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<title>Suppressing Output (The GNU Troff Manual)</title>
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<h3 class="section" id="Suppressing-Output-1">5.32 Suppressing Output</h3>
<dl class="first-deffn">
<dt class="deffn" id="index-_005cO_005bnum_005d"><span class="category-def">Escape sequence: </span><span><strong class="def-name"><code class="t">\O[</code><span class="r"><i class="slanted">num</i></span><code class="t">]</code></strong><a class="copiable-link" href='#index-_005cO_005bnum_005d'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-_005cO"></a>
<a class="index-entry-id" id="index-suppressing-output-_0028_005cO_0029"></a>
<a class="index-entry-id" id="index-output_002c-suppressing-_0028_005cO_0029"></a>
<p>Suppress GNU <code class="code">troff</code> output of glyphs and geometric objects. The
sequences <code class="code">\O2</code>, <code class="code">\O3</code>, <code class="code">\O4</code>, and <code class="code">\O5</code> are
intended for internal use by <code class="code">grohtml</code>.
</p>
<dl class="table">
<dt>‘<samp class="samp">\O0</samp>’</dt>
<dd><p>Disable the emission of glyphs and geometric objects to the output
driver, provided that this sequence occurs at the outermost suppression
level (see <code class="code">\O3</code> and <code class="code">\04</code> below). Horizontal motions
corresponding to non-overstruck glyph widths still occur.
</p>
</dd>
<dt>‘<samp class="samp">\O1</samp>’</dt>
<dd><p>Enable the emission of glyphs and geometric objects to the output
driver, provided that this sequence occurs at the outermost suppression
level.
</p></dd>
</dl>
<a class="index-entry-id" id="index-opminx"></a>
<a class="index-entry-id" id="index-opminy"></a>
<a class="index-entry-id" id="index-opmaxx"></a>
<a class="index-entry-id" id="index-opmaxy"></a>
<p><code class="code">\O0</code> and <code class="code">\O1</code> also reset the four registers <code class="code">opminx</code>,
<code class="code">opminy</code>, <code class="code">opmaxx</code>, and <code class="code">opmaxy</code> to −1. These
four registers mark the top left and bottom right hand corners of a box
encompassing all written or drawn output.
</p>
<dl class="table">
<dt>‘<samp class="samp">\O2</samp>’</dt>
<dd><p>At the outermost suppression level, enable emission of glyphs and
geometric objects, and write to the standard error stream the page
number and values of the four aforementioned registers encompassing
glyphs written since the last interpolation of a <code class="code">\O</code> sequence, as
well as the page offset, line length, image file name (if any),
horizontal and vertical device motion quanta, and input file name.
Numeric values are in basic units.
</p>
</dd>
<dt>‘<samp class="samp">\O3</samp>’</dt>
<dd><p>Begin a nested suppression level. <code class="command">grohtml</code> uses this mechanism
to create images of output preprocessed with <code class="command">gpic</code>,
<code class="command">geqn</code>, and <code class="command">gtbl</code>. At startup, GNU <code class="code">troff</code> is at
the outermost suppression level. <code class="command">pre-grohtml</code> generates these
sequences when processing the document, using GNU <code class="command">troff</code> with
the <code class="code">ps</code> output device, Ghostscript, and the PNM tools to produce
images in PNG format. They start a new page if the device is not
<code class="code">html</code> or <code class="code">xhtml</code>, to reduce the number of images crossing a
page boundary.
</p>
</dd>
<dt>‘<samp class="samp">\O4</samp>’</dt>
<dd><p>End a nested suppression level.
</p></dd>
</dl>
<dl class="table">
<dt>‘<samp class="samp">\O[5<var class="var">P</var><var class="var">file</var>]</samp>’</dt>
<dd><p>At the outermost suppression level, write the name <code class="code">file</code> to the
standard error stream at position <var class="var">P</var>, which must be one of
<code class="code">l</code>, <code class="code">r</code>, <code class="code">c</code>, or <code class="code">i</code>, corresponding to left,
right, centered, and inline alignments within the document,
respectively. <var class="var">file</var> is a name associated with the production of
the next image.
</p></dd>
</dl>
</dd></dl>
<dl class="first-deffn">
<dt class="deffn" id="index-_005cn_005b_002eO_005d"><span class="category-def">Register: </span><span><strong class="def-name"><code class="t">\n[.O]</code></strong><a class="copiable-link" href='#index-_005cn_005b_002eO_005d'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-_002eO"></a>
<a class="index-entry-id" id="index-suppression-nesting-level-register"></a>
<a class="index-entry-id" id="index-nesting-level_002c-suppression_002c-register"></a>
<a class="index-entry-id" id="index-level_002c-suppression-nesting_002c-register"></a>
<p>Output suppression nesting level applied by <code class="code">\O3</code> and <code class="code">\O4</code>
escape sequences.
</p></dd></dl>
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