[cairo] Difference in Cairo and Qt4 adjacent polygon rendering

Hezekiah M. Carty hcarty at atmos.umd.edu
Fri May 1 09:04:39 PDT 2009

Cairo community,

The PLplot library (http://plplot.sf.net/) has had support for
Cairo-based output for some time, and overall the resulting output has
been quite satisfactory.  Qt4-based output was recently added and it
has highlighted some differences in the output results from the two
libraries.  There are details listed at the following page:


To put it simply, the various Cairo-based vector output formats (PDF,
PS, ...) leave seams between adjacent polygons when viewed with
Evince.  The Qt4-based outputs do not have these seams, even when
viewed with Evince (see the above page for an example).  Both the
Cairo and Qt4 rendering devices in PLplot are provided with the same
input data and, as far as I can tell, they follow similar paths to
produce the final result.

Can anyone here provide some insight on this issue?  I see some
previous discussions about similar trouble in the past (see [1]
below), but none of the suggested answers seem to work for all cases.
The fact that Qt4 is able to produce adjacent, non-square polygons
which render cleanly in non-Qt4 viewers seems to indicate that there
is some hope for this working in Cairo as well.

Please let me know if I can provide any further information to make
this request clearer or more useful.

Thank you for your time,


[1] - http://lists.cairographics.org/archives/cairo/2007-August/011268.html
(rendering a tight mesh)

Hezekiah M. Carty
Graduate Research Assistant
University of Maryland
Department of Atmospheric and Oceanic Science

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