[NTG-context] Re: get measures as dimension in Lua

[Hans Hagen via ntg-context <ntg-context@ntg.nl>]

On 6/10/2024 7:08 AM, Max Chernoff wrote:
> Hi Hraban,
> 
> On Sun, 2024-06-09 at 22:12 +0200, Henning Hraban Ramm wrote:
>> when I define a measure on the TeX side, I used to get at the value in
>> Lua with tex.getdim, like:
>>
>> \definemeasure[Bleed][3mm]
>>
>> tex.getdimen("Bleed")
>>
>> But now I get "incorrect dimen name".
>> I need it as a dimension, since I do calculations with other dimensions
>> like "topspace".
>>
>> How should I do this correctly?
> 
> There doesn't appear to be any official interfaces to get the value of a
> measure from Lua, but the following should work okay:
> 
>      \definemeasure[mymeasure][10pt]
> 
>      \newdimen\mydimen \mydimen=10pt
> 
>      \definemeasure[measureexpr][1in + 27.73pt]
> 
>      \startluacode
>          -- Returns the unexpanded value of some variable in a namespace.
>          local function get_variable(namespace, variable)
>              -- -- Doesn't work since "measure" is defined as a "system namespace".
>              -- namespace = interfaces.getnamespace(namespace)
>              namespace = tokens.getters.macro("??" .. namespace)
>              return tokens.getters.macro(namespace .. variable)
>          end
> 
>          -- Gets the value of a measure and converts it to an integer in sp units.
>          local function get_measure(name)
>              return tex.sp(get_variable("measure", name))
>          end
> 
>          -- Gets the \dimexpr-evaluated value of a measure, in sp units.
>          local function get_measure_expr(name)
>              local namespace = tokens.getters.macro("??measure")
>              -- Undocumented, but seems to work as expected.
>              return tex.getdimensionvalue(namespace .. name)
>          end
> 
>          -- Print the values of the lengths.
>          print(("="):rep(80))
>          print("mymeasure:"  , get_measure("mymeasure")       )
>          print("mydimen:"    , tex.dimen["mydimen"]           )
>          print("measureexpr:", get_measure_expr("measureexpr"))
>          print(("="):rep(80))
>      \stopluacode
> 
>      \startTEXpage
>          \measure{mymeasure}
>          \the\mydimen
>          \measure{measureexpr}
>      \stopTEXpage
> 
> Thanks,
> -- Max

Indeed we can have:

     local namespace = tokens.getters.macro("??measure")

     function tex.getmeasure(name,asdimen)
         local value = tex.getdimensionvalue(namespace..name)
         if asdimen then
             return value .. "sp"
         else
             return value
         end

and when you want to avoid the namespace you can do:

     function tex.getmeasure(name,asdimen)
         local value = 
token.getexpansion("\\tointeger\\measured{"..name.."}")
         if asdimen then
             return value .. "sp"
         else
             return tonumber(value)
         end
     end

which is some 4 times slower. It'sindeed not documented (although there 
are some examples in accessors-001.tex) but it's in one of my todo's 
because I can use it in some places (there ar emopre such todo's) after 
which it will be discussed in one of the lowlelvel manuals

i'll add tex.getmeasure to the core (but a bit different)

Hans

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                                           Hans Hagen | PRAGMA ADE
               Ridderstraat 27 | 8061 GH Hasselt | The Netherlands
        tel: 038 477 53 69 | www.pragma-ade.nl | www.pragma-pod.nl
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