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auctex / doc / preview-dtxdoc.texi

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The main purpose of this package is the extraction of certain
environments (most notably displayed formulas) from @LaTeX{} sources
as graphics.  This works with @acronym{DVI} files postprocessed by either
Dvips and Ghostscript or dvipng, but it also works when you are
using PDF@TeX{}for generating PDF files (usually also postprocessed
by Ghostscript).

Current uses of the package include the @previewlatex{} package for
WYSIWYG functionality in the @AUCTeX{} editing environment,
generation of previews in LyX, as part of the operation of the
ps4pdf package, the tbook XML system and some other tools.

Producing @acronym{EPS} files with Dvips and its derivatives using the
@option{-E} option is not a good alternative: People make do by
fiddling around with @code{\thispagestyle@{empty@}} and hoping for the best
(namely, that the specified contents will indeed fit on single
pages), and then trying to guess the baseline of the resulting code
and stuff, but this is at best dissatisfactory.  The preview package
provides an easy way to ensure that exactly one page per request
gets shipped, with a well-defined baseline and no page decorations.
While you still can use the preview package with the `classic'

@example
dvips -E -i
@end example

@noindent
invocation, there are better ways available that don't rely on Dvips
not getting confused by PostScript specials.

For most applications, you'll want to make use of the @code{tightpage}
option.  This will embed the page dimensions into the PostScript or
PDF code, obliterating the need to use the @code{-E -i} options to Dvips.
You can then produce all image files with a single run of
Ghostscript from a single PDF or PostScript (as opposed to @acronym{EPS})
file.

Various options exist that will pass @TeX{} dimensions and other
information about the respective shipped out material (including
descender size) into the log file, where external applications might
make use of it.

The possibility for generating a whole set of graphics with a single
run of Ghostscript (whether from @LaTeX{} or PDF@LaTeX{}) increases
both speed and robustness of applications.  It is also feasible to
use dvipng on a @acronym{DVI} file with the options

@example
-picky -noghostscript
@end example

@noindent
to omit generating any image file that requires Ghostscript, then
let a script generate all missing files using Dvips/Ghostscript.
This will usually speed up the process significantly.

@menu
* Package options::
* Provided commands::
@end menu

@node Package options, Provided commands, The LaTeX style file, The LaTeX style file
@subsection Package options
The package is included with the customary

@example
\usepackage[@var{options}]@{preview@}
@end example

@noindent
You should usually load this package as the last one, since it
redefines several things that other packages may also provide.

The following options are available:

@table @w
@item @code{active}
is the most essential option.  If this option is not
specified, the @code{preview} package will be inactive and the document
will be typeset as if the @code{preview} package were not loaded,
except that all declarations and environments defined by the
package are still legal but have no effect.  This allows defining
previewing characteristics in your document, and only activating
them by calling @LaTeX{} as

@example
latex '\PassOptionsToPackage@{active@}@{preview@} \input@{@var{filename}@}'
@end example

@item @code{noconfig}
Usually the file @file{prdefault.cfg} gets loaded
whenever the @code{preview} package gets activated.  @file{prdefault.cfg} is
supposed to contain definitions that can cater for otherwise bad
results, for example, if a certain document class would otherwise
lead to trouble.  It also can be used to override any settings
made in this package, since it is loaded at the very end of it.
In addition, there may be configuration files specific for certain
@code{preview} options like @code{auctex} which have more immediate needs.
The @code{noconfig} option suppresses loading of those option files,
too.
@item @code{psfixbb}
Dvips determines the bounding boxes from the
material in the @acronym{DVI} file it understands.  Lots of PostScript
specials are not part of that.  Since the @TeX{} boxes do not make
it into the @acronym{DVI} file, but merely characters, rules and specials
do, Dvips might include far too small areas.  The option @code{psfixbb}
will include @file{/dev/null} as a graphic file in the ultimate upper
left and lower right corner of the previewed box.  This will make
Dvips generate an appropriate bounding box.
@item @code{dvips}
If this option is specified as a class option or to
other packages, several packages pass things like page size
information to Dvips, or cause crop marks or draft messages
written on pages.  This seriously hampers the usability of
previews.  If this option is specified, the changes will be undone
if possible.
@item @code{pdftex}
If this option is set, PDF@TeX{} is assumed as the
output driver.  This mainly affects the @code{tightpage} option.
@item @code{displaymath}
will make all displayed math environments
subject to preview processing.  This will typically be the most
desired option.
@item @code{floats}
will make all float objects subject to preview
processing.  If you want to be more selective about what floats to
pass through to a preview, you should instead use the
@code{\PreviewSnarfEnvironment} command on the floats you want to
have previewed.
@item @code{textmath}
will make all text math subject to previews.
Since math mode is used throughly inside of @LaTeX{} even for other
purposes, this works by redefining @code{\(}, @code{\)}
and @code{$} and the @code{math} environment (apparently some people use
that).  Only occurences of these text math delimiters in later
loaded packages and in the main document will thus be affected.
@item @code{graphics}
will subject all @code{\includegraphics} commands
to a preview.
@item @code{sections}
will subject all section headers to a preview.
@item @code{delayed}
will delay all activations and redefinitions the
@code{preview} package makes until @code{\}@code{begin@{document@}}.  The purpose
of this is to cater for documents which should be subjected to the
@code{preview} package without having been prepared for it.  You can
process such documents with

