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<hr/>
<a href="#move">&lt;move&gt;</a>
<a href="#diagonal-stem">&lt;diagonal-stem&gt;</a>
<a href="#interpolate">&lt;interpolate&gt;</a>
<a href="#interpolate-untouched-points">&lt;interpolate-untouched-points&gt;</a>
<a href="#untouch">&lt;untouch&gt;</a>
<a href="#align">&lt;align&gt;</a>
<a href="#align-midway">&lt;align-midway&gt;</a>
<a href="#shift">&lt;shift&gt;</a>
<a href="#shift-absolute">&lt;shift-absolute&gt;</a>
<a href="#move-point-to-intersection">&lt;move-point-to-intersection&gt;</a>
<a href="#set-coordinate">&lt;set-coordinate&gt;</a>
<a href="#flip-on">&lt;flip-off&gt;</a>
<a href="#flip-on">&lt;flip-on&gt;</a>
<a href="#toggle-points">&lt;toggle-points&gt;</a>
<a href="#mirp">&lt;mirp&gt;</a>
<a href="#mdrp">&lt;mdrp&gt;</a>
<a href="#miap">&lt;miap&gt;</a>
<a href="#mdap">&lt;mdap&gt;</a>
</div>

<div id="content">
     <h1>Instructions that Move Points</h1>

     <p>
       The most important Xgridfit instruction is &lt;move&gt;. This
       may move a point to an absolute position on the raster grid, to
       the nearest gridline (or rounded position), or to a position
       relative to another point. &lt;move&gt; does the work of the
       TrueType MIRP, MDRP, MSIRP, MIAP, MDAP and SCFS
       instructions. (Xgridfit provides equivalents of most of these
       primitive instructions, but their use is not recommended except
       in special circumstances.)
     </p>

     <p>
       Other commonly used instructions are &lt;shift&gt;,
       &lt;align&gt; and &lt;interpolate&gt;. These are generally
       subordinate to &lt;move&gt;: that is, after &lt;move&gt; has
       moved a point, these instructions are used to shift other
       points along with it (&lt;shift&gt;), align other points with
       it (&lt;align&gt;), or reposition some points so that they are
       properly located between it and another moved point
       (&lt;interpolate&gt;). Another instruction, &lt;delta&gt;,
       which moves a point an absolute distance at a specific size, is
       discussed in <a href="deltas.html">its own section</a>.
     </p>

     <p>
       Some of the following instructions should be avoided in favor
       of higher level instructions but are here in case they're
       needed, or in case the programmer wants to produce more
       efficient code. Such instructions have cryptic names (e.g.
       &lt;mirp&gt;) that echo the mnemonics for TrueType
       instructions.  Those that are suitable for frequent use have
       clearer, fuller names (e.g. &lt;shift&gt;).
     </p>

     <h3 id="move">&lt;move&gt;</h3>

     <p>
       Moves a point and, optionally, aligns other points with it or
       moves other points in relation to it.
     </p>

     <p>
       The only required item is a point to move.  Xgridfit moves this
       point differently depending on the presence or absence of a
       reference point (explicit or, in the case of a &lt;move&gt;
       nested within a &lt;move&gt;, implicit) and the "distance" or
       "pixel-distance" attribute:
     </p>

     <dl>
       <dt>no reference point or distance attribute</dt>
       <dd>
	 The point is moved to a position on the grid determined by
	 the current position of the point and the round state: for
	 example, if the round state is "to-grid," the point is moved
	 to the nearest grid line. If rounding is off, the point is
	 not moved, but "touched" as if it had been moved. In this
	 example, the point "bottom" is moved to the nearest position
	 halfway between two grid lines:
<pre>
&lt;move round="to-half-grid"&gt;
  &lt;point num="bottom"/&gt;
&lt;/move&gt;
</pre>
       </dd>

       <dt>reference point but no distance attribute</dt>
       <dd>
	 The point is moved so that its original distance from the
	 reference point is maintained. The distance is rounded in
	 accordance with the current round state. Here the original
	 distance between "bottom" and "top" is rounded (presumably
	 "to-grid"), and "top" is moved until it is that distance from
	 "bottom":
<pre>
&lt;move&gt;
  &lt;reference&gt;
    &lt;point num="bottom"/&gt;
  &lt;/reference&gt;
  &lt;point num="top"/&gt;
&lt;/move&gt;
</pre>
       </dd>

       <dt>reference point and distance attribute</dt>
       <dd>
	 "Distance" is a value from a &lt;control-value&gt; element;
	 the point is positioned this distance from the reference
	 point. The distance is rounded in accordance with the current
	 round state. Here the &lt;control-value&gt; "lc-height" is
	 rounded and "top" is moved until it is that distance from
	 "bottom":
<pre>
&lt;move distance="lc-height"&gt;
  &lt;reference&gt;
    &lt;point num="bottom"/&gt;
  &lt;/reference&gt;
  &lt;point num="top"/&gt;
&lt;/move&gt;
</pre>
       </dd>

