6 For advanced users

This package consists of two parts: a LaTeX style that splits the output into appropriate parts with one preview object on each page, and an Emacs-lisp part integrating the thing into Emacs (aided by AUCTeX).

6.1 The LaTeX style file

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

Current uses of the package include the preview-latex package for WYSIWYG functionality in the AUCTeX editing environment, generation of previews in LyX, as part of the operation of the pst-pdf package, the tbook XML system and some other tools.

Producing EPS files with Dvips and its derivatives using the -E option is not a good alternative: People make do by fiddling around with \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’

dvips -E -i

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 tightpage option. This will embed the page dimensions into the PostScript or PDF code, obliterating the need to use the -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 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 PDFLaTeX) increases both speed and robustness of applications. It is also feasible to use dvipng on a DVI file with the options

-picky -noghostscript

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.

6.1.1 Package options

The package is included with the customary

\usepackage[options]{preview}

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:

active

is the most essential option. If this option is not specified, the preview package will be inactive and the document will be typeset as if the 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

latex '\PassOptionsToPackage{active}{preview} \input{filename}'

noconfig

Usually the file prdefault.cfg gets loaded whenever the preview package gets activated. 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 preview options like auctex which have more immediate needs. The noconfig option suppresses loading of those option files, too.

psfixbb

Dvips determines the bounding boxes from the material in the DVI file it understands. Lots of PostScript specials are not part of that. Since the TeX boxes do not make it into the DVI file, but merely characters, rules and specials do, Dvips might include far too small areas. The option psfixbb will include /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.

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.

pdftex

If this option is set, PDFTeX is assumed as the output driver. This mainly affects the tightpage option.

xetex

If this option is set, XeTeX is assumed as the output driver. This mainly affects the tightpage option.

displaymath

will make all displayed math environments subject to preview processing. This will typically be the most desired option.

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 \PreviewSnarfEnvironment command on the floats you want to have previewed.

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 \(, \) and $ and the 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.

graphics

will subject all \includegraphics commands to a preview.

sections

will subject all section headers to a preview.

delayed

will delay all activations and redefinitions the preview package makes until \begin{document}. The purpose of this is to cater for documents which should be subjected to the preview package without having been prepared for it. You can process such documents with

latex '\RequirePackage[active,delayed,options]{preview}
\input{filename}'

This relaxes the requirement to be loading the preview package as last package.

driver

loads a special driver file prdriver.def. The remaining options are implemented through the use of driver files.

auctex

This driver will produce fake error messages at the start and end of every preview environment that enable the Emacs package preview-latex 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 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 \PassOptionsToPackage in order to effect the desired behaviour. In addition, prauctex.cfg will get loaded unless inhibited by the noconfig option. This caters for the most frequently encountered problematic commands.

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 preview-latex, I’d strongly recommend that you check out the RefTeX package which pretty much obliterates the need for this kind of functionality. If you still want it, standard LaTeX provides it with the showkeys package, and there is also the less encompassing showlabels package. Unfortunately, since those go to some pain not to change the page layout and spacing, they also don’t change preview’s idea of the TeX dimensions of the involved boxes. So if you are using preview for determing bounding boxes, those packages are mostly useless. The option showlabels offers a substitute for them.

tightpage

It is not uncommon to want to use the results of preview as graphic images for some other application. One possibility is to generate a flurry of EPS files with

dvips -E -i -Pwww -o outputfile.000 inputfile

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 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 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 tightpage option. That way a single command line like

gs -sDEVICE=png16m -dTextAlphaBits=4 -r300
-dGraphicsAlphaBits=4 -dSAFER -q -dNOPAUSE
-sOutputFile=outputfile%d.png inputfile.ps

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

The tightpage option actually also works when using the pdftex option and generating PDF files with PDFTeX. 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 dvips or 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 preview’s automatic extraction facilities, no problem: just don’t use any of the extraction options, and wrap everything to be previewed into preview environments. This is how LyX does its math previews.

If the pages under the tightpage option are just too tight, you can adjust by setting the length \PreviewBorder to a different value by using \setlength. The default value is 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 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 \PreviewBbAdjust with the help of \renewcommand. Its default value is

\newcommand \PreviewBbAdjust
{-\PreviewBorder -\PreviewBorder
\PreviewBorder  \PreviewBorder}

This adjusts the left, lower, right and upper borders by the given amount. The macro must contain 4 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 bp.

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).

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 {} braces, followed by a space. The last such pair is followed by a colon (:) if it is at the start of the preview snippet, and by a period (.) 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 preview-latex use this for keeping counters accurate when single previews are regenerated.

footnotes

This makes footnotes render as previews, and only as their footnote symbol. A convenient editing feature inside of Emacs.

