path: root/demo/neatroff.ms

.\" PSTITLE: Neatroff Introduction
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.post.info Title "Neatroff Introduction"
.post.info Author "Ali Gholami Rudi"
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\s+8Neatroff\m0\s-8
.AU
\fIAli Gholami Rudi\fP
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\s-3\fIUpdated in January 2020\s+3\fP\&
.sp 3
Neatroff is a new implementation of the Troff typesetting system in the C
programming language, which tries to address, as neatly as possible,
some of the shortcomings of the original Troff based on the ideas and
features available in Plan 9 Troff, Heirloom Troff, and Groff.
The latest versions of Neatroff, its PostScript and PDF post-processor,
Neatpost, and its eqn preprocessor, Neateqn,
are available at their home page (\*[post.url http://litcave.rudi.ir/ link]).
This document enumerates Neatroff's features, its new requests, and
its differences compared to other Troff implementations.  On the other
hand, the document \(lqGetting Started with Neatroff\(rq
(\*[post.url http://litcave.rudi.ir/neatstart.pdf link])
explains how to set up and use Neatroff.

.SH "Nomenklature"
Since there are several implementations of this family of roff typesetting
suites available, the Neatroff documentation needs to distinguish this
implementation from others to avoid confusion.  \(lqroff\(rq for example is the
main typesetting application, which may also exist under this name in other
typesetting suites of the same kind.  To avoid misinterpretation, the name
\(lqNeatroff\(rq will be used in these documents when addressing either the whole
typesetting suite as such or the roff binary of this typeseeting suit in the
sense of a brand name.  If these documents address the commandline usage of
\(lqroff\(rq or more general handling the binary itself, it uses the
name \(lqroff\(rq to name the binary being the result of the compilation
process.  Same goes for \(lqneatpost,\(rq \(lqneateqn,\(rq \(lqneatmkfn,\(rq and
\(lqneatrefer\(rq accordingly.

.bp
.SH "Noteworthy Features"
The following list describes the main extensions of Neatroff compared
to the original Troff (many of these extensions are available in
Groff and Heirloom Troff as well).  The number register \&.neat,
which is always one in Neatroff, can be used to distinguish Neatroff
from other Troff implementations.

.MH "UTF-8 encoding
In Neatroff, input files and characters, glyph names, ligatures,
hyphenation patterns and dictionary, as well as quoted escape sequence
delimiters and arguments of commands like .tr, .hc, .tc, .lc, .mc, and
\&.fc are in UTF-8 encoding.

.MH "Long macro, register, and environment names
When not in compatibility mode (activated with the -C command line option or the .cp
request, as in Groff), Neatroff supports long macro, register, and environment
names.  It also supports Groff-style escape sequences with long arguments
(for \\[], \\*[], \\$[], \\f[], \\g[], \\k[], \\m[], \\n[], and \\s[])
and interpolating string registers with arguments (\\*[xyz arg1 arg2 ...]).
Note that like Groff, Neatroff supports named environments and
is not limited to original Troff's three fixed environments.

.MH "Advanced font features, ligature, and pairwise kerning
Neatroff and Neatmkfn (which generates Neatroff's font descriptions)
support many of the advanced font features available in OpenType
fonts.  In a font, a set of substitution and positioning rules may be
specified, which are grouped into several features and scripts.  In
Neatroff, features can be enabled with \&.ff and the active script and
language can be selected with \&.ffsc.
Neatmkfn supports PostScript Type 1 fonts, TrueType fonts (TTF), and
OpenType fonts (OTF).  For the latter, however, it cannot extract
glyph bounding boxes, which are used by the Neateqn preprocessor.
Therefore, if an OpenType font is supposed to be used in Neateqn
blocks, it should be converted to TrueType first.

.MH "Whole paragraph text formatting
Neatroff supports filling whole paragraphs at once, to achieve
more uniform word spacing.  Like Heirloom Troff, the \&.ad request
accepts arguments p or pb, pl, and pr, which are equivalent to b, l,
and r, except that the filling is done for whole paragraphs, i.e.,
words are collected until a line break is issued.
This inevitably changes the behaviour of some requests and traps: several
lines may be collected and ready to be output while executing them.
For the end macro, Troff invokes the macro specified
with \&.em request without flushing the last incomplete line.
Neatroff follows the same behaviour even when formatting whole
paragraphs and does not write any of the collected lines to the output.
Since after the end macro no new page is started, collected lines may
be unexpectedly written to the end of the last page of the document.
To change that, the end macro can invoke the \&.br request.
For requests that cause a break, using \(aq as the control character
prevents writing any line of the collected paragraph to the output,
as expected.
The exception to this rule is \(aqbr, which formats the words
collected so far and outputs all resulting lines except the final
incomplete line (this is useful, for instance, for footnotes, which
should be inserted on the same page).