       <dt>distance attribute but no reference point</dt>
       <dd>
	 "Distance" is a value from a &lt;control-value&gt;
	 element; the point is positioned this distance from the grid
	 origin. The distance is rounded in accordance with the
	 current round state. Here the &lt;control-value&gt;
	 "lc-height" is rounded and "top" is moved until it is that
	 distance from the grid origin. If the freedom and projection
	 vectors are set to the <tt>y</tt> axis, the distance is
	 measured from the baseline:
<pre>
&lt;move distance="lc-height"&gt;
  &lt;point num="top"/&gt;
&lt;/move&gt;
</pre>
       </dd>

       <dt>reference point and pixel-distance attribute</dt>
       <dd>
	 "Pixel-distance" is a distance in pixels (e.g. "2p" or "2.0"
	 or "round(control-value(lc-height) * 0.8)").  The point is
	 positioned this distance from the reference point:
<pre>
&lt;move pixel-distance="2p"&gt;
  &lt;reference&gt;
    &lt;point num="left"/&gt;
  &lt;/reference&gt;
  &lt;point num="right"/&gt;
&lt;/move&gt;
</pre>
       </dd>

       <dt>pixel-distance attribute but no reference point</dt>
       <dd>
	 The point is positioned the specified distance from the grid
	 origin:
<pre>
&lt;move pixel-distance="2p"&gt;
  &lt;point num="right"/&gt;
&lt;/move&gt;
</pre>
       </dd>
     </dl>

     <p>
       A top-level &lt;move&gt;--one that is not a child of another
       &lt;move&gt; element--always leaves the RP0 reference pointer
       set to the point just moved. When another &lt;move&gt; follows,
       with a reference point that matches the point just moved,
       Xgridfit optimizes the output, "chaining" the instructions
       generated by &lt;move&gt;. Here is a series of chained
       &lt;move&gt; elements:
     </p>

<pre>
    &lt;move distance="std-stem-left-side" min-distance="no"&gt;
      &lt;reference&gt;
        &lt;point num="left-sidebearing"/&gt;
      &lt;/reference&gt;
      &lt;point num="stem-left"/&gt;
    &lt;/move&gt;
    &lt;move distance="lc-vert-stem"&gt;
      &lt;reference&gt;
        &lt;point num="stem-left"/&gt;
      &lt;/reference&gt;
      &lt;point num="stem-right-a"/&gt;
    &lt;/move&gt;
    &lt;move min-distance="no"&gt;
      &lt;reference&gt;
        &lt;point num="stem-right-a"/&gt;
      &lt;/reference&gt;
      &lt;point num="stem-right-b"/&gt;
    &lt;/move&gt;
</pre>

     <p>
       A number of subordinate moves may be packaged inside a
       &lt;move&gt; element. This is done by including
       &lt;interpolate&gt;, &lt;align&gt;, &lt;shift&gt;,
       &lt;delta&gt; and other &lt;move&gt; instructions after the
       &lt;point&gt; element. The parent &lt;move&gt; element supplies
       the reference point or points for those child elements that
       take reference points (&lt;delta&gt; does not); in such child
       elements the &lt;reference&gt; element should be omitted, the
       reference point(s) being implicit. Here are further notes on
       the behavior of nested elements:
     </p>

     <ul>
       <li>
	 The points and ranges in an &lt;align&gt; element are aligned
	 with the point moved by the &lt;move&gt; instruction.
       </li>

       <li>
	 You may include &lt;interpolate&gt; instructions if the
	 &lt;move&gt; instruction contains either an explicit or an
	 implicit reference point. The points and ranges in the
	 &lt;interpolate&gt; instructions are interpolated between the
	 reference point and the moved point.
       </li>

       <li>
	 The points, ranges and contours in a &lt;shift&gt; element
	 are shifted relative to the point moved by the &lt;move&gt;
	 instruction.
       </li>

       <li>
	 The point in a &lt;move&gt; element is moved relative to the
	 point moved by the parent &lt;move&gt; instruction. Unlike a
	 top-level &lt;move&gt;, a nested &lt;move&gt; does not leave
	 RP0 set to its &lt;point&gt;; rather, RP0 always continues to
	 point to the &lt;point&gt; in the parent &lt;move&gt;.
       </li>

       <li>
	 You may include &lt;delta&gt; elements both before and after
	 nested &lt;align&gt;, &lt;interpolate&gt;, &lt;shift&gt; and
	 &lt;move&gt; elements.  Deltas positioned before those
	 elements are executed immediately after the &lt;point&gt;
	 belonging to the parent &lt;move&gt; is moved, but before
	 other nested elements are executed. Normally these deltas are
	 used to make fine adjustments to the position of the point
	 just moved; if you omit the &lt;point&gt; element in a
	 &lt;delta-set&gt; here, the &lt;point&gt; belonging to the
	 parent &lt;move&gt; is assumed. The &lt;delta&gt; elements
	 that come after other nested elements are executed after all
	 those elements have been executed: use these to make fine
	 adjustments in the positions of the points moved by those
	 other instructions.
       </li>
     </ul>