@example
latex '\RequirePackage[active,delayed,@var{options}]@{preview@}
\input@{@var{filename}@}'
@end example

@noindent
This relaxes the requirement to be loading the @code{preview} package
as last package.
@item @var{driver}
loads a special driver file
@file{pr@var{driver}.def}.  The remaining options are implemented
through the use of driver files.
@item @code{auctex}
This driver will produce fake error messages at the
start and end of every preview environment that enable the Emacs
package @previewlatex{} in connection with @AUCTeX{} to pinpoint
the exact source location where the previews have originated.
Unfortunately, there is no other reliable means of passing the
current @TeX{} input position @emph{in} a line to external
programs.  In order to make the parsing more robust, this option
also switches off quite a few diagnostics that could be
misinterpreted.

You should not specify this option manually, since it will only be
needed by automated runs that want to parse the pseudo error
messages.  Those runs will then use @code{\PassOptionsToPackage} in
order to effect the desired behaviour.  In addition,
@file{prauctex.cfg} will get loaded unless inhibited by the @code{noconfig}
option.  This caters for the most frequently encountered
problematic commands.
@item @code{showlabels}
During the editing process, some people like to
see the label names in their equations, figures and the like.  Now
if you are using Emacs for editing, and in particular
@previewlatex{}, I'd strongly recommend that you check out the
Ref@TeX{} package which pretty much obliterates the need for this
kind of functionality.  If you still want it, standard @LaTeX{}
provides it with the @code{showkeys} package, and there is also the
less encompassing @code{showlabels} package.  Unfortunately, since
those go to some pain not to change the page layout and spacing,
they also don't change @code{preview}'s idea of the @TeX{} dimensions of
the involved boxes.  So if you are using @code{preview} for determing
bounding boxes, those packages are mostly useless.  The option
@code{showlabels} offers a substitute for them.
@item @code{tightpage}
It is not uncommon to want to use the results of
@code{preview} as graphic images for some other application.  One
possibility is to generate a flurry of @acronym{EPS} files with

@example
dvips -E -i -Pwww -o @var{outputfile}.000 @var{inputfile}
@end example

@noindent
However, in case those are to be processed further into graphic
image files by Ghostscript, this process is inefficient since all
of those files need to be processed one by one.  In addition, it
is necessary to extract the bounding box comments from the @acronym{EPS}
files and convert them into page dimension parameters for
Ghostscript in order to avoid full-page graphics.  This is not
even possible if you wanted to use Ghostscript in a@w{ }@emph{single}
run for generating the files from a single PostScript file, since
Dvips will in that case leave no bounding box information
anywhere.

The solution is to use the @code{tightpage} option.  That way a single
command line like

@example
@option{gs -sDEVICE=png16m -dTextAlphaBits=4 -r300
-dGraphicsAlphaBits=4 -dSAFER -q -dNOPAUSE
-sOutputFile=@var{outputfile}%d.png @var{inputfile}.ps}
@end example

@noindent
will be able to produce tight graphics from a single PostScript
file generated with Dvips @emph{without} use of the options
@code{-E -i}, in a single run.

The @code{tightpage} option actually also works when using the @code{pdftex}
option and generating PDF files with PDF@TeX{}.  The resulting PDF
file has separate page dimensions for every page and can directly
be converted with one run of Ghostscript into image files.

If neither @code{dvips} or @code{pdftex} have been specified, the
corresponding option will get autodetected and invoked.

If you need this in a batch environment where you don't want to
use @code{preview}'s automatic extraction facilities, no problem: just
don't use any of the extraction options, and wrap everything to be
previewed into @code{preview} environments.  This is how LyX does its
math previews.

