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Code Editor : graphical.html

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  <title>Mom -- Graphical Objects</title>
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<h1 class="docs">Graphical objects</h1>

<div style="text-align: center;">
<ul class="no-enumerator" style="margin-left: -2.5em;">
  <li><a href="#intro-graphical">Introduction to graphical objects</a></li>
  <li><a href="#behaviour">Graphical objects behaviour</a></li>
  <li><a href="#order">Order of arguments</a></li>
  <li><a href="#index-graphical">Index of graphical objects macros</a></li>
</ul>
</div>

<h2 id="intro-graphical" class="docs">Introduction to graphical objects</h2>

<p>
Groff has a number of
<a href="definitions.html#inlines">inline escapes</a>
for drawing rules, polygons, ellipses and splines.  All begin with
<kbd>\D</kbd> (presumably for &#8220;Draw&#8221;) and are documented
in the groff info manual:
<br/>
<span class="pre-in-pp">
  info groff => Escape index => \D
</span>
The escapes allow you to draw just about any simple graphical object
you can think of, but owing to their syntax, they&#8217;re not always easy
to read, which can make tweaking them difficult.  Additionally,
while they perform in a <i>consistent</i> manner, they don&#8217;t
always perform in an <i>expected</i> manner.
</p>

<p>
Experience shows that the most common graphical elements typesetters
need are rules (horizontal and vertical), boxes, and circles (or
ellipses).  For this reason, mom provides macros
to draw these objects in an easy-to-understand way; the results are
predictable, and mom&#8217;s syntax makes fixes or tweaks
painless.
</p>

<p id="graphical-example">
For example, if you want to draw a 2-inch square outline box at the left
margin using groff&#8217;s <kbd>\D</kbd> escapes, it looks like this:
<br/>
<span class="pre-in-pp">
             back up
               by
             weight
            +-------+
            |       |
   \D't 500'\h'-500u'\D'p 2i 0 0 2i -2i 0 0 -2i'
  |       |          |                        |
  +-------+          +------------------------+
   set rule          draw box, 1 line at a time
    weight
</span>

Obviously, this isn&#8217;t very efficient for something as simple as a
box.
</p>

<p>
Here&#8217;s the same box, drawn with mom&#8217;s box drawing
macro
<kbd><a href="#dbx">DBX</a></kbd>:
<br/>
<span class="pre-in-pp">
  left margin indent--+  +--box width
                      |  |
             .DBX .5  0  2i  2i
                  |          |
     rule weight--+          +--box depth
     (in points)
</span>
</p>

<p>
Mom&#8217;s graphical object macros allow&mdash;in fact,
require&mdash;giving the rule weight (&#8220;thickness&#8221;) for
the object (or saying that you want it filled), an indent from the
left margin where the object begins, the dimensions of the object,
and optionally a colour for the object.
</p>

<p>
There are no defaults for the arguments to mom'a graphical object
macros, which means you must supply the arguments every time you
invoke them.
</p>

<div class="box-tip">
<p class="tip">
<span class="note">Note:</span>
As stated above, mom only provides macros for commonly-used
graphical objects (rules, boxes, circles).  More complex objects
(polygons, non-straight lines, splines) must be drawn using
groff&#8217;s <kbd>\D</kbd> escapes.
</p>
</div>

<h3 id="behaviour" class="docs">Graphical object behaviour</h3>

<p>
Mom&#8217;s graphical object macros all behave in the following,
carved-in-stone ways:
</p>
<ol style="margin-top: -.5em; margin-bottom: -.5em;">
   <li>Objects are drawn from the
       <a href="definitions.html#baseline">baseline</a>
       down, including horizontal rules.</li>
   <li>Objects begin precisely at the left indent supplied as
       an argument to the macro.</li>
   <li>Objects are drawn from left to right.</li>
   <li>Enclosed objects (boxes, circles) are drawn from the
       perimeter <i>inward</i>.</li>
   <li>Objects return to their horizontal/vertical point of origin.</li>
</ol>

<p>
The consistency means that once you've mastered the very simple
order of arguments that applies to invoking graphical object
macros, you can draw objects with full confidence that you know
exactly where they&#8217;re placed and how much room they
occupy.  Furthermore, because all return to their point of origin,
you&#8217;ll know exactly where you are on the page.
</p>

