[metapost] arrowhead weirdness

[Peter Rolf]

Oliver Buerschaper schrieb:
>> You only have half of 'ahangle' as angle in the subdividing right
>> triangles.
>>
>> ahlength := 2u/sin(.5ahangle);
> 
> Arrg … that's what I didn't take into account.
> 
>> But changing your source at this point still doesn't work here.
> 
> Neither does it work here … for the record: using mptopdf 1.3.2 (mpost
> 0.993) in both cases here's my original version:
> 
> ---
> beginfig(1);
>     u := 0.5cm;
>     path p;
>     p := origin--(5u,0);
>     ahlength := 2u/sind(ahangle);
>     pickup pencircle scaled u;
>     drawarrow p;
>     draw p yshifted u withpen pencircle scaled 0.1bp withcolor red;
>     draw p yshifted u/2 withpen pencircle scaled 0.1bp withcolor red;
>     undraw p withpen pencircle scaled 0.1bp;
>     undraw arrowhead p withpen pencircle scaled 0.1bp;
> endfig;
> 
> 
> end;
> ---
> 
> with this output
> 
> 
> 
> 
> and here's the one with the corrected angle:
> 
> ---
> beginfig(1);
>     u := 0.5cm;
>     path p;
>     p := origin--(5u,0);

p := origin--(10u,0);

>     ahlength := 2u/sind(ahangle/2);
>     pickup pencircle scaled u;
>     drawarrow p;
>     draw p yshifted u withpen pencircle scaled 0.1bp withcolor red;
>     draw p yshifted u/2 withpen pencircle scaled 0.1bp withcolor red;

draw p yshifted 1.5u withpen pencircle scaled 0.1bp withcolor red;
draw p yshifted 2u withpen pencircle scaled 0.1bp withcolor red;

>     undraw p withpen pencircle scaled 0.1bp;
>     undraw arrowhead p withpen pencircle scaled 0.1bp;
> endfig;
> 
> 
> end;
> ---
> 
> Now this I don't understand at all:
> 
> 
> 
> 
> By the way, changing ahangle/2 into 0.5ahangle doesn't help either.
> 
> Any suggestions?
>


Look at the (dizzying) definition of arrowhead. It seems that the
intersection point can not be found correctly in case of a very small
path p.

Best wishes, Peter