path: root/doc/overview.texi

@c Copyright (C) 1992, 1993, 2004, 2011 Free Software Foundation, Inc.
@c This is part of the GNU font utilities manual.
@c For copying conditions, see the file fontutil.texi.

@node Overview
@chapter Overview

@cindex overview

This chapter gives an overview of what you do to create fonts using
these programs.  It also describes some things which are common to all
the programs.

Throughout this document, we refer to various source files in the
implementation.  If you can read C programs, you may find these
references useful as points of entry into the source when you are
confused about some program's behavior, or are just curious.

@menu
* Picture::                     A pictorial overview.
* Creating fonts::              How to use the programs together.
* Command-line options::        Many aspects of the command line are
  				  common to all programs.
* Font searching::              How fonts and other files are looked for.
* Font naming::                 How to name fonts.
@end menu


@node Picture
@section Picture

@cindex picture of program flow
@cindex information flow, picture of

Following is a pictorial representation of the typical order in which
these programs are used, as well as their input and output.

GSrenderfont is not in the picture since it is intended for an entirely
separate purpose (namely, making bitmaps from PostScript outlines).
Fontconvert also has many functions which are not needed for the basic
task of font creation from scanned images.

@smallexample
                                         ---------------
                 / --------------------- | fontconvert |
               /                         ---------------
               |                  	 ^     ^
scanned        v         |---------------|     |
image         TFM        v                     v
and IFI   -----------   GF   -------------  TFM, GF   --------  BZR
========> | imageto | ======> | charspace | =========> | limn | ======...
  ^       -----------         -------------     ^      --------
  |                                ^            |               (continued)
  v				  CMI           v
-------------                               --------
| imgrotate |                               | xbfe |
-------------                               --------



                                  Metafont source    ------  GF
                             |=====================> | mf | =========
 (continued)                 |                       ------
                             |
      BZR   ---------  TFM
... ======> | bzrto |========|=======================
            ---------        |
                ^            |
                |            |   PostScript Type 3 (pf3)
	       CCC           |======================
                             |
                             |
                             |    BPL    ------------  BZR
                             |=========> | bpltobzr | =====
                                         ------------
@end smallexample

@xref{File formats}, for more information on these file formats.


@node Creating fonts
@section Creating fonts

@cindex creating fonts, overview of
@cindex font creation, overview of
@cindex information flow, description of
@cindex overview of font creation

The previous section described pictorially the usual order in which these
programs are used.  This section will do the same in words.

Naturally, you may not need to go through all the steps described here.
For example, if you are not starting with a scanned image, but already
have a bitmap font, then the first step---running Imageto---is
irrelevant.

Here is a description of the usual font creation process, starting with
a scanned image of a type specimen and ending with fonts which can be
used by Ghostscript, @TeX{}, etc.

@enumerate

@item
@cindex image file, viewing
@cindex scanned image, viewing
To see what an image @var{I} consists of, run Imageto with either
@samp{-strips} or @samp{-epsf}.  This produces a bitmap font
@file{@var{I}sp} in which each character is simply a constant number of
scanlines from the image.

@item
Run Fontconvert (@pxref{Fontconvert}) on @file{@var{I}sp} with the
@samp{-tfm} option, to produce a TFM file.  This is because of
the next step:

@item
@flindex strips.tex
Run @TeX{} on @file{imageto/strips.tex}, telling @TeX{} to use the
font @file{@var{I}sp}.  This produces a DVI file which you can print or
preview as you usually do with @TeX{} documents.  (If you don't know how
to do this, you'll have to ask someone knowledgeable at your site, or
otherwise investigate.)  This will (finally) show you what is in the
image.

An alternative to the above steps is to run Imageto with the
@samp{-epsf} option.  This outputs an Encapsulated PostScript file with
the image given as a simple PostScript bitmap.  Then you can use
Ghostscript or some other PostScript interpreter to look at the EPS file.
This method is simpler, but has the disadvantage of using much more
disk space, and needing a PostScript interpreter.