If the pages under the @code{tightpage} option are just too tight, you
can adjust by setting the length @code{\PreviewBorder} to a different
value by using @code{\setlength}.  The default value is
@file{0.50001bp}, which is half of a usual PostScript point, rounded
up.  If you go below this value, the resulting page size may drop
below @code{1bp}, and Ghostscript does not seem to like that.  If you
need finer control, you can adjust the bounding box dimensions
individually by changing the macro @code{\PreviewBbAdjust} with the
help of @code{\renewcommand}.  Its default value is

@example
\newcommand \PreviewBbAdjust
@{-\PreviewBorder -\PreviewBorder
\PreviewBorder  \PreviewBorder@}
@end example

@noindent
This adjusts the left, lower, right and upper borders by the given
amount.  The macro must contain 4@w{ }@TeX{} dimensions after another,
and you may not omit the units if you specify them explicitly
instead of by register.  PostScript points have the unit@w{ }@code{bp}.
@item @code{lyx}
This option is for the sake of LyX developers.  It will
output a few diagnostics relevant for the sake of LyX' preview
functionality (at the time of writing, mostly implemented for math
insets, in versions of LyX starting with 1.3.0).
@item @code{counters}
This writes out diagnostics at the start and the
end of previews.  Only the counters changed since the last output
get written, and if no counters changed, nothing gets written at
all.  The list consists of counter name and value, both enclosed
in @code{@{@}} braces, followed by a space.  The last such pair is
followed by a colon (@code{:}) if it is at the start of the preview
snippet, and by a period (@file{.}) if it is at the end.  The order of
different diagnostics like this being issued depends on the order
of the specification of the options when calling the package.

Systems like @previewlatex{} use this for keeping counters accurate
when single previews are regenerated.
@item @code{footnotes}
This makes footnotes render as previews, and only
as their footnote symbol.  A convenient editing feature inside of
Emacs.
@end table

The following options are just for debugging purposes of the package
and similar to the corresponding @TeX{} commands they allude to:

@table @w
@item @code{tracingall}
causes lots of diagnostic output to appear in
the log file during the preview collecting phases of @TeX{}'s
operation.  In contrast to the similarly named @TeX{} command, it
will not switch to @code{\errorstopmode}, nor will it change the
setting of @code{\tracingonline}.
@item @code{showbox}
This option will show the contents of the boxes
shipped out to the @acronym{DVI} files.  It also sets @code{\showboxbreadth} and
@code{\showboxdepth} to their maximum values at the end of loading this
package, but you may reset them if you don't like that.
@end table

@node Provided commands, ,Package options, The LaTeX style file
@subsection Provided commands

@table @code
@item \begin@{preview@}@dots{}\end@{preview@}
The @code{preview} environment causes its contents
to be set as a single preview image.  Insertions like figures and
footnotes (except those included in minipages) will typically lead
to error messages or be lost.  In case the @code{preview} package has not
been activated, the contents of this environment will be typeset
normally.

@item \begin@{nopreview@}@dots{}\end@{nopreview@}
The @code{nopreview} environment will cause its
contents not to undergo any special treatment by the @code{preview}
package.  When @code{preview} is active, the contents will be discarded
like all main text that does not trigger the @code{preview} hooks.  When
@code{preview} is not active, the contents will be typeset just like the
main text.

Note that both of these environments typeset things as usual when
preview is not active.  If you need something typeset conditionally,
use the @code{\ifPreview} conditional for it.

@item \PreviewMacro
If you want to make a macro like
@findex \PreviewMacro
@code{\includegraphics} (actually, this is what is done by the
@code{graphics} option to @code{preview}) produce a preview image, you put a
declaration like

@example
\PreviewMacro[*[[!]@{\includegraphics@}
@end example

@noindent
or, more readable,

@example
\PreviewMacro[@{*[][]@{@}@}]@{\includegraphics@}
@end example

@noindent
into your preamble.  The optional argument to @code{\PreviewMacro}
specifies the arguments @code{\includegraphics} accepts, since this
is necessary information for properly ending the preview box.  Note
that if you are using the more readable form, you have to enclose
the argument in a @code{[@{} and @code{@}]} pair.  The inner braces are
necessary to stop any included @code{[]} pairs from prematurely ending
the optional argument, and to make a single @code{@{@}}
denoting an optional argument not get stripped away by @TeX{}'s
argument parsing.

