bug#4016: 23.1.50; docview: scrolling up breaks after setting a slice

bug#4016: 23.1.50; docview: scrolling up breaks after setting a slice

[Paer Kurlberg]

Please write in English if possible, because the Emacs maintainers
usually do not have translators to read other languages for them.

Your bug report will be posted to the emacs-pretest-bug@gnu.org
mailing list.

Please describe exactly what actions triggered the bug
and the precise symptoms of the bug:


View a dvi file (or pdf file for that matter) with DocView.

Set a slice by typing "ss" (invoking doc-view-set-slice) with x and y
coordinates zero, and maximum width and height, as suggested by the
prompt.  (In fact, any slice settings seems to trigger the phenomena.)

When hitting space (invoking doc-view-scroll-up-or-next-page), the
document is not scrolled up, and the following error message appears:

image-next-line: Invalid image specification

Note: By hitting "sr" (removing the slice) it is again possible to use
space to scroll up.

Remark: On a laptop with a small screen it would be very useful to set
slices to get rid of the large margins, and yet being able to scroll
through the document (even with a slice set, I cannot see the whole
page at once.)



If Emacs crashed, and you have the Emacs process in the gdb debugger,
please include the output from the following gdb commands:
    `bt full' and `xbacktrace'.
If you would like to further debug the crash, please read the file
/usr/share/emacs/23.1.50/etc/DEBUG for instructions.


In GNU Emacs 23.1.50.1 (i486-pc-linux-gnu, GTK+ Version 2.16.1)
 of 2009-07-31 on lansones, modified by Debian
 (emacs-snapshot package, version 1:20090730-1~jaunty1)
Windowing system distributor `The X.Org Foundation', version
 11.0.10600000
configured using `configure  '--build' 'i486-linux-gnu' '--host'
 'i486-linux-gnu' '--prefix=/usr' '--sharedstatedir=/var/lib'
 '--libexecdir=/usr/lib' '--localstatedir=/var'
 '--infodir=/usr/share/info' '--mandir=/usr/share/man'
 '--with-pop=yes'
 '--enable-locallisppath=/etc/emacs-snapshot:/etc/emacs:/usr/local/share/emacs/23.1.50/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/23.1.50/site-lisp:/usr/share/emacs/site-lisp'
 '--with-x=yes' '--with-x-toolkit=gtk' 'build_alias=i486-linux-gnu'
 'host_alias=i486-linux-gnu' 'CFLAGS=-DDEBIAN
 -DSITELOAD_PURESIZE_EXTRA=5000 -g -O2' 'LDFLAGS=-g -Wl,--as-needed'
 'CPPFLAGS=''

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

Major mode: DocView

Minor modes in effect:
  tooltip-mode: t
  tool-bar-mode: t
  mouse-wheel-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  global-auto-composition-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent input:
C-x C-f a r n o l d . d v i <return> <return> s s 0 
<return> 0 <return> 9 2 6 <return> 1 3 1 0 <return> 
SPC <help-echo> <help-echo> <help-echo> <help-echo> 
<help-echo> <help-echo> <help-echo> <help-echo> <help-echo> 
<help-echo> <help-echo> <help-echo> <help-echo> <help-echo> 
<help-echo> <help-echo> <help-echo> <help-echo> <menu-bar> 
<help-menu> <send-emacs-bug-report>

Recent messages:
Loading
/usr/share/emacs-snapshot/site-lisp/planner-el/planner-autoloads.el
(source)...done
Loading /etc/emacs/site-start.d/51planner-el.el (source)...done
Loading /etc/emacs/site-start.d/52remember-el.el (source)...
Loading /usr/share/emacs/site-lisp/remember-el/remember-autoloads.el
(source)...done
Loading /etc/emacs/site-start.d/52remember-el.el (source)...done
Loading /etc/emacs/site-start.d/60hyperspec.el (source)...done
For information about GNU Emacs and the GNU system, type C-h C-a.
DocView: using cached files!
Type C-c C-c to toggle between editing or viewing the document.
No key given.  Assumed normal.
image-next-line: Invalid image specification

Load-path shadows:
/usr/share/emacs/23.1.50/site-lisp/auctex/tex-mik

bug#4016: Acknowledgement (23.1.50; docview: scrolling up breaks after setting a slice)

[Paer Kurlberg]

In case it might be helpful: below is a backtrace.  It seems that the
problem is that image-get-display-property (called in the function
image-next-line) returns the list

((slice 0 0 1100 1600) (image :type png :file
  "/tmp/docview1000/arnold.dvi-b04e9949bb98146d331479915a45fc5b/page-1.png"
  :pointer arrow))

and therefore image-size complains since a "proper image" should be a
list whose car equals 'image.


BACKTRACE: 

Debugger entered--Lisp error: (error "Invalid image specification")
  image-size(((slice 0 0 1100 1600) (image :type png :file
  "/tmp/docview1000/arnold.dvi-b04e9949bb98146d331479915a45fc5b/page-1.png"
  :pointer arrow)))
  image-next-line(36)
  image-scroll-up(nil)
  doc-view-scroll-up-or-next-page()
  call-interactively(doc-view-scroll-up-or-next-page nil nil)

bug#4016: Acknowledgement (23.1.50; docview: scrolling up breaks after setting a slice)

[Tassilo Horn]

Paer Kurlberg <kurlberg@math.kth.se> writes:

> In case it might be helpful: below is a backtrace.  It seems that the
> problem is that image-get-display-property (called in the function
> image-next-line) returns the list
>
> ((slice 0 0 1100 1600) (image :type png :file
>   "/tmp/docview1000/arnold.dvi-b04e9949bb98146d331479915a45fc5b/page-1.png"
>   :pointer arrow))
>
> and therefore image-size complains since a "proper image" should be a
> list whose car equals 'image.

I can reproduce the error.  But I'm not too sure where the bug is
located.  According to the docs, the display property may be a single
display spec, or a list or vector of such.

,----[ (info "(elisp)Display Property") ]
| The value of the `display' property should be a display specification,
| or a list or vector containing several display specifications.
`----

So in that respect the slice + image spec are ok.

I think that maybe the C function

  int valid_image_p (object) Lisp_Object object;

in image.c should be adapted to accept lists/vectors including one image
spec.

Bye,
Tassilo

bug#4016: 23.1.50; docview: scrolling up breaks after setting a slice

[Lars Ingebrigtsen]

Paer Kurlberg <kurlberg@math.kth.se> writes:

> View a dvi file (or pdf file for that matter) with DocView.
>
> Set a slice by typing "ss" (invoking doc-view-set-slice) with x and y
> coordinates zero, and maximum width and height, as suggested by the
> prompt.  (In fact, any slice settings seems to trigger the phenomena.)
>
> When hitting space (invoking doc-view-scroll-up-or-next-page), the
> document is not scrolled up, and the following error message appears:
>
> image-next-line: Invalid image specification

(I'm going through old bug reports that unfortunately weren't resolved
at the time.)

I tried reproducing this in Emacs 28, but I got no errors when doing
this.  (The slice command is `c s' now(?), though.)

Are you still seeing this issue in recent Emacs versions?

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

bug#4016: 23.1.50; docview: scrolling up breaks after setting a slice

[Lars Ingebrigtsen]

kurlberg <kurlberg@math.kth.se> writes:

> I just tried it on emacs 26.3, and the problem seems to be gone, I think
> the bug thus can be marked as resolved. Thanks for looking into this.

Thanks for checking; closing this bug report then.