Re: [NTG-context] METAPOST: How do I get this 'max' cutafter to work?

21 Apr 2020


      On 4/21/2020 1:29 PM, Gerben Wierda wrote:
...
I have these two paths, but cutting doesn’t work because the path to be 
cut takes the wrong intersection regardless of how I direct the path to 
be cut after (reverse or not).
The path to cut after is a triangle with the base horizontal and the 
path to cut is a vertical line. The top of the triangle is the endpoint 
of the line and is selected as intersection by cutafter. This happens 
also if I reverse the triangle path, strangely enough. I have an 
alternative cutting algorithm, but that cuts as long as the length of 
cuttings is not 0, which is the case at the top too, so it won’t cut 
further.
I need a reliable algorithm to make a ‘maximum cutafter’. What might be 
a good approach?
G
path arrowHead;
arrowHead :=
   (542,-77.000186920166016)..controls 
(545.33333333333337,-77.000186920166016) and 
(548.66666666666663,-77.000186920166016)
   ..(552,-77.000186920166016)..controls 
(550.33333333333337,-73.666853586832687)
   and (548.66666666666663,-70.333520253499344)
   ..(547,-67.000186920166016)..controls 
(545.33333333333337,-70.333520253499344)
   and (543.66666666666663,-73.666853586832687)
   ..cycle;
path connection;
connection :=
   (420.00004959106445,-367)..controls (420.66670256708773,-367) and 
(421.333355543111,-367)
   ..(422.00000851913427,-367)..controls (425.33333917170194,-367) and 
(428.6666698242696,-367)
   ..(432.00000047683727,-367)..controls (442.00000015894574,-367) and 
(451.99999984105426,-367)
   ..(461.99999952316273,-367)..controls (464.76142345324098,-367) and 
(467,-364.76142382108867)
   ..(467,-361.99999997656772)..controls (467,-293.99999999218926) and 
(467,-226.00000000781074)
   ..(467,-158.00000002343228)..controls (467,-155.23857623850762) and 
(469.23857634039018,-153)
   ..(472.00000014901161,-153)..controls (495.33333338300389,-153) and 
(518.66666661699617,-153)
   ..(541.99999985098839,-153)..controls (544.76142368504975,-153) and 
(547,-150.76142367339932)
   ..(547,-147.99999983662815)..controls (547,-125.99999994554271) and 
(547,-104.00000005445727)
   ..(547,-82.000000163371837)..controls (547,-78.666668047283764) and 
(547,-75.333335931195691)
   ..(547,-72.000003815107618)..controls (547,-70.333398183460417) and 
(547,-68.666792551813217)
   ..(547,-67.000186920166016);
show connection cutafter arrowHead;
show connection cutafter (reverse arrowHead);
\startMPpage[instance=doublefun]

path arrowHead;
arrowHead :=
     (542,-77.000186920166016)..controls 
(545.33333333333337,-77.000186920166016) and
     (548.66666666666663,-77.000186920166016) 
..(552,-77.000186920166016)..controls
     (550.33333333333337,-73.666853586832687) and
     (548.66666666666663,-70.333520253499344) 
..(547,-67.000186920166016)..controls
     (545.33333333333337,-70.333520253499344) and
     (543.66666666666663,-73.666853586832687) ..cycle;

path connection;
connection :=
   (420.00004959106445,-367)..controls (420.66670256708773,-367) and
   (421.333355543111,-367) ..(422.00000851913427,-367)..controls
   (425.33333917170194,-367) and (428.6666698242696,-367)
   ..(432.00000047683727,-367)..controls (442.00000015894574,-367) and
   (451.99999984105426,-367) ..(461.99999952316273,-367)..controls
   (464.76142345324098,-367) and (467,-364.76142382108867)
   ..(467,-361.99999997656772)..controls (467,-293.99999999218926) and
   (467,-226.00000000781074) ..(467,-158.00000002343228)..controls
   (467,-155.23857623850762) and (469.23857634039018,-153)
   ..(472.00000014901161,-153)..controls (495.33333338300389,-153) and
   (518.66666661699617,-153) ..(541.99999985098839,-153)..controls
   (544.76142368504975,-153) and (547,-150.76142367339932)
   ..(547,-147.99999983662815)..controls (547,-125.99999994554271) and
   (547,-104.00000005445727) ..(547,-82.000000163371837)..controls
   (547,-78.666668047283764) and (547,-75.333335931195691)
   ..(547,-72.000003815107618)..controls (547,-70.333398183460417) and
   (547,-68.666792551813217) ..(547,-67.000186920166016);

pair a ; a := arrowHead intersection_point connection ;

draw connection cutafter arrowHead           withcolor red   withpen 
pencircle scaled 2mm ;
draw connection cutafter (reverse arrowHead) withcolor green withpen 
pencircle scaled 1mm ;

draw arrowHead;

draw a withcolor blue withpen pencircle scaled 3mm ;

currentpicture := currentpicture shifted (-bbwidth(currentpicture), 0) ;

draw connection cutafter a ;

draw arrowHead;


\stopMPpage

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