5.19.7 Font Effects and Text Underlining

Some requests and escape sequences apply simple transformations to glyph shapes, or draw rules beneath the text baseline (underlining). These features are largely vestiges of the days when output devices lacked a wide variety of fonts, and when nroff and troff were separate formatters. GNU troff retains support for them even though they are seldom needed nowadays.

Escape sequence: \H'height'

Escape sequence: \H'+height'

Escape sequence: \H'-height'

Register: \n[.height]

Set (increment, decrement) the height of the current font, but not its width. If height is zero, the formatter uses the font’s inherent height for its type size. The default scaling unit is ‘z’.

Changing the font height does not affect vertical spacing; dramatic changes may be better accompanied by an \x escape sequence to add extra pre-vertical space to the output line. Recall Manipulating Spacing.

The read-only register .height interpolates the font height.

As of this writing, only the ps and pdf output devices support this feature.

The formatter does not tokenize \H when reading it; the escape sequence updates the environment.¹⁹⁷ It thus can be used in requests that expect a single-character argument. We can alter the font height of a margin character as follows.¹⁹⁸

.mc \H'+5z'x\H'0'

In compatibility mode,¹⁹⁹ GNU troff behaves differently: it applies an increment or decrement to the current type size and not to the previously selected font height.

.cp 1
\H'+5'test \H'+5'test

prints the word ‘test’ twice with the same font height—five points larger than the current font size.

Escape sequence: \S'slant'

Register: \n[.slant]

Slant the glyphs of the currently selected font by slant degrees. Positive values slant in the direction of text flow. Only integer values are possible.

The read-only register .slant interpolates the font slant.

As of this writing, only the ps and pdf output devices support this feature.

The formatter does not tokenize \S when reading it; the escape sequence updates the environment.²⁰⁰ It thus can be used in requests that expect a single-character argument. We can apply a slant to a margin character as follows.²⁰¹

.mc \S'20'x\S'0'

This escape sequence is incorrectly documented in the AT&T troff manual: the slant is only assigned, never incremented or decremented.

Request: .ul [n]

Register: \n[.ul]

Underline (in nroff mode) or italicize (in troff mode; recall troff and nroff Modes) the next n productive input lines. A nonpositive argument cancels any pending underlining. Omitting the argument implies an n of ‘1’. The read-only register .ul stores the count of productive input lines remaining to be underlined, which is associated with the environment.²⁰²

When ul commences underlining, the formatter stores the currently selected font (strictly, its mounting position), and restores that font when underlining ceases. Use the uf request to select an alternative underline font.

The ul request does not cause spaces to be underlined.

Request: .cu [lines]

The cu request is similar to ul but underlines spaces as well (if a TTY output device is used).

Request: .uf font

Set the underline font (globally) used by ul and cu. By default, this is the font at mounting position 2. font is a font identifier or mounting position.

Request: .bd font [offset]

Request: .bd font1 font2 [offset]

Register: \n[.b]

Embolden font by overstriking its glyphs offset by offset units minus one.

Two syntax forms are available.

• Imitate a bold font unconditionally. The first argument specifies the font to embolden, and the second is the number of basic units, minus one, by which the two glyphs are offset. If the second argument is missing, emboldening is turned off.

  font is a font identifier or mounting position.

  offset is available in the .b read-only register if a special font is active; in the bd request, its default unit is ‘u’.

• Imitate a bold form conditionally. Embolden font1 by offset only if font font2 is the current font. This request can be issued repeatedly to set up different emboldening values for different current fonts. If the second argument is missing, emboldening is turned off for this particular current font.

  Because the emboldening is conditional, it applies only if the glyph to be formatted is not available in the current font. font1 must therefore be a special font, configured either with the special directive in its font description file or with the fspecial request).

Request: .cs font [width [em-size]]

Apply constant glyph spacing to font font. The advance width of every glyph in the font—the amount the drawing position moves horizontally after setting the glyph—becomes width/36 ems. The em-size argument overrides the font’s em size; omitting it preserves the formatter’s usual recomputation of font’s em size from the type size in effect each time that font is selected. Omitting both the second and third arguments deactivates constant glyph spacing for font font.

The default scaling unit for em-size is ‘z’; width is an integer.