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

10 Jun 2024

      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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