.MH "Paragraph formatting algorithm
For deciding at what points to break a paragraph into lines, Neatroff
assigns a cost to each possible outcome: a cost of 100 is assigned to
each stretchable space that has to be stretched 100 percent.  The cost
grows quadratically and the cost of stretching a space 200 percent is 400.
There are requests that adjust the algorithm Neatroff uses for
performing paragraph formatting.
The \&.hycost request changes the cost of hyphenating words.  The
default value is zero.
The \\j escape sequence, as in Heirloom Troff, specifies the extra
cost of a line break after a word; for instance, in \(lqHello\\j'10000'
world\(rq, the words are not split by the line breaking algorithm,
unless absolutely necessary (i.e., if other options are more costly).
The escape sequence \\\(ti introduces non-breakable stretchable space.
Also, to prevent paragraphs with
very short last lines, the \&.pmll (paragraph minimum line length)
sets the minimum length of a formatted line, specified as a
percentage of \\n(.l; \(lq.pmll 15\(rq, for instance, ensures that
the length of last line of each paragraph is at least 15% of its other
lines; otherwise, a cost proportional to the value specified
as its second argument is added.

.MH "Controlling word spaces
The \&.ssh request sets the amount (in percentage) by which the
stretchable spaces in a line may be shrunk while formatting lines.
The default value is zero.
Also, the second
argument of the \&.ss request specifies sentence space, as in Groff or
Heirloom Troff.

.MH "Macros and their arguments
In a macro, \\$* is replaced with the macro's arguments separated
by spaces.  \\$@ is like \\$*, but quotes the arguments as well.
\\$\(ha is like \\$@, except that it escapes the double quotes
in the arguments.
The arguments can be shifted with a \&.shift request.
Neatroff also supports blank line macro (.blm) and
leading space macro (.lsm).

.MH "Text direction
Neatroff supports changing the text direction to render right-to-left languages.
The \&.<< and \&.>> requests specify text direction and the \\< and \\> escape
sequences change it temporarily for including words in the reverse
direction.  The value of number registers \&.td and \&.cd indicate the
current text and temporary directions respectively; zero means
left-to-right and one means right-to-left.  Neatroff starts processing
text direction, after the first invocation of \&.<< or \&.>>.

.MH "Keshideh justification and cursive scripts
A new adjustment type (.ad k) allows inserting Keshideh characters
before justifying text with hyphenation and spaces.  Neatroff also
supports cursive scripts, which require connecting glyphs at their
cursive attachment positions, as defined in the fonts.

.MH "Font manipulation
In Neatroff, the mapping between Troff character names and glyphs in a
font can be modified with the \&.fmap request: \(lq.fmap F C G\(rq
maps Troff character C to the glyph with device-specific name G for
font F.  When this glyph does not exist in F, Neatroff assumes that
the character C is not present in the font.  When G is missing, the
effect of \&.fmap for character C is cancelled.  Neatroff also implements
Groff's \&.fspecial and \&.fzoom requests: after \(lq.fspecial FN S1
S2 ...\(rq, when the current font is FN, the fonts S1, S2, ... are
assumed to be special.  Also, \(lq.fzoom FN zoom\(rq scales font FN by
the second argument after dividing it by 1000.

.MH "Colour support
Neatroff supports colours with the .cl request and the \\m[] escape sequence.
Unlike Groff, colours need not be defined beforehand and can be
specified directly.  The argument of \\m can be predefined colour
names (e.g. blue), predefined colour numbers (0 for black, 1 for red,
2 for green, 3 for yellow, 4 for blue, 5 for magenta, 6 for cyan, and
7 for white), #rgb and #rrggbb for specifying colours in hexadecimal
RGB format, #g and #gg for specifying grey with the given hexadecimal
level, and empty (\\m[]) for the previous colour.  The current colour
is available in the \&.m number register.