@item
If the original was not scanned in the normal orientation, the image
must be rotated 90 degrees in some direction and/or flipped end for end.
(Sometimes we have not scanned in the normal orientation because the
physical construction of the book we were scanning made it difficult or
impossible.)  In this case, you must rotate the image to be upright.
The program IMGrotate does this, given the @samp{-flip} or
@samp{rotate-clockwise} option.  Given an image @var{RI}, this outputs
the upright image @var{I}.

@item
Once you have an upright image @var{I}, you can use Imageto
(@pxref{Imageto}) to extract the characters from the image and make a
bitmap font @file{@var{I}.@var{dpi}gf}, where @var{dpi} is the
resolution of the image in pixels per inch.  (If the image itself does
not contain the resolution, you must specify it on the command line with
@samp{-dpi}.)  To do this, you must first prepare an IFI file describing
the image.  @xref{IFI files}, for a description of IFI files.

@item
@flindex testfont.tex
To view the resulting GF file, run Fontconvert to make a TFM file, as
above.  Then run @TeX{} on @file{testfont.tex} and use the @code{\table}
or @code{\sample} commands to produce a font table.  Next, print or
preview the DVI file that @TeX{} outputs, as before.  This will probably
reveal problems in your IFI file, e.g., that not all the characters are
present, or that they are not in the right positions.  So you need to
iterate until the image is correctly processed.

@file{testfont.tex} should have come with your @TeX{} distribution.  If
for some reason you do not have it, you can use the one distributed in
the @file{data} directory.

@item
Once all the characters have been properly extracted from the image, you
have a bitmap font.  Unlike the above, the following steps all interact
with each other, in the sense that fixing problems found at one stage may
imply changes in an earlier stage.  As a result, you must expect to
iterate them several (billion) times.

At any rate, given a bitmap font @var{f} you then run Charspace
(@pxref{Charspace}) to add side bearings to @var{f}, producing a new
bitmap font, say @var{g}, and a corresponding TFM file
@file{@var{g}.tfm}.  To do this, you must prepare a CMI file specifying
the side bearings.  @xref{CMI files}, for a description of CMI files.

@item
To fit outlines to the characters in a bitmap font, run Limn
(@pxref{Limn}).  Given the bitmap font @var{g}, it produces the BZR
(@pxref{BZR files}) outline font @file{@var{g}.bzr}.  The side bearings
in @var{g} are carried along.

Although Limn will (should) always be able to fit some sort of outline
to the bitmaps, you can get the best results only by fiddling with the
(unfortunately numerous) parameters.  @xref{Invoking Limn}.

@item
To convert from the BZR file @file{@var{g}.bzr} that Limn outputs to a
font format that a typesetting program can use, run BZRto
(@pxref{BZRto}).  While developing a font, we typically convert it to a
Metafont program (with the @samp{-metafont} option).

As you get closer to a finished font, you may want to prepare a CCC file
(@pxref{CCC files}) to tell BZRto how construct composite characters
(pre-accented `A's, for example) to complete the font.

@item
Given the font in Metafont form, you can then either make
the font at its true size for some device, or make an enlarged version
to examine the characters closely.  @xref{Metafont and BZRto}, for the
full details.

Briefly, to do the former, run Metafont with a @code{mode} of whatever
device you wish (the mode @code{localfont} will get you the most
common local device, if Metafont has been installed properly).  Then you
can use @file{testfont.tex} to get a font sample, as described above.

To do the latter, run Metafont with no assignment to @code{mode}.  This
should get you @code{proof} mode.  You can then use GFtoDVI to get a DVI
file with one character per page, showing you the control points Limn
chose for the outlines.

@item
Problems can arise at any stage.  For example, the character spacing
might look wrong; in that case, you should fix the CMI files and rerun
Charspace (and all subsequent programs, naturally).  Or the outlines
might not match the bitmaps very well; then you can change the
parameters to Limn, or use XBfe (@pxref{XBfe}) to hand-edit the bitmaps
so Limn will do a better job.  (To eliminate some of tedium of fixing
digitization problems in the scanned image, you might want to use the
filtering options in Fontconvert before hand-editing; see @ref{Character
manipulation options}.)

