# [NTG-context] runtime problem with metafun() code

Hans Hagen pragma at wxs.nl
Mon Jan 27 13:12:01 CET 2014

On 1/25/2014 1:58 PM, Peter Rolf wrote:
> Am 25.01.2014 01:07, schrieb Hans Hagen:
>> On 1/24/2014 7:41 PM, Peter Rolf wrote:
>>> Am 24.01.2014 14:45, schrieb Hans Hagen:
>>>> On 1/24/2014 1:35 PM, Peter Rolf wrote:
>>>>> Hi,
>>>>>
>>>>> I try to create a Metapost path in lua and it works so far for the
>>>>> attached example. But a call of that function from another lua function
>>>>> sadly fails (no path visible after call). The code seems to be executed
>>>>> later (the output from 'show pid;' appears somewhere later in the log).
>>>>>
>>>>> How can I ensure that the code is executed at runtime?
>>>>
>>>> I don't understand the issue but isn't there a
>>>>
>>>>       metafun("draw p;")
>>>>
>>>> missing then?
>>>>
>>> Setting the bounding box has the same effect, as drawing something.
>>> Both methods avoid that the emtpy graphic is ignored by ConTeXt.
>>>
>>> Anyhow, the MP path is not available in metapost.variables after the
>>> function call. If there is no other way I have to call the function from
>>> the TeX side (like in the attached example). Will look into that
>>> tomorrow.
>>
>> %D We also provide an outputless run:
>>
>> \unexpanded\def\startMPcalculation
>>
> I tried that command, but couldn't get it to work on the lua side.
>
> The first pure MP line after context.startMPcalculation() raises a lua
> error and a combination with metafun() is also not working. So how to
> use this in lua?
>
>
> Anyhow, the problem is the execution time of the MP graphic. I changed
> the attached example a bit, so that you can see it.
> The inspect() in drops.foo() gives an empty table, while the second
> inspect on the TeX side shows the path "drops:foo".
>
> I need the path right after the call (it needs to be adapted to IM
> afterwards; mainly scaling and shifting). Is there a way to "force" the
> execution of the graphic without switching back to the TeX side?

context(function() inspect(metapost.variables) end) -- empty here
end

or

function drops.bar()
inspect(metapost.variables)
end

context(drops.bar) -- empty here
end

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