[Libreoffice-bugs] [Bug 90262] Some animated gif files do not loop infinitely when inserted in the presentation

[bugzilla-daemon at bugs.documentfoundation.org]

https://bugs.documentfoundation.org/show_bug.cgi?id=90262

--- Comment #8 from Alex H. <alexhfromnorthholland at gmail.com> ---
The CERN download links no longer work, but I can confirm that for the April
2015 attachment, Impress loops only once. (This is with a self-built
6.1.0.0.alpha0+ on Windows 10.)

However, I have reason to believe that that GIF does not comply with the
standard. I don't know how authoritative this is, but on
http://giflib.sourceforge.net/whatsinagif/bits_and_bytes.html it says:

  "The Netscape 2.0 looping block must appear immediately
  after the global color table of the logical screen
  descriptor."

That is not the case with this GIF; the Netscape extension appears much later.
In the reader (libo-core\vcl\source\filter\igif\gifread.cxx), there is this:

  if( aAnimation.Count() == 1 )
  {
    aAnimation.SetDisplaySizePixel( Size( nGlobalWidth, nGlobalHeight ) );
    aAnimation.SetLoopCount( nLoops );
  }

so what happens is that nLoops is processed only when the bitmap for the first
animation frame is created. For this GIF, nLoops is the default 1 at this
point, because the Netscape extension has not been seen yet.

I can confirm, on the other hand, that Firefox 57.0.3 does loop infinitely
here, so perhaps LibreOffice is wrong. Again, I'm not sure about what the
standard requires.

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