[NTG-context] Re: mtx-synctex.lua question

8 Dec 2023

      Hi Hans (and anyone else interested in synctex),

On Fri, Dec  8, 2023 at 11:38 (-0400), Jim wrote:
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Hi Hans,
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On Fri, Dec  8, 2023 at 15:03 (+0100), Hans Hagen wrote:
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On 12/7/2023 7:23 PM, Jim wrote:
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Hi,
...
...
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In mtx-synctex.lua, inside
local function findlocation(filename,page,xpos,ypos,tolerance)
there is the following code:
for s=1,tolerance,max(tolerance//10,1) do
locate( s, 0) if fi ~= 0 then tl = s ; goto done end
locate(-s, 0) if fi ~= 0 then tl = s ; goto done end
locate( s, s) if fi ~= 0 then tl = s ; goto done end
locate( s,-s) if fi ~= 0 then tl = s ; goto done end
locate(-s, s) if fi ~= 0 then tl = s ; goto done end
locate(-s,-s) if fi ~= 0 then tl = s ; goto done end
end
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Is the omission of the
locate(0, s) ...
and
locate(0, -s) ...
cases intentional, or is that an oversight?
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If intentional, can someone explain the rationale to me?
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it's too long ago to remember the reason ... did you test with and without?
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I did not.  Yet.
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But on your suggestion, I will give it a try and get back to you.
I modified mtx-synctex.lua as follows:
% diff /usr/local/context/tex/texmf-context/scripts/context/lua/mtx-synctex.lua mtx-synctex-jd.lua 
279a280
...
-- JD added (0, +/-s) cases for testing
282a284,285
...
locate( 0, s) if fi ~= 0 then tl = s ; goto done end
                    locate( 0,-s) if fi ~= 0 then tl = s ; goto done end
and then wrote the following quick and dirty shell script to create log
files for comparison:

---------------------------------------------------------------------
#! /bin/zsh

# File:		    compare-my-synctex-version
# Author:	    Jim Diamond
# Created:	    2023/12/08 13:27:23
#
# Purpose:	    Run some tests to compare ConTeXt's mtx-synctex-lua to
#		    my own version, vis-a-vis the backward-search
#		    functionality.
#
# Notes:	    Assumes $1 is a valid ConTeXt synctex file,
#		    $2 is a valid page within that file, and
#		    $3, if present, is a valid 

DEFAULT_TOLERANCE=300

if [[ $# < 2 || $# > 3 || ! -r $1 ]]
then
    echo >&2 "Usage: $0 <synctex file> <page> [tolerance]"
    echo >&2 "       tolerance default is $DEFAULT_TOLERANCE."
    exit 1
fi

st_file=$1
page=$2
if [[ $3 != "" ]]
then
    tolerance=$3
else
    tolerance=$DEFAULT_TOLERANCE
fi

x_vals=`seq 100 50 550`
y_vals=`seq 100 50 700`

old_results=${st_file}_page_${page}_tol_${tolerance}_using_current.out
new_results=${st_file}_page_${page}_tol_${tolerance}_using_new.out

if [[ -e $old_results || -e $new_results ]]
then
    printf >&2 "$0: at least one of\n\t%s\nor\n\t%s\nexists; quitting.\n" \
	$old_results $new_results
    exit 1
fi

# Get rid of the extra newline from mtxrun as done below.
for x in $=x_vals
do
    for y in $=y_vals
    do
	printf "%3d, %3d: " $x $y
	out=`mtxrun --script synctex --goto --direct \
	    --page=$page --x=$x --y=$y --tolerance=$tolerance $st_file`
	echo $out
    done
done | tee $old_results

echo

for x in $=x_vals
do
    for y in $=y_vals
    do
	printf "%3d, %3d: " $x $y
	out=`mtxrun --script mtx-synctex-jd.lua --goto --direct \
	    --page=$page --x=$x --y=$y --tolerance=$tolerance $st_file`
	echo $out
    done
done | tee $new_results
---------------------------------------------------------------------

and ran it on one page of one synctex file for a few different values of
tolerance (300, 200, 100 and 50).  To briefly summarize, the modified
script found a small number of matches that the original script didn't,
occasionally the line number was different (almost always by 1, but a few
times more), and the tolerance returned by this test version was also <= the
tolerance returned by the current version.

Admittedly, with the other two directions added in, a more extensive test
(a total of a bit under 14 minutes CPU time on a Ryzen 4700U) showed the
new version is about 0.5% slower, so there is a very minor downside.  (I'd
happily spend the extra matches for the minuscule amount of CPU time, but
others may not.)

Cheers.
                                Jim