info-mode image alt text display (patch)

[Kevin Ryde <user42@zip.com.au>]

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I'd like to propose this change to get Info-display-images-node
showing the the text alternative parts of @image blobs, if the tty
can't show the graphics.  Such text is of course provided specifically
for when the graphics can't be shown.  It can be an ascii art
rendition, or merely a few words about what you could have seen.

2007-03-25  Kevin Ryde  <user42@zip.com.au>

	* info.el (Info-display-images-node): On a text-only terminal, show
	the "text" or "alt" parts of the image blobs.


You can see the effect on the foo.info file below.  Currently the
images are only blank lines, with my change it comes out like

	This is an alt bit.

	This is a text bit from a .txt file.

	Or if no text parts at all then you get:
	[image:foo.png]

foo.texi and bar.txt below are the sources.  Copy any random png files
to create foo.png and bar.png.



[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #2: info.el.image-alts.diff --]
[-- Type: text/x-diff, Size: 2194 bytes --]

*** info.el.~1.497.~	2007-03-12 10:14:41.000000000 +1100
--- info.el	2007-03-25 11:23:26.000000000 +1000
***************
*** 1315,1330 ****
  	      nil t)
  	(let* ((start (match-beginning 1))
  	       (parameter-alist (Info-split-parameter-string (match-string 2)))
! 	       (src (cdr (assoc-string "src" parameter-alist)))
! 	       (image-file (if src (if (file-name-absolute-p src) src
! 				     (concat default-directory src))
! 			     ""))
! 	       (image (if (file-exists-p image-file)
! 			  (create-image image-file)
! 			"[broken image]")))
! 	  (if (not (get-text-property start 'display))
! 	      (add-text-properties
! 	       start (point) `(display ,image rear-nonsticky (display)))))))
      (set-buffer-modified-p nil)))
  
  ;; Texinfo 4.7 adds cookies of the form ^@^H[NAME CONTENTS ^@^H].
--- 1315,1339 ----
  	      nil t)
  	(let* ((start (match-beginning 1))
  	       (parameter-alist (Info-split-parameter-string (match-string 2)))
!                (src (cdr (assoc-string "src" parameter-alist))))
!           (if (display-images-p)
!               (let* ((image-file (if src (if (file-name-absolute-p src) src
!                                            (concat default-directory src))
!                                    ""))
!                      (image (if (file-exists-p image-file)
!                                 (create-image image-file)
!                               "[broken image]")))
!                 (if (not (get-text-property start 'display))
!                     (add-text-properties
!                      start (point) `(display ,image rear-nonsticky (display)))))
!             ;; text-only display, show alternative text if provided, or
!             ;; otherwise a clue that there's meant to be a picture
!             (delete-region start (point))
!             (insert (or (cdr (assoc-string "text" parameter-alist))
!                         (cdr (assoc-string "alt" parameter-alist))
!                         (and src
!                              (concat "[image:" src "]"))
!                         "[image]"))))))
      (set-buffer-modified-p nil)))
  
  ;; Texinfo 4.7 adds cookies of the form ^@^H[NAME CONTENTS ^@^H].

[-- Attachment #3: foo.info --]
[-- Type: application/octet-stream, Size: 371 bytes --]

[-- Attachment #4: foo.texi --]
[-- Type: application/x-texinfo, Size: 253 bytes --]

[-- Attachment #5: bar.txt --]
[-- Type: text/plain, Size: 37 bytes --]

This is a text bit from a .txt file.

[-- Attachment #6: Type: text/plain, Size: 142 bytes --]

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