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

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 \errorstopmode, nor will it change the setting of \tracingonline.

showbox

This option will show the contents of the boxes shipped out to the DVI files. It also sets \showboxbreadth and \showboxdepth to their maximum values at the end of loading this package, but you may reset them if you don’t like that.

6.1.2 Provided commands

\begin{preview}…\end{preview}

The 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 preview package has not been activated, the contents of this environment will be typeset normally.

\begin{nopreview}…\end{nopreview}

The nopreview environment will cause its contents not to undergo any special treatment by the preview package. When preview is active, the contents will be discarded like all main text that does not trigger the preview hooks. When 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 \ifPreview conditional for it.

\PreviewMacro

If you want to make a macro like \includegraphics (actually, this is what is done by the graphics option to preview) produce a preview image, you put a declaration like

\PreviewMacro[*[[!]{\includegraphics}

or, more readable,

\PreviewMacro[{*[][]{}}]{\includegraphics}

into your preamble. The optional argument to \PreviewMacro specifies the arguments \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 [{ and }] pair. The inner braces are necessary to stop any included [] pairs from prematurely ending the optional argument, and to make a single {} denoting an optional argument not get stripped away by TeX’s argument parsing.

The letters simply mean

*

indicates an optional * modifier, as in \includegraphics*.

[

^^A] indicates an optional argument in brackets. This syntax is somewhat baroque, but brief.

[]

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.

!

indicates a mandatory argument.

{}

indicates the same. Again, be sure to have that additional level of braces around the whole argument specification.

?delimiter{true case}{false case}

is a conditional. The next character is checked against being equal to delimiter. If it is, the specification true case is used for the further parsing, otherwise false case will be employed. In neither case is something consumed from the input, so {true case} will still have to deal with the upcoming delimiter.

@{literal sequence}

will insert the given sequence literally into the executed call of the command.

-

will just drop the next token. It will probably be most often used in the true branch of a ? specification.

#{argument}{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 [] option could manually be implemented with the option string ?[{#{[#1]}{[{#1}]}}{}. PStricks users might enjoy this sort of flexibility.

:{argument}{replacement}

is again a transformation rule. As opposed to #, however, the result of the transformation is parsed again. You’ll rarely need this.

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 #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 [#1].

\PreviewMacro*

A similar invocation \PreviewMacro* simply throws the macro and all of its arguments declared in the manner above away. This is mostly useful for having things like \footnote not do their magic on their arguments. More often than not, you don’t want to declare any arguments to scan to \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 \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 #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 [] since the command usually gets thrown away.

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

\PreviewMacro*[{[]}][#1{}]{\footnote}

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 preview-latex.

\PreviewEnvironment

The macro \PreviewEnvironment works just as \PreviewMacro does, only for environments.

\PreviewEnvironment*

And the same goes for \PreviewEnvironment* as compared to \PreviewMacro*.

\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

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

\PreviewOpen

\PreviewClose

Those Macros form a matched preview pair. This is for macros that behave similar as \begin and \end of an environment. It is essential for the operation of \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 nopreview environment. Similarly, the macro treated with \PreviewClose will close an environment even when inactive.

\ifPreview

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

6.2 The Emacs interface

You can use M-x customize-group RET preview-latex RET in order to customize these variables, or use the menus for it. We explain the various available options together with explaining how they work together in making preview-latex work as intended.

preview-LaTeX-command

When you generate previews on a buffer or a region, the command in preview-LaTeX-command gets run (that variable should only be changed with Customize since its structure is somewhat peculiar, though expressive). As usual with AUCTeX, you can continue working while this is going on. It is not a good idea to change the file until after preview-latex has established where to place the previews which it can only do after the LaTeX run completes. This run produces a host of pseudo-error messages that get parsed by preview-latex at the end of the LaTeX run and give it the necessary information about where in the source file the LaTeX code for the various previews is located exactly. The parsing takes a moment and will render Emacs busy.

preview-LaTeX-command-replacements

This variable specifies transformations to be used before calling the configured command. One possibility is to have ‘\pdfoutput=0 ’ appended to every command starting with ‘pdf’. This particular setting is available as the shortcut ‘preview-LaTeX-disable-pdfoutput’. Since preview-latex can work with PDF files by now, there is little incentive for using this option, anymore (for projects not requiring PDF output, the added speed of ‘dvipng’ might make this somewhat attractive).

preview-required-option-list

preview-LaTeX-command uses preview-required-option-list in order to pass options such as auctex, active and dvips to the preview package. This means that the user need (and should) not supply these in the document itself in case he wants to be able to still compile his document without it turning into an incoherent mass of little pictures. These options even get passed in when the user loads preview explicitly in his document.

