On 2015-06-15 21:07+0100 Phil Rosenberg wrote: > I will have to try out git blame then. I imagined that something so well embedded would predate our git usage, but I guess our svn history was brought in too.
Yes, Hazen and I were careful to preserve our history back to the start in ~1992 which in retrospect was really a smart idea because of facilities like "git blame". > I guess you have as little idea as me then about how it is intended to work? Hi Phil: Actually, if "it" refers to the notcrossed function, I do think I understand exactly what it is supposed to do, and I tried to explain it on my previous post which you quoted and which I quote again below. I suspect you may have just read my first comment below and then quit. :-) Alan > > -----Original Message----- > From: "Alan W. Irwin" <ir...@beluga.phys.uvic.ca> > Sent: 15/06/2015 19:18 > To: "Phil Rosenberg" <p.d.rosenb...@gmail.com> > Cc: "Arjen Markus" <arjen.mar...@deltares.nl>; > "plplot-devel@lists.sourceforge.net" <plplot-devel@lists.sourceforge.net> > Subject: Re: [Plplot-devel] Bug in notcrossed() function of plfill.c > > Hi Phil: > > "git blame" is your friend for figuring out who authored what, and it > turns out I am virtually (except for a change by Hez) the sole author > of notcrossed, but IIRC, that built on top of what Arjen had done before > with (embedded logic rather than a function) > which built on top of what Maurice had done before.... > > > On 2015-06-15 11:10+0100 Phil Rosenberg wrote: > >> Hi Arjen >> >> I've just copied the code below as I don't just have time at the >> moment to sort a git patch (The plot I was making is for a >> presentation this afternoon!). The old code has been commented out >> with /* */ and my new code is directly above that from the #ifdef >> onwards. >> >> Basically I get that the variable factor will be zero for parallel >> lines and I get that there is a precision limit on that due to >> floating point rounding. However I don't understand how factor_NBCC >> works as a test. >> >> For the bug in question the inputs were xA1=20994, yA1=12219, >> xA2=4915, yA2=12561 xB1=20979, yB1=12219, xB2=20979, yB2=12221. >> Although perhaps the As and Bs were reversed, but the flagging should >> be identical. > > I (and presumably the rest here) were having a hard time figuring out > whether those two lines mathematically intersected or not. So I have > prepared a plot (see attached) that demonstrates that the two lines _do_ > mathematically intersect (where the red line is a clipped portion of the A > line > segment and the yellow line is the B line segment in totality.) > > Note however, that all the xA1, etc. values have a precision of +/- 2 > because of rounding issues so the purpose of the PL_NBCC = 2 fuzz > factor is to make sure that the result are not subject to such > rounding issues, i.e., notcrossed only returns 0 status if the > crossing would occur regardless of shifts of +/- 2 in each of the xA, > yA, xB, and yB coordinates. And of course, in this case when the > second line segment only has a length of 2, the crossing result is > never going to be definite so you will always get a non-zero return > code from notcrossed. > > If that explanation makes sense to you, but you still feel noncrossed > needs a fix, please send that in git format-patch form so I can > conveniently evaluate your proposed logic change. But I suspect the > noncrossed logic is fine, and the fix for the issue you found needs to > be made in another part of our code to deal correctly with non-zero > return values from notcrossed. > > By the way, I hope your presentation went well despite the > distraction introduced by this PLplot bug you discovered at > the last minute. > > 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 > __________________________ __________________________ 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 __________________________ ------------------------------------------------------------------------------ _______________________________________________ Plplot-devel mailing list Plplot-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/plplot-devel
