/usr/share/doc/xgridfit/html/reference.html is in xgridfit-doc 2.3-2.
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<a href="#absolute"><absolute></a>
<a href="#add"><add></a>
<a href="#alias"><alias></a>
<a href="#align"><align></a>
<a href="#align-midway"><align-midway></a>
<a href="#call-function"><call-function></a>
<a href="#call-glyph"><call-glyph></a>
<a href="#call-macro"><call-macro></a>
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<a href="#minimum"><minimum></a>
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<a href="#modifier"><modifier></a>
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<a href="#params"><param></a>
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<a href="#point"><point></a>
<a href="#pre-program"><pre-program></a>
<a href="#ps-private"><ps-private></a>
<a href="#push"><push></a>
<a href="#range"><range></a>
<a href="#restore-default"><restore-default></a>
<a href="#reference"><reference></a>
<a href="#round"><round></a>
<a href="#round-state"><round-state></a>
<a href="#set"><set></a>
<a href="#set-auto-flip"><set-auto-flip></a>
<a href="#set-control-value"><set-control-value></a>
<a href="#set-control-value-cut-in"><set-control-value-cut-in></a>
<a href="#set-coordinate"><set-coordinate></a>
<a href="#set-delta-base"><set-delta-base></a>
<a href="#set-delta-shift"><set-delta-shift></a>
<a href="#set-dropout-control"><set-dropout-control></a>
<a href="#set-dropout-type"><set-dropout-type></a>
<a href="#set-dual-projection-vector"><set-dual-projection-vector></a>
<a href="#set-equal"><set-equal></a>
<a href="#set-freedom-vector"><set-freedom-vector></a>
<a href="#set-minimum-distance"><set-minimum-distance></a>
<a href="#set-projection-vector"><set-projection-vector></a>
<a href="#set-round-state"><set-round-state></a>
<a href="#set-single-width"><set-single-width></a>
<a href="#set-single-width-cut-in"><set-single-width-cut-in></a>
<a href="#set-vectors"><set-vectors></a>
<a href="#shift"><shift></a>
<a href="#shift-absolute"><shift-absolute></a>
<a href="#srp"><srp></a>
<a href="#store-projection-vector"><store-freedom-vector></a>
<a href="#store-projection-vector"><store-projection-vector></a>
<a href="#subtract"><subtract></a>
<a href="#szp"><szp></a>
<a href="#toggle-points"><toggle-points></a>
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<a href="#set-control-value"><with-control-value></a>
<a href="#set-control-value-cut-in"><with-control-value-cut-in></a>
<a href="#set-delta-base"><with-delta-base></a>
<a href="#set-delta-shift"><with-delta-shift></a>
<a href="#set-freedom-vector"><with-freedom-vector></a>
<a href="#set-minimum-distance"><with-minimum-distance></a>
<a href="#with-param"><with-param></a>
<a href="#set-projection-vector"><with-projection-vector></a>
<a href="#set-round-state"><with-round-state></a>
<a href="#set-single-width"><with-single-width></a>
<a href="#set-single-width-cut-in"><with-single-width-cut-in></a>
<a href="#set-vectors"><with-vectors></a>
<a href="#xgridfit-el"><xgridfit></a>
<a href="#zone"><zone></a>
</div>
<div id="content">
<h1>Element Reference</h1>
<h2 id="absolute"><absolute></h2>
<p>
Converts negative to positive numbers; positive numbers stay
positive.
</p>
<pre>
<absolute value="line-width" result-to="lw"/></pre>
<h3>Content</h3>
<p>None.</p>
<h3>Attributes</h3>
<dl>
<dt>value</dt>
<dd>
Required, except when <absolute> is the child of a
<formula>. Any value or expression. The value to operate on.
</dd>
<dt>result-to</dt>
<dd>
Optional; not allowed when <absolute> is the child of
a <formula>. The name of a variable or control value
in which to store the result. If <tt>result-to</tt> is
omitted where allowed and <tt>value</tt> is a variable or
control value, the result is written to <tt>value</tt>. If
<tt>value</tt> cannot be written to, the compiler issues a
warning and the result is left on the stack.
</dd>
</dl>
<h2 id="add"><add></h2>
<p>
Adds two numbers together.
</p>
<pre>
<add value1="line-width" value2="1p"/></pre>
<h3>Content</h3>
<p>None.</p>
<h3>Attributes</h3>
<dl>
<dt>value1, value2</dt>
<dd>
Required, except when <add> is the child of a
<formula>. Any value or expression. These are the values to
add together.
