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+;;; image-file.el --- Support for visiting image files
+;;
+;; Copyright (C) 2000 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 2, 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; see the file COPYING.  If not, write to the
+;; Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+;; Boston, MA 02111-1307, USA.
+
+;;; Commentary:
+
+;; Defines a file-name-handler hook that transforms visited (or
+;; inserted) image files so that they are by displayed as 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-handler-enabled nil
+  "True if visiting an image file will actually display the image.
+A file is considered an image file if its filename matches one of the
+regexps in `image-file-regexps'.
+
+Setting this variable directly does not take effect;
+use either \\[customize] or the function `set-image-file-handler-enabled'."
+  :type 'boolean
+  :set (lambda (sym val) (set-image-file-handler-enabled val))
+  :initialize 'custom-initialize-default
+  :require 'image-file
+  :group 'image)
+
+(defcustom image-file-regexps
+  '("\\.png$" "\\.jpeg$" "\\.jpg$" "\\.gif$" "\\.tiff$" "\\.x[bp]m$")
+  "*A list of regexps matching files that should be displayed as images.
+
+Setting this variable directly does not take effect until the next time
+`set-image-file-handler-enabled' is called (which happens automatically
+when using \\[customize]."
+  :type '(repeat regexp)
+  :set (lambda (sym val)
+         (set-default sym val)
+         (when image-file-handler-enabled
+           ;; Re-initialize the image-file handler
+           (set-image-file-handler-enabled t)))
+  :initialize 'custom-initialize-default
+  :group 'image)
+
+;;;###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'."
+  (let ((rval
+         (image-file-call-underlying #'insert-file-contents-literally
+                                     'insert-file-contents
+                                     file visit beg end replace)))
+    (when (and image-file-handler-enabled (or (null beg) (zerop beg)) (null end))
+      ;; Make image into a picture, but only if the whole file was inserted
+      (let* ((ibeg (point))
+             (iend (+ (point) (cadr rval)))
+             (data
+              (string-make-unibyte (buffer-substring-no-properties ibeg iend)))
+             (image
+              (create-image data nil t))
+             (props
+              `(display ,image
+                        intangible ,image
+                        rear-nonsticky (display)
+                        ;; This a cheap attempt to make the whole buffer
+                        ;; read-only when we're visiting the file.
+                        ,@(and visit
+                               (= ibeg (point-min))
+                               (= iend (point-max))
+                               '(read-only t front-sticky (read-only))))))
+        (add-text-properties ibeg iend props)))
+    rval))
+
+(defun image-file-handler (operation &rest args)
+  "File name handler for inserting image files.
+OPERATION is the operation to perform, on ARGS.
+See `file-name-handler-alist' for details."
+  (if (eq operation 'insert-file-contents)
+      (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
+(defun set-image-file-handler-enabled (enabled)
+  "Enable or disable visiting image files as real images, as per ENABLED.
+The regexp in `image-file-regexp' is used to determine which filenames are
+considered image files."
+  ;; 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
+  (when enabled
+    (let ((regexp
+           (concat "\\("
+                   (mapconcat 'identity image-file-regexps "\\|")
+                   "\\)")))
+      (setq file-name-handler-alist
+            (cons (cons regexp 'image-file-handler) file-name-handler-alist))))
+  (setq-default image-file-handler-enabled enabled))
+
+;;;###autoload
+(defun enable-image-file-handler ()
+  "Enable visiting image files as real images.
+The regexp in `image-file-regexp' is used to determine which filenames are
+considered image files."
+  (interactive)
+  (set-image-file-handler-enabled t))
+
+(defun disable-image-file-handler ()
+  "Disable visiting image files as real images."
+  (interactive)
+  (set-image-file-handler-enabled nil))
+
+(provide 'image-file)
+
+;;; image-file.el ends here