[NTG-context] Setting and measuring boxes TeX/Lua

[Jano Kula]

Hello again, Hans!

On Thu, 26 Nov 2020 at 09:18, Hans Hagen <j.hagen at xs4all.nl> wrote:

> (this mechanism is already kind of old, there are also other cheats
> possible)
>

Diving into functions and using context.stepwise() worked, until I've got
to: /cldf-stp.lua:48: bad argument #1 to 'resume' (thread expected) and
other errors. It was triar/error approach, not exactly knowing how
context.stepwise() works, and I was some more lua functions and iterations
before needing expansion.

Therefore I've changed the strategy (cannot give up):

   - Create named buffers with formatted content (and store measures)
   before they are needed.
   - When needed, use the reference to the buffer.

Tests looked promising. After \starttext buffers and measures are known
(both TeX & Lua). Also tested in functions, etc.
But inside the first \xmlsetup, they are not expanded anymore, they are
typeset (like \typebuffer).

   - How to have them expanded in \xmlsetup?
   - Is other mechanism better suited for storing typeset blocks than
   buffers (and will survive \xmlsetup)?
   - If none of them is possible, what are the *other **cheats *then?

Thanks,
Jano

MWE attached

% BUFFERS
\startluacode
-- fill buffers
for i=1,1000 do
    local content = "framed-" .. i
    context.startbuffer( { i } )
    context.StartBox()
    context.bold(i)context.par()
    context.color( { "red" }, content )
    context.StopBox()
    context.copy(false,0)
    context.stopbuffer()
    print(">>", i)
end
\stopluacode

\def\StartBox{\setbox0=\hbox\bgroup\framed[width=50mm,
                                           background=color,
                                           backgroundcolor=gray,
                                           frame=off,align={flushleft}]%
                                           \bgroup%
                                                \vbox\bgroup}
\def\StopBox{\egroup\egroup\egroup}% close vbox, framed, hbox

\def\MeasureBuffer[#1]{\setbox0\hbox{\getbuffer[#1]}%
                       ht: \the\ht0\par}


% XML
\startbuffer[doc]
<?xml version "1.0"?>
<document>
    <section>section</section>
    <section>section</section>
</document>
\stopbuffer

\startxmlsetups xml:name
    \xmlsetsetup{\xmldocument}{*}{-}
    \xmlsetsetup{\xmldocument}{document}{xml:name:*}
\stopxmlsetups

\xmlregistersetup{xml:name}

\startxmlsetups xml:name:document
    \Title{inside xml:name:document}
    \Title{TeX}
    \MeasureBuffer[333]
    \getbuffer[333]
    \Title{Lua}
    \startluacode
    context.MeasureBuffer({"444"})
    context.getbuffer({"444"})
    \stopluacode
\stopxmlsetups

\def\Title#1{\blank{\bf #1}\par}


\starttext

\Title{TeX}
\MeasureBuffer[111]
\getbuffer[111]

\Title{Lua}
\startluacode
context.MeasureBuffer({"222"})
context.getbuffer({"222"})
\stopluacode

\xmlprocessbuffer{xml:name}{doc}{}

\stoptext
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