[Poppler-bugs] [Bug 93129] New: radial gradients rendering

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=93129

            Bug ID: 93129
           Summary: radial gradients rendering
           Product: poppler
           Version: unspecified
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: cairo backend
          Assignee: poppler-bugs at lists.freedesktop.org
          Reporter: michael.leitner at frm2.tum.de

Created attachment 120150
  --> https://bugs.freedesktop.org/attachment.cgi?id=120150&action=edit
uncompressed pdf with radial gradient

I notice that using evince/atril through a number of versions, corresponding to
libpoppler versions 0.18 through 0.33, the gradients as in the attached pdf do
not render properly. 
The pdf specifications allow radial gradients, that essentially consist of
linearly interpolating between a start and an end circle (with different
positions and radii). According to my incomplete tests, if start and end circle
have exactly the same radii, everything works correctly. Also, if the end
circle is smaller than the start circle and the distances of the centers of the
circles is not too large, it works. However, if the end circle is only slightly
smaller than the start circle and/or the distance is larger, it seems as if the
interpolation goes in the wrong direction: the position of the end circle is
flipped through the center of the start circle, its radius is larger (and not
smaller), and the colors used for drawing the intermediate circles are all the
start color of the gradient. In the attached example you can play around with
the last number on line 67, you will see that at precisely 50 the error occurs
(though this thresholds depends on the relative positions of the circles). 
Tests on a number of other pdf viewers not using poppler all render fine.
However, I am not sure whether poppler itself (via its invocation of cairo) or
cairo has the bug: using poppler-utils' pdftoppm works okay, while pdftocairo
renders incorrect pngs, and using it to convert pdf to pdf produces pdfs that
do not render correctly on any viewer.

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