     <p>
       You should use this nesting or packaging feature to build
       programming structures around the visible structures of the
       glyph. The payoffs for doing so are more compact and legible
       program code and more compact and efficient output. As an
       example, here are the horizontal instructions for a letter
       <b>n</b>:
     </p>

<pre>
    &lt;move distance="fhijklmnt-left-side"&gt;
      &lt;reference&gt;
	&lt;point num="left-sidebearing"/&gt;
      &lt;/reference&gt;
      &lt;point num="left-left"/&gt;
      &lt;move distance="top-serif-x-width"&gt;
	&lt;point num="top-serif-end"/&gt;
      &lt;/move&gt;
      &lt;move distance="lc-serif-width"&gt;
	&lt;point num="left-serif-left-end"/&gt;
      &lt;/move&gt;
      &lt;move distance="lc-vert-stroke"&gt;
	&lt;point num="left-right-a"/&gt;
	&lt;align&gt;
	  &lt;point num="left-right-b"/&gt;
	&lt;/align&gt;
	&lt;move distance="lc-serif-width"&gt;
	  &lt;point num="left-serif-right-end"/&gt;
	&lt;/move&gt;
      &lt;/move&gt;
    &lt;/move&gt;

    &lt;move distance="hnu-width"&gt;
      &lt;reference&gt;
	&lt;point num="left-left"/&gt;
      &lt;/reference&gt;
      &lt;point num="right-right"/&gt;
      &lt;delta&gt;
	&lt;delta-set size="4" distance="-8"/&gt;
      &lt;/delta&gt;
      &lt;move distance="lc-serif-width"&gt;
	&lt;point num="right-serif-right-end"/&gt;
      &lt;/move&gt;
      &lt;move distance="lc-vert-stroke"&gt;
	&lt;point num="right-left"/&gt;
	&lt;move distance="lc-serif-width"&gt;
	  &lt;point num="right-serif-left-end"/&gt;
	&lt;/move&gt;
      &lt;/move&gt;
    &lt;/move&gt;
</pre>

     <p>
       The first &lt;move&gt; block relates to the left "leg" of the
       <b>n</b>. First the point <tt>left-left</tt> is positioned
       relative to the <tt>left-sidebearing</tt> point; then the
       points that define the left ends of the serifs are positioned
       relative to <tt>left-left</tt>. Then <tt>left-right-a</tt> is
       positioned relative to <tt>left-left</tt>,
       <tt>left-right-b</tt> is aligned with <tt>left-right-a</tt>,
       and the right end of the left serif is positioned relative to
       <tt>left-right-a</tt>. The second &lt;move&gt; block works in a
       similar way, each element nested inside a &lt;move&gt; taking
       that element's &lt;point&gt; as a reference point. Note that
       the &lt;delta&gt; in this element moves the point
       <tt>right-right</tt>.
     </p>

     <img src="n-hroz.png" alt="instructions for the letter n"/>

     <p>
       The figure above illustrates this code graphically, the
       thick lines showing the relationship among the reference points
       and moved points of the top-level &lt;move&gt; elements, and
       the thin lines showing the subordinate moves.
     </p>

     <p>
       Remember that &lt;move&gt; elements are not "chained" inside
       other &lt;move&gt; elements as top-level &lt;move&gt; elements
       are. Rather, after a nested &lt;move&gt; RP0 always points to
       the &lt;point&gt; moved by the parent &lt;move&gt;. One might
       say that chaining inside the &lt;move&gt; is vertical, from
       parent to child, while otherwise is it horizontal, from sibling
       to sibling.
     </p>

     <p>
       Elements nested inside a &lt;move&gt; must come in the
       following order:
     </p>

     <ul>
       <li>&lt;delta&gt;</li>
       <li>&lt;align&gt;,
       &lt;interpolate&gt;,
       &lt;shift&gt; (in any order),</li>
       <li>&lt;move&gt;</li>
       <li>&lt;delta&gt;</li>
     </ul>

     <p>
       You may include more than one of each of these nested
       elements. Note that the order of &lt;align&gt;,
       &lt;interpolate&gt; and &lt;shift&gt; is not significant:
       Xgridfit sets the order in which these elements are
       executed. Normally this should not be a problem, as it would be
       very odd if the content of these elements were to overlap.
     </p>

