Как изменить расстояние между строками latex

setlength{parskip}{1pt plus2pt}

We also discuss some useful TeX/LaTeX macros, higher-level commands written and constructed using a sequence of constituent commands.

Commands used for paragraph spacing

The following commands (primitives and macros) can be used to affect paragraph spacing. Some are explored in more detail which can be accessed by following the link from the command name.

Primitive commands

• parindent: the amount of indentation (white space) added to the first line of a paragraph.
• parskip: the amount of flexible white space (“glue”) placed between paragraphs.
• rightskip: flexible spacing (glue) inserted to the right of each line in a paragraph.
• leftskip: flexible spacing (glue) inserted to the left of each line in a paragraph.
• baselineskip: the value of this parameter serves two roles:
  • it sets the desired distance between the baselines of text in a paragraph;
  • it is used to calculate the (variable) amount of space (glue) added between lines in order to achieve the desired baseline-to-baseline distance (see later in the article).
• lineskiplimit: a parameter whose value defines the minimum acceptable distance between two adjacent lines of a paragraph.
• lineskip: the amount of space (glue) inserted between two lines in a paragraph if the calculated baselineskip glue would result in lines being too close together.
• parfillskip: very flexible glue added at the end of the last line in a paragraph in order to “fill it” with white space; for a visual example, refer to the illustration in the section Visualizing other types of paragraph glue.

Macro commands

The following TeX/LaTeX macro commands are often used to modify paragraph spacing:

• offinterlineskip and nointerlineskip: commands which can be used to switch off calculation and insertion of baselineskip glue;
• baselinestretch: a command which stores a numeric factor used to calculate the value of baselineskip when a font is selected. It has a default value of 1;
• linespread: this command can be used to change the current value of baselinestretch.

Flexible spacing (glue)

TeX engines achieve spacing effects, including within or between paragraphs, through the use of a flexible white space called glue which can be stretched or shrunk according to the amount of space required. If you want to learn about TeX’s concept of glue, more details can be found in the following Overleaf articles:

• Exploring underfull or overfull boxes and badness calculations
• How TeX calculates glue settings in an hbox
• Understanding underfull and overfull box warnings.

The fundamentals: parameter commands and examples

In this section we explain a number of paragraph-related parameter commands and provide examples of their use.

parindent (TeX primitive)

This parameter command sets the amount of indentation (white space) added to the first line of a paragraph. It can be changed by using LaTeX’s setlength command; for example, to indent paragraphs by 15pt set parindent to 15pt by writing:

setlength{parindent}{15pt}

Note that:

• you can change parindent within a group, ensuring its effect is localized to paragraphs in that group;
• parindent can be negative, producing an “outdent” rather than an indent;
• by default LaTeX does not indent the first paragraph following a document section heading (section{...} etc).

The following example demonstrates the use of parindent.

documentclass{article}
% Choose a conveniently small page size
usepackage[paperheight=16cm,paperwidth=12cm,textwidth=8cm]{geometry}
% Create a command to hold a paragraph of text
newcommand{testpar}{texttt{stringparindent=theparindent }When TeX{} typesets a paragraph it treats each individual character as a 2D ``box'' with a specific width, height and depth.par}
begin{document}

% Set parskip to put 10pt between paragraphs
setlength{parskip}{10pt}

% Set the value of parindent to 0pt
setlength{parindent}{0pt}
testpar

% Set the value of parindent to 10pt
setlength{parindent}{10pt}
testpar

% Set parindent in a group
{setlength{parindent}{50pt}testpar}

% Now parindent is again 10pt
testpar

% Yes, you can have a negative parindent
setlength{parindent}{-20pt}
testpar
end{document}

 Open this example in Overleaf

This example produces the following output:

parskip (TeX primitive)

The legibility of text can be enhanced by separating paragraphs with an amount of white space that will vary according to some design aesthetic. TeX/LaTeX allow users to control that inter-paragraph spacing via the parskip parameter command.

• Advice from the parskip package: The parskip package advises that directly modifying parskip can “result in vertical spaces in unexpected places” (within a LaTeX document). The parskip package attempts to fix spacing issues that might arise from changes to the value of parskip—such as within table of contents and list environments. See also the parskip package section of this article.