Inevitably, as one problem gets fixed you notice new ones @dots{}

@end enumerate


@menu
* Font creation example::       A real-life example.
@end menu

@node Font creation example
@subsection Font creation example

@cindex font creation, example of
@cindex creating a font, example of
@cindex example of font creation
@cindex Garamond roman, creating

@cindex English, Paul
This section gives a real-life example of font creation for the Garamond
roman typeface, which we worked on concomitantly with developing the
programs.  We started from a scanned type specimen of 30 point Monotype
Garamond, scanned using a Xerox 9700 scanner loaned to us from
Interleaf, Inc.  (Thanks to Paul English and others at Interleaf for
this loan.)

@enumerate

To begin, we used Imageto as follows to look at the image file we had
scanned (@pxref{Viewing an image}).  Each line is a separate command.
@example
imageto -strips ggmr.img
fontconvert -tfm ggmrsp.1200
echo ggmrsp | tex strips.tex
xdvi -p 1200 -s 10 strips.dvi
@end example

@item
@flindex ggmr.ifi
Next, we created the file @file{ggmr.ifi} (distributed in the
@file{data} directory), listing the characters in the order they
appeared in the image, guessing at baseline offsets and (if necessary)
including bounding box counts.  Then we ran Imageto again, this time to
get information about the baselines and spurious blotches in the image.
We use the @samp{-encoding} option since some of the characters in the
image are not in the default @code{ASCII} encoding.
@example
imageto -print-guidelines -print-clean-info -encoding=gnulatin ggmr.img
@end example

@item
Based on the information gleaned from that run, we decided on the final
baselines, adjusted the bounding box counts for broken-up characters,
and extracted the font (@pxref{Image to font conversion}).  (In truth,
this took several iterations.)  The design size of the original image
was stated in the book to be 30@dmn{pt}.  We noticed several
blotches in the image we needed to ignore, and so we added
@code{.notdef} lines to @file{ggmr.ifi} as appropriate.
@example
imageto -verbose -baselines=121,130,120 \
  -designsize=30 -encoding=gnulatin ggmr.img
@end example

@item
To smooth some of the rough edges caused by the scanner's rasterization
errors, we filtered the bitmaps with Fontconvert (@pxref{Fontconvert}).
@example
fontconvert -verbose -gf -tfm -filter-passes=3 -filter-size=3 \
  ggmr30.1200 -output=ggmr30a
@end example

@item
For a first attempt at intercharacter and interword spacing, we created
@file{ggmr.1200cmi} (also distributed in the @file{data} directory) and
ran Charspace (@pxref{Charspace}), producing @file{ggmr30b.1200gf} and
@file{ggmr30b.tfm}.  To see the results, we ran @file{ggmr30b} through
@file{testfont.tex}, modified the CMI file, reran Charspace, etc., until
the output was somewhat reasonable.  We didn't try to fine-tune the
spacing here, since we knew the following steps would affect the
character shapes, which in turn would affect the spacing.
@example
charspace -verbose -cmi=ggmr.1200cmi ggmr30a.1200 -output=ggmr30b
@end example

@item
Next we ran @file{ggmr30b.1200gf}, created by Charspace, through Limn to
produce the outline font in BZR form, @file{ggmr30b.bzr}.  We couldn't
know what the best values of all the fitting parameters were the first
time, so we just increased the ones which are relative to the
resolution.
@example
limn -verbose -corner-surround=4 -filter-surround=6 \
  -filter-alternative-surround=3 -subdivide-surround=6 \
  -tangent-surround=6 ggmr30b.1200
@end example

@item
Then we converted @file{ggmr30b.bzr} to a Metafont program using BZRto
(@pxref{BZRto}), and then ran Metafont to create TFM and GF files we
could typeset with (@pxref{Metafont and BZRto}).  In order to keep the
Metafont-generated files distinct from the original TFM and GF files, we
use the output stem @file{ggmr30B}.  To see the results at the usual
10@dmn{pt}, we then ran the Metafont output through @file{sample.tex} (a
one-line wrapper for @file{testfont.tex}: @samp{\input testfont \sample
\end}).
@example
bzrto -verbose -metafont ggmr30b -output=ggmr30B
mf '\mode:=localfont; input ggmr30B'
echo ggmr30B | tex sample
dvips sample
@end example

