imagemagic in image-mode and image-dired-thumbnail-mode?

[Vitalie Spinu]

Hello, 

For a new process-output-image-manipulation project I was looking for a
generic image mode. Surprisingly, it looks like none of the existing
modes is flexible/customizable/feature rich enough to be used as a
prototype for such a project.
 
Particularly, an essential feature for image scaling, imagemagic, is
still not supported by basic image modes. Image-dired-thumbnail-mode has
no idea of imagemagic at all.  Image-mode cannot open imagemagic types
as image-toggle-display-image hardcodes image type:

╭──────── #616 ─ lisp/image-mode.el ──
│        (type (image-type file-or-data nil data-p))
╰──────── #616 ─

Is there a hidden reason why image scaling is not yet implemented?

   ;; Not yet implemented.
   ;; (defvar image-transform-minor-mode-map
   ;;   (let ((map (make-sparse-keymap)))
   ;;     ;; (define-key map  [(control ?+)] 'image-scale-in)
   ;;     ;; (define-key map  [(control ?-)] 'image-scale-out)
   ;;     ;; (define-key map  [(control ?=)] 'image-scale-none)
   ;;     ;; (define-key map "c f h" 'image-scale-fit-height)
   ;;     ;; (define-key map "c ]" 'image-rotate-right)
   ;;     map)
   ;;   "Minor mode keymap `image-transform-mode'.")


I naturally wonder if there should be a global user custom variable
like:

   (defcustom image-view-type (and (image-type-available-p 'imagemagick)
                                   'imagemagick))

with all image modes taking it into account?

On a related note, wouldn't image-mode be better off if implemented on
top of some image-thumbnail-mode? Or maybe better, shouldn't image-mode
support multiple images per buffer, and then other modes like
image-dired-thumbnail-mode to derive from it?

    Vitalie