To manually set the current value of parskip use LaTeX’s setlength command; for example, to separate paragraphs by 3pt you can write:

setlength{parskip}{3pt}

The following example demonstrates the use of parskip:

documentclass{article}
% Choose a conveniently small page size
usepackage[paperheight=16cm,paperwidth=12cm,textwidth=8cm]{geometry}
% Create a command to hold a paragraph of text
newcommand{testpar}{noindent The current value of texttt{stringparskip} is texttt{theparskip}. When TeX{} typesets a paragraph it treats each individual character as a 2D~``box'' with a specific width, height and depth.par}
begin{document}
testpar
% Set parskip to 5pt 
setlength{parskip}{5pt}testpar
% Set parskip to 10pt
setlength{parskip}{10pt}testpar
% Set parskip to 25pt (but in a group)
{setlength{parskip}{25pt}testpar}
% Group ends, now parskip is again 10pt
testpar
% Yes, you can have a negative parskip
setlength{parskip}{-20pt}testpar
end{document}

 Open this example in Overleaf

This example produces the following output:

Flexible parskip

Traditionally, parskip is not a fixed value, which would result in the same amount of space between all paragraphs. Instead, parskip is usually defined as a “flexible space” (called glue) which enables TeX to stretch or shrink the space between paragraphs, helping to fit content on the page and find a “good” place for a page break.

To make parskip flexible you would write it in the form of a glue specification:

setlength{parskip}{fixed amount plus amount to stretch minus amount to shrink}

where plus and minus are keywords used by TeX/LaTeX to identify the amount to stretch or amount to shrink contained in a glue specification. The Overleaf article Exploring underfull or overfull boxes and badness calculations contains a more in-depth discussion of glue.

For example, to enable parskip to vary between 3 + 1 = 4pt and 3 — 1 = 2pt you could write

setlength{parskip}{3pt plus1pt minus1pt}

leftskip and rightskip (TeX primitives)

TeX engines provide two parameter commands which add space (glue) to the left and right of each line in the typeset paragraph. As their names suggest:

• leftskip inserts space (glue) to the left of each line in a paragraph;
• rightskip inserts space (glue) to right left of each line in a paragraph.

The following examples use leftskip and rightskip to directly modify paragraph alignment; however… changes to text alignment are usually best achieved via suitable LaTeX environments or packages—for example, see the Overleaf article on text alignment. Although we demonstrate the behaviour of some low-level (primitive) parameter commands provided by TeX engines, it is generally advisable to use appropriate LaTeX packages wherever possible.

Making leftskip fixed and rightskip flexible

The following example produces two paragraphs: the first uses LaTeX’s default values for leftskip and rightskip and the second paragraph is typeset using the following settings:

leftskip 10pt 
rightskip 0pt plus 1 fill

Open the following Overleaf project to see the output:

documentclass{article}
title{Second leftskip and rightskip example}
% Choose a conveniently small page size
usepackage[paperheight=16cm,paperwidth=12cm,textwidth=8cm]{geometry}
% Set the value of some paragraph-related parameters
setlength{lineskip}{3.5pt}
setlength{lineskiplimit}{2pt}
setlength{parindent}{20pt}
setlength{baselineskip}{12pt}

begin{document}
input text.tex % A generated TeX file which defines the macros
% mytextA and mytextB, each containing the text for a paragraph.
% Typeset a paragraph with default values of leftskip and rightskip

mytextB
 
% Set leftskip and rightskip to new values
leftskip 10pt
rightskip 0pt plus 1fill
vspace{8pt}

% Now re-typeset the same paragraph
mytextB

end{document}

 Open this example as an Overleaf LaTeX project

This example generates the following output:

The following graphic is an annotated version of the second paragraph produced by the example above. It is designed to highlight and show the amount of leftskip and rightskip glues inserted in the paragraph lines, together with the parindent space for the first line:

Note that leftskip glue has a fixed size (10pt) but rightskip glue has stretched to provide any amount of white space required to fill up the right-hand side of each line. This “flexibility” is due to the specification of rightskip which contains plus 1 fill—providing an “infinitely stretchable” form of glue.

