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<hr>
<h3 class="section" id="Drawing-Geometric-Objects-1">5.26 Drawing Geometric Objects</h3>
<a class="index-entry-id" id="index-drawing-requests"></a>
<a class="index-entry-id" id="index-requests-for-drawing"></a>
<p>A few of the formatter’s escape sequences draw lines and other geometric
objects. Combined with each other and with page motion commands
(see <a class="pxref" href="Page-Motions.html">Page Motions</a>), a wide variety of figures is possible. For
complex drawings, these operations can be cumbersome; the preprocessors
<code class="code">gpic</code> or <code class="code">ggrn</code> are typically used instead.
</p>
<p>The <code class="code">\l</code> and <code class="code">\L</code> escape sequences draw horizontal and
vertical sequences of glyphs, respectively. Even the simplest of
output devices supports them.
</p>
<dl class="first-deffn">
<dt class="deffn" id="index-_005cl_0027l_0027"><span class="category-def">Escape sequence: </span><span><strong class="def-name"><code class="t">\l<code class="code">'</code></code><span class="r"><i class="slanted">l</i></span><code class="t"><code class="code">'</code></code></strong><a class="copiable-link" href='#index-_005cl_0027l_0027'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-_005cl"></a>
</dd><dt class="deffnx def-cmd-deffn" id="index-_005cl_0027lc_0027"><span class="category-def">Escape sequence: </span><span><strong class="def-name"><code class="t">\l<code class="code">'</code></code><span class="r"><i class="slanted">lc</i></span><code class="t"><code class="code">'</code></code></strong><a class="copiable-link" href='#index-_005cl_0027lc_0027'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-drawing-horizontal-lines-_0028_005cl_0029"></a>
<a class="index-entry-id" id="index-horizontal-line_002c-drawing-_0028_005cl_0029"></a>
<a class="index-entry-id" id="index-line_002c-horizontal_002c-drawing-_0028_005cl_0029"></a>
<p>Draw a horizontal line of length <var class="var">l</var> from the drawing position.
Rightward motion is positive. Afterward, the drawing position is at the
right end of the line. The default scaling unit is ‘<samp class="samp">m</samp>’.
</p>
<a class="index-entry-id" id="index-baseline-rule-special-character_0028_005c_005bru_005d_0029"></a>
<a class="index-entry-id" id="index-glyph_002c-underscore-_0028_005c_005bru_005d_0029"></a>
<a class="index-entry-id" id="index-line-drawing-glyph"></a>
<a class="index-entry-id" id="index-glyph_002c-for-line-drawing"></a>
<p>The optional second parameter <var class="var">c</var> is a character with which to
draw the line. The default is the baseline rule special character,
<code class="code">\[ru]</code>.
</p>
<a class="index-entry-id" id="index-dummy-character-_0028_005c_0026_0029_002c-effect-on-_005cl-escape-sequence"></a>
<a class="index-entry-id" id="index-character_002c-dummy-_0028_005c_0026_0029_002c-effect-on-_005cl-escape-sequence"></a>
<p>If <var class="var">c</var> is a valid scaling unit, put <code class="code">\&</code> after <var class="var">l</var> to
disambiguate the input.
</p>
<div class="example">
<div class="group"><pre class="example-preformatted">.de textbox
\[br]\\$*\[br]\l'|0\[rn]'\l'|0\[ul]'
..
</pre></div></div>
<p>The foregoing outputs a box rule (a vertical line), the text
argument(s), and another box rule. We employ the boundary-relative
motion operator ‘<samp class="samp">|</samp>’. Finally, the line-drawing escape sequences
draw a radical extender (a form of overline) and an underline from the
drawing position to the position coresponding to beginning of the
<em class="emph">input</em> line. The drawing position returns to just after the
right-hand box rule because the lengths of the drawn lines are negative,
as noted above.
