Re: [boost] GGL Review

Subject: Re: [boost] GGL Review
From: Stefan Strasser (strasser_at_[hidden])
Date: 2009-11-16 13:16:11

Am Monday 16 November 2009 15:06:54 schrieb Brandon Kohn:
> Phil Endecott wrote:
> > The other controversial implementation issue is floating-point
> > robustness.  I'm still not clear what the position of this library is on
> > that.  Are we just given assurances that it seems to be robust in
> > real-world use, or is it believed that it actually is certainly robust?
> > I expected to see this discussed in the library documentation, but I
> > don't see anything - maybe I've missed it.  If it is "believed to be
> > robust in real-world use", it would be helpful to describe the possible
> > failure modes (e.g. segfault, runs forever, or just outputs the wrong
> > answer.)
>
> This is an issue that troubles me as well. I think that a floating point
> computational geometry library is possibly a first for Boost in that you
> often have heuristics rather than algorithms due to the fuzzy effect of
> using floating types in comparison predicates. One of the more useful
> features of the library (GGL) would of course be the boolean operations.
> The problem however is clearly going to be robustness.
> I have never 
> encountered a robust floating point boolean operation library in my 9
> years of working in the geometry domain.

I think the question of this review is not whether some algorithms in GGL have 
limitations, as long as they are documented, but if the concepts and 
algorithm/strategy interface is sufficient to allow the implementation of 
specialized algorithms. is this the case?
luke seems to be willing to integrate his Boost.Robust2DIntegerPolygon into 
GGL, but he also seems to have some concerns if he'll be able to do that 
using GGL's polygon representation. those should be addressed before GGL is 
accepted.

I was surprised that Polygon was accepted on a 6 to 4 vote, even though 
a "geometry core" library was right around the corner. I don't think people 
were aware of that during the review, iirc there was a lot of talk 
about "waiting" for a generic geometry library.

a future review process should make it possible to postpone or reschedule a 
review.