@item
This 10@dmn{pt} output looked too small to us.  So we changed the design
size to 26@dmn{pt} (finding the value took several iterations) with
Fontconvert (@pxref{Fontconvert}), then reran Charspace, Limn, BZRto,
Metafont, etc., as above.  We only show the Fontconvert step here; the
others have only the filenames changed from the invocations above.
@example
fontconvert -verbose -gf -tfm -designsize=26 ggmr30b.1200 -output=ggmr26c
@end example

@item
After this, the real work begins.  We ran the Metafont program
@file{ggmr26D.mf} in @code{proof} mode, followed by GFtoDVI, so we could
see how well Limn did at choosing the control points for the outlines.
@xref{Proofing with Metafont}.  (The @code{nodisplays} tells Metafont
not to bother displaying each character in a window online.)
@example
mf '\mode:=proof; nodisplays; input ggmr26D'
gftodvi ggmr26D.3656gf
@end example

@item
From this, we went and hand-edited the font @file{ggmr26d.1200gf} with
XBfe (@pxref{XBfe}), and/or tinkered with the options to Limn, trying to
make the outlines reasonable.  We still haven't finished @dots{}
@end enumerate


@node Command-line options
@section Command-line options

@cindex arguments, specifying program
@cindex command-line options, syntax of
@cindex options, specifying program
@cindex program arguments, syntax of
@cindex syntax of command-line options

@findex getopt_long_only
Since these programs do not have counterparts on historical Unix
systems, they need not conform to an existing interface.  We chose to
have all the programs use the GNU function @code{getopt_long_only} to
parse command lines.

As a result, you can give the options in any order, interspersed as you
wish with non-option arguments; you can use @samp{-} or @samp{--} to
start an option; you can use any unambiguous abbreviation for an option
name; you can separate option names and values with either @samp{=} or
one or more spaces; and you can use filenames that would otherwise look
like options by putting them after an option @samp{--}.

By convention, all the programs accept only one non-option argument,
which is taken to be the name of the main input file.

If a particular option with a value is given more than once, it is the
last value which is used.

For example, the following command line specifies the options
@samp{foo}, @samp{bar}, and @samp{verbose}; gives the value @samp{abc}
to the @samp{baz} option, and the value @samp{xyz} to the @samp{quux}
option; and specifies the filename @file{-myfile-}.

@example
-foo --bar -verb -abc=baz -quux karl -quux xyz -- -myfile-
@end example

@menu
* Main input file::             Each program operates on a ``main'' font.
* Options: Common options.      Some options are accepted by all programs.
* Specifying character codes::  Ways of specifying single characters.
* Values: Common option values.  Some options need more information.
@end menu


@node Main input file
@subsection The main input file

@cindex main input files
@cindex input filename, specifying

By convention, all the programs accept only one non-option argument,
which they take to be the name of the main input file.

Usually this is the name of a bitmap font.  By their nature, bitmap
fonts are for a particular resolution.  You can specify the resolution
in two ways: with the @samp{-dpi} option (see the next section), or by
giving an extension to the font name on the command line.

For example, you could specify the font @code{foo} at a resolution of
300@dmn{dpi} to the program @var{program} in either of these two ways
(@samp{$ } being the shell prompt):
@example
$ @var{program} foo.300
$ @var{program} -dpi=300 foo
@end example

You can also say, e.g., @samp{@var{program} foo.300gf}, but the @samp{gf} is
ignored.  These programs always look for a given font in PK format
before looking for it in GF format, under the assumption that if both
fonts exist, and have the same stem, they are the same.

@xref{File lookups, , File lookups, kpathsea, Kpathsearch library}, for
more details of the filename lookup.


@node Common options
@subsection Common options

@cindex options, common
@cindex arguments, common command-line

Certain options are available in all or most of the programs.  Rather
than writing identical descriptions in the chapters for each of the
programs, they are described here.

This first table lists common options which do not convey anything about
the input.  They merely direct the program to print additional output.

@table @samp

@item -help
@opindex -help
@cindex help, online
Prints a usage message listing all available options on standard error.
The program exits after doing so.