</p></dd></dl>
<dl class="first-deffn">
<dt class="deffn" id="index-_005cL_0027l_0027"><span class="category-def">Escape sequence: </span><span><strong class="def-name"><code class="t">\L<code class="code">'</code></code><span class="r"><i class="slanted">l</i></span><code class="t"><code class="code">'</code></code></strong><a class="copiable-link" href='#index-_005cL_0027l_0027'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-_005cL"></a>
</dd><dt class="deffnx def-cmd-deffn" id="index-_005cL_0027lc_0027"><span class="category-def">Escape sequence: </span><span><strong class="def-name"><code class="t">\L<code class="code">'</code></code><span class="r"><i class="slanted">lc</i></span><code class="t"><code class="code">'</code></code></strong><a class="copiable-link" href='#index-_005cL_0027lc_0027'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-drawing-vertical-lines-_0028_005cL_0029"></a>
<a class="index-entry-id" id="index-vertical-line-drawing-_0028_005cL_0029"></a>
<a class="index-entry-id" id="index-line_002c-vertical_002c-drawing-_0028_005cL_0029"></a>
<a class="index-entry-id" id="index-line-drawing-glyph-1"></a>
<a class="index-entry-id" id="index-glyph-for-line-drawing"></a>
<a class="index-entry-id" id="index-box-rule-glyph-_0028_005c_005bbr_005d_0029"></a>
<a class="index-entry-id" id="index-glyph_002c-box-rule-_0028_005c_005bbr_005d_0029"></a>
<p>Draw a vertical line of length <var class="var">l</var> from the drawing position.
Downward motion is positive. The default scaling unit is ‘<samp class="samp">v</samp>’. The
default character is the box rule, <code class="code">\[br]</code>. As with vertical
motion escape sequences, text processing continues where the line ends.
<code class="code">\L</code> is otherwise similar to <code class="code">\l</code>.
</p>
<div class="example">
<div class="group"><pre class="example-preformatted">$ nroff <<EOF
This is a \L'3v'test.
EOF
⇒ This is a
⇒ |
⇒ |
⇒ |test.
</pre></div></div>
<p>When writing text, the drawing position is at the text baseline; recall
<a class="ref" href="Page-Geometry.html">Page Geometry</a>.
</p></dd></dl>
<p>The <code class="code">\D</code> escape sequence provides <em class="dfn">drawing commands</em> that
direct the output device to render geometrical objects rather than
glyphs. Specific devices may support only a subset, or may feature
additional ones; consult the man page for the output driver in use.
Terminal devices in particular implement almost none. See <a class="xref" href="Graphics-Commands.html">Graphics Commands</a>.
</p>
<p>Rendering starts at the drawing position; when finished, the drawing
position is left at the rightmost point of the object, even for closed
figures, except where noted. GNU <code class="code">troff</code> draws stroked (outlined)
objects with the stroke color, and shades filled ones with the fill
color. See <a class="xref" href="Colors.html">Colors</a>. Coordinates <var class="var">h</var> and <var class="var">v</var> are horizontal
and vertical motions relative to the drawing position or previous point
in the command. The default scaling unit for horizontal measurements
(and diameters of circles) is ‘<samp class="samp">m</samp>’; for vertical ones, ‘<samp class="samp">v</samp>’.
</p>
<p>Circles, ellipses, and polygons can be drawn filled or stroked. These
are independent properties; if you want a filled, stroked figure, you
must draw the same figure twice using each drawing command. A filled
figure is always smaller than an outlined one because the former is
drawn only within its defined area, whereas strokes have a line
thickness (set with ‘<samp class="samp">\D't'</samp>’).
</p>
<div class="example">
<div class="group"><pre class="example-preformatted">\h'1i'\v'1i'\
\# increase line thickness
\Z'\D't 5p''\
\# draw stroked (unfilled) polygon
\Z'\D'p 3 3 -6 0''\
\# draw filled (solid) polygon
\Z'\D'P 3 3 -6 0''
</pre></div></div>
<dl class="first-deffn">
<dt class="deffn" id="index-_005cD_0027command-argument-_2026_0027"><span class="category-def">Escape sequence: </span><span><strong class="def-name"><code class="t">\D<code class="code">'</code></code><span class="r"><i class="slanted">command argument …</i></span><code class="t"><code class="code">'</code></code></strong><a class="copiable-link" href='#index-_005cD_0027command-argument-_2026_0027'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-_005cD"></a>
<p>Drawing command escape sequence parameters begin with an ordinary
character, <var class="var">command</var>, selecting the type of object to be drawn,
followed by <var class="var">argument</var>s whose meaning is determined by
<var class="var">command</var>.
</p>
<dl class="table">
<dt id='index-drawing-a-spline-_0028_005cD_0027_007e-_2026_0027_0029'><span><code class="code">\D'~ <var class="var">h1</var> <var class="var">v1</var> … <var class="var">hn</var> <var class="var">vn</var>'</code><a class="copiable-link" href='#index-drawing-a-spline-_0028_005cD_0027_007e-_2026_0027_0029'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-spline_002c-drawing-_0028_005cD_0027_007e-_2026_0027_0029"></a>
<p>Draw a B-spline to each point in sequence, leaving the drawing position
at (<var class="var">hn</var>, <var class="var">vn</var>).