<h3 id="order" class="docs">Order of arguments</h3>

<p>
The order of arguments to the graphical object macros is the same
for every macro:
</p>
<ul style="margin-top: -.5em; margin-bottom: -.5em;">
  <li>the <kbd><span style="text-decoration: underline">W</span></kbd>eight of the rule
  <ul style="margin-left: -.75em;">
    <li>if the object is enclosed (i.e. is a box or circle), the
        weight of the rule if you want the object outlined</li>
    <li>the single word, <kbd>SOLID</kbd>, may be used in place
        of the <b>weight</b> argument if you want the
        object filled</li>
  </ul></li>
  <li>the <kbd><span style="text-decoration: underline">I</span></kbd>ndent from the current left margin at
      which to begin the object</li>
  <li>the <kbd><span style="text-decoration: underline">L</span></kbd>ength of the object, if applicable</li>
  <li>the <kbd><span style="text-decoration: underline">D</span></kbd>epth of the object, if applicable</li>
  <li>the <kbd><span style="text-decoration: underline">C</span></kbd>olour of the object (optional)</li>
</ul>

<p>
A simple mnemonic for the order of arguments is &#8220;<b>WILD
C</b>ard&#8221;.  If you fix the mnemonic in your brain and apply
a little judicious reasoning, you&#8217;ll always remember how to
draw graphical objects.  The &#8220;judicious reasoning&#8221; means
that, for example, horizontal rules don&#8217;t require a depth and
vertical rules don&#8217;t require a length.  Thus, in the case of
drawing a horizontal rule, you supply the macro
<kbd><a href="#drh">DRH</a></kbd>
with only the arguments (from the mnemonic) that apply: <b>W-I-L</b> (and
possibly <b>C</b>).
</p>

<div class="macro-list-container">
<h3 id="index-graphical" class="macro-list">Graphical objects macros</h3>

<ul class="macro-list">
  <li><a href="#drh">DRH</a>
      &ndash; horizontal rules</li>
  <li><a href="#drv">DRV</a>
      &ndash; vertical rules</li>
  <li><a href="#dbx">DBX</a>
      &ndash; box</li>
  <li><a href="#dcl">DCL</a>
      &ndash; circles or ellipses</li>
</ul>
</div>

<div class="macro-id-overline">
<h3 id="drh" class="macro-id">Drawing horizontal rules</h3>
</div>

<div class="box-macro-args">
Macro: <b>DRH</b> <kbd class="macro-args">&lt;none&gt; | &lt;weight&gt;  &lt;indent&gt; &lt;length&gt; [&lt;colour&gt;]</kbd>
</div>

<p class="requires">
&bull;&nbsp;
the argument to <kbd class="normal">&lt;weight&gt;</kbd> is in
<a href="definitions.html#picaspoints" class="normal">points</a>,
but do <span class="normal">NOT</span> append the
<a href="definitions.html#unitsofmeasure">unit of measure</a>,
<kbd class="normal">p</kbd>
<br/>
&bull;&nbsp;
<kbd class="normal">&lt;indent&gt;</kbd>
and
<kbd class="normal">&lt;length&gt;</kbd>
require a unit of measure
<br/>
&bull;&nbsp;
arithmetic expressions to
<kbd class="normal">&lt;indent&gt;</kbd>
and
<kbd class="normal">&lt;length&gt;</kbd>
must be surrounded by parentheses
</p>

<p>
If all you want is to draw a rule from your current left
margin to your current right margin (in other words, a &quot;full
measure&quot; rule), you may invoke <kbd>.DRH</kbd> without any
arguments.
</p>
<div class="box-tip">
<p class="tip">
<span class="note">Note:</span>
DRH is the only graphical object macro that may be invoked
without arguments.  The weight (&#8220;thickness&#8221;) of
the rule is determined by the argument you last gave the
macro
<a href="inlines.html#rule-weight">RULE_WEIGHT</a>.
DRH, used this way, is exactly equivalent to entering the
<a href="definitions.html#inlines">inline escape</a>, <a
href="inlines.html#inline-rule-mom"><kbd>\*[RULE]</kbd></a>.
</p>
</div>

<p style="margin-top: -.5em;">
To draw horizontal rules of a specified length, you must, at
a minimum, supply DRH with the arguments <kbd>weight,</kbd>
<kbd>indent</kbd> (measured from the current left margin) and
<kbd>length</kbd>.
</p>

<p>
Optionally, you may give a <kbd>colour</kbd> argument.  The colour
may be either one defined with
<a href="color.html#newcolor">NEWCOLOR</a>,
or a named X-colour inititialized with
<a href="color.html#xcolor">XCOLOR</a>,
or an X-colour alias (again, initialized with XCOLOR).
</p>

<p>
Say, for example, you want to draw a 1-1/4 point horizontal rule
that starts 2 picas from the current left margin and runs for 3
inches.  To do so, you'd invoke <kbd>.DRH</kbd> like this:
<br/>
<span class="pre-in-pp">
      weight  length
         |      |
  .DRH 1.25 2P 3i
            |
          indent
</span>
(Note that the rule weight argument, which is expressed in points,
must NOT have the unit of measure <kbd>p</kbd> appended to it.)
</p>

