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		Apr JUN Aug 17 2005 2006 2007
58 captures 01 Dec 1998 - 20 Oct 2021

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Some notes on TeX4ht

Some samples of documents I have produced:

• A Unix tutorial
• Reference sheets for the C++ Standard Template Library (STL)
• Algorithms
• Containers

Reusing GIF's

The most time-consuming part of the conversion is generating the .gif images. I've tried to speed this up a bit by reusing images generated from prior runs. The script below will work on most Unix systems as well as Win32 systems with the CygWin32 system. The basic idea: when tex4ht generates a .gif image from a .ps file, a checksum is computed for the .ps file and saved in a separate file. Just before tex4ht generates a .gif image from a .ps file, a check is made to see if such a checksum file is left over from a prior run. If a checksum file exists, and if the saved checksum matches the checksum of the current .ps file, then no .ps-to-.gif translation is done. Instead, the old .gif file is reused. This scheme isn't perfect.

• It's possible (though unlikely) for different images to have the same checksum. If you think this is happening, just delete the .cksum files and reprocess.
• If you alter the document in such a way that a single image is added or removed, all images from that point on will be regenerated. A more elaborate script could be written to search all the checksums in the directory and use any matching image. This might also help in situations where a commonly recurring mathematical expression results in dozens of identical .gifs, which can dramatically slow down a browser.

• A "sh"-like shell (although this script is simple enough to be easily re-written in almost any scripting language, including perl, if you have it).
• grep (used to remove lines where dvips inserts the date on which the .ps file was created)
• cksum, the Unix utility for computing file checksums. If you don't have this, other programs could be used. If desperate, use wc or even just extract the file length from a directory listing.

Installation

Place the script below somewhere within your executable path. Call it "convertif". Then look at your tex4ht.env file. Find the line that contains the conversion command for generating gifs. It's the one that begins with the "G" and should look something like:

Gconvert -crop 0x0 -density 110x110 -transparency '#FFFFFF' tmp.ps %%3

Edit this line by adding "convertif %%1 tmp.ps %%3 " in front of the rest of the command. For example,

Gconvertif %%1 tmp.ps %%3 convert -crop 0x0 -density 110x110 -transparency '#FFFFFF' tmp.ps %%3

The Script

#!/bin/sh
#
#  Usage:
#     convertif idvFile psfile giffile convert-command ...
#  Processes psfile to convert to gif format.  First checks to see if
#  directory already contains an acceptable file.
#
#
# Compute the checksum for the .ps file
COUNT1=`grep -v CreationDate $2 | grep -v DVIPSSource | cksum`
echo "$2 checksum is /" $COUNT1 "/"
#
#  Do we have a saved checksum?
#
if test -r $3.cksum
then
  echo "found $3.cksum"
  COUNT2=`cat $3.cksum`
  echo "Old checksum is /" $COUNT2 "/"
  #
  #  Are the checksums equal?
  #
  if test "$COUNT1" =  "$COUNT2"
  then
    #
    #  Yes.  We don't need to regenerate the .gif
    #
    echo "Reusing $3"
    cp $3 .
  else
     #
     #  No.  Save the checksum and generate the .gif
     #     (Throw out the 1st three command arguments and treat
     #     the remaining command arguments as a command to execute).
     #
     echo $COUNT1 > $3.cksum
     shift 3
     $*
  fi
else
  #
  #  No.  Save the checksum and generate the .gif
  #     (Throw out the 1st three command arguments and treat
  #     the remaining command arguments as a command to execute).
  #
  echo $COUNT1 > $3.cksum
  shift 3
  $*
fi