Making rightskip fixed and leftskip flexible

The following example produces two paragraphs: the first uses LaTeX’s default values for leftskip and rightskip and the second paragraph is typeset using the following settings:

leftskip 0pt plus 1 fill
rightskip 10pt

Open the following Overleaf project to see the output:

documentclass{article}
title{leftskip and rightskip examples}
% Choose a conveniently small page size
usepackage[paperheight=16cm,paperwidth=12cm,textwidth=8cm]{geometry}
% Set the value of some paragraph-related parameters
setlength{lineskip}{3.5pt}
setlength{lineskiplimit}{2pt}
setlength{parindent}{20pt}
setlength{baselineskip}{12pt}

begin{document}
input text.tex % A generated TeX file which defines the macros
% mytextA and mytextB, each containing the text for a paragraph.
% Typeset a paragraph with default values of leftskip and rightskip

mytextB

% Set leftskip and rightskip to new values
rightskip 10pt
leftskip 0pt plus 1fill
vspace{8pt}

% Now re-typeset the same paragraph
mytextB

end{document}

 Open this example as an Overleaf LaTeX project

This example generates the following output:

The following graphic is an annotated version of the second paragraph produced by example above. It is designed to highlight and show the amount of leftskip and rightskip glues inserted in the paragraph lines, together with the parindent space for the first line:

Note that rightskip glue has a fixed size (10pt) but leftskip glue has stretched to provide any amount of white space required to fill up the left-hand side of each line. This “flexibility” is due to the specification of leftskip which contains plus 1 fill—providing an “infinitely stretchable” form of glue.

Setting leftskip and rightskip to flexible values

The following example produces two paragraphs: the first uses LaTeX’s default values for leftskip and rightskip and the second uses the following, flexible, glue settings:

leftskip 0pt plus 1fill
rightskip 0pt plus 1fill

These settings result in paragraph lines being centered:

documentclass{article}
title{leftskip and rightskip examples}
% Choose a conveniently small page size
usepackage[paperheight=16cm,paperwidth=12cm,textwidth=8cm]{geometry}
% Set the value of some paragraph-related parameters
setlength{lineskip}{3.5pt}
setlength{lineskiplimit}{2pt}
setlength{parindent}{20pt}
setlength{baselineskip}{12pt}

begin{document}
input text.tex % A generated TeX file which defines the macros
% mytextA and mytextB which define text for two paragraphs
% Typeset a paragraph with default values of leftskip and rightskip

mytextB

% Set leftskip and rightskip to "extremely flexible" glue settings
leftskip 0pt plus 1fill
rightskip 0pt plus 1fill
vspace{20pt}

% Now re-typeset the same paragraph
mytextB

end{document}

 Open this example as an Overleaf LaTeX project

This example generates the following output:

The following graphic is an annotated version of the second paragraph produced by example above. It is designed to highlight and show the amount of leftskip and rightskip glues inserted in the paragraph lines, together with the parindent space for the first line:

Note that both leftskip and rightskip are specified as 0pt plus 1fill making them equally “infinitely flexible”; consequently, they stretch by the same amount which results in typeset lines being centred.

Setting leftskip and rightskip in a group

The following example shows how to make temporary changes to leftskip and rightskip by enclosing them inside a group. In our example the group is created by begingroup… endgroup, as shown in the following code fragment:

begingroup
leftskip 0pt plus 1fill
rightskip 0pt plus 1fill
mytextB
endgroup

The first paragraph is typeset using “extremely flexible” glue for leftskip and rightskip:

leftskip 0pt plus 1fill
rightskip 0pt plus 1fill

but the second paragraph uses LaTeX’s default values:

documentclass{article}
title{Another leftskip and rightskip example}
% Choose a conveniently small page size
usepackage[paperheight=16cm,paperwidth=12cm,textwidth=8cm]{geometry}
% Set the value of some paragraph-related parameters
setlength{lineskip}{3.5pt}
setlength{lineskiplimit}{2pt}
setlength{parindent}{20pt}
setlength{baselineskip}{12pt}

begin{document}
input text.tex % A generated TeX file which defines the macros
% mytextA and mytextB which define text for two paragraphs
% Here we change leftskip and rightskip to "extremely flexible" glue settings
% within a group created by begingroup ... endgroup

begingroup
leftskip 0pt plus 1fill
rightskip 0pt plus 1fill
mytextB
endgroup

% Now re-typeset the same paragraph after the group has closed
% causing leftskip and rightskip revert to their previous values 

vspace{20pt}
mytextB

end{document}

 Open this example as an Overleaf LaTeX project

This example generates the following output:

Note: The settings for (effects of) leftskip and rightskip are restricted to the paragraph within the group created by begingroup… endgroup. After the group has been closed, the next paragraph is typeset using LaTeX’s default values for leftskip and rightskip.

baselineskip (TeX primitive)

It is generally accepted typesetting practice that lines of text within paragraphs should be equally spaced, except where certain lines contain large elements, such as mathematics or an image, which make it impossible to preserve constant interline spacing for such lines.

TeX/LaTeX provide commands and mechanisms which enable users to exercise some degree of control over interline spacing. One such command is baselineskip which gets, or sets, the value of a parameter that determines the preferred interline spacing (baseline-to-baseline distance) in a typeset paragraph.

To typeset the current value of baselineskip you can write

To set baselineskip to some value (a LaTeX length such as pt) you can write

setlength{baselineskip}{value}

For example, to set baselineskip to 12pt you can write

setlength{baselineskip}{12pt}

We can demonstrate the role of baselineskip by using the following (typical) paragraph:

and adding annotations which show the baseline-to-baseline distance controlled by baselineskip:

The diagram also shows the interline “glue”: a calculated amount of white space added between lines—we’ll further discuss this later in the article.

baselineskip and other parameters

baselineskip is one of four core parameters which control the amount of space inserted between lines of a paragraph; the others are:

• lineskip
• lineskiplimit
• prevdepth

Later in the article we’ll explore how these four parameters are used to calculate interline glue values.

baselineskip example (fixed space)

The following example opens in Overleaf to create a project containing a file called text.tex which defines the commands mytextA and mytextB—both commands typeset a paragraph. For convenience, the Overleaf project uses a small page size because that assists with preparing graphics and images for this help page.

documentclass{article}
title{Demonstrating baselineskip}
% Choose a conveniently small page size
usepackage[paperheight=16cm,paperwidth=12cm,textwidth=8cm]{geometry}
% Set the value of some paragraph-related parameters (we will discuss these)
setlength{lineskip}{3.5pt}
setlength{lineskiplimit}{2pt}
setlength{parindent}{20pt}
% Set the value of baselineskip---change the value to see the effect
setlength{baselineskip}{12pt}

begin{document}
input text.tex % A generated TeX file which defines the macros
% mytextA and mytextB, each of which typeset a paragraphs

% Firstly, typeset two paragraphs with the default baselineskip
mytextAmytextB

% Now change baselineskip to a larger value and typeset
% another paragraph
setlength{baselineskip}{24pt}
mytextA

end{document}

 Open this example as an Overleaf LaTeX project

This example generates the following output:

The paragraph on page 2 has widely spaced lines because baselineskip was set to 24pt.

baselineskip example (flexible space)

The following example specifies a baselineskip value which has an extremely flexible (so-called “infinite”) stretch component:

baselineskip=12pt plus1fil

Because of this flexibility, white space between paragraph lines can stretch by any amount required to fill the page. Such flexibility would result in paragraphs having very different amounts of space between their constituent lines of text, which might not be aesthetically pleasing or easy to read.

documentclass{article}
usepackage{blindtext}
title{Flexible texttt{stringbaselineskip} demo}
author{Overleaf}
date{January 2022}

begin{document}

maketitle
We’ll provide verb|baselineskip| with a very flexible ``stretch'' component by assigning the value texttt{12pt plus1fil}: verb|baselineskip=12pt plus1fil|.baselineskip=12pt plus1fil 
section{Introduction}
Add a paragraph that will now stretch to fill the page. blindtext

end{document}

 Open this example in Overleaf

This example produces the following output:

A few notes on glue

Some of the following notes are taken from the Overleaf article exploring underfull or overfull boxes and badness calculations, reproduced here for convenience.

