Re: Bug in lmt_arrow

[Aditya Mahajan via ntg-context <ntg-context@ntg.nl>]

On Sun, 14 Nov 2021, Hans Hagen wrote:

> On 11/14/2021 4:33 AM, Aditya Mahajan via ntg-context wrote:
> > Hi,
> > 
> > There is a bug in lmt_arrow. If given a "non-cycle" path, lmt_arrow
> > completes the cycle.
> > 
> >      \starttext
> > 
> >      \startMPcode
> >        newpath p;
> >        ahfactor := 5;
> >        p := origin .. (1cm, 1cm) .. (2cm, 0);
> >        draw lmt_arrow
> >             [
> >               path = p,
> >               location = "percentage",
> >               percentage = 50,
> >               alternative = "curved",
> >             ]
> >             withpen pencircle scaled 1bp;
> >      \stopMPcode
> >      \stoptext
> > 
> > With 2021.11.11, I get the attached file. Note that lmt_arrow has drawn the
> > "cycle" version of the path, even though p does not have a cycle.
> > 
> > I have looked at the code and cannot figure out why this is happening.
> 
> it happens in the 'direct' variant (metapost.registerdirect) where a boolean
> is passed as signal and that boolean then is also picked up by the (shared)
> path injector as (old school) signal that a path is closed while it should
> instead consutl the closed field in a path table (sounds more complex than it
> is)
> 
> so in the end it is a nasty side effect of the fast inject code path (shared
> function with different stack values; i'll probably have to ditch a "low level
> backward compatibility feature no one uses anyway" some day)
> 
> i uploaded a fix that you can test when the bins are compiled at
> 
> 	https://build.contextgarden.net/#/waterfall?tags=c.luametatex
> 
> new bins then in:
> 
> 	https://dl.contextgarden.net/build/luametatex/
> 
> (fyi: in the mp code you see that the path p is 'get' from the lua end where
> it got passed to by parameter)

Thanks! Works perfectly here.

> (interesting that it didn't show up sooner, maybe most users have closed paths
> and/or most lmt_ features used closed paths)

I was reusing two year old code and took me a while to figure out why the output was suddenly wrong. 

Aditya
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