The default includes an option counters that is controlled by the boolean variable

preview-preserve-counters

This option will cause the preview package to emit information that will assist in keeping things like equation counters and section numbers reasonably correct even when you are regenerating only single previews.

preview-default-option-list

preview-default-preamble

If the document does not call in the package preview itself (via \usepackage) in the preamble, the preview package is loaded using default options from preview-default-option-list and additional commands specified in preview-default-preamble.

preview-fast-conversion

This is relevant only for DVI mode. It defaults to ‘On’ and results in the whole document being processed as one large PostScript file from which the single images are extracted with the help of parsing the PostScript for use of so-called DSC comments. The bounding boxes are extracted with the help of TeX instead of getting them from Dvips. If you are experiencing bounding box problems, try setting this option to ‘Off’.

preview-prefer-TeX-bb

If this option is ‘On’, it tells preview-latex never to try to extract bounding boxes from the bounding box comments of EPS files, but rather rely on the boxes it gets from TeX. If you activated preview-fast-conversion, this is done, anyhow, since there are no EPS files from which to read this information. The option defaults to ‘Off’, simply because about the only conceivable reason to switch off preview-fast-conversion would be that you have some bounding box problem and want to get Dvips’ angle on that matter.

preview-scale-function

preview-reference-face

preview-document-pt-list

preview-default-document-pt

preview-scale-function determines by what factor images should be scaled when appearing on the screen. If you specify a numerical value here, the physical size on the screen will be that of the original paper output scaled by the specified factor, at least if Emacs’ information about screen size and resolution are correct. The default is to let preview-scale-from-face determine the scale function. This function determines the scale factor by making the size of the default font in the document match that of the on-screen fonts.

The size of the screen fonts is deduced from the font preview-reference-face (usually the default face used for display), the size of the default font for the document is determined by calling preview-document-pt. This function consults the members of preview-document-pt-list in turn until it gets the desired information. The default consults first preview-parsed-font-size, then calls preview-auctex-font-size which asks AUCTeX about any size specification like 12pt to the documentclass that it might have detected when parsing the document, and finally reverts to just assuming preview-default-document-pt as the size used in the document (defaulting to 10pt).

If you find that the size of previews and the other Emacs display clashes, something goes wrong. preview-parsed-font-size is determined at \begin{document} time; if the default font size changes after that, it will not get reported. If you have an outdated version of preview.sty in your path, the size might not be reported at all. If in this case AUCTeX is unable to find a size specification, and if you are using a document class with a different default value (like KomaScript), the default fallback assumption will probably be wrong and preview-latex will scale up things too large. So better specify those size options even when you know that LaTeX does not need them: preview-latex might benefit from them. Another possibility for error is that you have not enabled AUCTeX’s document parsing options. The fallback method of asking AUCTeX about the size might be disabled in future versions of preview-latex since in general it is more reliable to get this information from the LaTeX run itself.

preview-fast-dvips-command

preview-dvips-command

The regular command for turning a DVI file into a single PostScript file is preview-fast-dvips-command, while preview-dvips-command is used for cranking out a DVI file where every preview is in a separate EPS file. Which of the two commands gets used depends on the setting of preview-fast-conversion. The printer specified here by default is -Pwww by default, which will usually get you scalable fonts where available. If you are experiencing problems, you might want to try playing around with Dvips options (See (dvips)Command-line options).

The conversion of the previews into PostScript or EPS files gets started after the LaTeX run completes when Emacs recognizes the first image while parsing the error messages. When Emacs has finished parsing the error messages, it activates all detected previews. This entails throwing away any previous previews covering the same areas, and then replacing the text in its visual appearance by a placeholder looking like a roadworks sign.

preview-nonready-icon-specs

This is the roadworks sign displayed while previews are being prepared. You may want to customize the font sizes at which preview-latex switches over between different icon sizes, and the ascent ratio which determines how high above the base line the icon gets placed.

preview-error-icon-specs

preview-icon-specs

Those are icons placed before the source code of an opened preview and, respectively, the image specs to be used for PostScript errors, and a normal open preview in text representation.

preview-inner-environments

This is a list of environments that are regarded as inner levels of an outer environment when doing preview-environment. One example when this is needed is in \begin{equation}\begin{split}…\end{split}\end{equation}, and accordingly split is one entry in preview-inner-environments.

6.3 The preview images

preview-image-type

preview-image-creators

preview-gs-image-type-alist

What happens when LaTeX is finished depends on the configuration of preview-image-type. What to do for each of the various settings is specified in the variable preview-image-creators. The options to pass into Ghostscript and what Emacs image type to use is specified in preview-gs-image-type-alist.

preview-image-type defaults to png. For this to work, your version of Ghostscript needs to support the png16m device. If you are experiencing problems here, you might want to reconfigure gs-image-type-alist or preview-image-type. Reconfiguring preview-image-creators is only necessary for adding additional image types.