     <p>
       The &lt;compile-if&gt; element is not permitted in a
       &lt;move&gt;, but nested elements may be compiled conditionally
       with the <tt>compile-if</tt> attribute. For example, one set of
       deltas can be compiled if a font is bold and another if it is
       not bold (a "bold" constant, either true (1) or false (0) being
       defined in the top level of your program):
     </p>
     <pre>
       &lt;move&gt;
         &lt;point num="p"/&gt;
         &lt;delta compile-if="bold"/&gt;
           &lt;delta-set size="5" distance="2"/&gt;
         &lt;/delta&gt;
         &lt;delta compile-if="not(bold)"/&gt;
           &lt;delta-set size="3" distance="-1"/&gt;
         &lt;/delta&gt;
       &lt;/delta&gt;
˙     </pre>

     <p>
       Bypassing the Control Value Table by using the pixel-distance
       attribute is usually unnecessary. Yet this attribute may
       occasionally be useful. For example, here is a function that
       guarantees at least one pixel of space between a character and
       the diacritic above it:
     </p>
     
<pre>
    &lt;function id="ensure-diacritic-gap"&gt;
      &lt;param name="char-top"/&gt;
      &lt;param name="diacritic-bottom"/&gt;
      &lt;param name="diacritic-contour"/&gt;
      &lt;variable id="d"/&gt;
      &lt;with-vectors axis="y"&gt;
        &lt;measure-distance result-to="d"&gt;
          &lt;point num="char-top"/&gt;
          &lt;point num="diacritic-bottom"/&gt;
        &lt;/measure-distance&gt;
        &lt;if test="d &amp;lt; 1p"&gt;
          &lt;move pixel-distance="1p" round="no"&gt;
            &lt;reference&gt;
              &lt;point num="char-top"&gt;
            &lt;/reference&gt;
            &lt;point num="diacritic-bottom"/&gt;
            &lt;shift&gt;
              &lt;contour num="diacritic-contour"/&gt;
            &lt;/shift&gt;
          &lt;/move&gt;
        &lt;/if&gt;
      &lt;/with-vectors&gt;
    &lt;/function&gt;
</pre>
     

<h4>Attributes</h4>

<dl>
  <dt>distance</dt>
  <dd>
    A value from a &lt;control-value&gt; element.  If
    a <tt>distance</tt> is specified, the target point is positioned
    that distance either from the reference point or from the grid
    origin. If a <tt>distance</tt> is not specified, the distance from
    the original outline is used. In either case,
    the <tt>distance</tt> is measured along the projection
    vector.
  </dd>
     
  <dt>pixel-distance</dt>
  <dd>
    A distance in pixels. If a <tt>pixel-distance</tt> is specified,
    the target point is positioned that distance either from the
    reference point or from the grid origin. The <tt>distance</tt> and
     <tt>pixel-distance</tt> attributes are not compatible.
     If a <tt>distance</tt> attribute is present, the
     <tt>pixel-distance</tt> attribute is not consulted.
  </dd>

  <dt>round</dt>
  <dd>
    Whether and how to round the <tt>distance</tt> or
    <tt>pixel-distance</tt>.  The default value is <tt>yes</tt>, which
    means to round it according to the current setting (to the grid,
    if you haven't changed it). If you specify
    <tt>no</tt>, no rounding will be done. To use one of the standard
    round states, use <tt>to-grid, to-half-grid, to-double-grid,
    down-to-grid</tt> or <tt>up-to-grid</tt>.  To use a custom round
    state, use its name. Finally, any
    number (constant, variable) is passed to SROUND for the TrueType
    engine to interpret.  Setting the round state with this attribute
    has no effect except in this instruction: the round state returns
    to its former value after the instruction is executed. If several
    &lt;move&gt; instructions use the same round state, it is more
    efficient to enclose them in a &lt;with-round-state&gt; element
    than to include a <tt>round</tt> attribute with each one. That is
    also true if the <tt>round</tt> value is to be <tt>no</tt>: in
    that case use <tt>&lt;with-round-state round="no"&gt;</tt> and
    omit the <tt>round</tt> attribute for the &lt;move&gt;
    instructions.
  </dd>

  <dt>cut-in</dt>
  <dd>
    Whether to use the Control Value cut-in; or a cut-in value to
    use. Legal values are <tt>yes</tt>, <tt>no</tt> or any number; the
    default value is <tt>yes</tt>. If the value of this attribute
    is <tt>no</tt>, the value of the <tt>round</tt> attribute must
    also be <tt>no</tt>. (This is a peculiarity of the TrueType
    instruction set and has nothing to do with Xgridfit.) This
    attribute has an effect only when the <tt>distance</tt> attribute
    is present.
  </dd>

  <dt>min-distance</dt>

  <dd>
    Whether to maintain a minimum distance between the reference point
    and the target point; or the minimum distance to use: legal values
    are <tt>yes</tt> (the default), <tt>no</tt>, or any number. This
    attribute has an effect only when there is a reference point.
  </dd>

