Re: MP: problem connecting paths.

[Fabrice L via ntg-context <ntg-context@ntg.nl>]

Dear Mikael,

> Le 20 déc. 2021 à 12:14, Mikael Sundqvist <mickep@gmail.com> a écrit :
> 
> Hi,
> 
> I will try again. What if you do
> 
> newcircleA := newcircleA scrutinized 2;
> 
> after your definition of newcircleA?

Once I understood I had to compile with LMTX, this works like magic ! I spent hours to find a solution… but here is a solution ! 
Thanks a lot ! 
> 
> /Mikael

Fabrice.
> 
> 
> On Mon, Dec 20, 2021 at 3:45 PM Fabrice L <fabrice.alpha@gmail.com> wrote:
>> 
>> Thanks Mikael,
>> 
>> Le 20 déc. 2021 à 02:21, Mikael Sundqvist via ntg-context <ntg-context@ntg.nl> a écrit :
>> 
>> Hi,
>> 
>> would it be an option for you to do
>> 
>> newcircleA := circleA cutbefore P1 cutafter P2 -- cycle ;
>> 
>> In that case you avoid extra points.
>> 
>> 
>> You are right, in this simple case, your solution avoid the problem, and is applicable in some of my cases (I have to rethink the code). Thanks for the proposition !
>> But in others cases this is not possible (I think). Imagine I wish to do a « partial moon » from the two circles in my minimal example (see bottom right of the attached pdf):
>> 
>> 
>> newcircleA := circleA cutbefore P1 cutafter P2 .. reverse(circleB cutbefore P1 cutafter P2)  .. cycle;
>> 
>> I need 10 points to define the shape, but as my connections are duplicated, I have 12 points.
>> 
>> The solution (I thought) would be to use the « & » operator :
>> newcircleA := circleA cutbefore P1 cutafter P2 & reverse(circleB cutbefore P1 cutafter P2) & cycle ;
>> 
>> But this does not work (same reason as before: "! Paths don't touch; `&' will be changed to `..'.").
>> 
>> The compete minimal code (if somebody wants to plus with it) is here :
>> 
>> % ———————————————————————
>> \startMPpage
>> path circleA , circleB ;
>> pair P[];
>> defaultscale := 0.4 ;
>> 
>> circleA := fullcircle scaled 1in randomized 3 ;
>> circleB := fullcircle scaled 1in randomized 3 shifted(0.3in,0.3in) ;
>> 
>> draw circleA withcolor blue ;
>> draw circleB withcolor red ;
>> 
>> P[1] := circleA intersectionpoint circleB ;
>> dotlabel.lft("$P_1$",P[1]) ;
>> dotlabel.rt("$\blue\tfx P_0^A$",point 0 of circleA) ;
>> P[2] := reverse(circleA) intersectionpoint circleB ;
>> dotlabel.rt("$P_2$",P[2]) ;
>> dotlabel.rt("$\red\tfx P_0^B$",point 0 of circleB) ;
>> 
>> path newcircleA , newcircleB ;
>> % newcircleA := (circleA cutbefore P1 cutafter P2 ) & (P2 -- P1) & cycle  ;
>> % previous line gives an error :
>> % "! Paths don't touch; `&' will be changed to `..'."
>> newcircleA := circleA cutbefore P1 cutafter P2 -- (P2 -- P1) -- cycle  ;
>> newcircleA := newcircleA xshifted 2in ;
>> draw newcircleA  withcolor darkgreen ;
>> 
>> newcircleB := (circleB cutafter P1)  -- (P1 -- P2) -- (circleB cutbefore P2 ) & cycle ;
>> newcircleB := newcircleB xshifted 2in ;
>> draw newcircleB withcolor black ;
>> drawpoints newcircleA ; drawpointlabels newcircleA ;
>> 
>> % Mikael solution
>> newcircleA := circleA cutbefore P1 cutafter P2 -- cycle ;
>> newcircleA := newcircleA yshifted -1.5in ;
>> draw newcircleA  withcolor darkgreen ;
>> drawpoints newcircleA ; drawpointlabels newcircleA ;
>> 
>> % partial moon
>> newcircleA := circleA cutbefore P1 cutafter P2
>> .. reverse(circleB cutbefore P1 cutafter P2) .. cycle;