<p>
If, in addition, you want the rule blue:
<br/>
<span class="pre-in-pp">
  .DRH 1.25 2P 3i blue
</span>
</p>

<h3 class="docs">How mom handles the positioning of horizontal rules</h3>

<p>
Horizontal rules are drawn from left to right, and from the baseline
down. &#8220;From the baseline down&#8221; means that if you request
a rule with a weight of four points, the four points of rule fall
entirely below the baseline.
</p>

<p>
Furthermore, after the rule is drawn, mom returns you to the current
left margin, at the same vertical position on the page as when DRH
was invoked.  In other words, DRH causes no movement on the page,
either horizontal or vertical.
</p>

<div class="macro-id-overline">
<h3 id="drv" class="macro-id">Drawing vertical rules</h3>
</div>

<div class="box-macro-args">
Macro: <b>DRV</b> <kbd class="macro-args">&lt;weight&gt;  &lt;indent&gt; &lt;depth&gt; [&lt;colour&gt;]</kbd>
</div>

<p class="requires">
&bull;&nbsp;
the argument to <kbd class="normal">&lt;weight&gt;</kbd> is in
<a href="definitions.html#picaspoints" class="normal">points</a>,
but do <span class="normal">NOT</span> append the
<a href="definitions.html#unitsofmeasure">unit of measure</a>,
<kbd class="normal">p</kbd>
<br/>
&bull;&nbsp;
<kbd class="normal">&lt;indent&gt;</kbd>
and
<kbd class="normal">&lt;depth&gt;</kbd>
require a unit of measure
<br/>
&bull;&nbsp;
arithmetic expressions to
<kbd class="normal">&lt;indent&gt;</kbd>
and
<kbd class="normal">&lt;depth&gt;</kbd>
must be surrounded by parentheses
</p>

<p>
To draw vertical rules of a specified length, you must, at
a minimum, supply DRV with the arguments <kbd>weight,</kbd>
<kbd>indent</kbd> (measured from the current left margin) and
<kbd>depth</kbd>.
</p>

<p>
Say, for example, you want to draw a 3/4-point vertical rule that
starts 19-1/2 picas from the current left margin and has a depth of
6 centimeters.  To do so, you'd invoke <kbd>.DRV</kbd> like this:
<br/>
<span class="pre-in-pp">
       weight   depth
         |        |
  .DRV .75 19P+6p 6c
             |
           indent
</span>
(Note that the rule weight argument, which is expressed in points,
must NOT have the unit of measure <kbd>p</kbd> appended to it.)
</p>

<p>
If, in addition, you want the rule red:
<br/>
<span class="pre-in-pp">
  .DRV .75 19P+6p 6c red
</span>
</p>

<h3 class="docs">How mom handles the positioning of vertical rules</h3>

<p>
Vertical rules are drawn from the baseline down, and from left to
right. &quot;Left to right&quot; means that if you request a rule
with a weight of four points, the four points of rule fall entirely
to the left of the indent given to DRV.
</p>

<p>
Furthermore, after the rule is drawn, mom returns you to the current
left margin, at the same vertical position on the page as when DRV
was invoked.  In other words, DRV causes no movement on the page,
either horizontal or vertical.
</p>

<div class="macro-id-overline">
<h3 id="dbx" class="macro-id">Drawing boxes</h3>
</div>

<div class="box-macro-args">
Macro: <b>DBX</b> <kbd class="macro-args">&lt; &lt;weight&gt; | SOLID &gt; &lt;indent&gt; &lt;length&gt; &lt;depth&gt; [&lt;colour&gt;]</kbd>
</div>

<p class="requires">
&bull;&nbsp;
the argument to <kbd class="normal">&lt;weight&gt;</kbd> is in
<a href="definitions.html#picaspoints" class="normal">points</a>,
but do <span class="normal">NOT</span> append the
<a href="definitions.html#unitsofmeasure">unit of measure</a>
<kbd class="normal">p</kbd>
<br/>
&bull;&nbsp;<kbd class="normal">&lt;indent&gt;</kbd>,
<kbd class="normal">&lt;length&gt;</kbd>,
and
<kbd class="normal">&lt;depth&gt;</kbd>
require a unit of measure
<br/>
&bull;&nbsp;
arithmetic expressions to
<kbd class="normal">&lt;indent&gt;</kbd>,
<kbd class="normal">&lt;length&gt;</kbd>,
and
<kbd class="normal">&lt;depth&gt;</kbd>
must be surrounded by parentheses
</p>

<p>
To draw boxes of specified dimensions, you must, at a minimum,
supply DBX with the arguments <kbd>weight</kbd> or <kbd>SOLID</kbd>,
<kbd>indent</kbd> (measured from the current left margin),
<kbd>length</kbd> and <kbd>depth</kbd>.
</p>