.MH "Hyphenation
The \&.hpf request loads hyphenation patterns, exceptions, and
character mappings from the addresses specified via its arguments.
The specified files should contain nothing but utf-8 patterns,
exceptions and mappings respectively (i.e. no TeX code), just like the
files whose names end with \&.pat.txt, \&.hyp.txt and \&.chr.txt in
CTAN for TeX (\*[post.url https://mirror.ctan.org/language/hyph-utf8/tex/generic/hyph-utf8/patterns/txt/ link]).
The \&.hpfa request is like \&.hpf, except that it does not clear the
previous hyphenation patterns and exceptions.  The second and third
arguments of these requests are optional.  With no arguments, these
requests load English hyphenation patterns and exceptions.  Also the
\&\(lq.hcode abcd...\(rq request, assigns the hyphenation code of b to
a and the hyphenation code of d to c; initially all upper-case ASCII
letters are mapped to their lower-case forms.

.MH "Filled drawing objects
Neatroff supports Groff-style polygons and filled drawing objects (p,
C, E and P commands for \\D escape sequence).  In Neatroff, however,
there is no specific background colour; objects are filled with the
current colour (.m number register).  Furthermore, in Neatroff
the edges of polygons can be lines, arcs, or splines; a letter among the
arguments of \\D'p ..' specifies the type of the subsequent
edges: \(oql\(cq, \(oqa\(cq, and \(oq\(ti\(cq for lines, arcs,
and splines respectively.

.MH "Conditional escape sequence
Neatroff supports a new escape sequence for conditional interpolation:
the escape sequence \\?'cond@expr1@expr2@', evaluates cond (exactly as
if it were a \&.if condition) and interpolates expr1, if the condition
is true, and expr2, otherwise.  The delimiter (@ in this example) can
be any character, but may not be part of the condition; for numerical
expressions, for instance, it cannot be a digit, an operator sign, or
a scale indicator, unless separated from the condition with \\&.  The
final delimiter, and even expr2, may be omitted, thus \\?'cond@expr'
is valid; Neatroff interpolates expr if cond is true.

.MH "Neatpost-specific device functions
Neatpost can produce both PostScript and PDF.  The escape sequences
\\X'eps img.eps [width [height]]' and \\X'pdf img.pdf [width [height]]'
in Neatroff instruct Neatpost to include the given EPS or PDF file;
the former works only when the output is PostScript and the latter
when the output is PDF.  They include the given EPS/PDF file with its
lower left corner at the current point.  If the width or height are
given (in basic units), the image is scaled appropriately.  Neatroff
also supports \\X'rotate deg' for rotating the current page around the
current point.  For creating a document outline (bookmark tree),
Neatpost supports \\X'mark desc page offset level', and for creating
named references, Neatpost supports \\X'name label page offset'.
Also, \\X'link destination width height' can be used to create links;
its first argument for internal references (defined with \\X'name ...')
should start with a # sign.

.MH "Helper Macro Packages
In addition to the standard Troff macro packages, such as -ms, -mm,
and -me, which are imported from Plan 9 Troff, Neatroff comes with a
few convenient helper macro packages as follows (these macros are
included in neatroff_make): for drawing simple tables without the tbl
preprocessor -mtbl, for invoking Neatpost device functions like
including EPS and PDF images -mpost, for drawing simple charts and
graphs -mgr, for floating objects -mkeep.
Some Groff-specific macros are implemented in -mgnu, such as open,
opena, close, write, pso, and mso.  Also, -men and -mfa include
-ms-like macros for creating short English and Farsi documents.

.bp
.SH "Summary of New Requests"
This is the list of new requests available in Neatroff compared
to those documented in \(lqTroff User's Manual\(rq by Ossanna
and Kernighan.

.NR "\&.ad p*" "b" "adjust" "E"
With values pl, pr, pb, and p, this request instructs Neatroff to perform
whole-paragraph line formatting.  Also, the value k enables Keshideh
justification (kp is the equivalent for whole-paragraph formatting).

.NR "\&.blm M" "\-" "disabled" "\-"
Specify the blank line macro.  If specified, each blank line is
treated as an invocation of this macro.

.NR "\&.chop R" "\-" "none" "\-"
Remove the last character of a string register.

