Re: Metafun: how to draw a straight line past the end points

[Aditya Mahajan <adityam@umich.edu>]

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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