  <dt>color</dt>
  <dd>
    Distance type: <tt>black</tt>, <tt>white</tt> or
    <tt>gray</tt> (the default).  This applies only when there is a
    reference point.
  </dd>

  <dt>compile-if</dt>
  <dd>
    The &lt;move&gt; instruction and all its contents are compiled
    only if the expression in the <tt>compile-if</tt> attribute
    evaluates as true (non-zero). The instruction is also compiled if
    this attribute is omitted.
  </dd>
</dl>


<h3 id="diagonal-stem">&lt;diagonal-stem&gt;</h3>

<p>
  Given two lines (making up a diagonal stem), makes the second line
  parallel to the first, subject to the operation of the Control Value
  cut-in. If one &lt;align&gt; element is present, the points it
  contains are aligned with the second line; if there are two, the
  first set of points is aligned with the first line and the second
  set with the second line. You may, and often should, set a new
  minimum distance value with the <tt>min-amount</tt> attribute. At
  the end of this instruction the minimum distance will be reset to
  its former value.
</p>

<p>
  Usually it doesn't make a lot of sense to round the distance when
  calling this instruction; and yet the default value of
  <tt>round</tt> is <tt>yes</tt> for compatibility with other, similar
  instructions.  You'll probably want to set the <tt>round</tt>
  attribute to <tt>no</tt>; but if you have several
  &lt;diagonal-stem&gt; instructions together, enclose them in a
  <tt>&lt;with-round-state round="no"&gt;</tt> element to turn off
  rounding beforehand and on again afterwards. In this case, do not
  include the <tt>round</tt> attribute with the &lt;diagonal-stem&gt;
  elements.
</p>

<p>
  By default this instruction does not set the Freedom Vector, since
  the best setting of that vector varies with circumstances. If you
  want the Freedom Vector to be the same as the Projection Vector, set
  <tt>freedom-vector="yes"</tt>.
</p>

<p>
  This instruction is not suitable for use inside a function (though
  you may do so if the &lt;line&gt; elements contain points rather
  than <tt>ref</tt> attributes). Also, I'm not sure whether it will
  work if the various points are in different zones. It may, but I
  don't guarantee it.
</p>

<p>
  Example:
</p>
<pre>
  &lt;diagonal-stem min-distance="yes" distance="cap-thin-diag" round="no"&gt;
    &lt;line ref="left-left-line"/&gt;
    &lt;line ref="left-right-line"/&gt;
    &lt;align&gt;
      &lt;point num="left-right-b"/&gt;
      &lt;point num="left-right-c"/&gt;
    &lt;/align&gt;
  &lt;/diagonal-stem&gt;
</pre>

<h4>Attributes</h4>

<dl>
<dt>distance</dt>

<dd>A value from a &lt;control-value&gt; element: this
     controls the width of the diagonal stem.
</dd>

<dt>round</dt>

<dd>Whether and how to round the distance the point is to
be moved. The default value is <tt>yes</tt>, which means to
round it according to the current setting (to the grid,
if you haven't changed it). If you specify <tt>no</tt>, no
rounding will be done. The other values specify
one of the standard kinds of rounding or a custom round-state.
Setting the
round state with this attribute has no effect except
in this instruction: the round state returns to its
former value after the instruction is executed. If
several &lt;diagonal-stem&gt; instructions use the same round
state, it is more efficient to call &lt;set-round-state&gt;
before and after that group than to include a <tt>round</tt>
attribute with each one. That is also true if the
<tt>round</tt> value is to be <tt>no</tt>: in that case call
<tt>&lt;set-round-state round-state="no"/&gt;</tt> before and omit
the <tt>round</tt> attribute for the &lt;diagonal-stem&gt; instructions.</dd>

<dt>cut-in</dt>

<dd>Whether to use the Control Value cut-in. Legal values
are <tt>yes</tt> and <tt>no</tt>; the default is <tt>yes</tt>. If the
value of this attribute is <tt>no</tt>, the value of the
<tt>round</tt> attribute must also be <tt>no</tt>. (This is a
peculiarity of the TrueType instruction set and has
nothing to do with Xgridfit.) This attribute has an
effect only when a distance is specified.</dd>

     <dt>min-distance</dt>
     <dd>Whether to maintain a minimum distance between the
          points in the first line and the points in the second:
          legal values are <tt>yes</tt> (the default) and
          <tt>no</tt>.</dd>

     <dt>min-amount</dt>
          <dd>The value of the minimum-distance setting in pixels. The
          default value of this setting (1p) is more often than
          not appropriate for vertical and horizontal stems, but
          usually needs to be changed for diagonal stems to look
          their best. This attribute applies only to the present
          instruction. The minimum-distance setting resumes its former
          value after this instruction.</dd>

     <dt>color</dt>
     <dd>Distance type: <tt>black</tt>, <tt>white</tt> or
          <tt>gray</tt> (the default).</dd>