.NR "\&.cl C" "0" "previous" "E"
Change text colour.  The current colour is available in the number
register \\n(.m.  With no arguments, the previous colour is selected.
The format of the argument and the \\m escape sequence are described
in the previous section.

.NR "\&.co SRC DST" "\-" "none" "\-"
Copy the contents of register SRC into register DST.

.NR "\&.co+ SRC DST" "\-" "none" "\-"
Append the contents of register SRC to register DST.

.NR "\&.co> R F" "\-" "none" "\-"
Copy the contents of register R into file F.

.NR "\&.co< R F" "\-" "none" "\-"
Read the contents of register R from file F.

.NR "\&.char C DEF" "\-" "\-" "\-"
Define Troff character C.
If DEF is missing, previous definitions for character C are removed.

.NR "\&.ochar FN C DEF" "\-" "\-" "\-"
Define Troff character C only for font FN.
If DEF is missing, previous definitions
for character C are removed.

.NR "\&.rchar C" "\-" "\-" "\-"
Remove the definition of character C.

.NR "\&.eos S T" "S=\&.?!  T='"")]*" "none" "\-"
Specify sentence characters.  The first argument specifies
the characters that end a sentence and the second argument
specifies the characters ignored after them.

.NR "\&.fzoom F N" "1000" "none" "\-"
Magnify the given font by N/1000.

.NR "\&.fp N F L" "\-" "none" "\-"
In Neatroff, if instead of the position of the font to be mounted, N
is a dash, the position of the font is decided automatically: if a
font with the same name is already mounted, the same position is
reused.  Otherwise the font is mounted on the next available
position.

.NR "\&.ff F +F1 -F2" "\-" "none" "\-"
Enable or disable font features; the first argument specifies the
font and the rest of the arguments specify feature names,
prefixed with a plus to enable or a minus to disable.
When a feature is enabled, all substitution and positioning rules
of a font with that feature name are applied when laying out the
glyphs.

.NR "\&.ffsc F SC LN" "\-" "none" "\-"
Specify font's script and language.  A Neatroff font description
specifies a set of rules for each script and language, grouped into
several features.  With this request, only the rules for the specified
script and language are enabled.  By default, or when SC is missing,
all scripts are selected.  When LN is missing, the rules of the
default language of the selected script are enabled.

.NR "\&.fspecial F S1 S2" "\-" "none" "\-"
Set special fonts when the current font is F.

.NR "\&.fmap FN CH GID" "\-" "none" "\-"
Map Troff character CH to glyph with device dependent name GID for
font FN.  When gid is missing, the effect of mapping CH is cancelled.
Neatroff implicitly calls \&.fmap for all aliases in font descriptions
(character definitions whose second column is ").

.NR "\&.hycost N N2 N3" "0" "none" "E"
Change the cost of hyphenating words when adjusting lines.
An argument of 100 assigns to each hyphenation the cost of stretching
a space one hundred percent while formatting.  The second and third
arguments specify additional costs for two and three consecutive
hyphenated lines (only when formatting whole paragraphs).

.NR "\&.hlm n" "0" "0" "E"
Set the maximum number of consecutive hyphenated lines (only when
formatting whole paragraphs).  The current value is available via
\\n[.hlm].  An argument of zero or a negative number implies no
limit.

.NR "\&.hydash C" "\\\\:\\\\(hy\\\\(en\\\\(em-\\\\-\\\\(--" "none" "\-"
Specify the list of characters after which words may be broken (even
when hyphenation is disabled) without inserting hyphens.

.NR "\&.hystop C" "\\\\%" "none" "\-"
Specify hyphenation inhibiting characters.  Words containing any of
the given characters are not hyphenated, unless after dashes
(characters specified via \&.hydash) or hyphenation indicators (\\%).

.NR "\&.hpf P H C" "\-" "English" "\-"
Set hyphenation files for patterns, exceptions, and mappings.
With no arguments, loads English hyphenation patterns and exceptions.

.NR "\&.hpfa P H C" "\-" "English" "\-"
Like, \&.hpf, but do not clear the previous hyphenation patterns.

.NR "\&.hcode abcd..." "\-" "none" "\-"
Assign the hyphenation code of b to a and the hyphenation code of d to c.

