crash when taking a screenshot with libpng 1.5.6 and later

[Nasenbaer]

during network game I wanted to take a screenshot of my economy. The game crashed with:

terminate called after throwing an instance of '_wexception'
  what(): [/home/development/widelands/widelands/src/graphic/graphic.cc:749] Graphic::save_png: could not set png setjmp

libpng used is v. 1.5.7
I ran Widelands in opengl mode.

[Hans Joachim Desserud (hjd)]

Could you check if this is reproducible
* in single player games
* in local multiplayer games (just run two instances of WL on your computer)

I have not been able to reproduce this, but then again I haven't tried with a network game, so there might be some strange edge case somewhere.

[Nasenbaer (nasenbaer)]

happens everytime over here... even in sdl mode, so the problem must lie somewhere deep inside libpng. :-/

[Shevonar (shevonar)]

Recently someone changed some code to make it work with libpng 1.5.x. Most probably that is the reason for this bug.

[Borim (borim)]

I tested it with tinos windows build (revision 6153) and no problems, but I dont know which libpng is used there.

Also I tested it with my own build on linux and everything works fine. revision 6153, installed libpng: libpng12-0 version 1.2.46-3ubuntu

so the older libs seems to work.

[Hans Joachim Desserud (hjd)]

Also works fine with libpng 1.4.8-1 on Arch, fwiw. Looks like some 1.5.x issue...

[Jens Beyer (qcumber-some)]

The crash happens with libpng-1.5.6 and later.

With libpng-1.5.5 it works perfectly.

If you get rid of that strange dummy flush function in graphic.cc you get the error message

libpng error: internal write transform logic error

This message has been introduced in libpng-1.5.6.

I guess something in the vicinity of this error message is the real culprit.

[Nasenbaer (nasenbaer)]

From pngwrite.c :

   /* At this point the row_info pixel depth must match the 'transformed' depth,
    * which is also the output depth.
    */
   if (row_info.pixel_depth != png_ptr->pixel_depth ||
      row_info.pixel_depth != png_ptr->transformed_pixel_depth)
      png_error(png_ptr, "internal write transform logic error");

[Hans Joachim Desserud (hjd)]

Libpng 1.5.8 recently hit Arch, so now I'm able to reproduce it here as well.

[Hans Joachim Desserud (hjd)]

Seems like this also affects campaign maps! Bug 931141.

[SirVer (sirver)]

I have not investigated this, but campaign maps are the only maps that ship with images as extra data (the portraits of the speeking characters). Likely the loading code there is not valid for libpng 1.5. Also, the writing code (when savegames are written) will not be working anymore and need to be investigated further.

[SirVer (sirver)]

Released in build17-rc1.