[metapost] MetaFont: Unexpected behavior of intersections times

luigi scarso luigi.scarso at gmail.com
Sat Apr 2 13:38:36 CEST 2011


The following metafont code

%%%%%%%%%
batchmode;
message "p1:=(33.09007380767,-33.8895224139) .. controls
(33.370612519531,-33.905534970703) and (33.65115125,-33.9215475) ..
(33.93169,-33.93756);";
path p[];
p1:=(33.09007380767,-33.8895224139) .. controls
(33.370612519531,-33.905534970703) and (33.65115125,-33.9215475) ..
(33.93169,-33.93756);

p2:=(38.1058,-34.00049) .. controls (36.39993,-34.00049) and
(34.44913,-34.0004125) .. (32.79190125,-33.86743875);
numeric t,u; (t,u) = p1 intersectiontimes p2;
show t,u;
message "" ;


message "p1:=(33.09007380767,-33.8895224139);";
p1:=(33.09007380767,-33.8895224139) ;
p2:=(38.1058,-34.00049) .. controls (36.39993,-34.00049) and
(34.44913,-34.0004125) .. (32.79190125,-33.86743875);
numeric t,u; (t,u) = p1 intersectiontimes p2;
show t,u;
message "" ;

message "p1:=(33.93169,-33.93756);";
p1:=(33.93169,-33.93756);
p2:=(38.1058,-34.00049) .. controls (36.39993,-34.00049) and
(34.44913,-34.0004125) .. (32.79190125,-33.86743875);
numeric t,u; (t,u) = p1 intersectiontimes p2;
show t,u;
message "" ;

bye.
%%%%%%%%%
gives as output

This is METAFONT, Version 2.718281 (TeX Live 2009/Debian) (base=mf
2011.1.30)  2 APR 2011 13:33
**a
(a.mf
p1:=(33.09007380767,-33.8895224139) .. controls (33.370612519531,-33.9055349707
03) and (33.65115125,-33.9215475) .. (33.93169,-33.93756);
>> -1
>> -1
p1:=(33.09007380767,-33.8895224139);
>> 0
>> 0.94043
p1:=(33.93169,-33.93756);
>> -1
>> -1
 )

Is it corrected ?
Given that p1 is inside p2, perhaps in this case intersectiontimes
correctly doesn't find any  intersection --- there are infinite
intersections. But I'm a bit surprised .


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