New command image-transform-fit-to-window

* lisp/image-mode.el (image-auto-resize, image-transform-resize):
Add new value 'fit-window', meaning to scale the image up or down
to fit the window.  (Bug#)
(image-transform-fit-to-window): New command.
(image-transform-fit-to-height, image-transform-fit-to-width):
Make obsolete in favor of above new command.
(image-mode-map): Bind "s w" to 'image-transform-fit-to-window'.
Move binding for obsolete command 'image-transform-fit-to-width'
to "s i".
(image-mode-map): Add menu entry for
'image-transform-fit-to-window'.  Remove menu entries for above
obsolete commands.
* doc/emacs/files.texi (Image Mode): Update documentation.
(image-transform-fit-both): Doc fix.

doc/emacs/files.texi

@@ -2205,11 +2205,11 @@ window, so this is only necessary if you customize the default
 behavior by using the options @code{image-auto-resize} and
 @code{image-auto-resize-on-window-resize}.
 
-@findex image-transform-fit-both
+@findex image-transform-fit-to-window
 @findex image-transform-set-scale
 @findex image-transform-reset
 To resize the image manually you can use the command
-@code{image-transform-fit-both} bound to @kbd{s b}
+@code{image-transform-fit-to-window} bound to @kbd{s w}
 that fits the image to both the window height and width.
 To scale the image specifying a scale factor, use the command
 @code{image-transform-set-scale} bound to @kbd{s s}.

etc/NEWS

@@ -377,6 +377,24 @@ To improve security, if an sql product has ':password-in-comint' set
 to t, a password supplied via the minibuffer will be sent in-process,
 as opposed to via the command-line.
 
+** Image Mode
+
++++
+*** New command 'image-transform-fit-to-window'.
+This command fits the image to the current window by scaling down or
+up as necessary.  Unlike 'image-transform-fit-both', this does not
+only scale the image down, but up as well.  It is bound to "s w" in
+Image Mode by default.
+
++++
+*** 'image-transform-fit-to-(height|width)' are now obsolete.
+Use the new command 'image-transform-fit-to-window' instead.
+The keybinding for 'image-transform-fit-to-width' is now 's i'.
+
+---
+*** User option 'image-auto-resize' can now be set to 'fit-window'.
+This works like 'image-transform-fit-to-window'.
+
 ** Image-Dired
 
 +++

lisp/image-mode.el

@@ -58,16 +58,20 @@ It is called with one argument, the initial WINPROPS.")
   "Non-nil to resize the image upon first display.
 Its value should be one of the following:
  - nil, meaning no resizing.
- - t, meaning to fit the image to the window height and width.
+ - t, meaning to scale the image down to fit in the window.
+ - `fit-window', meaning to fit the image to the window.
  - `fit-height', meaning to fit the image to the window height.
  - `fit-width', meaning to fit the image to the window width.
- - A number, which is a scale factor (the default size is 1)."
+ - A number, which is a scale factor (the default size is 1).
+
+Resizing will always preserve the aspect ratio of the image."
   :type '(choice (const :tag "No resizing" nil)
-                 (other :tag "Fit height and width" t)
-                 (const :tag "Fit height" fit-height)
-                 (const :tag "Fit width" fit-width)
+                 (const :tag "Fit to window" fit-window)
+                 (const :tag "Fit to window height" fit-height)
+                 (const :tag "Fit to window width" fit-width)
+                 (other :tag "Scale down to fit window" t)
                  (number :tag "Scale factor" 1))
-  :version "27.1"
+  :version "29.1"
   :group 'image)
 
 (defcustom image-auto-resize-on-window-resize 1
@@ -82,12 +86,16 @@ resizing according to the value specified in `image-auto-resize'."
 