</p>
</dd>
<dt id='index-arc_002c-drawing-_0028_005cD_0027a-_2026_0027_0029'><span><code class="code">\D'a <var class="var">hc</var> <var class="var">vc</var> <var class="var">h</var> <var class="var">v</var>'</code><a class="copiable-link" href='#index-arc_002c-drawing-_0028_005cD_0027a-_2026_0027_0029'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-drawing-an-arc-_0028_005cD_0027a-_2026_0027_0029"></a>
<p>Draw a circular arc centered at (<var class="var">hc</var>, <var class="var">vc</var>) counterclockwise
from the drawing position to a point (<var class="var">h</var>, <var class="var">v</var>) relative to the
center. <a class="footnote" id="DOCF105" href="groff.html_fot.html#FOOT105"><sup>105</sup></a>
</p>
</dd>
<dt id='index-circle_002c-stroked_002c-drawing-_0028_005cD_0027c-_2026_0027_0029'><span><code class="code">\D'c <var class="var">d</var>'</code><a class="copiable-link" href='#index-circle_002c-stroked_002c-drawing-_0028_005cD_0027c-_2026_0027_0029'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-drawing-a-stroked-circle-_0028_005cD_0027c-_2026_0027_0029"></a>
<a class="index-entry-id" id="index-stroked-circle_002c-drawing-_0028_005cD_0027c-_2026_0027_0029"></a>
<a class="index-entry-id" id="index-circle_002c-outlined_002c-drawing-_0028_005cD_0027c-_2026_0027_0029"></a>
<a class="index-entry-id" id="index-drawing-an-outlined-circle-_0028_005cD_0027c-_2026_0027_0029"></a>
<a class="index-entry-id" id="index-outlined-circle_002c-drawing-_0028_005cD_0027c-_2026_0027_0029"></a>
<p>Draw a circle of diameter <var class="var">d</var> with its leftmost point at the drawing
position.
</p>
</dd>
<dt id='index-circle_002c-filled_002c-drawing-_0028_005cD_0027C-_2026_0027_0029'><span><code class="code">\D'C <var class="var">d</var>'</code><a class="copiable-link" href='#index-circle_002c-filled_002c-drawing-_0028_005cD_0027C-_2026_0027_0029'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-drawing-a-filled-circle-_0028_005cD_0027C-_2026_0027_0029"></a>
<a class="index-entry-id" id="index-filled-circle_002c-drawing-_0028_005cD_0027C-_2026_0027_0029"></a>
<a class="index-entry-id" id="index-circle_002c-solid_002c-drawing-_0028_005cD_0027C-_2026_0027_0029"></a>
<a class="index-entry-id" id="index-drawing-a-solid-circle-_0028_005cD_0027C-_2026_0027_0029"></a>
<a class="index-entry-id" id="index-solid-circle_002c-drawing-_0028_005cD_0027C-_2026_0027_0029"></a>
<p>As ‘<samp class="samp">\D'C <span class="r">…</span>'</samp>’, but the circle is filled.
</p>
</dd>
<dt id='index-ellipse_002c-stroked_002c-drawing-_0028_005cD_0027e-_2026_0027_0029'><span><code class="code">\D'e <var class="var">h</var> <var class="var">v</var>'</code><a class="copiable-link" href='#index-ellipse_002c-stroked_002c-drawing-_0028_005cD_0027e-_2026_0027_0029'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-drawing-a-stroked-ellipse-_0028_005cD_0027e-_2026_0027_0029"></a>
<a class="index-entry-id" id="index-stroked-ellipse_002c-drawing-_0028_005cD_0027e-_2026_0027_0029"></a>
<a class="index-entry-id" id="index-ellipse_002c-outlined_002c-drawing-_0028_005cD_0027e-_2026_0027_0029"></a>
<a class="index-entry-id" id="index-drawing-an-outlined-ellipse-_0028_005cD_0027e-_2026_0027_0029"></a>
<a class="index-entry-id" id="index-outlined-ellipse_002c-drawing-_0028_005cD_0027e-_2026_0027_0029"></a>
<p>Draw an ellipse of width <var class="var">h</var> and height <var class="var">v</var> with its leftmost
point at the drawing position.
