Re: question for metapost experts

[Hans Hagen <pragma@wxs.nl>]

On 8/10/2017 2:07 PM, Schmitz Thomas A. wrote:
> 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)

p intersection_point q

(also sets intersection_found)

> 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
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If your question is of interest to others as well, please add an entry to the Wiki!

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