     <dt>freedom-vector</dt>
          <dd>Set this to <tt>yes</tt> if you want the Freedom Vector
          to be the same as the
          Projection Vector. The default is <tt>no</tt>.</dd>
     <dt>save-vectors</dt>
          <dd>If <tt>yes</tt>, both the Projection Vector and the Freedom Vector
          are guaranteed to be the same after this intruction as they
          were before. The default is <tt>no</tt>.</dd>
</dl>


<h3 id="interpolate">&lt;interpolate&gt;</h3>

<p>
To "interpolate" a point is to move it so that its
position relative to two reference points is what it was in
the original outline. If the distance between the two
reference points is not what it was in the original
outline, the point is positioned so that its
relationship to the reference points is proportionally
correct.</p>

<p>The &lt;interpolate&gt; element must contain at
least one point to interpolate.
It may contain any number of &lt;point&gt;s and &lt;range&gt;s.
Like most other elements that move points, it may contain a
&lt;reference&gt; element; but this element must contain
two &lt;point&gt;s, not just one.</p>

<p>
  This instruction may be nested inside a &lt;move&gt; element
  containing a reference point, or inside a &lt;move&gt; nested in
  another &lt;move&gt;, and so having an implicit reference point. In
  an &lt;interpolate&gt; element so placed reference points are
  needed; the points it contains are automatically interpolated
  between the &lt;move&gt; element's explicit or implicit reference
  point and its moved point.
</p>

<p>
  Example:
</p>
<pre>
  &lt;interpolate&gt;
    &lt;reference&gt;
      &lt;point num="top"/&gt;
      &lt;point num="bottom"/&gt;
    &lt;/reference&gt;
    &lt;point num="bar-top-left"/&gt;
  &lt;/interpolate&gt;
</pre>

<h4>Attributes</h4>

<dl>
  <dt>compile-if</dt>
  <dd>
    The &lt;interpolate&gt; instruction is compiled only if the
    expression in the compile-if attribute evaluates as true
    (non-zero). The instruction is also compiled if this attribute is
    omitted.
  </dd>
  <dt>round</dt>
  <dd>
    If this attribute is included with any value other than "no," all
    points referenced by &lt;point&gt; elements will be aligned to the
    grid after being interpolated. Points referenced by &lt;range&gt;
    and &lt;set&gt; elements are unaffected. The possible values of
    <tt>round</tt> are the same as those for <a
    href="reference.html#set-round-state">&lt;set-round-state&gt; and
    &lt;with-round-state&gt;</a>. Note that the value "yes" will use
    the current round state; so it is usually not necessary to specify
    a round state here.
  </dd>
</dl>

<h3 id="interpolate-untouched-points">&lt;interpolate-untouched-points&gt;</h3>

<p>Interpolates all points that have not been moved or
"touched" by instructions so that they are positioned
correctly relative to points that have been moved.
Most of the time you will want to place this
instruction at the end of the program for each
glyph.</p>

<h4>Attribute</h4>

<dl>
     <dt>axis</dt>
          <dd>Interpolation always takes place along the
          x or the y axis. If you omit this attribute,
          interpolation takes place along both axes.</dd>
</dl>

<h3 id="untouch">&lt;untouch&gt;</h3>

<p>A point that has been moved is "touched." This
untouches it so that it will be affected by
the &lt;interpolate-untouched-points&gt; instruction.</p>

<h3 id="align">&lt;align&gt;</h3>

<p>
  Moves one or more points along the freedom vector until aligned with
  a reference point. Points are "aligned" when their distance from
  each other, measured along the projection vector, is zero. When the
  projection vector is "x," aligned points end up stacked vertically;
  when it is "y" they end up in a horizontal line. When the projection
  vector is set to a line, the aligned points end up arrayed along an
  imaginary line orthogonal to the projection vector.
</p>

<p>
  The &lt;align&gt; element must contain at least one point to align.
  It may contain any number of &lt;point&gt;s and &lt;range&gt;s.  An
  optional &lt;reference&gt; element contains the point to align
  with. If the reference point is omitted, the current setting of RP0
  is used.
</p>

<p>
  The &lt;align&gt; element may be nested in a &lt;move&gt; element,
  in which case it is not necessary to include a &lt;reference&gt;:
  the &lt;point&gt; of the parent &lt;move&gt; is implicitly the
  reference point.
</p>

<p>
  Example:
</p>
<pre>
  &lt;align&gt;
    &lt;reference&gt;
      &lt;point num="left-left-b"/&gt;
    &lt;/reference&gt;
    &lt;range ref="knob-range"/&gt;
  &lt;/align&gt;
</pre>

<h4>Attribute</h4>

<dl>
  <dt>compile-if</dt>
  <dd>
    The &lt;align&gt; instruction is compiled only if the
    expression in the compile-if attribute evaluates as true
    (non-zero). The instruction is also compiled if this attribute is
    omitted.
  </dd>
</dl>

