Hi Alan, Phil,

I tried Phil's example on Cygwin - PLplot as built on my installation does have 
a wxWidgets driver - but unfortunately that fails to run:


unknown error in plD_init_wxwidgets., aborting operation


unknown error in plD_bop_wxwidgets., aborting operation


unknown error in plD_line_wxwidgets., aborting operation


I then tried it with other drivers, but none demonstrated the sort of problem 
Phil mentions (I did not quite expect that to happen, but it never hurts to 



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> -----Original Message-----
> From: Alan W. Irwin [mailto:ir...@beluga.phys.uvic.ca]
> Sent: Tuesday, September 13, 2016 11:59 PM
> To: Phil Rosenberg
> Cc: Arjen Markus; plplot-devel@lists.sourceforge.net
> Subject: Re: [Plplot-devel] Bug in notcrossed() function of plfill.c
> On 2016-09-13 10:44+0100 Phil Rosenberg wrote:
> > On 13 September 2016 at 03:27, Alan W. Irwin <ir...@beluga.phys.uvic.ca>
> wrote:
> >> There is a substantial testing requirement for fill changes. The
> >> reason for that is we have had years of mostly good user experience
> >> with the present fill algorithm so I feel it is important that
> >> anybody that changes the fill algorithm in any further way needs to
> >> demonstrate with substantial testing that their change does not
> >> introduce fill regressions.
> >>
> >> I have alluded previously to automated fill regression testing (for
> >> all our standard examples that directly or indirectly use fill and
> >> all our file devices).  The core of the idea is to compare old and
> >> updated plot file results using imagemagick image differences.  Do
> >> you agree this general approach (supplemented by actually looking at the 
> >> "fill"
> >> subset of our examples for each of our interactive devices) is the
> >> way forward to insure that our further fill changes do not introduce
> >> more issues than they fix?
> >
> > I think this is a good idea in general to avoid all sorts of
> > regressions.
> Good.
> > Would it be easier to use the svg output and diff as the svg examples
> > can be built on all systems?
> Presumably you are aware of this already, but it should be mentioned that one
> issue with diff results is you cannot reliably compare results from two 
> different
> floating-point (FP) platforms because FP errors propagate to rounded results 
> on
> two such platforms in different ways.  So it is essential to calculate both 
> the old and
> revised fill result with exactly the same FP platform (i.e., you cannot store 
> plot
> results from one FP platform to compare with plot results from other FP 
> platforms).
> Another issue with using diff even for the same FP platform is any significant
> change in the fill code is likely to cause real differences, e.g., the 
> effective
> boundaries of the filled regions will be slightly different.  In fact, this 
> is a problem for
> all fully automated methods I can think of to test for fill regressions; 
> there are going
> to be large local changes (as boundaries change slightly) in results, but so 
> long as
> the final result looks OK (i.e., no obvious holes in any fill region and no 
> significantly
> overfilled regions) then the change does not count as a significant fill 
> regression.
> As a result of this concern, I am now thinking along the lines of an 
> interactive script
> (i.e., not completely automated so it will be tiring to use unless we are 
> careful with
> the selection of what images to compare).  At the heart of the script, 
> imagemagick
> would calculate the normalized difference of the old and modified image 
> results, and
> then simultanously display old, modified, and difference image results to help
> evaluate by visual means (as opposed to fully automated means) whether any
> significant regression has occurred.  (Of course, for those cases where the
> normalized difference image is zero, the script could simply skip the visual
> comparison to speed up the comparison).
> I have mentioned imagemagick here because I am reasonably familiar with it, 
> and it
> is one of the primary collections of software that is used on Unix to 
> manipulate and
> display images. However, you should also note that imagemagick is available 
> as a
> binary download on Windows (see <http://www.imagemagick.org/script/binary-
> releases.php>).
> Furthermore, even though it appears not to be specifically packaged for Cygwin
> such packaging has occurred for the MinGW-w64/MSYS2 platform so if the generic
> windows binary download does not work, there is that other Windows platform
> alternative to try as well.
> Alan
> __________________________
> Alan W. Irwin
> Astronomical research affiliation with Department of Physics and Astronomy,
> University of Victoria (astrowww.phys.uvic.ca).
> Programming affiliations with the FreeEOS equation-of-state implementation for
> stellar interiors (freeeos.sf.net); the Time Ephemerides project 
> (timeephem.sf.net);
> PLplot scientific plotting software package (plplot.sf.net); the libLASi 
> project
> (unifont.org/lasi); the Loads of Linux Links project (loll.sf.net); and the 
> Linux
> Brochure Project (lbproject.sf.net).
> __________________________
> Linux-powered Science
> __________________________

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