[NTG-context] Metafun: how to draw a straight line past the end points

[Otared Kavian]

Thanks Aditya!
One can learn a lot with your answers !
In the Metafun manual I see enlonged but I did not know to use it.

Best regards: Otared

> On 9 Dec 2020, at 21:38, Aditya Mahajan <adityam at umich.edu> wrote:
> 
> On Wed, 9 Dec 2020, Otared Kavian wrote:
> 
>> Hi Aditya,
>> 
>> Thanks for the alternative method, which comes handy if one wishes to extend the straight line by a different amount at either end:
>> 
>> \starttext
>> \startMPcode
>>   z1 = (1cm,3cm) ;
>>   z2 = (5cm, 9cm) ;
>>   z3 = 1cm * dir(angle (z2 - z1)) shifted z2 ;
>>   z4 = -.5cm*dir(angle(z2 - z1)) shifted z1 ;
>>   draw z1 -- z3 ; 
>>   draw z4 -- z1 ;
>>   draw z1 -- z2 withcolor red ;
>> \stopMPcode
>> \stoptext
> 
> Or just redefine shortened to accept a pair! 
> 
> \startMPdefinitions
> primarydef p shortened d =
>    reverse ( ( reverse (p enlonged -xpart paired(d)) ) enlonged -ypart paired(d) )
> enddef ;
> \stopMPdefinitions
> 
> 
> 
> \starttext
> \startMPpage
> z1 = (1cm,3cm) ;
> z2 = (5cm, 9cm) ;
> draw (z1--z2) shortened (-1cm,-2cm)  withcolor blue ;
> draw (z1--z2) withcolor red ;
> 
> \stopMPpage
> \stoptext
> 
> Now that if you really want to shorten a path, then cutends works better than shortened
> 
> \startMPdefinitions
> primarydef p shortened d =
>    reverse ( ( reverse (p enlonged -xpart paired(d)) ) enlonged -ypart paired(d) )
> enddef ;
> \stopMPdefinitions
> 
> 
> \starttext
> \startMPpage
> z1 = (1cm,3cm) ;
> z2 = (5cm, 9cm) ;
> path p, q;
> p := z1 {up} .. {right} z2;
> q := p shifted (6cm, 0);
> 
> draw p withcolor red ;
> draw p shortened (1cm,2cm)  withcolor blue ;
> 
> draw q withcolor green ;
> draw q cutends (1cm,2cm)  withcolor blue ;
> 
> \stopMPpage
> \stoptext
> 
> Aditya
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