[Libreoffice-bugs] [Bug 48342] New: FILESAFE skewX and skewY values are not matching the ODF 1.2 spec

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=48342

             Bug #: 48342
           Summary: FILESAFE skewX and skewY values are not matching the
                    ODF 1.2 spec
    Classification: Unclassified
           Product: LibreOffice
           Version: LibO 3.4.5 release
          Platform: Other
        OS/Version: All
            Status: UNCONFIRMED
          Severity: normal
          Priority: medium
         Component: Drawing
        AssignedTo: libreoffice-bugs at lists.freedesktop.org
        ReportedBy: kossebau at kde.org


The ODF 1.2 spec, section 19.228 draw:transform, defines the transform elements
"skewX" and "skewY" like this:
--- 8< ---
* skewX(<skew-angle>), specifies a skew transformation by
  <rotate-angle> degrees along the x-axis. 
* skewY(<skew-angle>), specifies a skew transformation by
  <rotate-angle> degrees along the y-axis. 
--- 8< ---
(the bad <rotate-angle>s have been reported to odf-comment ml by me). But
LibreOffice (Draw) stores for as skewX and skewY values the radian value, not
the degree one. Additionally the angle is given clockwise, not
counterclock-wise, like known from the same SVG elements.

Cmp. SVG 1.1 spec, section 7.6 The transform attribute:
--- 8< ---
skewX(<skew-angle>), which specifies a skew transformation along the x-axis.
--- 8< ---
and referenced from this, section 7.4 Coordinate system transformations:
--- 8< ---
* A skew transformation along the x-axis is equivalent to [...]
  [1 0 tan(a) 1 0 0], which has the effect of skewing X coordinates
  by angle a.
* A skew transformation along the y-axis is equivalent to [...]
  [1 tan(a) 0 1 0 0], which has the effect of skewing Y coordinates
  by angle a.
--- 8< ---

What to do about this?
a) Fix the loading/storing code and adapt to the spec, and have all ODF
consumers check the producer of the file and work around the wrong skewX/Y
value format?
b) Or be pragmatic and (try to) adapt the spec, given that LO and OOo have
created lots of documents with the wrong value format? No idea if that is
possible.

Either way, this needs to be fixed, if we want ODF to be a good document spec,
right? :)

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