>> % & (reverse(circleB) cutbefore P2 cutafter P1) & cycle;
>> newcircleA := newcircleA shifted(2in,-1.5in) ;
>> draw newcircleA  withcolor magenta ;
>> drawpoints newcircleA ; drawpointlabels newcircleA ;
>> 
>> \stopMPpage
>> % ———————————————————————
>> 
>> Thanks for any help !
>> Fabrice.
>> 
>> 
>> /Mikael
>> 
>> On Mon, Dec 20, 2021 at 5:30 AM Fabrice L via ntg-context
>> <ntg-context@ntg.nl> wrote:
>> 
>> 
>> Dear list,
>> 
>> I have a problem connecting path with the operator « & » (page 16 Metafun manual). The problem is illustrated by the code (and the joined PDF) which follows.
>> 
>> I draw random cycled  forms (left part of the figure) and when they interact, they are modified to « fit together » (right part of the figure) . When building these new forms, I connect paths (usually two or three depending on position 0 of the path); the last point a path is the same as the first point of the next path ; for exemple, to modify the blue circle, named « circleA », I take the circle A from P1 to P2, then a segment from P2 to P1 and cycle to have a closed path. So I should be able to do :
>> 
>> newcircleA := circleA cutbefore P1 cutafter P2 & (P2 -- P1) & cycle  ;
>> 
>> The « & » operator is supposed to work (if I understand correctly) in this case, but I have this error message :
>> 
>> "! Paths don't touch; `&' will be changed to `..’."
>> 
>> Which I do not understand since the paths « touch ». There was a similar question last year, without a clear answer («
>> METAPOST subpath rounding issue »https://www.mail-archive.com/ntg-context@ntg.nl/msg94294.html).
>> 
>> A solution is to ignore the repeating points :
>> newcircleA := circleA cutbefore P1 cutafter P2 -- (P2 -- P1) -- cycle  ;
>> but this new shape has 9 points instead of 7. The problem is that I do these operations a number of times, and the length of a path (in the number of points) is increasing and cause trouble when I look for intersections with others shapes.
>> 
>> Here is the MWE:
>> 
>> \startMPpage
>> path circleA , circleB ;
>> pair P[];
>> 
>> circleA := fullcircle scaled 1in randomized 3 ;
>> circleB := fullcircle scaled 1in randomized 3 shifted(0.3in,0.3in) ;
>> 
>> draw circleA withcolor blue ;
>> draw circleB withcolor red ;
>> 
>> P[1] := circleA intersectionpoint circleB ;
>> dotlabel.lft("$P_1$",P[1]) ;
>> dotlabel.rt("$\blue\tfx P_0^A$",point 0 of circleA) ;
>> P[2] := reverse(circleA) intersectionpoint circleB ;
>> dotlabel.rt("$P_2$",P[2]) ;
>> dotlabel.rt("$\red\tfx P_0^B$",point 0 of circleB) ;
>> 
>> path newcircleA , newcircleB ;
>> % newcircleA := circleA cutbefore P1 cutafter P2 & (P2 -- P1) & cycle  ;
>> % previous line gives an error :
>> % "! Paths don't touch; `&' will be changed to `..'."
>> newcircleA := circleA cutbefore P1 cutafter P2 -- (P2 -- P1) -- cycle  ;
>> newcircleA := newcircleA xshifted 2in ;
>> draw newcircleA  withcolor darkgreen ;
>> 
>> newcircleB := (circleB cutafter P1)  -- (P1 -- P2) -- (circleB cutbefore P2 ) & cycle ;
>> newcircleB := newcircleB xshifted 2in ;
>> draw newcircleB withcolor black ;
>> drawpoints newcircleA ; drawpointlabels newcircleA ;
>> 
>> \stopMPpage
>> 
>> 
>> 
>> 
>> I would appreciate any help ! Thanks !
>> Fabrice.
>> 
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