying operation operation args)))

(defun image-file-call-underlying (function operation &rest args)
  "Call FUNCTION with `image-file-handler' and OPERATION inhibited.
Optional argument ARGS are the arguments to call FUNCTION with."
  (let ((inhibit-file-name-handlers
	 (cons 'image-file-handler
	       (and (eq inhibit-file-name-operation operation)
		    inhibit-file-name-handlers)))
	(inhibit-file-name-operation operation))
    (apply function args)))


;;;###autoload
(define-minor-mode auto-image-file-mode
  "Toggle visiting of image files as images (Auto Image File mode).

An image file is one whose name has an extension in
`image-file-name-extensions', or matches a regexp in
`image-file-name-regexps'."
  :global t
  :group 'image
  ;; Remove existing handler
  (let ((existing-entry
	 (rassq 'image-file-handler file-name-handler-alist)))
    (when existing-entry
      (setq file-name-handler-alist
	    (delq existing-entry file-name-handler-alist))))
  ;; Add new handler, if enabled
  (when auto-image-file-mode
    (push (cons (image-file-name-regexp) 'image-file-handler)
	  file-name-handler-alist)))


(provide 'image-file)

;;; image-file.el ends here