 (defvar-local image-transform-resize nil
   "The image resize operation.
+Non-nil to resize the image upon first display.
 Its value should be one of the following:
  - nil, meaning no resizing.
- - t, meaning to fit the image to the window height and width.
+ - t, meaning to scale the image down to fit in the window.
+ - `fit-window', meaning to fit the image to the window.
  - `fit-height', meaning to fit the image to the window height.
  - `fit-width', meaning to fit the image to the window width.
- - A number, which is a scale factor (the default size is 1).")
+ - A number, which is a scale factor (the default size is 1).
+
+Resizing will always preserve the aspect ratio of the image.")
 
 (defvar-local image-transform-scale 1.0
   "The scale factor of the image being displayed.")
@@ -455,8 +463,9 @@ call."
 
     ;; Transformation keys
     (define-key map "sf" 'image-mode-fit-frame)
+    (define-key map "sw" 'image-transform-fit-to-window)
     (define-key map "sh" 'image-transform-fit-to-height)
-    (define-key map "sw" 'image-transform-fit-to-width)
+    (define-key map "si" 'image-transform-fit-to-width)
     (define-key map "sb" 'image-transform-fit-both)
     (define-key map "ss" 'image-transform-set-scale)
     (define-key map "sr" 'image-transform-set-rotation)
@@ -511,12 +520,10 @@ call."
 	"--"
 	["Fit Frame to Image" image-mode-fit-frame :active t
 	 :help "Resize frame to match image"]
-	["Fit Image to Window (Best Fit)" image-transform-fit-both
-	 :help "Resize image to match the window height and width"]
-	["Fit to Window Height" image-transform-fit-to-height
-	 :help "Resize image to match the window height"]
-	["Fit to Window Width" image-transform-fit-to-width
-	 :help "Resize image to match the window width"]
+        ["Fit Image to Window" image-transform-fit-to-window
+         :help "Resize image to match the window height and width"]
+        ["Fit Image to Window (Scale down only)" image-transform-fit-both
+         :help "Scale image down to match the window height and width"]
 	["Zoom In" image-increase-size
 	 :help "Enlarge the image"]
 	["Zoom Out" image-decrease-size
@@ -837,7 +844,8 @@ was inserted."
 	    filename))
 	 ;; If we have a `fit-width' or a `fit-height', don't limit
 	 ;; the size of the image to the window size.
-	 (edges (when (eq image-transform-resize t)
+         (edges (when (or (eq image-transform-resize t)
+                          (eq image-transform-resize 'fit-window))
 		  (window-inside-pixel-edges (get-buffer-window))))
 	 (max-width (when edges
 		      (- (nth 2 edges) (nth 0 edges))))
@@ -884,6 +892,13 @@ was inserted."
                                 ;; Type hint.
                                 :format (and filename data-p))))
 
+    ;; Handle `fit-window'.
+    (when (eq image-transform-resize 'fit-window)
+      (setq image
+            (cons (car image)
+                  (plist-put (cdr image) :width
+                             (plist-get (cdr image) :max-width)))))
+
     ;; Discard any stale image data before looking it up again.
     (image-flush image)
     (setq image (append image (image-transform-properties image)))
@@ -1494,21 +1509,29 @@ return value is suitable for appending to an image spec."
 (defun image-transform-fit-to-height ()
   "Fit the current image to the height of the current window."
   (interactive)
+  (declare (obsolete nil "29.1"))
   (setq image-transform-resize 'fit-height)
   (image-toggle-display-image))
 
 (defun image-transform-fit-to-width ()
   "Fit the current image to the width of the current window."
+  (declare (obsolete nil "29.1"))
   (interactive)
   (setq image-transform-resize 'fit-width)
   (image-toggle-display-image))
 
 (defun image-transform-fit-both ()
-  "Fit the current image both to the height and width of the current window."
+  "Scale the current image down to fit in the current window."
   (interactive)
   (setq image-transform-resize t)
   (image-toggle-display-image))
 
+(defun image-transform-fit-to-window ()
+  "Fit the current image to the height and width of the current window."
+  (interactive)
+  (setq image-transform-resize 'fit-window)
+  (image-toggle-display-image))
+
 (defun image-transform-set-rotation (rotation)
   "Prompt for an angle ROTATION, and rotate the image by that amount.
 ROTATION should be in degrees."