The letters simply mean

@table @w
@item @code{*}
indicates an optional @code{*} modifier, as in
@code{\includegraphics*}.
@item @code{[}
^^A]
indicates an optional argument in brackets.  This syntax
is somewhat baroque, but brief.
@item @code{[]}
also indicates an optional argument in brackets.  Be
sure to have encluded the entire optional argument specification
in an additional pair of braces as described above.
@item @code{!}
indicates a mandatory argument.
@item @code{@{@}}
indicates the same.  Again, be sure to have
that additional level of braces around the whole argument
specification.
@item @code{?}@var{delimiter}@{@var{true case}@}@{@var{false case}@}
is a
conditional.  The next character is checked against being equal to
@var{delimiter}.  If it is, the specification @var{true case} is
used for the further parsing, otherwise @var{false case} will be
employed.  In neither case is something consumed from the input,
so @{@var{true case}@} will still have to deal with the upcoming
delimiter.
@item @code{@@}@{@var{literal sequence}@}
will insert the given sequence
literally into the executed call of the command.
@item @code{-}
will just drop the next token.  It will probably be most
often used in the true branch of a @code{?} specification.
@item @code{#}@{@var{argument}@}@{@var{replacement}@}
is a transformation
rule that calls a macro with the given argument and replacement
text on the rest of the argument list.  The replacement is used in
the executed call of the command.  This can be used for parsing
arbitrary constructs.  For example, the @code{[]} option could manually
be implemented with the option string @code{?[@{#@{[#1]@}@{[@{#1@}]@}@}@{@}}.
PStricks users might enjoy this sort of flexibility.
@item @code{:}@{@var{argument}@}@{@var{replacement}@}
is again a
transformation rule.  As opposed to @code{#}, however, the result of
the transformation is parsed again.  You'll rarely need this.
@end table


There is a second optional argument in brackets that can be used to
declare any default action to be taken instead.  This is mostly for
the sake of macros that influence numbering: you would want to keep
their effects in that respect.  The default action should use @code{#1}
for referring to the original (not the patched) command with the
parsed options appended.  Not specifying a second optional argument
here is equivalent to specifying@w{ }@code{[#1]}.

@item \PreviewMacro*
A similar invocation
@code{\PreviewMacro*} simply throws the macro and all of its
arguments declared in the manner above away.  This is mostly useful
for having things like @code{\footnote} not do their magic on their
arguments.  More often than not, you don't want to declare any
arguments to scan to @code{\PreviewMacro*} since you would want the
remaining arguments to be treated as usual text and typeset in that
manner instead of being thrown away.  An exception might be, say,
sort keys for @code{\cite}.

A second optional argument in brackets can be used to declare any
default action to be taken instead.  This is for the sake of macros
that influence numbering: you would want to keep their effects in
that respect.  The default action might use @code{#1} for referring to
the original (not the patched) command with the parsed options
appended.  Not specifying a second optional argument here is
equivalent to specifying@w{ }@code{[]} since the command usually gets thrown
away.

As an example for using this argument, you might want to specify

@example
\PreviewMacro*\footnote[@{[]@}][#1@{@}]
@end example

@noindent
This will replace a footnote by an empty footnote, but taking any
optional parameter into account, since an optional paramter changes
the numbering scheme.  That way the real argument for the footnote
remains for processing by @previewlatex{}.

@item \PreviewEnvironment
The macro
@findex \PreviewEnvironment
@code{\PreviewEnvironment} works just as @code{\PreviewMacro} does,
only for environments.  @item \PreviewEnvironment*
And the
same goes for @code{\PreviewEnvironment*} as compared to
@code{\PreviewMacro*}.

@item \PreviewSnarfEnvironment
This macro does not typeset
the original environment inside of a preview box, but instead
typesets just the contents of the original environment inside of the
preview box, leaving nothing for the original environment.  This has
to be used for figures, for example, since they would

@enumerate
@item produce insertion material that cannot be extracted to the
preview properly,
@item complain with an error message about not being in outer par
mode.
@end enumerate


@item \PreviewOpen
@item \PreviewClose
Those Macros form a matched preview pair.  This is for macros that
behave similar as @code{\begin} and @code{\end} of an environment.  It
is essential for the operation of @code{\PreviewOpen} that the macro
treated with it will open an additional group even when the preview
falls inside of another preview or inside of a @code{nopreview}
environment.  Similarly, the macro treated with @code{PreviewClose}
will close an environment even when inactive.

@item \ifPreview
In case you need to know whether
@code{preview} is active, you can use the conditional @code{\ifPreview}
together with @code{\else} and @code{\fi}.

@end table