[Bug 1834314] [NEW] Tk: bad output when converting image to PNG

[Christopher A. Chavez]

Public bug reported:

Ubuntu 16.04 (amd64)
Tk 8.6.5 (tk8.6 8.6.5-1)


The PNG support in Tk causes bad PNG files to be written.

Note that the TkImg extension (libtk-img) is NOT what exhibits this
issue.

This issue was noticed as part of a test suite for Tcl::pTk, a Perl
Tcl/Tk wrapper: https://rt.cpan.org/Ticket/Display.html?id=128803

I ran a Lubuntu 16.04.6 amd64 live CD, installed tk8.6 8.6.5-1, and
could reproduce the reporter's issue. Using a Tcl/Tk example, I
confirmed the issue was in Tcl/Tk rather than the Perl wrapper. However,
I could not reproduce this issue on 18.04 i386 (tk8.6 8.6.8-4) nor 19.04
amd64 (tk8.6 8.6.9-2), so I suspect this issue has been resolved by the
newer upstream releases of Tk 8.6 in more recent Ubuntu versions.

It turns out that the release notes for Tcl/Tk 8.6.7 mention a "PNG
writing" issue having been addressed: see
https://sourceforge.net/projects/tcl/files/Tcl/8.6.7/tcltk-release-
notes-8.6.7.txt/view . I believe this is the corresponding upstream Tk
ticket: https://core.tcl-lang.org/tk/tktview/10f2e7872b . That issue
turned out to be caused Tcl, rather than Tk; ticket: https://core.tcl-
lang.org/tcl/tktview/b26e38a3e4 , check-in: https://core.tcl-
lang.org/tcl/info/e5b3cf7279 . Even if this is indeed the issue I've
observed, I am not sure if it is practical to patch this issue, or to
backport a later Tcl/Tk release to 16.04.

Below is a test script to reproduce the issue (run using tclsh8.6 or
wish8.6). Xcamel.gif can be obtained from https://github.com/eserte
/perl-tk/raw/master/Tk/Xcamel.gif or likely can be substituted.


package require Tk
# not doing `package require Img`--use PNG support included in Tk

image create photo icon -file "Xcamel.gif" -format gif
button .b -image icon
pack .b

icon write "Xcamel.png" -format png

# the following line will fail with "unfinalized data stream in PNG data"
image create photo icon2 -file "Xcamel.png" -format png
button .b2 -image icon2
pack .b2

** Affects: tk8.6 (Ubuntu)
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1834314

Title:
  Tk: bad output when converting image to PNG

Status in tk8.6 package in Ubuntu:
  New

Bug description:
  Ubuntu 16.04 (amd64)
  Tk 8.6.5 (tk8.6 8.6.5-1)

  
  The PNG support in Tk causes bad PNG files to be written.

  Note that the TkImg extension (libtk-img) is NOT what exhibits this
  issue.

  This issue was noticed as part of a test suite for Tcl::pTk, a Perl
  Tcl/Tk wrapper: https://rt.cpan.org/Ticket/Display.html?id=128803

  I ran a Lubuntu 16.04.6 amd64 live CD, installed tk8.6 8.6.5-1, and
  could reproduce the reporter's issue. Using a Tcl/Tk example, I
  confirmed the issue was in Tcl/Tk rather than the Perl wrapper.
  However, I could not reproduce this issue on 18.04 i386 (tk8.6
  8.6.8-4) nor 19.04 amd64 (tk8.6 8.6.9-2), so I suspect this issue has
  been resolved by the newer upstream releases of Tk 8.6 in more recent
  Ubuntu versions.

  It turns out that the release notes for Tcl/Tk 8.6.7 mention a "PNG
  writing" issue having been addressed: see
  https://sourceforge.net/projects/tcl/files/Tcl/8.6.7/tcltk-release-
  notes-8.6.7.txt/view . I believe this is the corresponding upstream Tk
  ticket: https://core.tcl-lang.org/tk/tktview/10f2e7872b . That issue
  turned out to be caused Tcl, rather than Tk; ticket: https://core.tcl-
  lang.org/tcl/tktview/b26e38a3e4 , check-in: https://core.tcl-
  lang.org/tcl/info/e5b3cf7279 . Even if this is indeed the issue I've
  observed, I am not sure if it is practical to patch this issue, or to
  backport a later Tcl/Tk release to 16.04.

  Below is a test script to reproduce the issue (run using tclsh8.6 or
  wish8.6). Xcamel.gif can be obtained from https://github.com/eserte
  /perl-tk/raw/master/Tk/Xcamel.gif or likely can be substituted.


  package require Tk
  # not doing `package require Img`--use PNG support included in Tk

  image create photo icon -file "Xcamel.gif" -format gif
  button .b -image icon
  pack .b

  icon write "Xcamel.png" -format png

  # the following line will fail with "unfinalized data stream in PNG data"
  image create photo icon2 -file "Xcamel.png" -format png
  button .b2 -image icon2
  pack .b2

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