[metapost] Curl in middle of path guarantees break?

[Shriramana Sharma]

Hello thanks for your reply which confirms my observation. However it
is curious that there appear to be *some* cases where a curl value
does not cause breakage of smoothness:

beginfig ( 1 ) ;
a = 100 ;
y1 = y2 = y3 = a ; y4 = y5 = y6 = 0 ;
x1 = x4 = 0 ; x2 = x5 = a ; x3 = x6 = 2a ;
draw z5 .. z4 .. z1 .. z3 .. z6 .. cycle ;
draw z5 .. z4 .. z1 { curl 0.61 } .. z3 .. z6 .. cycle ;
drawdot z1 withpen pencircle scaled 5 ;
endfig ;
end;

At z1 I have the predir and postdir values of:

(0.751863301783091,0.659319024017833)
(0.752311739754363,0.658807290660754)

... from Asymptote (ehm). Conceivably it could be tuned to an almost
perfect match. Apparently 0.61 is close to something like the
"natural" curl value for z1...

Anyhow, it seems clear that a curl is not generally part of a
specification of smoothness.


-- 
Shriramana Sharma