[metapost] luamplib fails to process string with "char 0"

[Hans Hagen]

On 7/29/2021 1:16 PM, Toby Thurston wrote:
> consider the following MP program, which is trying to print the Greek 
> alphabet in the default font using the default TeX encoding, which puts 
> Gamma at position zero
> 
> prologues := 3;
> outputtemplate := "%j%c.eps";
> 
> beginfig(1);
> string AB;
> 
> AB = ("AB" & char 0 & char 1 & "EZH" & char 2 & "IK"
>            & char 3 & "MNO" & char 4 & char 5 & "P"
>            & char 6 & "T"   & char 7 & char 8 & "X"
>            & char 9 & char 10);
> 
> draw AB infont "cmmi10" shifted 10 up;
> draw AB infont "eurm10" shifted 10 down;
> draw bbox currentpicture;
> endfig;
> end.
> 
> 
> if I run this through `mpost`  (MetaPost 2.00 (TeX Live 2021) (kpathsea 
> version 6.3.3)) I get two lines with the expected 24 Greek characters in 
> each, with a box around them.
> 
> But if I change the program to wrap it up with luamplib like this:
> 
> \documentclass{standalone}
> \usepackage{luamplib}
> \begin{document}
> \begin{mplibcode}
> beginfig(1);
> string AB;
> AB = ("AB" & char 0 & char 1 & "EZH" & char 2 & "IK"
>            & char 3 & "MNO" & char 4 & char 5 & "P"
>            & char 6 & "T"   & char 7 & char 8 & "X"
>            & char 9 & char 10);
> draw AB infont "cmmi10" shifted 10 up;
> draw AB infont "eurm10" shifted 10 down;
> draw bbox currentpicture;
> endfig;
> \end{mplibcode}
> \end{document}
> 
> and run it through `lualatex` (This is LuaHBTeX, Version 1.13.0 (TeX 
> Live 2021) then all I get are the first two characters in each string. 
>   In other words it stops at char 0 (Gamma).
> Oddly the bbox is still large enough for the whole string…
> 
> any thoughts?
just avoid 0 chars (\nul) in a luatex related workflow ... data gets 
passed through c string handling so it can indicate an end of string; 
using "infont' is anyway worse that btex ... etex where you can use \char 0

Hans


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