bug#22453: [PATCH] Support for switching to hexl-mode from image mode

[Alexander Kuleshov]

We can easily switch to text mode from the image mode by the
pressing of C-c C-c. But sometimes, it is more useful to open
an image in hex format. This patch provides new keybinding
for the image mode - C-c C-x which works like C-c C-c, but
executes switch to the hexl-mode. Like switching to text mode,
switching to hex mode supports switching back to the image-mode.

The patch contains following changes:

* lisp/image-mode.el: adapted comments at the top of file;
* lisp/image-mode.el: added new menu item to the Image menu:
'Show as hex';
* lisp/image-mode.el: added description of the new keybinding
to the image-mode help;
* lisp/image-mode.el: all help messages in minibuffer adapted
to new keybinding;
* lisp/image-mode.el: image-toggle-hex-display function added
which checks current mode and switch into text or image mode
depends on it;
* lisp/image-mode.el: add image-mode-to-text helper for 
image-toggle-as-hex and image-toggle-as-text functions. It
is built on top of image-toggle-as-text function and used
for auto-mode-alist related preparation before switching
into text or hexl mode.

Patch tested on top of emacs-25 branch on fedora 23 with all
Linux related configured options.
---
 lisp/image-mode.el | 96 ++++++++++++++++++++++++++++++++++++++++--------------
 1 file changed, 71 insertions(+), 25 deletions(-)

diff --git a/lisp/image-mode.el b/lisp/image-mode.el
index e549b49..5ee00bb 100644
--- a/lisp/image-mode.el
+++ b/lisp/image-mode.el
@@ -24,8 +24,8 @@
 ;;; Commentary:
 
 ;; Defines a major mode for visiting image files
-;; that allows conversion between viewing the text of the file
-;; and viewing the file as an image.  Viewing the image
+;; that allows conversion between viewing the text of the file,
+;; hex of the file and viewing the file as an image.  Viewing the image
 ;; works 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
@@ -374,6 +374,7 @@ image-mode-map
   (let ((map (make-sparse-keymap)))
     (set-keymap-parent map special-mode-map)
     (define-key map "\C-c\C-c" 'image-toggle-display)
+    (define-key map "\C-c\C-x" 'image-toggle-hex-display)
     (define-key map (kbd "SPC")       'image-scroll-up)
     (define-key map (kbd "S-SPC")     'image-scroll-down)
     (define-key map (kbd "DEL")       'image-scroll-down)
@@ -406,6 +407,8 @@ image-mode-map
       '("Image"
        ["Show as Text" image-toggle-display :active t
         :help "Show image as text"]
+       ["Show as Hex" image-toggle-hex-display :active t
+        :help "Show image as hex"]
        "--"
        ["Fit to Window Height" image-transform-fit-to-height
         :visible (eq image-type 'imagemagick)
@@ -480,6 +483,7 @@ image-mode-map
 (defvar image-minor-mode-map
   (let ((map (make-sparse-keymap)))
     (define-key map "\C-c\C-c" 'image-toggle-display)
+    (define-key map "\C-c\C-x" 'image-toggle-hex-display)
     map)
   "Mode keymap for `image-minor-mode'.")
 
@@ -490,8 +494,8 @@ bookmark-make-record-function
 ;;;###autoload
 (defun image-mode ()
   "Major mode for image files.
-You can use \\<image-mode-map>\\[image-toggle-display]
-to toggle between display as an image and display as text.
+You can use \\<image-mode-map>\\[image-toggle-display] or 
\\<image-mode-map>\\[image-toggle-hex-display]
+to toggle between display as an image and display as text or hex.
 
 Key bindings:
 \\{image-mode-map}"
@@ -530,7 +534,7 @@ image-mode
        (run-mode-hooks 'image-mode-hook)
        (let ((image (image-get-display-property))
              (msg1 (substitute-command-keys
-                    "Type \\[image-toggle-display] to view the image as "))
+                    "Type \\[image-toggle-display] or 
\\[image-toggle-hex-display] to view the image as "))
              animated)
          (cond
           ((null image)
@@ -559,7 +563,7 @@ image-mode
 ;;;                         (substitute-command-keys
 ;;;                          "\\[image-toggle-animation] to animate."))))
           (t
-           (message "%s" (concat msg1 "text."))))))
+           (message "%s" (concat msg1 "text or hex."))))))
 
