emacs/lisp/image/image-converter.el

;;; image-converter.el --- Converting images from exotic formats -*- lexical-binding: t -*-

;; Copyright (C) 2019 Free Software Foundation, Inc.

;; Author: Lars Magne Ingebrigtsen <larsi@gnus.org>
;; Keywords: images

;; 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:

;; The main interface function here is `image-convert'.

;;; Code:

(require 'cl-generic)
(eval-when-compile (require 'cl-lib))

(defcustom convert-external-images nil
  "If non-nil, `create-image' will use external converters for exotic formats.
Emacs handles most of the common image formats (JPEG, PNG, GIF
and so on) internally, but images that doesn't have native
support in Emacs can still be displayed by Emacs if external
conversion programs (like ImageMagick \"convert\", GraphicsMagick
\"gm\" or \"ffmpeg\") are installed."
  :group 'image
  :type 'bool
  :version "27.1")

(defcustom image-converter nil
  "What external converter to use.
`imagemagick', `graphicsmagick' and `ffmpeg' are supported."
  :group 'image
  :type 'symbol
  :version "27.1")

(defvar image-converter-regexp nil
  "A regexp that matches the file name suffixes that can be converted.")

(defvar image-converter--converters
  '((graphicsmagick :command "gm convert" :probe "-list format")
    (imagemagick :command "convert" :probe "-list format")
    (ffmpeg :command "ffmpeg" :probe "-decoders"))
  "List of supported image converters to try.")

(defun image-convert-p (file)
  "Return `image-convert' if FILE can be converted."
  ;; Find an installed image converter.
  (unless image-converter
    (image-converter--find-converter))
  (and image-converter
       (string-match image-converter-regexp file)
       'image-convert))

(defun image-convert (image)
  "Convert IMAGE to a format Emacs can display.
IMAGE can either be a file name, which will make the return value
a string with the image data.  It can also be an image object as
returned by `create-image'.  If so, it has to be an image object
where created with DATA-P nil (i.e., it has to refer to a file)."
  ;; Find an installed image converter.
  (unless image-converter
    (image-converter--find-converter))
  (unless image-converter
    (error "No external image converters installed"))
  (when (and (listp image)
             (not (plist-get (cdr image) :file)))
    (error "Only images that refer to files can be converted"))
  (with-temp-buffer
    (set-buffer-multibyte nil)
    (when-let ((err (image-converter--convert
                     image-converter
                     (if (listp image)
                         (plist-get (cdr image) :file)
                       image))))
      (error "%s" err))
    (if (listp image)
        ;; Return an image object that's the same as we were passed,
        ;; but ignore the :type and :file values.
        (apply #'create-image (buffer-string) 'png t
               (cl-loop for (key val) on (cdr image) by #'cddr
                        unless (memq key '(:type :file))
                        append (list key val)))
      (buffer-string))))

(defun image-converter--value (type elem)
  "Return the value of ELEM of image converter TYPE."
  (plist-get (cdr (assq type image-converter--converters)) elem))

(cl-defmethod image-converter--probe ((type (eql graphicsmagick)))
  "Check whether the system has GraphicsMagick installed."
  (with-temp-buffer
    (let ((command (split-string (image-converter--value type :command) " "))
          formats)
      (when (zerop (apply #'call-process (car command) nil '(t nil) nil
                          (append (cdr command)
                                  (split-string
                                   (image-converter--value type :probe) " "))))
        (goto-char (point-min))
        (when (re-search-forward "^-" nil t)
          (forward-line 1)
          ;; Lines look like
          ;; "   8BIM P  rw-  Photoshop resource format".
          (while (re-search-forward "^ *\\([A-Z0-9]+\\) +. +r" nil t)
            (push (downcase (match-string 1)) formats)))
        (nreverse formats)))))

(cl-defmethod image-converter--probe ((type (eql imagemagick)))
  "Check whether the system has ImageMagick installed."
  (with-temp-buffer
    (let ((command (split-string (image-converter--value type :command) " "))
          formats)
      ;; Can't check return value; ImageMagick convert usually returns
      ;; a non-zero result on "-list format".
      (apply #'call-process (car command) nil '(t nil) nil
             (append (cdr command)
                     (split-string (image-converter--value type :probe) " ")))
      (goto-char (point-min))
      (when (re-search-forward "^-" nil t)
        (forward-line 1)
        ;; Lines look like
        ;; "      WPG* r--   Word Perfect Graphics".
        (while (re-search-forward "^ *\\([A-Z0-9]+\\)\\*? +r" nil t)
          (push (downcase (match-string 1)) formats)))
      (nreverse formats))))

(cl-defmethod image-converter--probe ((type (eql ffmpeg)))
  "Check whether the system has ffmpeg installed."
  (with-temp-buffer
    (let ((command (image-converter--value type :command))
          formats)
      (when (zerop (call-process command nil '(t nil) nil
                                 (image-converter--value type :probe)))
        (goto-char (point-min))
        (when (re-search-forward "^ *-" nil t)
          (forward-line 1)
          ;; Lines look like
          ;; " V....D alias_pix            Alias/Wavefront PIX image"
          (while (re-search-forward "^ *V[^ ]+ +\\([a-z0-9_]+\\)" nil t)
            (push (match-string 1) formats)))
        (nreverse formats)))))

(defun image-converter--find-converter ()
  "Find an installed image converter."
  (dolist (elem image-converter--converters)
    (when-let ((formats (image-converter--probe (car elem))))
      (setq image-converter (car elem)
            image-converter-regexp (concat "\\." (regexp-opt formats) "\\'")))))

(cl-defmethod image-converter--convert ((type (eql graphicsmagick)) file)
  "Convert using GraphicsMagick."
  (image-converter--convert-magick type file))

(cl-defmethod image-converter--convert ((type (eql imagemagick)) file)
  "Convert using ImageMagick."
  (image-converter--convert-magick type file))

(defun image-converter--convert-magick (type file)
  (let ((command (split-string (image-converter--value type :command) " ")))
    (unless (zerop (apply #'call-process (car command)
                          nil t nil
                          (append (cdr command)
                                  (list (expand-file-name file) "png:-"))))
      ;; If the command failed, hopefully the buffer contains the
      ;; error message.
      (buffer-string))))

(cl-defmethod image-converter--convert ((type (eql ffmpeg)) file)
  "Convert using ffmpeg."
  (unless (zerop (call-process (image-converter--value type :command)
                               nil '(t nil) nil
                               "-i" (expand-file-name file)
                               "-c:v" "png" "-f" "image2pipe" "-"))
    "ffmpeg error when converting"))

(provide 'image-converter)

;;; image-converter.el ends here