.NR "\&.in2" "0" "previous" "E"
Right-side indentation.  The current right-side indentation is
available in register \\n(.I.

.NR "\&.ti2" "0" "\-" "E"
Right-side temporary indentation.

.NR "\&.kn N" "1" "none" "E"
Enable or disable pairwise kerning (the current value is available through \\n[.kn]).

.NR "\&.lsm M" "\-" "disabled" "\-"
Specify the leading space macro.  If specified, for each line with
leading spaces, this macro is invoked.  The register \\n[lsn] holds
the number of leading spaces removed from the line.

.NR "\&.pmll N C" "0" "0" "E"
Set paragraph minimum line length in percentage.  To shorter lines,
Neatroff assigns a cost proportional to the value specified as the
second argument (or 100, if missing) when formatting paragraphs.
Number registers \\n[.pmll] and \\n[.pmllcost] store the
values passed to \&.pmll.

.NR "\&.>>  \&.<<" "left-to-right" "\-" "E"
Render text in left-to-right or right-to-left direction.  See the
first section for an explanation of the escape sequences \\> and \\<.

.NR "\&.shift N" "\-" "N=1" "\-"
Shift macro arguments by N positions.

.NR "\&.ssh N" "0" "0" "E"
Set the amount stretchable spaces in formatted lines may be
shrunk in percentage (available through \\n[.ssh]).

.NR "\&.ss M N" "M=12 N=12" "none" "E"
The second argument sets sentence space size (available in \\n[.sss]).

.NR "\&.tkf FN S1 N1 S2 N2" "\-" "none" "\-"
Enable track kerning for font FN.  If the point size is at most
S1, the width of each character is increased by N1 points, if it
is at least S2, the width of each character is increased by N2
points, and if it is between S1 and S2, the width of each character
is increased by a value between N1 and N2, relative to the
difference between the current point size and S1.

.bp
.SH "Notes"
.sp -1
.MH "The standard macro packages
The standard Troff macro packages and a top-level build script to
obtain and install Neatroff are available in the neatroff_make git
repository (\*[post.url http://litcave.rudi.ir/ link]).
\(lqGetting Started with Neatroff\(rq (\*[post.url http://litcave.rudi.ir/neatstart.pdf link])
explains how to use this repository.

.MH "Formatting equations with Neateqn
Neateqn is an eqn preprocessor for Neatroff.  It implements many
of the extensions introduced in Groff's eqn preprocessor.  It
can use TeX's Computer Modern-style bracket-building symbols, if
available.
\(lqTypesetting Mathematics with Neateqn\(rq (\*[post.url http://litcave.rudi.ir/neateqn.pdf link])
introduces Neateqn.

.MH "Generating the output device
The Neatmkfn program (\*[post.url https://github.com/aligrudi/neatmkfn link])
generates Neatroff font descriptions for AFM, TrueType, and OpenType fonts.
It includes a script to create a complete output device for Neatroff.

.MH "Missing requests
A few requests of the original Troff are not implemented:
\&.pi, .cf, .rd, .pm, .ul, .cu, .uf, \\H, and \\S.

.MH "Porting and distribution
Given that Neatroff, Neatpost, Neatmkfn, and Neateqn can be compiled
with Neatcc, porting them to other Unix variants besides Linux should
not be difficult.  Note that Neatroff is released under the ISC
licence.

.MH "List of OpenType font features
As mentioned in previous sections, font features can be enabled and
disabled with the \&.ff request.  For a list of OpenType features in
general and their descriptions, see
the list of typographic features in Wikipedia (\*[post.url https://en.wikipedia.org/wiki/List_of_typographic_features link])
or OpenType specification (\*[post.url http://www.microsoft.com/typography/OTSPEC/featurelist.htm link]).

.bp
.SH "Font Description Files"
The format of font description files in Neatroff, although still mostly
backward compatible, has been slightly changed.  The value of special,
spacewidth, and ligatures parameters retain their old meanings; sizes
and name parameters are ignored, however.  The value of the fontname
parameter in Neatroff specifies the device name of the font
(e.g. Times-Roman); Neatpost uses it to map Troff fonts to PostScript fonts.
In the charset section, the forth field is always the
device-specific name of the glyph (accessible with the \\N escape sequence)
and the optional fifth field specifies the glyph's code (the fourth field
of the original Troff).