<p>
Say, for example, you want to draw a 1/2 point outline box that
starts one inch from the current left margin and has the dimensions 
12 picas x 6 picas.  To do so, you'd invoke <kbd>.DBX</kbd> like this:
<br/>
<span class="pre-in-pp">
         indent   depth
           |        |
  .DBX .5  1i  12P  6P
        |       |
     weight   length
</span>
(Note that the box weight argument, which is expressed in points,
must NOT have the unit of measure <kbd>p</kbd> appended to it.)
</p>

<p>
If you want the same box, but solid (&#8220;filled&#8221;) rather
than drawn as an outline:
<br/>
<span class="pre-in-pp">
  .DBX SOLID 1i 12P 6P
</span>
Additionally, if you want the box green:
<br/>
<span class="pre-in-pp">
  .DBX .5 1i 12P 6P green
   or
  .DBX SOLID 1i 12P 6P green
</span>
</p>

<h3 class="docs">How mom handles the positioning of boxes</h3>

<p>
Boxes are drawn from the baseline down, from left to right, and
from the perimeter <i>inward</i>. &#8220;From the perimeter
inward&#8221; means that if you request a box weight of six points,
the 6-point rules used to draw the outline of the box fall entirely
<i>within</i> the dimensions of the box.
</p>

<p>
Furthermore, after the box is drawn, mom returns you to the current
left margin, at the same vertical position on the page as when DBX
was invoked.  In other words, DBX causes no movement on the page,
either horizontal or vertical.
</p>

<div class="macro-id-overline">
<h3 id="dcl" class="macro-id">Drawing circles (ellipses)</h3>
</div>

<div class="box-macro-args">
Macro: <b>DCL</b> <kbd class="macro-args">&lt; &lt;weight&gt; | SOLID &gt; &lt;indent&gt; &lt;length&gt; &lt;depth&gt; [&lt;colour&gt;]</kbd>
</div>

<p class="requires">
&bull;&nbsp;the argument to <kbd class="normal">&lt;weight&gt;</kbd> is in
<a href="definitions.html#picaspoints" class="normal">points</a>,
but do <span class="normal">NOT</span> append the
<a href="definitions.html#unitsofmeasure">unit of measure</a>,
<kbd class="normal">p</kbd>
<br/>
&bull;&nbsp;
the arguments
<kbd class="normal">&lt;indent&gt;</kbd>,
<kbd class="normal">&lt;length&gt;</kbd>
and
<kbd class="normal">&lt;depth&gt;</kbd>
require a unit of measure
<br/>
&bull;&nbsp;
arithmetic expressions to
<kbd class="normal">&lt;indent&gt;</kbd>,
<kbd class="normal">&lt;length&gt;</kbd>
and
<kbd class="normal">&lt;depth&gt;</kbd>
must be surrounded by parentheses
</p>

<p>
To draw circles of specified dimensions, you must, at a minimum,
supply DCL with the arguments <kbd>weight</kbd> or <kbd>SOLID</kbd>,
<kbd>indent</kbd> (measured from the current left margin),
<kbd>length</kbd> and <kbd>depth</kbd>.
</p>

<p>
Say, for example, you want to draw a 1/2 point outline circle
(ellipse, actually, in this case) that starts one inch from the
current left margin and has the dimensions 6 centimeters x 3
centimeters.  To do so, you'd invoke <kbd>.DCL</kbd> like this:
<br/>
<span class="pre-in-pp">
         indent  depth
           |       |
  .DCL .5  1i  6c  3c
        |      |
     weight  length
</span>
(Note that the box weight argument, which is expressed in points,
must NOT have the unit of measure <kbd>p</kbd> appended to it.)
</p>

<p>
If you want the same box, but solid (&#8220;filled&#8221;) rather
than drawn as an outline:
<br/>
<span class="pre-in-pp">
  .DCL SOLID 1i 6c 3c
</span>
Additionally, if you want the circle yellow:
<br/>
<span class="pre-in-pp">
  .DCL .5 1i 6c 3c yellow
   or
  .DCL SOLID 1i 6c 3c yellow
</span>
</p>

<h3 class="docs">How mom handles the positioning of circles (ellipses)</h3>

<p>
Circles (ellipses) are drawn from the baseline down, from left
to right, and from the perimeter <i>inward</i>. &#8220;From the
perimeter inward&#8221; means that if you request a circle weight of
six points, the 6-point rule used to draw the outline of the circle
or ellipse falls entirely <i>within</i> the dimensions of the
circle or ellipse.
</p>

<p>
Furthermore, after the circle is drawn, mom returns you to the
current left margin, at the same vertical position on the page as
when DCL was invoked.  In other words, DCL causes no movement on the
page, either horizontal or vertical.
</p>

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Code Editor : graphical.html