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144 lines
6.3 KiB
Plaintext
144 lines
6.3 KiB
Plaintext
README for DTL package - Thu 9 March 1995
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-----------------------------------------
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Author: Geoffrey Tobin <G.Tobin@ee.latrobe.edu.au>
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Version: 0.6.1
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CTAN Archive-path: dviware/dtl
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Brief Description:
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DTL (DVI Text Language) files are equivalent to TeX's DVI files,
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but are humanly readable, instead of binary. Two programs are
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provided to translate between DVI and DTL: dv2dt, dt2dv.
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dt2dv warns if byte addresses or string lengths recorded in a DTL
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file are incorrect, then overrides them. This makes DTL files
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editable. It also allows quoted apostrophes (\') and quoted quotes
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(\\) in strings. The current DTL variety, sequences-6, separates
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font paths into directory and font, which makes them freely editable.
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In this release, DTL line numbers are correctly calculated, and three
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memory leaks have been fixed.
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Keywords: dvi, TeX
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Includes:
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Makefile README dt2dv.c dtl.h dv2dt.c
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man2ps dtl.doc dvi.doc dt2dv.man dv2dt.man
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hello.tex example.tex tripvdu.tex edited.txt
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Motivation:
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When TeX has typeset a document, it writes its handiwork to a DVI
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file, for DVI processing software (such as viewers, printer drivers,
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dvidvi, and dvicopy) to read.
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The file dvi.doc lists the DVI file commands, with their opcodes
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(byte values), nominal command names, arguments, and meanings. For a
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detailed description of DVI file structure, see one of these:
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1. Donald E. Knuth's book _TeX: The Program_;
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2. The file tex.web, which contains source and documentation for TeX:
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CTAN: systems/knuth/tex/tex.web
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3. The source for Knuth's dvitype program:
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CTAN: systems/knuth/texware/dvitype.web
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4. Joachim Schrod's DVI drivers standard document, the relevant part
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of which is at
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CTAN: dviware/driv-standard/level-0
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Sometimes human beings are interested to see exactly what TeX has
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produced, for example when viewing or printing of the DVI file gives
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unexpected results. However, a DVI file is a compact binary
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representation, so we need software to display its contents.
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Binary file editors, when available, can show the DVI bytes, but not
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their meanings, except for the portions that represent embedded text.
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In particular, the command names are not shown, and the command
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boundaries are not respected.
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By contrast, Knuth's dvitype program is designed as an example of a
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DVI driver. However, dvitype is inconvenient for studying the DVI
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file alone, for the following reasons:
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1. Being a DVI driver, dvitype endeavors to read the TFM font metric
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files referenced in the DVI file. If a TFM file is absent, dvitype
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quits with an error message.
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2. When it starts, it prompts the user interactively for each of a
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series of options.
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3. Even the least verbose option gives masses of information that is
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not contained in the DVI file, coming instead from a combination of
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the data in the DVI file and TFM files.
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4. It does NOT show the DVI information in a way that accurately
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reflects the structure of the DVI file.
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5. Its output, if redirected to a file, produces a very large file.
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6. There is no automated procedure for converting the output of
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dvitype back to a DVI file, and doing it by hand is totally
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unreasonable.
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The first disadvantage is a killer if a TFM file is absent.
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Disadvantages two to four make dvitype very inconvenient for studying
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a DVI file. The fifth problem makes dvitype's output tedious,
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disk-hungry (so one deletes it almost immediately), and unsuitable for
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file transfer.
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The sixth disadvantage of dvitype is important to those people who are
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interested in editing DVI files. Since the DVI files refer explicitly
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to their own internal byte addresses, it's very easy to mess up a DVI
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file if one were to try to edit it directly, even apart from the problem
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of how to recognise a command.
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So an exact, concise, textual representation of a DVI file is needed,
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but dvitype does not produce one.
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Resolution:
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Therefore, working from Joachim Schrod's description, I designed DTL
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and its conversion programs dv2dt (DVI -> DTL) and dt2dv (DTL -> DVI),
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which are provided as C sources:
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dtl.h
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dv2dt.c
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dt2dv.c
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Although I was motivated by the TFM <-> PL conversion provided by
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Knuth's tftopl and pltotf programs, I deliberately designed DTL to be
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a much more concise and literal translation than the `property list'
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structure exemplified by PL. The result is that a DTL file is
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typically three times the size of its equivalent DVI file. The
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document dtl.doc lists the correspondence between the DTL command
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names and the (nominal) DVI command names.
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A clear advantage of an exact two-way conversion is that we can check
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(and prove) whether the converters worked truly on a given DVI file.
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The provided plain TeX files:
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example.tex
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tripvdu.tex
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can be used to test whether the compiled programs are behaving
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sensibly. Whereas example.tex is a simple document that uses a
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variety of plain TeX commands, tripvdu.tex provides a kind of
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`trip test' for DVI processor programs. Both documents are taken,
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with permission, from Andrew K. Trevorrow's dvitovdu (alias dvi2vdu)
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distribution (and are also part of the dvgt viewer distribution).
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The Makefile might have to be edited for your site, as it assumes
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gcc for your C compiler. Makefile compiles dv2dt and dt2dv, then
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runs tex on example.tex and tripvdu.tex, and also converts the
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resulting DVI files to DTL files, back to DVI files (with a change
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of name), then back again to DTL files, so that the results can be
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compared using a textual differencing program. (Many computer systems
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have such a program; on unix, as assumed by Makefile, this is named
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`diff'; ms-dos has one named `comp'.) This should produce a
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zero-length .dif file for each document, proving that the two DTL
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files are identical.
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A keen tester might also use a binary difference program on the DVI
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files, to check that they are identical, as they need to be. (On unix
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systems, the `diff' program suffices for that purpose.)
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Note:
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In representing numeric quantities, I have mainly opted to use
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decimal notation, as this is how most of us are trained to think.
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However, for the checksums in the `fd' (font definition) commands, I
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chose octal notation, as this is used for checksums in Knuth's PL
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files, against which DVI files must be compared when a DVI driver
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loads a font.
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Caveat:
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The length of DTL commands is limited by the size of the line buffer
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in dt2dv.c.
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End of README
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