@item -log
@opindex -log
@cindex log file
Write information about everything the program is doing to the file
@file{@var{foo}.log}, where @var{foo} is the root part of the main input
file.

@item -verbose
@opindex -verbose
@cindex verbose output
@cindex progress reports
@cindex status reports
@cindex standard output, used for verbose output
@cindex file used for verbose output
Prints brief status reports as the program runs, typically the character
code of each character as it is processed.  This usually goes to
standard output; but if the program is outputting other information
there, it goes to standard error.

@item -version
@opindex -version
@cindex version number, finding
Prints the version number of the program on standard output.  If a main
input file is supplied, processing continues; otherwise, the program
exits normally.

@end table

This second table lists common options which change the program's
behavior in more substantive ways.

@table @samp

@item -dpi @var{dpi}
@cindex dpi, specifying explicitly
@cindex resolution, specifying explicitly
@opindex -dpi
Look for the main input font at a resolution of @var{dpi} pixels per
inch.  The default is to infer the information from the main input
filename (@pxref{Main input file}).

@item -output-file @var{fname}
@opindex -output-file
Write the main output of the program to @var{fname}.  If @var{fname} has
a suffix, it is used unchanged; otherwise, it is extended with some
standard suffix, such as @file{@var{resolution}gf}.  Unless @var{fname}
is an absolute or explicitly relative pathname, the file is written in
the current directory.

@item -range @code{@var{start}-@var{end}}
@opindex -range
Only look at the characters between the character codes @var{start} and
@var{end}, inclusive.  The default is to look at all characters in the
font.  @xref{Specifying character codes}, for the precise syntax of
character codes.

@end table


@node Specifying character codes
@subsection Specifying character codes

@cindex character codes, specifying

@flindex charcode.c
@flindex charspec.c
Most of the programs allow you to specify character codes for various
purposes.  Character codes are always parsed in the same way (using the
routines in @file{lib/charcode.c} and @file{lib/charspec.c}).

You can specify the character code directly, as a numeric value,
or indirectly, as a character name to be looked up in an encoding
vector.

@menu
* Named character codes::       Character names are looked up in the encoding.
* Numeric character codes::     Decimal, octal, hex, or ASCII.
@end menu


@node Named character codes
@subsubsection Named character codes

@cindex character codes, as names
@cindex naming characters

If a string being parsed as a character code is more than one character
long, or starts with a non-digit, it is always looked up as a name in
an encoding vector before being considered as a numeric code.  We do
this because you can always specify a particular value in one of the
numeric formats, if that's what you want.

The encoding vector used varies with the program; you can always define
an explicit encoding vector with the @samp{-encoding} option.  If you
don't specify one explicitly, programs which must have an encoding
vector use a default; programs which can proceed without one do not.
@xref{Encoding files}, for more details on encoding vectors.

As a practical matter, the only character names which have length one
are the 52 letters, @samp{A}--@samp{Z}, @samp{a}--@samp{z}.  In virtually
all common cases, the encoding vector and the underlying character set
both have these in their ASCII positions.  (The exception is machines
that use the EBCDIC encoding.)


@node Numeric character codes
@subsubsection Numeric character codes

@cindex character codes, numeric

The following variations for numeric character codes are allowed.  The
examples all assume the character set is ASCII.

@itemize @bullet

@item
@cindex octal character code
Octal numerals preceded by a zero are taken to be an octal number.  For
example, @kbd{0113} also means decimal 75.  If a would-be character code
starts with a zero but contains any characters other than the digits
@samp{0} through @samp{7}, it is invalid.

@item
@cindex hexadecimal character code
Hexadecimal ``digits'' preceded by @samp{0x} or @samp{0X} are taken to
be a hexadecimal number.  Case is irrelevant.  For example, @kbd{0x4b},
@kbd{0X4b}, @kbd{0x4B}, and @kbd{0X4B} all mean decimal 75.  As with
octal, a would-be character code starting with @samp{0x} and containing
any characters other than @samp{0}--@samp{9}, @samp{a}--@samp{f}, and
@samp{A}--@samp{F} is invalid.

