Path: utzoo!mnetor!uunet!husc6!wjh12!bb
From: bb@wjh12.harvard.edu (Brent Byer)
Newsgroups: comp.text
Subject: Re: pic bug (not quite)
Message-ID: <199@wjh12.harvard.edu>
Date: 19 Apr 88 15:18:49 GMT
References: <921@hsi.UUCP> <197@wjh12.harvard.edu> <720@unm-la.UUCP>
Reply-To: bb@wjh12.UUCP (Brent Byer)
Organization: Textware Intl., Cambridge MA
Lines: 58
Keywords: pic

In article <720@unm-la.UUCP> jay@unm-la.UUCP (Jay Plett) writes:
>In article <197@wjh12.harvard.edu>, bb@wjh12.harvard.edu (Brent Byer) writes:
>> In article <921@hsi.UUCP> stevens@hsi.UUCP (Richard Stevens) writes:
>> >I've encountered the following bug in pic, and was wondering if
>> >anyone has a fix.  I'm using the pic that came with DWB 2.0.
>
>> >[ description of problem with misaligned arrowheads in pic output ]
>
>> The bug is not really in pic; anal analysis of pic's output
>> will show it to be correct.  So, the problem is actually
>> in some combination of ditroff and your post-processor.
>
>> ... It's because of this tighter-than-you-thought inter-relationship ...
>
>Can you please elaborate on this inter-relationship?

I wouldn't want to deprive you of the joy of discovery. :-) * 0.4999

>What am I overlooking?

A very small, but quite significant detail.

>...  I just ran through my pic an input file which produces
>vertical and oblique lines with arrowheads at both ends.  I
>ran the resulting output through 4 different versions of
>ditroff (including DWB 2.0), and each of those through 4
>separate postprocessors from 4 different vendors.  Not a
>misaligned arrowhead in the bunch.

Either you did not examine the output very closely, or
you were lucky in your choice of input file.

I suggest you create a more "random" pic input file.  Try this:

	.PS
	for i = 1 to 10 do X
	arrow down
	move up
	move right .357i
	X
	.PE

Since the problem will exist with any combination of ditroff
and post-processor, just choose one combo (to save time and resources).
Examine the resulting hard-copy carefully.  Once you notice the
discrepancy, work backwards examining the post-processor output file
and the ditroff output file.

Be warned that when you do discover the answer, the resulting flash
will be very bright; sunglasses may be advised. :-)

Another caution: the problem is generic to (but not in) pic,
not arrowheads specifically.  There is *no* perfect solution,
but some are (acceptably) more perfect than others.

[ Enjoy the challenge, Jay.   Dinner in six months? ]

	brent byer