[cairo] Different output between Linux and Mac

Surith cairo at surith.net
Sun Mar 15 22:43:50 PDT 2009

I don't know enough to explain the differences, but you might want to
send the mailing list the pixman versions too.

On Sun, Mar 15, 2009 at 10:19 PM, Neil Mayhew
<neil_mayhew at users.sourceforge.net> wrote:
> Hi,
> I have a program that outputs to SVG, PDF, PS, or PNG. It is written using
> cairomm. The same sources build on both Linux and Mac OS X. However, I get
> slightly different outputs on the two platforms. I have dumped the
> coordinates I am giving to move_to and line_to, and these are identical on
> the two platforms (to six significant digits, at least, the default
> precision for std::cout). Also, both platforms are using Intel CPUs.
> However, the cairo output is not identical.
> It's easiest to compare the SVG outputs, using diff/meld, but the PS output
> exhibits the same differences. Also the PNG outputs are slightly different:
> I used ImageMagick to subtract one image from the other and viewed the
> resulting image which was all black except for a couple of noticeable lines
> in the same places that I am seeing differences in the SVG/PS output.
> The SVG/PS differences are localized to an endpoint of just one line segment
> in the middle of two longer paths. Everything else is the same, down to the
> last digit. However, although these differences are not visually noticeable
> (they are in the 4th decimal place) they are causing me a problem with my
> regression tests. I have checked sample output into my source repo from
> Linux, but when I am developing on Mac I get different output so I can't
> check for regressions without manually inspecting the output.
> Am I correct in thinking that I should get identical output on the different
> platforms? If not, why would almost all the output be the same except for
> just a few places? I noticed that the coordinates I dumped from my code and
> the coordinates in the SVG are the same up to the 3rd or 4th digit, but are
> completely different thereafter.
> The package version of cairo on my Linux system (Ubuntu Jaunty alpha) is
> 1.8.6-1ubuntu2. On Mac I am using MacPorts and the version is "1.8.6,
> Revision 4". I can send sample output and code if desired.
> Thanks for any help offered.
> --Neil
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