@item
@cindex decimal character code
A decimal number (consisting of more than one numeral) is itself.  For
example, @kbd{75} means the character code decimal 75.  As before, a
would-be character code starting with @samp{1}--@samp{9} and containing
any characters other than @samp{0}--@samp{9} is invalid.

@item
A single digit, or a single character not in the encoding vector as a
name, is taken to represent its value in the underlying character set.
For example, @kbd{K} means the character code decimal 75, and @kbd{0}
(the numeral zero) means the character code decimal 48 (if the machine
uses ASCII).

@item
If the string being parsed as a character code starts with a digit, the
appropriate one of the previous cases is applied.  If it starts with any
other character, the string is first looked up as a name.

@end itemize

@cindex maximum character code
Character codes must be between zero and 255 (decimal), inclusive.


@node Common option values
@subsection Common option values

@cindex common option values
@cindex option values
The programs have a few common conventions for how to specify option
values that are more complicated than simple numbers or strings.

@cindex list as option values
@cindex option value of a list
@cindex option values, taking from a file
Some options take not a single value, but a list.  In this case, the
individual values are separated by commas or whitespace, as in
@samp{-omit=1,2,3} or @samp{-omit="1 2 3"}.  Although using whitespace to
separate the values is less convenient when typing them interactively,
it is useful when you have a list that is so long you want to put it in
the file.  Then you can use @file{cat} in conjunction with shell quoting
to get the value: @samp{-omit="`cat file`"}.

@cindex keyword/value list as option values
@cindex option value of a keyword/value list
Other options take a list of values, but each value is a keyword
and a corresponding quantity, as in @samp{-fontdimens
@var{name}:@var{real},@var{name},@var{real}}.

@cindex percentages as option values
@cindex option value of a percentage
Finally, a few options take percentages, which you specify as an integer
between 0 and 100, inclusive.


@node Font searching
@section Font searching

@cindex font searching algorithm

These programs use the same environment variables and algorithms for
finding font files as does (the Unix port of) @TeX{} and its friends.

You specify the default paths in the top-level Makefile.  The
environment variables @code{TEXFONTS}, @code{PKFONTS}, @code{TEXPKS},
and @code{GFFONTS} override those paths.  Both the default paths and the
environment variable values should consist of a colon-separated list of
directories.

@vindex GFFONTS @r{environment variable}
@vindex PKFONTS @r{environment variable}
@vindex TEXFONTS @r{environment variable}
@vindex TEXPKS @r{environment variable}
Specifically, a TFM file is looked for along the path specified by
@code{TEXFONTS}; a GF file along @code{GFFONTS}, then @code{TEXFONTS}; a
PK file along @code{PKFONTS}, then @code{TEXPKS}, then @code{TEXFONTS}.

@xref{Path specifications, , Path specifications, kpathsea, Kpathsea
library}, for details of interpretation of environment variable values.


@node Font naming
@section Font naming

@cindex naming font files
@cindex font files, naming

Naming font files has always been a difficult proposition at best.  On
the one hand, the names should be as portable as possible, so the
fonts themselves can be used on almost any platform.  On the
other hand, the names should be as descriptive and comprehensive as
possible.  The best compromise we have been able to work out is
described in a separate document: @ref{Top, , Introduction, fontname,
Filenames for @TeX{} fonts}.  @xref{Archives}, for where to obtain.

Filenames for GNU project fonts should start with @samp{g}, for the
``source'' abbreviation of ``GNU''.

@cindex fonts, versions of
Aside from a general font naming scheme, when @emph{developing} fonts
you must keep the different versions straight.  We do this by appending
a ``version letter'' @samp{a}, @samp{b}, @dots{} to the main bitmap
filename.  For example, the original Garamond roman font we scanned was
a 30 point size, so the main filename was @file{ggmr30} (@samp{g} for
GNU, @samp{gm} for Garamond, @samp{r} for roman).  As we ran the font
through the various programs, we named the output @file{ggmr30b},
@file{ggmr30c}, and so on.

@cindex outline fonts, naming
Since the outline fonts produced by BZRto are scalable, we do not
include the design size in their names.  (BZRto removes a trailing
number from the input name by default.)