question for metapost experts

10 Aug 2017

      Hi all,

this one is for all the metapos/metafun experts out there (Alan, are you there?). For a counter in one of my slide backgrounds, I have to calculate an intersectionpoint, given in percentage of the difference between current page and last page. I have always had some difficulties on the first run, when the value of the last page isn’t known yet and hence not written to the tuc file, but the error
...
! The paths don't intersect.
<to be read again>
used to disappear in subsequent runs. Now, ConTeXt doesn’t compile the file at all and stops on this error. There is an error message I haven’t seen before:
...
intersectionpoint->...The paths don't intersect");
origin.else:0.5[point.x_.o...
<to be read again>
;
<*> ... ;z13 = (z11 -- z12) intersectionpoint qw ;
draw z13 withcolor (0.1,0....
This error message was generated by an `errmessage'
command, so I can't give any explicit help.
Pretend that you're Miss Marple: Examine all clues,
and deduce the truth by inspired guesses.
Is there a way to make this conditional, such as (pseudocode)

if q intersects p:
 z = q intersectionpoint p ;
else:
 z = (0,0) ;
fi ; 

I hope that this would allow ConTeXt to proceed and calculate the point correctly on the second run.

Thanks, and all best

Thomas

Schmitz Thomas A.

Hans Hagen

Schmitz Thomas A.

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