The white space that TeX inserts between lines of a paragraph, baselineskip, is a form of flexible spacing called glue. A glue value can be specified three components:

• a fixed amount;
• an amount it can stretch;
• an amount it can shrink,

Consequently, a baselineskip value can be specified like this:

baselineskip=fixed amount plus amount to stretch minus amount to shrink

where

• plus and minus are keywords that TeX engines understand;
• fixed amount is referred to as the normal component of the glue (also called the natural width of the glue);
• amount to stretch is referred to as the stretch component of the glue;
• amount to shrink is referred to as the shrink component of the glue.

The fixed amount is required for all glue values but amount to stretch and amount to shrink are both optional—if either, or both, are missing they are set to a value of 0.

Usually, baselineskip glue is specified with a fixed amount only, the stretch and shrink components are zero, otherwise paragraph lines would have irregular (variable) spacing, which might not be aesthetically pleasing.

offinterlineskip and nointerlineskip (macros)

These macros are often used to prevent insertion of interline glue between lines of a paragraph. Readers interested in more detail can jump ahead to the relevant article sections which explain how these macros work.

• offinterlineskip: See the article section Zero-sized interline glue: offinterlineskip.
• nointerlineskip: See the article section Preventing interline glue: prevdepth and nointerlineskip.

Paragraph structure and line space calculations

Using the capabilities of LuaTeX it is possible to post-process a typeset paragraph to visualize boundaries of constituent characters (glyphs), lines and glues from which it is constructed. We’ll start with a short sequence of graphics to help visualize the “boxes and glue” model that TeX engines use to typeset text contained in a paragraph.

Paragraph structure

When TeX typesets a paragraph it treats individual characters as miniature boxes, each with its own width, height and depth and those character-box widths are used to calculate the optimum locations for linebreaks. In addition, space characters contained within the text, and used to separate individual words, are converted to a form of flexible space (glue) which provides the spacing needed to achieve each linebreak.

The following sequence of 7 graphics show the core components of a typeset paragraph: various types of boxes and glue. The first graphic shows a typeset paragraph together with an annotated version which highlights various elements within the paragraph. However, the annotated paragraph contains a lot of information so the subsequent graphics isolate various components to (hopefully) make them easier to understand.

• The next graphic depicts paragraph lines as gray boxes separated by glue that is represented by horizontal green strips. That glue is calculated to ensure the baseline-to-baseline distance is equal to (i.e., the value of) baselineskip:

• The next image represents typeset characters as boxes: to visualize how TeX engines process characters for the purpose of producing linebreaks:

• The next image shows boxes within boxes: the larger paragraph lines (boxes) containing smaller boxes (individual characters):

• The next image shows the amount of space between words in each line: these inter-word spaces are produced by converting space characters to flexible glues that are stretched or shrunk to produce the correct length for each line of text. Note carefully that the size of these spaces vary from line-to line:

• The next image combines the character boxes and corresponding glues (space) placed between individual words:

Visualizing other types of paragraph glue

The following paragraphs were also typeset and processed using LuaTeX to show other types of glue within, and between, a pair of paragraphs. Note that rightskip and leftskip are both set to 0pt, so they are not shown:

• parskip glue (light blue) placed between the two typeset paragraphs;
• individual words are separated by interword glue (yellow) created by converting space characters in the input to variable-sized white space (glue) in the typeset output. Glue arising from interword spaces is stretched or shrunk to achieve visually pleasing linebreaks;
• baselineskip glue (light green) placed between lines—the exact amount of baselineskip glue is calculated using the mechanism discussed below;
• lineskip glue (red) being used in the second paragraph—due to the low box contained in the second-to-last line;
• parfillskip glue (dark green) placed at the end of the last line in each paragraph.

Dealing with deeper (or taller) lines (boxes)

As shown by graphics in the previous section, a typeset paragraph is a vertical stack of “boxes”, separated by some white space, which TeX calls “glue”. As the paragraph is processed, and the individual lines (boxes) are stacked, the vertical list (stack) grows in a downward direction, toward the bottom of the page. Although TeX/LaTeX try to ensure paragraph lines are stacked with baselines separated by a constant distance of baselineskip, it’s not always possible to achieve that because certain lines can have a larger-than-usual height or depth.

