bug#22442: 25.0.50; --with-cairo does not display PNG on GNU/Linux

bug#22442: 25.0.50; --with-cairo does not display PNG on GNU/Linux

[Paul Eggert]

To reproduce the problem, configure Emacs --with-cairo, and then run these shell 
commands:

wget https://upload.wikimedia.org/wikipedia/commons/f/f5/All_palaeotemps.png
emacs -Q All_palaeotemps.png

Emacs shows a blank (or sometimes garbled) screen instead of the image.

I think the problem is that lookup_rgb_color is returning garbage.

Here are more details about the configuration, built on Fedora 23 x86-64:

In GNU Emacs 25.0.50.55 (x86_64-unknown-linux-gnu, GTK+ Version 3.18.6, cairo 
version 1.14.2)
  of 2016-01-22 built on penguin.cs.ucla.edu
Repository revision: 27a0919cde7a6dce93aeba63b5ce7d0834f48531
Configured using:
  'configure --enable-gcc-warnings --with-cairo'

Configured features:
XPM JPEG TIFF GIF PNG RSVG CAIRO IMAGEMAGICK SOUND GPM DBUS GCONF
GSETTINGS NOTIFY ACL LIBSELINUX GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF
XFT ZLIB TOOLKIT_SCROLL_BARS GTK3 X11

Important settings:
   value of $LC_ALL: en_US.utf8
   value of $LC_COLLATE: en_US.UTF-8
   value of $LC_CTYPE: en_US.UTF-8
   value of $LC_MESSAGES: en_US.UTF-8
   value of $LANG: C
   locale-coding-system: utf-8-unix

bug#22442: 25.0.50; --with-cairo does not display PNG on GNU/Linux

[Paul Eggert]

I installed a patch which should make Bug#22442 easier to reproduce:

./configure --with-cairo --enable-checking
make
wget https://upload.wikimedia.org/wikipedia/commons/f/f5/All_palaeotemps.png
src/emacs -Q All_palaeotemps.png

This should make Emacs dump core.

I'll CC: this to Jan D. as he's expert in this area.

bug#22442: 25.0.50; --with-cairo does not display PNG on GNU/Linux

[Eli Zaretskii]

> From: Paul Eggert <eggert@cs.ucla.edu>
> Date: Sat, 23 Jan 2016 00:27:08 -0800
> 
> To reproduce the problem, configure Emacs --with-cairo, and then run these shell 
> commands:
> 
> wget https://upload.wikimedia.org/wikipedia/commons/f/f5/All_palaeotemps.png
> emacs -Q All_palaeotemps.png
> 
> Emacs shows a blank (or sometimes garbled) screen instead of the image.

Due to this and other issues with Cairo, and the lack of an active
developer who could work on fixing them, should we perhaps say in NEWS
that --with-cairo is still experimental?

Thanks.

bug#22442: 25.0.50; --with-cairo does not display PNG on GNU/Linux

[Eli Zaretskii]

> From: Paul Eggert <eggert@cs.ucla.edu>
> Date: Sat, 23 Jan 2016 01:12:03 -0800
> Cc: Jan D <jan.h.d@swipnet.se>
> 
> I'll CC: this to Jan D. as he's expert in this area.

Alas, Jan is no longer working on Emacs.

bug#22442: 25.0.50; --with-cairo does not display PNG on GNU/Linux

[Paul Eggert]

Eli Zaretskii wrote:
> should we perhaps say in NEWS
> that --with-cairo is still experimental?

Sounds good, thanks, I added a couple of lines to that effect.

bug#22442: 25.0.50; --with-cairo does not display PNG on GNU/Linux

[Paul Eggert]

The bug appears to have been "fixed" by this commit:

http://git.savannah.gnu.org/cgit/emacs.git/commit/?h=emacs-25&id=190d365f90d741b09e817d9878afd256505e1944

I don't know how to explain this. Possibly Emacs tries to convert a pixel to 
RGB, this signals an error, and then Emacs falls back on something else that 
works. Hard to believe that this is the desired behavior, so I'll leave 
Bug#22442 open.

bug#22442: 25.0.50; --with-cairo does not display PNG on GNU/Linux

[Mark Oteiza]

Paul Eggert <eggert@cs.ucla.edu> writes:

> The bug appears to have been "fixed" by this commit:
>
> http://git.savannah.gnu.org/cgit/emacs.git/commit/?h=emacs-25&id=190d365f90d741b09e817d9878afd256505e1944
>
> I don't know how to explain this. Possibly Emacs tries to convert a
> pixel to RGB, this signals an error, and then Emacs falls back on
> something else that works. Hard to believe that this is the desired
> behavior, so I'll leave Bug#22442 open.

From ./configure --help it looks like emacs automatically picks up
imagemagick. This issue may be the same as reported in bug#21110

bug#22442: [PATCH] Fix compilation erorr when --enable-gcc-warnings passed

[Paul Eggert]

Alexander Kuleshov wrote:
> Even without it I can't reproduce this bug. I've checkout to the previous
> commit (035bd8159fe5bcea15eacc8a23ab54f4bc3b6f17) and configured and
> built emacs with:
>
> ./configure --enable-link-time-optimization --without-pop \
> --without-kerberos --without-kerberos5 --without-hesiod   \
> --with-sound=alsa --with-x-toolkit=gtk3 --with-xpm --with-jpeg \
> --with-tiff --with-gif --with-png --with-rsvg --with-cairo     \
> --with-xml2 --with-imagemagick --with-xft --without-libotf     \
> --with-xim --with-xaw3d --with-dbus --without-gconf            \
> --without-gsettings --without-selinux --with-gnutls --with-zlib \
> --with-modules --with-file-notification=inotify --without-makeinfo \
> --with-x && make
>
> Than I've opened image as you described in thehttp://bugs.gnu.org/22442
> and it works perfectly for me.

I tried the same scenario and I get a blank image on the screen. Perhaps it 
depends on the imagemagick or cairo version or whatever. I'm running Emacs on 
Fedora 23 x86-64, and displaying on Ubuntu 15.10 x86-64 via an ssh -X link.

If I use the current emacs-25 commit () but keep everything else the same, Emacs 
displays the binary text of the image with a message in the bottom line "Cannot 
display image: (This Emacs mishandles this image file type)", which is what I 
would expect from the current code. I don't know why I wasn't observing this 
behavior earlier, but at least now I know that Bug#22442 is still kicking.

As Mark says, Bug#22442 and Bug#21110 are probably the same bug, so I'll merge 
them. I can't recommend --with-cairo at this point.

bug#22442: 25.0.50; --with-cairo does not display PNG on GNU/Linux

[Dmitry Gutov]

On 23.01.2016 10:27, Paul Eggert wrote:
> wget 
> https://upload.wikimedia.org/wikipedia/commons/f/f5/All_palaeotemps.png
> emacs -Q All_palaeotemps.png

Seems to work fine now. Latest emacs-26 and master, with Cairo and 
ImageMagick.