Subject: bug#6639: 24.0.50; [PATCH]image-mode: Sliced Images cannot be scrolled up

From: [email-masked] (Shyam | ശ്യാം കാരനാട്ട് | Karanatt)
Date: Thu, 15 Jul 2010 14:18:25 +0530

trying to scroll up a sliced image, shows an error, 
"image-next-line: Invalid image specification"

Steps to reproduce the error:

1)Open a pdf file in doc-view mode, and slice the image by pressing 
"s s"( i.e doc-view-set-slice), and giving the parameters.

2)scroll the page with C-n or image-next-line or image-scroll-up
That shows the error message
 "image-next-line: Invalid image specification" 

OR 

1)open an image file "~/test-image.png", or insert an image file to a buffer with:
(insert-image (create-image "~/test-image.png")). 
2) set, slice property for the image with add-text-properties function,
for example:

(let ((inhibit-read-only t)
      (X 50)
      (Y 50)
      (WIDTH 300)
      (HEIGHT 300))
  (add-text-properties 
   (point-min)
   (point-max)
   `(display (,(list 'slice X Y WIDTH HEIGHT)
	      (image :type png :file "~/test-image.png")))))

3)Scroll up the image by pressing C-n(i.e image-next-line) or M-x image-scroll-up
that shows the following messages:

image-next-line: Invalid image specification

Or with (setq debug-on-error t) you get this:

Debugger entered--Lisp error: (error "Invalid image specification")
  image-size(((slice 50 50 300 300) (image :type png :file "~/page-15.png")))
  image-next-line(1)
  call-interactively(image-next-line nil nil)

image-next-line in image-mode.el is relying on function image-size,
which is to be fed with the image display property of the form (image
...). But if the image is sliced, it will have (slice ..) display
property attached, which image-next-line is not taking care of. The
patch attached, checks if it is a an image property.  If there is slice
property, it takes the image height from the slice property instead. It
also won't mind having other display properties than image and slice too
to be included on display properties, as it assoc's the value of image
and slice.

I saw the bug while reading ebooks on doc-view with margins sliced out.

Happy Hacking
Shyam K

In GNU Emacs 24.0.50.2 (i686-pc-linux-gnu, GTK+ Version 2.20.1)
 of 2010-06-01 on shyam.laptop
Windowing system distributor `The X.Org Foundation', version 11.0.10801902
configured using `configure  '--prefix=/usr/''

Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: en_US.UTF-8
  value of $XMODIFIERS: nil
  locale-coding-system: utf-8-unix
  default enable-multibyte-characters: t

# Bazaar merge directive format 2 (Bazaar 0.90)
# revision_id: [email-masked]
# author: Shyam Karanatt<[email-masked]>
# target_branch: file:///media/sda5/home/shyam/bazaar-\
#   emacs/emacs/clean-trunk/
# testament_sha1: d49bcb73c9113f671bfbafd26c333a809b85cbec
# timestamp: 2010-07-15 13:29:40 +0530
# base_revision_id: [email-masked]
# 
# Begin patch
=== modified file 'lisp/image-mode.el'
--- lisp/image-mode.el	2010-07-14 15:57:54 +0000
+++ lisp/image-mode.el	2010-07-15 07:52:17 +0000
@@ -157,9 +157,15 @@
 	((< n 0)
 	 (image-set-window-vscroll (max 0 (+ (window-vscroll) n))))
 	(t
-	 (let* ((image (image-get-display-property))
+	 (let* ((image-display (image-get-display-property))
+		(image (if (eq (car image-display) 'image) 
+			   image-display
+			 (assoc 'image image-display)))
+		(slice (assoc 'slice image-display))
 		(edges (window-inside-edges))
 		(win-height (- (nth 3 edges) (nth 1 edges)))
-		(img-height (ceiling (cdr (image-size image)))))
+		(img-height (if slice 
+				(nth 4 slice)
+			      (ceiling (cdr (image-size image))))))
 	   (image-set-window-vscroll (min (max 0 (- img-height win-height))
 					  (+ n (window-vscroll))))))))