The height and depth of each paragraph line is determined by the maximum distance that line’s content extends above or below the baseline; consequently, paragraphs containing material with a relatively large height or depth, such as inline math or graphics, are likely to produce individual lines with correspondingly large heights and/or depths. For such lines, TeX/LaTeX may be unable to stack them such that their baselines are separated from other lines by the baselineskip amount. Clearly, TeX/LaTeX need a “fallback mechanism” to handle such lines by calculating a suitable amount of space to insert between each pair of lines affected by large heights and/or depths.

lineskip and lineskiplimit (TeX primitives)

That fallback mechanism involves the parameter commands lineskip and lineskiplimit together with a third parameter called prevdepth. Readers interested in further details can jump ahead to the article section How the space (glue) between paragraph lines is calculated.

The example project, below, typesets a single paragraph whose last line has a relatively large depth due a shifted text box (hbox). The paragraph is typeset using these settings:

setlength{baselineskip}{12pt}
setlength{lineskip}{3.5pt}
setlength{lineskiplimit}{2pt}
setlength{parindent}{20pt}

Use the link below the following code to open an Overleaf project:

documentclass{article}
% Use a conveniently small page size
usepackage[paperheight=16cm,paperwidth=12cm,textwidth=8cm]{geometry}
% Set some important parameters
setlength{baselineskip}{12pt}
setlength{lineskip}{3.5pt}
setlength{lineskiplimit}{2pt}
setlength{parindent}{20pt}
% Input file defining testpar 
input testpar.tex
title{A sample paragraph for lineskip}
begin{document}
testpar % A macro created in the Overleaf project
end{document}

 Open this example in Overleaf.

This example produces the following output:

The following graphic uses an annotated version of the paragraph produced by the previous Overleaf project. Here, we zoom in to focus on the last paragraph line, indicating the use of lineskip glue (shown in red) caused by the depth of the shifted text box:

The final line of the paragraph text has a larger-than-usual depth, preventing TeX from maintaining the constant baseline-to-baseline distance specified by the value baselineskip (12pt). As indicated by arrows on the right-hand side of the graphic, TeX/LaTeX try to ensure a fixed distance (12pt) between pairs of lines—the value of baselineskip. However, for the last pair of lines TeX has separated them by an amount greater than 12pt and uses the value of lineskip for the interline glue instead of a value calculated using baselineskip.

The following sections explore and explain the details of TeX’s calculations of interline glue values.

How the space (glue) between paragraph lines is calculated

For current purposes we’ll very briefly mention TeX’s page-construction process, albeit in a highly simplified way! Once TeX has finished typesetting a paragraph, by completing hyphenation and determining linebreaks, you can think of that paragraph data as being stored in a temporary memory location. TeX then needs to move that paragraph data, line-by-line, to a new memory location which stores material destined for the current output page.

When TeX moves the paragraph data, line-by-line, it is, in effect, building a vertical stack of lines (TeX boxes) which grows downward toward the bottom of the page. As it moves paragraph lines to the current page TeX tries to ensure those lines will be spaced equally, having consistent vertical (baseline-to-baseline) spacing equal to the value baselineskip. When a new line is transferred to the current page, the TeX engine temporarily records that line’s depth because it will be used to calculate the amount of interline glue (white space) between that line and the line placed after it.

Glue size calculations

Let’s start by summarizing the interline spacing features provided by TeX engines:

• keeping a constant distance between baselines, a distance equal to baselineskip;
• provide spacing for any lines with a relatively large height or depth;
• a capability to switch off insertion of interline glue—either automatically or under user control. For example:
  • TeX engines automatically disable insertion of interline glue after a rule in vertical mode;
  • the macros offinterlineskip and nointerlineskip allow users to temporarily switch off insertion of interline glue—those macros have different effects, as we’ll see below.