<h3 id="align-midway">&lt;align-midway&gt;</h3>

<p>Must contain two &lt;point&gt; elements. Moves these along
the freedom vector until they are aligned midway
between their original positions. Measurement is
along the projection vector.</p>

<h3 id="shift">&lt;shift&gt;</h3>

     <p>Shifts one or more points, ranges, contours and zones
     by the distance between the current position of the reference
     point and its original position. Note that this does not
     guarantee that the shifted elements will maintain their original
     distance from the reference point (use &lt;move&gt; or
     &lt;mdrp&gt; for that).</p>

     <p>The &lt;shift&gt; element may contain points, ranges,
     contours and zones in any combination and order. The following
     is perfectly correct:</p>
     
<pre>
     &lt;shift&gt;
       &lt;reference&gt;
         &lt;point num="ref-pt"/&gt;
       &lt;/reference&gt;
       &lt;point num="move-pt-1"/&gt;
       &lt;range ref="move-rg-1"/&gt;
       &lt;contour num="0"/&gt;
       &lt;point num="move-pt-2"/&gt;
       &lt;range ref="move-rg-2"/&gt;
     &lt;/shift&gt;
</pre>

     <p>But note that all the points are shifted first, then all the
     ranges, then all the contours, and finally any zones. The order
     of child elements in the &lt;shift&gt; element is not significant; but this is less confusing:</p>

<pre>
     &lt;shift&gt;
       &lt;reference&gt;
         &lt;point num="ref-pt"/&gt;
       &lt;/reference&gt;
       &lt;point num="move-pt-1"/&gt;
       &lt;point num="move-pt-2"/&gt;
       &lt;range ref="move-rg-1"/&gt;
       &lt;range ref="move-rg-2"/&gt;
       &lt;contour num="0"/&gt;
     &lt;/shift&gt;
</pre>

     <p>
       The &lt;shift&gt; element may be nested in a &lt;move&gt;
       element, in which case it is not necessary to include a
       &lt;reference&gt;: the &lt;point&gt; of the parent &lt;move&gt;
       is implicitly the reference point.
     </p>


<h4>Attributes</h4>

<dl>
  <dt>reference-ptr</dt>
  <dd>
    Addresses a technical detail: the SHP, SHC and SHZ instructions
    can use either RP1 or RP2, and this attribute determines
    which. Chiefly useful if the RP you want to use has already been
    set; otherwise the default (RP1) should do fine. Xgridfit
    automatically sets this correctly when a &lt;shift&gt; instruction
    is nested inside a &lt;move&gt; instruction.
  </dd>
  <dt>compile-if</dt>
  <dd>
    The &lt;align&gt; instruction is compiled only if the
    expression in the compile-if attribute evaluates as true
    (non-zero). The instruction is also compiled if this attribute is
    omitted.
  </dd>
  <dt>round</dt>
  <dd>
    Causes any points referenced by &lt;point&gt; elements to be moved
    to rounded positions after the shift. &lt;set&gt; and
    &lt;range&gt; elements are not affected. Works like the
    <tt>round</tt> attribute on the <a
    href="#interpolate">&lt;interpolate&gt;</a> element.
  </dd>
</dl>

     <h3 id="shift-absolute">&lt;shift-absolute&gt;</h3>
     
     <p>Moves one or more points along the freedom vector by
          a fixed amount (expressed in pixels); it does not use the
          projection vector. The &lt;shift-absolute&gt;
          element must contain at
          least one point to shift: that is, a &lt;range&gt; or a &lt;point&gt;
          element.
          It may contain any number of &lt;point&gt;s and &lt;range&gt;s.</p>
     
     
     <h4>Attribute</h4>
     <dl>
          <dt>pixel-distance</dt>
          <dd>The distance (in pixels) to shift
               the points.</dd>
     </dl>
     
     <h3 id="move-point-to-intersection">&lt;move-point-to-intersection&gt;</h3>

<p>Moves a point to the intersection of two lines.
Each of the lines must be wholly in
a single zone, so if specifying the zone use the <tt>zone</tt>
attribute of the &lt;line&gt; elements rather than the <tt>zone</tt>
attributes of the &lt;point&gt; elements that make up the
lines. Example:</p>
<pre>
  &lt;move-point-to-intersection&gt;
    &lt;point num="pt"/&gt;
    &lt;line&gt;
      &lt;point num="line-a1"/&gt;
      &lt;point num="line-a2"/&gt;
    &lt;/line&gt;
    &lt;line&gt;
      &lt;point num="line-b1"/&gt;
      &lt;point num="line-b2"/&gt;
    &lt;/line&gt;
  &lt;/move-point-to-intersection&gt;
</pre>


<h3 id="set-coordinate">&lt;set-coordinate&gt;</h3>

<p>Moves a &lt;point&gt; to a coordinate determined by the
freedom and projection vectors. On the rare occasions when
you need a command like this one, it is probably better to
use &lt;move&gt; with the <tt>pixel-distance</tt> attribute.</p>