</p>
</dd>
<dt id='index-ellipse_002c-filled_002c-drawing-_0028_005cD_0027E-_2026_0027_0029'><span><code class="code">\D'E <var class="var">x</var> <var class="var">y</var>'</code><a class="copiable-link" href='#index-ellipse_002c-filled_002c-drawing-_0028_005cD_0027E-_2026_0027_0029'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-drawing-a-filled-ellipse-_0028_005cD_0027E-_2026_0027_0029"></a>
<a class="index-entry-id" id="index-filled-ellipse_002c-drawing-_0028_005cD_0027E-_2026_0027_0029"></a>
<a class="index-entry-id" id="index-ellipse_002c-solid_002c-drawing-_0028_005cD_0027E-_2026_0027_0029"></a>
<a class="index-entry-id" id="index-drawing-a-solid-ellipse-_0028_005cD_0027E-_2026_0027_0029"></a>
<a class="index-entry-id" id="index-solid-ellipse_002c-drawing-_0028_005cD_0027E-_2026_0027_0029"></a>
<p>As ‘<samp class="samp">\D'e <span class="r">…</span>'</samp>’, but the ellipse is filled.
</p>
</dd>
<dt id='index-line_002c-drawing-_0028_005cD_0027l-_2026_0027_0029'><span><code class="code">\D'l <var class="var">dx</var> <var class="var">dy</var>'</code><a class="copiable-link" href='#index-line_002c-drawing-_0028_005cD_0027l-_2026_0027_0029'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-drawing-a-line-_0028_005cD_0027l-_2026_0027_0029"></a>
<p>Draw line from the drawing position to (<var class="var">h</var>, <var class="var">v</var>).
</p>
<p>The following is a macro for drawing a box around a text argument; for
simplicity, the box margin is a fixed at 0.2<span class="dmn">m</span>.
</p>
<div class="example">
<div class="group"><pre class="example-preformatted">.de TEXTBOX
. nr @wd \w'\\$1'
\h'.2m'\
\h'-.2m'\v'(.2m - \\n[rsb]u)'\
\D'l 0 -(\\n[rst]u - \\n[rsb]u + .4m)'\
\D'l (\\n[@wd]u + .4m) 0'\
\D'l 0 (\\n[rst]u - \\n[rsb]u + .4m)'\
\D'l -(\\n[@wd]u + .4m) 0'\
\h'.2m'\v'-(.2m - \\n[rsb]u)'\
\\$1\
\h'.2m'
..
</pre></div></div>
<p>The argument is measured with the <code class="code">\w</code> escape sequence. Its width
is stored in register <code class="code">@wd</code>. <code class="code">\w</code> also sets the registers
<code class="code">rst</code> and <code class="code">rsb</code>; these contain its maximum vertical extents of
the argument. Then, four lines are drawn to form a box, offset by the
box margin.
</p>
</dd>
<dt id='index-polygon_002c-stroked_002c-drawing-_0028_005cD_0027p-_2026_0027_0029'><span><code class="code">\D'p <var class="var">h1</var> <var class="var">v1</var> … <var class="var">hn</var> <var class="var">vn</var>'</code><a class="copiable-link" href='#index-polygon_002c-stroked_002c-drawing-_0028_005cD_0027p-_2026_0027_0029'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-drawing-a-stroked-polygon-_0028_005cD_0027p-_2026_0027_0029"></a>
<a class="index-entry-id" id="index-stroked-polygon_002c-drawing-_0028_005cD_0027p-_2026_0027_0029"></a>
<a class="index-entry-id" id="index-polygon_002c-outlined_002c-drawing-_0028_005cD_0027p-_2026_0027_0029"></a>
<a class="index-entry-id" id="index-drawing-an-outlined-polygon-_0028_005cD_0027p-_2026_0027_0029"></a>
<a class="index-entry-id" id="index-outlined-polygon_002c-drawing-_0028_005cD_0027p-_2026_0027_0029"></a>
<p>Draw polygon with vertices at drawing position and each point in
sequence. GNU <code class="code">troff</code> closes the polygon by drawing a line from
(<var class="var">hn</var>, <var class="var">vn</var>) back to the initial drawing position.
Afterward, the drawing position is left at (<var class="var">hn</var>, <var class="var">vn</var>).
</p>
</dd>
<dt id='index-polygon_002c-filled_002c-drawing-_0028_005cD_0027P-_2026_0027_0029'><span><code class="code">\D'P <var class="var">dx1</var> <var class="var">dy1</var> <var class="var">dx2</var> <var class="var">dy2</var> …'</code><a class="copiable-link" href='#index-polygon_002c-filled_002c-drawing-_0028_005cD_0027P-_2026_0027_0029'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-drawing-a-filled-polygon-_0028_005cD_0027P-_2026_0027_0029"></a>
<a class="index-entry-id" id="index-filled-polygon_002c-drawing-_0028_005cD_0027P-_2026_0027_0029"></a>
<a class="index-entry-id" id="index-polygon_002c-solid_002c-drawing-_0028_005cD_0027P-_2026_0027_0029"></a>
<a class="index-entry-id" id="index-drawing-a-solid-polygon-_0028_005cD_0027P-_2026_0027_0029"></a>
<a class="index-entry-id" id="index-solid-polygon_002c-drawing-_0028_005cD_0027P-_2026_0027_0029"></a>
<p>As ‘<samp class="samp">\D'P <span class="r">…</span>'</samp>’, but the polygon is filled.
