# [NTG-context] passvariable(); path problem

Peter Rolf indiego at gmx.net
Sun Oct 6 15:05:07 CEST 2013

```Am 06.10.2013 00:37, schrieb Hans Hagen:
> On 10/5/2013 5:52 PM, Peter Rolf wrote:
>> I played around with it, but I have problems to understand the format of
>> the returned path.
>>
>> Example:
>> % --------
>> \setuppagenumber[state=stop]
>>
>> \starttext
>> \nopdfcompression
>>
>> \startMPpage
>>    path p;
>>    p:= (20,20){up} .. {down}(200,100);
>>    passvariable("path",p);
>>    draw p ;
>> \stopMPpage
>>
>> \ctxlua{inspect{metapost.variables["path"]}}
>> \stoptext
>> % -------
>>
>> The PDF code of the path is (mainly)
>>
>> 20.000000 20.000000 m
>> 20.000000 190.342880 200.000000 184.016693 200.000000 100.000000 c
>>
>> "path" contains
>>
>> table={
>>   {
>>    { 200, 100, 200, 184.0167, 200, 100 },
>>   },
>> }
>>
>> The end point and the second control point are the same, as in the PDF
>> code. But how do I calculate the starting point and the first control
>> point from the returned values?
>
> something
>
> local prev = nil
> for i=1,#path do
>     local current = path[i]
>     if not prev then
>         print(current[1],current[2],"m")
>     else
>         print(prev[5],prev[6],prev[3],prev[4],current[1],current[2],"c")
>     end
>     prev = current
> end
> -- close last to first if needed
>
>> And is the type of operation (line, curve,..) given by the number of
> values?
>
> by analyzing using thresholds (one can just use "c" always, as "l" is an
> optimization)
>
> Hans
>

Thanks for the explanation. I think I have understood the scheme (but I
might be wrong, because this doesn't help me with my example).

Where is the starting point['20 20'] in the returned example path? Same
is true for the first control point ['20 190.34']. Either I'm missing
something, or the returned path data is incomplete.

Peter

```