     <h4>Attribute</h4>

<dl>
     <dt>coordinate</dt>
          <dd>The new coordinate in pixels.</dd>
</dl>

      <h3 id="flip-on">&lt;flip-off&gt;<br/>&lt;flip-on&gt;</h3>

      <p>
	"Flips" a range of points so that they all become either
	on-line points or off-line points. The &lt;flip-off&gt; and
	&lt;flip-on&gt; elements must contain a single &lt;range&gt;
	element. The range operated upon always runs from the lowest
	point to the highest. The &lt;range&gt; element may contain a
	<tt>zone</tt> attribute, in which case the operation takes
	place in the specified zone.
      </p>

<h3 id="toggle-points">&lt;toggle-points&gt;</h3>

<p>Any of the points that are on-line become off-line,
and any that are off-line become on-line.
The &lt;toggle-points&gt; element must contain at
least one point to toggle: that is, a &lt;range&gt; or a &lt;point&gt;
element.
It may contain any number of &lt;point&gt;s and &lt;range&gt;s.</p>


<h3 id="mirp">&lt;mirp&gt;</h3>

<p>Corresponds to the MIRP instruction, but attempts, insofar as it
is practical, to separate rounding and the cvt cut-in. You can
specify <tt>round="no"</tt> and <tt>cut-in="yes"</tt> or both
<tt>no</tt> or both <tt>yes</tt>,
but not <tt>round="yes"</tt> and <tt>cut-in="no"</tt>.
That produces an error-message.</p>

<p>This will take care of setting RP0 beforehand if a reference point
is included.</p>


<h4>Attributes</h4>

<dl>
     <dt>distance</dt>
          <dd>distance (from a &lt;control-value&gt; element) relative to the
          reference point (or to RP0 if that was set by a
          previous instruction).</dd>
     <dt>round</dt>
          <dd>whether/how to round the distance. If <tt>yes</tt> is specified,
          the round bit is set and nothing more is done: so the
          current round state is used. If <tt>to-grid</tt>, <tt>to-half-grid</tt> or
          to <tt>to-double-grid</tt>, the round state is set as specified, the
          instruction is executed, and then the earlier round state
          is restored. The default is <tt>yes</tt>.</dd>
     <dt>cut-in</dt>
          <dd>whether to use the cvt cut-in. If rounding is used, this
          will always be <tt>yes</tt>, even if you set it to <tt>no</tt>.</dd>
     <dt>min-distance</dt>
          <dd>whether to observe the current minimum distance (1p
          unless you set it differently using set-minimum-distance).
          The default is <tt>yes</tt>.</dd>
     <dt>set-rp0</dt>
          <dd>whether to set reference point 0 to point at the moved point
          after the instruction is executed. The default value is
          <tt>no</tt>.</dd>
     <dt>color</dt>
          <dd>Or distance-type, or compensation for engine characteristics.
          Whatever. It's got to be gray, black or white, and here
          gray is the default.</dd>
</dl>

<h3 id="mdrp">&lt;mdrp&gt;</h3>

<p>Corresponds to the MDRP instruction.</p>

<p>Similar to &lt;mirp&gt;. This will also take care of setting RP0 beforehand if a
reference point is supplied.</p>


<h4>Attributes</h4>

<dl>
     <dt>round</dt>
          <dd>Whether/how to round the distance from the reference point.</dd>
     <dt>min-distance</dt>
          <dd>Whether to maintain a minimum distance from the reference
          point.</dd>
     <dt>set-rp0</dt>
          <dd>Whether to set RP0 to the moved point after the move.</dd>
     <dt>color</dt>
          <dd>Or distance-type, or compensation for engine characteristics.
          Whatever. It's got to be gray, black or white, and here
          gray is the default.</dd>
</dl>

<h3 id="miap">&lt;miap&gt;</h3>

     <p>Corresponds to the MIAP instruction.</p>

     <p>As with mirp, it will try to separate rounding and the cvt cut-in.</p>

     <p>Must contain one point element.</p>

<h4>Attributes</h4>

<dl>
     <dt>distance</dt>
          <dd>Distance relative to grid origin</dd>
     <dt>round</dt>
          <dd>Whether/how to round the distance</dd>
     <dt>cut-in</dt>
          <dd>Whether to use the cvt cut-in</dd>
</dl>

<h3 id="mdap">&lt;mdap&gt;</h3>

     <p>Corresponds to the MDAP instruction</p>

     <p>Will round a point to the grid if the <tt>round</tt> attribute
     is not <tt>no</tt>; otherwise
     will just touch the point (i.e. mark it as moved).</p>


<h4>Attributes</h4>

<dl>
     <dt>round</dt>
          <dd>Whether and how to round</dd>
</dl>
</div>
</body>
</html>