In addition to the old charset section of the original Troff, Neatroff
supports a new syntax for defining characters and kerning pairs.  Lines
starting with the word \(lqchar\(rq define characters (similar to lines in
the charset section) and lines starting with \(lqkern\(rq specify kerning pairs.
For the latter, \(lqkern\(rq is followed by three tokens: the name of the
first glyph, the name of the second glyph, and the amount of kerning
between them.  Specifying the name of glyphs (the fourth field after \(lqchar\(rq)
instead of character names allows specifying kerning pairs for glyphs
not mapped to any characters (may be done later with a \&.fmap request) or
specifying kerning pairs only once for all aliases of a character.
Here are a few lines of a font description file for Neatroff, created
with Neatmkfn.

.cc.beg
.ta 5 10 15 20 25
name R
fontname Times-Roman
spacewidth 25
ligatures fi fl 0
# the list of characters
char	!	33	2	exclam	33
char	.	25	0	period	46
char	A	72	2	A	65
char	B	67	2	B	66
char	C	67	2	C	67
# the kerning pairs
kern	A	C	-5
kern	A	period	-1
.cc.end
.LP
The width column of the character definition lines can optionally
include four more numbers, separated with commas, that describe the
bounding boxes of the glyphs.  The bounding boxes are used in the \\w
escape sequence; after this escape sequence, the value of the bbllx,
bblly, bburx and bbury number registers are modified to represent the
bounding box of the argument of \\w.

To use the advanced features present in TrueType and OpenType fonts,
Neatroff supports lines that define substitution and positioning
rules (lines starting with \(lqgsub\(rq and \(lqgpos\(rq respectively).
Note that unlike Heirloom Troff, which implements non-contextual
single-character substitutions, Neatroff implements many of the more
complex OpenType substitution and positioning features.  The following
example shows how such features are defined in Neatroff font
descriptions:

.cc.beg
.ta 5 10 15 20 25
gsub liga:latn 4 -gl1 -gl2 -gl3 +gl123
gpos kern:latn 2 gl1:+0+0-5+0 gl2
.cc.end
.LP
In this example, the first line defines a 3-character ligature (with
feature name \(lqliga\(rq and script name \(lqlatn\(rq) and the second
defines pairwise kerning for the pair of glyphs gl1 and gl2
(decreasing the horizontal advance of gl1 by 5 basic units; with
feature name \(lqkern\(rq and script name \(lqlatn\(rq).  The patterns
can be longer and more detailed, defining context or glyph groups, to
support OpenType features that require them; for examples, see the
files generated by Neatmkfn.

.bp
.SH "Source Code Organization
The following figure shows where Neatroff's major
layers and features are implemented in its source tree.
.sp -1

.KS
.RT
.PS
# part(title, description)
define part { [
M:	box ht 0.5 wid 2.3
.ps 15
	$1 at 1/2 <M.w, M.nw> + (.2, 0) ljust
.ps 9
	$2 at 1/2 <M.w, M.sw> + (.2, 0) ljust
.ps 20
] }
# part2(title, description)
define part2 { [
M:	box ht 0.3 wid 2.6
.ps 13
	$1 ljust at M.w + (.2, 0)
.ps 9
	$2 ljust at M + (-.4, 0)
.ps 20
] }
.ps 20
lineht = .3
HEAD:	"\s(17\fI\fP\s0"
	down
	move .3
IN:	part("in.c", "Input handling")
	arrow
CP:	part("cp.c", "Copy-mode interpretation")
	arrow
TR:	part("tr.c", "Troff request/macro execution")
	arrow
REN:	part("ren.c", "Rendering, traps, and diversions")
	arrow
OUT:	part("out.c", "Generating Troff output")
	"\s(17\fI\fP\s0" at HEAD + (3, 0)
	move .3
REG:	part2("reg.c", "Registers and environments")
	move down 0.2
FMT:	part2("wb.c", "Word buffer")
	move same
	part2("eval.c", "Integer expression evaluation")
	move same
	part2("fmt.c", "Line formatting")
	move same
DEV:	part2("dev.c", "Output device")
	move same
FONT:	part2("font.c", "Fonts")
	move same
	part2("hyph.c", "Tex hyphenation")
	move same
	part2("dir.c", "Text direction")
.PE
.KE