The decision whether to add interline glue and, if so, how much of which type, goes like this:

• Should interline glue be added? TeX decides this by testing whether the depth of the last line added to the list is less than the special value of –1000pt (points). Note that –1000pt is an arbitrary “sentinel” value used internally by TeX engines.
  • Note: The value of “depth of the last line added”, which TeX records internally, is also known as the “previous depth”. TeX engines provide the parameter command prevdepth—which can, in certain circumstances, be used to get or set the value of “previous depth”. The macro nointerlineskip makes use of prevdepth.

• TeX tests whether depth of previous line is greater than –1000pt?
  • Yes it is (need to add glue):
    • calculate the value Δ, where Δ = baselineskip – (depth of previous line) – (height of next line)
    • compare Δ to the value of lineskiplimit, a parameter used to define the minimum acceptable distance between two lines, as measured by the distance between the bottom of the upper line and the top of the lower line.
    • If Δ < lineskiplimit:
      • the lines are too close so insert the minimum acceptable spacing which is lineskip
    • If Δ >= lineskiplimit:
      • the lines are not too close so use Δ as the amount of glue to insert
  • No it is not (do not add glue):
    • Add the next line (box) without inserting any glue

The following graphic summarizes the interline glue process:

An example of interline glue calculations

In the following example we assume that TeX/LaTeX is using the following command parameter values:

baselineskip=12pt
lineskip=3.5pt
lineskiplimit=2pt

We’ll look at the interline glue calculation for the first two lines of this paragraph:

In the next image, the TeX engine has processed the first paragraph line and moved it to the vertical list it is building. It keeps track of that line’s depth (d1) which is 2.1528 (points):

Next, TeX is ready to add a second line to the list it is building: that line has a height (h2) which is 6.9444 (points) and, incidentally, a depth, d2 of 0 (points):

At this point, TeX needs to calculate the amount of space (glue, g1) to insert between these two lines:

The following image shows the glue calculations for this pair of lines:

The final image shows the two lines moved across to the current page with the calculated amount of interline glue placed between them:

Yet another parameter: prevdepth

As noted above, when TeX is creating a vertical stack (list) of boxes, it stores the depth of the last box added to that list. That stored depth value is known as the “previous depth” which can be accessed via the parameter command prevdepth.

The prevdepth command can be used only when TeX is in a vertical mode; i.e., between paragraphs or inside vertical boxes: vbox, vtop or vcenter (note: vcenter boxes can only be used in math mode).

prevdepth provides read and write access to the value of “previous depth”:

• to read access the current value of prevdepth you can write:

• to set the current value of prevdepth to some value, a length in points, mm, etc, you can write:

setlength{prevdepth}{some value}

If you try to use verbprevdepth in circumstances it was not designed for, such as within a paragraph or inside an hbox you’ll get an error

with additional information telling you it can only be used in vertical mode.

Preventing interline glue: prevdepth and nointerlineskip

One use of prevdepth is to prevent TeX performing the baseline calculations used to add interline glue between items in a vertical list, such as the lines of a paragraph. Using prevdepth to represent depth of previous line we can re-state the glue calculations (pictured above) as follows:

if(prevdepth > –1000pt) 
{
     Δ = baselineskip — prevdepth — (height of current line)

     if(Δ < lineskiplimit)
       interline glue = lineskip
     else
       interline glue = Δ
}
else
{
     Stack the box without adding
     any interline glue
}

Internally, TeX engines recognize a so-called “sentinel” value of prevdepth which can be used to disable calculating and adding interline glue. That sentinel value is –1000pt, which can be seen in the first line of the pseudo-code above:

TeX will not add interline glue unless prevdepth is greater than –1000pt— which provides the mechanism used by the nointerlineskip macro to prevent baseline glue being added between the next pair of boxes in a vertical list.