Most devices make preview-latex start up a single Ghostscript process for the entire preview run (as opposed to one per image) and feed it either sections of a PDF file (if PDFLaTeX was used), or (after running Dvips) sections of a single PostScript file or separate EPS files in sequence for conversion into PNG format which can be displayed much faster by Emacs. Actually, not in sequence but backwards since you are most likely editing at the end of the document. And as an added convenience, any preview that happens to be on-screen is given higher priority so that preview-latex will first cater for the images that are displayed. There are various options customizable concerning aspects of that operation, see the customization group Preview Gs for this.

Another noteworthy setting of preview-image-type is ‘dvipng’: in this case, the ‘dvipng’ program will get run on DVI output (see below for PDF). This is in general much faster than Dvips and Ghostscript. In that case, the option

preview-dvipng-command

will get run for doing the conversion, and it is expected that

preview-dvipng-image-type

images get produced (‘dvipng’ might be configured for other image types as well). You will notice that preview-gs-image-type-alist contains an entry for dvipng: this actually has nothing to with ‘dvipng’ itself but specifies the image type and Ghostscript device option to use when ‘dvipng’ can’t be used. This will obviously be the case for PDF output by PDFLaTeX, but it will also happen if the DVI file contains PostScript specials in which case the affected images will get run through Dvips and Ghostscript once ‘dvipng’ finishes.

Note for pLaTeX and upLaTeX users: It is known that dvipng is not compatible with pLaTeX and upLaTeX. If preview-image-type is set to ‘dvipng’ and (u)pLaTeX is used, ‘dvipng’ just fails and preview-latex falls back on Dvips and Ghostscript.

preview-gs-options

Most interesting to the user perhaps is the setting of this variable. It contains the default antialiasing settings -dTextAlphaBits=4 and -dGraphicsAlphaBits=4. Decreasing those values to 2 or 1 might increase Ghostscript’s performance if you find it lacking.

Running and feeding Ghostscript from preview-latex happens asynchronously again: you can resume editing while the images arrive. While those pretty pictures filling in the blanks on screen tend to make one marvel instead of work, rendering the non-displayed images afterwards will not take away your attention and will eventually guarantee that jumping around in the document will encounter only prerendered images.

6.4 Misplaced previews

If you are reading this section, the first thing is to check that your problem is not caused by x-symbol in connection with an installation not supporting 8-bit characters (see x-symbol interoperation). If not, here’s the beef:

As explained previously, Emacs uses pseudo-error messages generated by the ‘preview’ package in order to pinpoint the exact source location where a preview originated. This works in running text, but fails when preview material happens to lie in macro arguments, like the contents of \emph. Those macros first read in their entire argument, munge it through, perhaps transform it somehow, process it and perhaps then typeset something. When they finally typeset something, where is the location where the stuff originated? TeX, having read in the entire argument before, does not know and actually there would be no sane way of defining it.

For previews contained inside such a macro argument, the default behaviour of preview-latex is to use a position immediately after the closing brace of the argument. All the previews get placed there, all at a zero-width position, which means that Emacs displays it in an order that preview-latex cannot influence (currently in Emacs it is even possible that the order changes between runs). And since the placement of those previews is goofed up, you will not be able to regenerate them by clicking on them. The default behaviour is thus somewhat undesirable.

The solution (like with other preview problems) is to tell the LaTeX ‘preview’ package how to tackle this problem (see The LaTeX style file). Simply, you don’t need \emph do anything at all during previews! You only want the text math previewed, so the solution is to use \PreviewMacro*\emph in the preamble of your document which will make LaTeX ignore \emph completely as long as it is not part of a larger preview (in which case it gets typeset as usual). Its argument thus becomes ordinary text and gets treated like ordinary text.

Note that it would be a bad idea to declare \PreviewMacro*[{{}}]\emph since then both \emph as well as its argument would be ignored instead of previewed. For user-level macros, this is almost never wanted, but there may be internal macros where you might want to ignore internal arguments.

The same mechanism can be used for a number of other text-formatting commands like \textrm, \textit and the like. While they all use the same internal macro \text@command, it will not do to redefine just that, since they call it only after having read their argument in, and then it already is too late. So you need to disable every of those commands by hand in your document preamble.

Actually, we wrote all of the above just to scare you. At least all of the above mentioned macros and a few more are already catered for by a configuration file prauctex.cfg that gets loaded by default unless the ‘preview’ package gets loaded with the noconfig option. You can make your own copy of this file in a local directory and edit it in case of need. You can also add loading of a file of your liking to preview-default-preamble, or alternatively do the manual disabling of your favorite macro in preview-default-preamble, which is customizable in the Preview Latex group.