On Sun, 14 Nov 2021, Aditya Mahajan via ntg-context wrote:

> 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.

Spoke too soon. Now straight lines don't work:

    \starttext

    \startMPcode
      newpath p;
      ahfactor := 5;
      p := origin .. (3cm,0);
      draw lmt_arrow
           [
             path = p, 
             location = "percentage",
             percentage = 50,
             alternative = "curved", 
           ]
           withpen pencircle scaled 1bp;
    \stopMPcode
    \stoptext


gives

metapost        > trace > This is MPLIB for LuaMetaTeX, version 3.11, running in scaled mode.
metapost        > trace > 
metapost        > trace > loading metafun for lmtx, including the plain 1.004 base definitions
metapost        > trace > 
metafun         > log >
metafun         > log > error: This can't happen (division by zero)
metafun         > log >
metapost        > trace > <macro> arrowhead -> <expr> -> begingroup.save.q,e,r;pair.e;e=point.length(EXPR2)of(EXPR2);path.q;q=gobble((EXPR2)shifted-e.cutafter.makepath(pencircle.scaled(2ahlength)))cuttings;if.ahvariant>0:path.r;r=gobble((EXPR2)shifted-e.cutafter.makepath(pencircle.scaled((1-ahdimple)*2ahlength)))cuttings;fi(q.rotated(ahangle/2)&reverse.q.rotated-(ahangle/2)if.ahvariant=1:--point0of.r--elseif.ahvariant=2:...point0of.r...else:--fi.cycle)shifted.e.endgroup
metapost        > trace > <to be read again> endgroup
metapost        > trace > <argument> pushparameters "arrow" ; save a ; string a ; a := getparameter "alternative" ; save l ; string l ; l := getparameter "location" ; save k ; string k ; k := getparameter "kind" ; save p ; path p ; p := getparameter "path" ; interim ahvariant := if a = "dimpled" : 1 elseif a = "curved" : 2 else : 0 fi ; interim ahdimple := getparameter "dimple" ; interim ahscale := getparameter "scale" ; interim ahangle := getparameter "angle" ; interim ahlength := getparameter "length" ; if not getparameter "headonly" : draw p ; fi ; if hasparameter "pen" : if hasoption "pen" "auto" : ahlength := ( getparameter "penscale" ) * boundingradius ( currentpen ) ; else : ahlength := ( getparameter "penscale" ) * boundingradius ( getparameterpen "pen" ) ; fi ; fi ; if k = "draw" : draw elseif k = "both" : filldraw else : fill fi if l = "middle" : midarrowhead p ; elseif l = "percentage" : arrowheadonpath ( p , ( getparameter "percentage" ) / 100 ) ; elseif l = "both" : arrowhead p ; if k = "draw" : draw elseif k = "both" : filldraw else : fill fi arrowhead reverse p ; else : arrowhead p ; fi ; popparameters ;
metapost        > trace > <macro> image -> (TEXT3)-> begingroup.save.currentpicture;picture.currentpicture;currentpicture:=nullpicture;(TEXT3);currentpicture.if.str(SUFFIX2)<>"":shifted(mfun_labxf(SUFFIX2)*lrcorner.p+mfun_labyf(SUFFIX2)*ulcorner.p+(1-mfun_labxf(SUFFIX2)-mfun_labyf(SUFFIX2))*llcorner.p)fi.endgroup
metapost        > trace > <macro> lmt_do_arrow -> -> begingroup.image(pushparameters"arrow";save.a;string.a;a:=getparameter"alternative";save.l;string.l;l:=getparameter"location";save.k;string.k;k:=getparameter"kind";save.p;path.p;p:=getparameter"path";interim.ahvariant:=if.a="dimpled":1elseif.a="curved":2else:0fi;interim.ahdimple:=getparameter"dimple";interim.ahscale:=getparameter"scale";interim.ahangle:=getparameter"angle";interim.ahlength:=getparameter"length";if.not.getparameter"headonly":draw.p;fi;if.hasparameter"pen":if.hasoption"pen""auto":ahlength:=(getparameter"penscale")*boundingradius(currentpen);else:ahlength:=(getparameter"penscale")*boundingradius(getparameterpen"pen");fi;fi;if.k="draw":draw.elseif.k="both":filldraw.else:fill.fi.if.l="middle":midarrowhead.p;elseif.l="percentage":arrowheadonpath(p,(getparameter"percentage")/100);elseif.l="both":arrowhead.p;if.k="draw":draw.elseif.k="both":filldraw.else:fill.fi.arrowhead.reverse.p;else:arrowhead.p;fi;popparameters;)endgroup
metapost        > trace > <scantokens> lmt_do_arrow
metafun         > log >
metafun         > log > I'm broken. Please show this to someone who can fix can fix it and try
again
metafun         > log >
metapost        > trace > <direct> newpath p; ahfactor := 5; p := origin .. (3cm,0); draw lmt_arrow [ path = p, location = "percentage", percentage = 50, alternative = "curved", ] withpen pencircle scaled 1bp; ;
metapost        > trace > 


Aditya