From: Gerben Wierda <gerben.wierda@rna.nl>
To: mailing list for ConTeXt users <ntg-context@ntg.nl>
Subject: Re: METAPOST subpath rounding issue
Date: Fri, 8 May 2020 14:58:08 +0200 [thread overview]
Message-ID: <1B24BCDF-DBF8-4D69-A162-66DB44E8A6CE@rna.nl> (raw)
In-Reply-To: <D2FA66B7-82B8-41C9-BC13-D797C0F93B9B@scorecrow.com>
[-- Attachment #1.1: Type: text/plain, Size: 3040 bytes --]
> On 8 May 2020, at 00:46, ntg@scorecrow.com wrote:
>
>
>
>> On 7 May 2020, at 20:28, Gerben Wierda <gerben.wierda@rna.nl> wrote:
>>
>> I have a METAPOST algorithm that splits a path at a certain time in two, does something with both ends (not the ends where they were split) and then rejoins them.
>>
>> In very rare cases this crashes, because the subpath doesn’t work as expected.
>>
>> firstPart := subpath (0,halfWayTime) of workingConn;
>> secondPart := subpath (halfWayTime,pathTimeLen) of workingConn;
>>
>> may sometimes result in something like this:
>>
>> metapost log > >> Path at line 0:
>> metapost log > (273,-427)..controls (259.50666666666666,-427) and (246.01333333333335,-427)
>> metapost log > ..(232.52000000000001,-427)
>> metapost log >
>> metapost log > >> Path at line 0:
>> metapost log > (232.51999999999998,-427)..controls (161.68000000000001,-427) and (90.840000000
>> metapost log > 000003,-427)
>> metapost log > ..(20,-427)
>>
>> As can be seen in these (rare) cases the two calls to subpath result in a different point resulting from both. so, when I later try to rejoin them with & it fails:
>>
>> metapost log > ! Paths don't touch; '&' will be changed to '..'.
>> metapost log > <to be read again>
>>
>> Which means subpath doesn’t always exactly do what I expect it to do (and many explanations, but not the official manual) state. Again, this is rare.
>>
>> I’ve done this to work around it but I wondered if there was a better (reliable) solution
>>
>> save cutFirstPart; path cutFirstPart; cutFirstPart := firstPart maxcutbefore fromPicOutline;
>> save cutSecondPart; path cutSecondPart; cutSecondPart := secondPart maxcutafter toPicOutline;
>> if ((xpart point 0 of cutSecondPart) <> (xpart point infinity of cutFirstPart))
>> or ((ypart point 0 of cutSecondPart) <> (ypart point infinity of cutFirstPart)):
>> resultConn := cutFirstPart--cutSecondPart;
>> else:
>> resultConn := cutFirstPart & cutSecondPart;
>> fi
>
> A crude test of
>
> path pb;
> pb:=(5.5cm,0cm)--(5.5cm,0cm)--(10.5cm,0cm);
> draw pb;
>
> gives no errors so why not just join using -- all the time and save the test?
Because the double exact points are also creating (different) problems in my algorithm as they make the path have 'no direction' at that point (direction is (0,0).
G
>
> --
> Bruce Horrocks
> Hampshire, UK
>
> ___________________________________________________________________________________
> If your question is of interest to others as well, please add an entry to the Wiki!
>
> maillist : ntg-context@ntg.nl / http://www.ntg.nl/mailman/listinfo/ntg-context
> webpage : http://www.pragma-ade.nl / http://context.aanhet.net
> archive : https://bitbucket.org/phg/context-mirror/commits/
> wiki : http://contextgarden.net
> ___________________________________________________________________________________
[-- Attachment #1.2: Type: text/html, Size: 18436 bytes --]
[-- Attachment #2: Type: text/plain, Size: 493 bytes --]
___________________________________________________________________________________
If your question is of interest to others as well, please add an entry to the Wiki!
maillist : ntg-context@ntg.nl / http://www.ntg.nl/mailman/listinfo/ntg-context
webpage : http://www.pragma-ade.nl / http://context.aanhet.net
archive : https://bitbucket.org/phg/context-mirror/commits/
wiki : http://contextgarden.net
___________________________________________________________________________________
next prev parent reply other threads:[~2020-05-08 12:58 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-07 19:28 Gerben Wierda
2020-05-07 22:46 ` ntg
2020-05-08 12:58 ` Gerben Wierda [this message]
2020-05-09 21:53 ` Bruce Horrocks
2020-05-09 22:01 ` Bruce Horrocks
2020-05-10 18:17 ` Gerben Wierda
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=1B24BCDF-DBF8-4D69-A162-66DB44E8A6CE@rna.nl \
--to=gerben.wierda@rna.nl \
--cc=ntg-context@ntg.nl \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).