     (error
      (image-mode-as-text)
@@ -585,19 +589,10 @@ image-minor-mode
       (add-hook 'change-major-mode-hook (lambda () (image-minor-mode -1)) nil 
t)))
 
 ;;;###autoload
-(defun image-mode-as-text ()
+(defun image-mode-to-text ()
   "Set a non-image mode as major mode in combination with image minor mode.
-A non-image major mode found from `auto-mode-alist' or Fundamental mode
-displays an image file as text.  `image-minor-mode' provides the key
-\\<image-mode-map>\\[image-toggle-display] to switch back to `image-mode'
-to display an image file as the actual image.
-
-You can use `image-mode-as-text' in `auto-mode-alist' when you want
-to display an image file as text initially.
-
-See commands `image-mode' and `image-minor-mode' for more information
-on these modes."
-  (interactive)
+A non-mage major mode found from `auto-mode-alist' or fundamental mode
+displays an image file as hex."
   ;; image-mode-as-text = normal-mode + image-minor-mode
   (let ((previous-image-type image-type)) ; preserve `image-type'
     (if image-mode-previous-major-mode
@@ -625,12 +620,49 @@ image-mode-as-text
     ;; Enable image minor mode with `C-c C-c'.
     (image-minor-mode 1)
     ;; Show the image file as text.
-    (image-toggle-display-text)
-    (message "%s" (concat
-                  (substitute-command-keys
-                   "Type \\[image-toggle-display] to view the image as ")
-                  (if (image-get-display-property)
-                      "text" "an image") "."))))
+    (image-toggle-display-text)))
+
+(defun image-mode-as-hex ()
+  "Set a non-image mode as major mode in combination with image minor mode.
+A non-mage major mode found from `auto-mode-alist' or fundamental mode
+displays an image file as hex.  `image-minor-mode' provides the key
+\\<image-mode-map>\\[image-toggle-hex-display] to switch back  to `image-mode'
+to display an image file as the actual image.
+
+You can use `image-mode-as-text' in `auto-mode-alist' when you wanto
+to display an image file as text initially.
+
+See commands `image-mode' and `image-minor-mode' for more information
+on these modes."
+  (interactive)
+  (image-mode-to-text)
+  ;; Turn on hexl-mode
+  (hexl-mode)
+  (message "%s" (concat
+                 (substitute-command-keys
+                  "Type \\[image-toggle-hex-display] or 
\\[image-toggle-display] to view the image as ")
+                 (if (image-get-display-property)
+                     "hex" "an image or text") ".")))
+
+(defun image-mode-as-text ()
+  "Set a non-image mode as major mode in combination with image minor mode.
+A non-image major mode found from `auto-mode-alist' or Fundamental mode
+displays an image file as text.  `image-minor-mode' provides the key
+\\<image-mode-map>\\[image-toggle-display] to switch back to `image-mode'
+to display an image file as the actual image.
+
+You can use `image-mode-as-text' in `auto-mode-alist' when you want
+to display an image file as text initially.
+
+See commands `image-mode' and `image-minor-mode' for more information
+on these modes."
+  (interactive)
+  (image-mode-to-text)
+  (message "%s" (concat
+                 (substitute-command-keys
+                  "Type \\[image-toggle-display] or 
\\[image-toggle-hex-display] to view the image as ")
+                 (if (image-get-display-property)
+                     "text" "an image or hex") ".")))
 
 (define-obsolete-function-alias 'image-mode-maybe 'image-mode "23.2")
 
@@ -725,6 +757,18 @@ image-toggle-display-image
     (if (called-interactively-p 'any)
        (message "Repeat this command to go back to displaying the file as 
text"))))
 
+(defun image-toggle-hex-display ()
+  "Toggle between image and text display.
+If the current buffer is displaying an image file as an image,
+call `image-mode-as-hex' to switch to text.  Otherwise, display
+the image by calling `image-mode'."
+  (interactive)
+  (if (image-get-display-property)
+      (image-mode-as-hex)
+    (if (eq major-mode 'fundamental-mode)
+        (image-mode-as-hex)
+      (image-mode))))
+
 (defun image-toggle-display ()
   "Toggle between image and text display.
 If the current buffer is displaying an image file as an image,
@@ -733,7 +777,9 @@ image-toggle-display
   (interactive)
   (if (image-get-display-property)
       (image-mode-as-text)
-    (image-mode)))
+    (if (eq major-mode 'hexl-mode)
+        (image-mode-as-text)
+      (image-mode))))
 
 (defun image-kill-buffer ()
   "Kill the current buffer."
-- 
2.7.0.25.gfc10eb5