</p>
<p>The following macro is like the ‘<samp class="samp">\D'l'</samp>’ example, but shades the
box. We draw the box before writing the text because colors in GNU
<code class="code">troff</code> have no transparency; in othe opposite order, the filled
polygon would occlude the text.
</p>
<div class="example">
<div class="group"><pre class="example-preformatted">.de TEXTBOX
. nr @wd \w'\\$1'
\h'.2m'\
\h'-.2m'\v'(.2m - \\n[rsb]u)'\
\M[lightcyan]\
\D'P 0 -(\\n[rst]u - \\n[rsb]u + .4m) \
(\\n[@wd]u + .4m) 0 \
0 (\\n[rst]u - \\n[rsb]u + .4m) \
-(\\n[@wd]u + .4m) 0'\
\h'.2m'\v'-(.2m - \\n[rsb]u)'\
\M[]\
\\$1\
\h'.2m'
..
</pre></div></div>
</dd>
<dt id='index-line-thickness-_0028_005cD_0027t-_2026_0027_0029'><span><code class="code">\D't <var class="var">n</var>'</code><a class="copiable-link" href='#index-line-thickness-_0028_005cD_0027t-_2026_0027_0029'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-thickness-of-lines-_0028_005cD_0027t-_2026_0027_0029"></a>
<p>Set the stroke thickness of geometric objects to <var class="var">n</var> basic units. A
zero <var class="var">n</var> selects the minimal supported thickness. A negative
<var class="var">n</var> selects a thickness proportional to the type size; this is the
default.
</p></dd>
</dl>
</dd></dl>
<p>In a hazy penumbra between text rendering and drawing commands we locate
the bracket-building escape sequence, <code class="code">\b</code>. It can assemble
apparently large glyphs by vertically stacking ordinary ones.
</p>
<dl class="first-deffn">
<dt class="deffn" id="index-_005cb_0027contents_0027"><span class="category-def">Escape sequence: </span><span><strong class="def-name"><code class="t">\b<code class="code">'</code></code><span class="r"><i class="slanted">contents</i></span><code class="t"><code class="code">'</code></code></strong><a class="copiable-link" href='#index-_005cb_0027contents_0027'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-_005cb"></a>
<a class="index-entry-id" id="index-pile_002c-glyph-_0028_005cb_0029"></a>
<a class="index-entry-id" id="index-glyph-pile-_0028_005cb_0029"></a>
<a class="index-entry-id" id="index-stacking-glyphs-_0028_005cb_0029"></a>
<p>Pile and center a sequence of glyphs vertically on the output line.
<em class="dfn">Piling</em> stacks glyphs corresponding to each character in
<var class="var">contents</var>, read from left to right, and placed from top to bottom.
GNU <code class="code">troff</code> separates the glyphs vertically by 1<span class="dmn">m</span>, and the
pile itself is centered 0.5<span class="dmn">m</span> above the text baseline. The
horizontal drawing position is then advanced by the width of the widest
glyph in the pile.
</p>
<a class="index-entry-id" id="index-_005cb_002c-limitations-of"></a>
<a class="index-entry-id" id="index-limitations-of-_005cb-escape-sequence"></a>
<p>This rather inflexible positioning algorithm doesn’t work with the
<code class="code">dvi</code> output device since its bracket pieces vary in height.
Instead, use the <code class="code">geqn</code> preprocessor.
</p>
<p><a class="ref" href="Manipulating-Spacing.html">Manipulating Spacing</a> describes how to adjust the vertical spacing
of the output line with the <code class="code">\x</code> escape sequence.
</p>
<p>The application of <code class="code">\b</code> that lends its name is construction of
brackets, braces, and parentheses when typesetting mathematics. We
might construct a large opening (left) brace as follows.
</p>
<div class="example">
<div class="group"><pre class="example-preformatted">\b'\[lt]\[bv]\[lk]\[bv]\[lb]'
</pre></div></div>
<p>See <cite class="cite">groff_char<span class="r">(7)</span></cite> for a list of special character
identifiers.
</p></dd></dl>
</div>
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