nointerlineskip has a definition equivalent to:

defnointerlineskip{
prevdepth–1000pt
}

Note that nointerlineskip provides a one-off deactivation of interline glue calculations because the value of prevdepth is continually updated as new boxes are added to the current vertical list, as demonstrated in the following example:

noindent The following verb|hbox|es are processed when TeX{} is in so-called textit{outer vertical mode}. After processing (typesetting), these boxes are appended to the current page and stacked vertically with interline glue inserted between them:

hbox{j}
hbox{p}
hbox{g}

Now, immediately after after the box verb|hbox{j}|, we set verb|prevdepth| to texttt{-1000pt} which prevents interline glue being placed between the boxes verb|hbox{j}| and verb|hbox{p}|: 

hbox{j}setlength{prevdepth}{-1000pt}
hbox{p}
hbox{g}

Observe that interline glue textit{is} placed between the boxes verb|hbox{p}| and verb|hbox{g}| because the value of verb|prevdepth| is updated after verb|hbox{p}| is processed and added to the list: the value of verb|prevdepth| becomes the depth of the box verb|hbox{p}|. When verb|hbox{g}| is added to the vertical list the value of verb|prevdepth| is no longer texttt{-1000pt}; consequently, interline glue can now be added.

 Open this example in Overleaf

This example produces the following output:

Zero-sized interline glue: offinterlineskip

It is possible to remove all interline spacing via the macro command nointerlineskip, which has a definition equivalent to:

defoffinterlineskip{%
baselineskip=-1000pt
lineskip=0pt
lineskiplimit=maxdimen
}

Note that maxdimen is 16383.99998pt, the largest length that TeX can use.

The following graphic shows the core interline glue calculations and the various parameter values used by the macro nointerlineskip:

The following graphic shows the pseudo-code fragment which results from substituting the nointerlineskip macro values into the glue calculations. It demonstrates how the nointerlineskip macro works by setting values for baselineskip and lineskiplimit such that the interline glue will always be lineskip glue of 0pt.

offinterlineskip and non-zero lineskip

The nointerlineskip macro sets lineskip to zero but, as the following Overleaf project demonstrates, you can combine nointerlineskip with non-zero values of lineskip to achieve line spacing effects.

documentclass{article}
title{Demonstrating non-zero lineskip}
% Choose a conveniently small page size
usepackage[paperheight=16cm,paperwidth=12cm,textwidth=8cm]{geometry}
begin{document}

offinterlineskip % This sets lineskip to 0pt

setlength{lineskip}{5pt} % We want non-zero lineskip

input text.tex % A generated TeX file which defines the macros
% mytextA and mytextB, each of which typesets a paragraph

mytextA % Typeset a paragraph

% Now change lineskip to a flexible glue value and typeset
% another paragraph

setlength{lineskip}{5pt plus5pt minus5pt}

mytextA

end{document}

 Open this example as an Overleaf LaTeX project

This example generates the following output:

You can localize the effect(s) of using offinterlineskip and lineskip (and other spacing commands) by enclosing them in a group:

begingroup
offinterlineskip
setlength{lineskip}{5pt}
...your paragraph(s) here

endgroup

documentclass[12pt,a4paper]{book} 
usepackage{xcolor}
usepackage{lipsum}
usepackage{setspace}

renewcommand{baselinestretch}{1.5} 

begin{document}
lipsum[1]
{setstretch{1.0}color{blue}
lipsum[2]
}
lipsum[3]
end{document}

14

documentclass[12pt,a4paper]{book} 
usepackage{lipsum}
usepackage{setspace}

begin{document}

onehalfspacing % Set line spacing to 1.5

lipsum[1]

singlespacing % Reset line spacing to 1 from here on
lipsum[2]
onehalfspacing % Reset line spacing to 1.5 from here on

lipsum[3]
end{document}

1

usepackage{setspace}

begin{spacing}{1.125}
…
end{spacing}

1

documentclass[12pt,a4paper]{book} 
usepackage{xcolor}
usepackage{lipsum}
usepackage{setspace}

renewcommand{baselinestretch}{1.5} 

begin{document}
lipsum[1]
{setstretch{1.0}color{blue}
lipsum[2]
}
lipsum[3]
end{document}

14

documentclass[12pt,a4paper]{book} 
usepackage{lipsum}
usepackage{setspace}

begin{document}

onehalfspacing % Set line spacing to 1.5

lipsum[1]

singlespacing % Reset line spacing to 1 from here on
lipsum[2]
onehalfspacing % Reset line spacing to 1.5 from here on

lipsum[3]
end{document}

1

usepackage{setspace}

begin{spacing}{1.125}
…
end{spacing}

1