</dd>
<dt>result-to</dt>
<dd>
Optional; not allowed when <add> is the child of a
<formula>. If <tt>result-to</tt> is omitted where
allowed, Xgridfit attempts to write the result to
<tt>value1</tt>. If <tt>value1</tt> cannot be written to,
the compiler issues a warning and the result is left on the
stack.
</dd>
</dl>
<h2 id="alias"><alias></h2>
<p>
Provides access to a value under some other name. The value
can be a control-value, constant, variable, or any value that
can be resolved to a number either at compile time or run
time. The <alias> element can appear at the top level of
a program (as a child of <xgridfit>), or along with
other declarations at the beginning of <glyph>,
<function>, <macro> or <pre-program>
elements. An alias takes precedence over all other elements,
so in the case of name collisions the alias is always
used. Here is a simple example:
</p>
<pre>
<control-value name="lc-vert-stroke" value="0"/>
<alias name="lc-vert-stem" target="lc-vert-stroke"/></pre>
<p>
Now a <move> element with attribute
<tt>distance="lc-vert-stem"</tt> will use the control-value
named <tt>lc-vert-stroke</tt>. If another control-value is
named <tt>lc-vert-stem</tt> it will be invisible. If you want
the alias to be used in just one glyph program, declare it as
a child of <glyph> rather than as a child of
<xgridfit>.
</p>
<h3>Content</h3>
<p>None.</p>
<h3>Attributes</h3>
<dl>
<dt>name</dt>
<dd>
Required. A name: any sequence of letters, numbers, hyphens,
periods; no spaces permitted. This is the name under which
the program may now access the value.
</dd>
<dt>target</dt>
<dd>
Required. A name: any sequence of letters, numbers, hyphens,
periods; no spaces permitted. The name of the value which is
being renamed.
</dd>
</dl>
<h2 id="align"><align></h2>
<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 <align> element must contain at least one object to
align. It may contain any number of <point>s,
<range>s and <set>s. An optional
<reference> element contains the point to align with. If
the reference point is omitted, the current setting of RP0 is
used.
</p>
<p>
<align> can and frequently should be nested inside a
<move> element, in which case points are aligned
relative to the point that is the target of the
<move>. In both of the following cases point "m" is
aligned with point "r":
</p>
<pre>
<align>
<reference>
<point num="r"/>
</reference>
<point num="m"/>
</align>
<move>
<point num="r"/>
<align>
<point num="m"/>
</align>
</move></pre>
<h3>Content</h3>
<p>
One or more <point>, <range> and <set>
elements.
</p>
<h3>Attribute</h3>
<dl>
<dt>compile-if</dt>
<dd>
Optional. Any value or expression that can be resolved to a
number at compile time. If true (non-zero), the
<align> element is compiled; otherwise the compiler
passes it over.
</dd>
</dl>
<h2 id="align-midway"><align-midway></h2>
<p>
Must contain two <point> elements. Moves these along the
freedom vector until they are aligned midway between their
original positions. Measurement is along the projection
vector.
</p>
<pre>
<align-midway>
<point num="a"/>
<point num="b"/>
</align-midway></pre>
<h3>Content</h3>
<p>
Two <point> elements, both required.
</p>
<h3>Attributes</h3>
<p>None.</p>
<h2 id="call-function"><call-function></h2>
<p>
Calls a function (defined via the <function> element) by
name. Parameters may be passed to the function by including
several <with-param> elements; or, if the function is to
be called repeatedly, several <param-set> elements, each
containing the <with-param> elements for one call to the
function.
</p>
<p>
If the function returns a value, it can be assigned to a
variable via the <tt>result-to</tt> attribute. Note, however,
that if a <call-function> element contains more than one
<param-set>, only the value returned by the last
iteration of the function is returned.
</p>
<pre>
<call-function name="cap-serif-width">
<param-set>
<with-param name="ref-pt" value="left-left"/>
<with-param name="move-pt" value="top-serif-end"/>
</param-set>
<param-set>
<with-param name="ref-pt" value="left-left"/>
<with-param name="move-pt" value="bottom-serif-end"/>
</param-set>
</call-function></pre>
<h3>Contents</h3>
<p>
Either several <with-param> elements (if the function is
to be called just once) or several <param-set> elements.
</p>
<h3>Attribute</h3>
<dl>
<dt>name</dt>
<dd>
Required. The name of the function to call.
</dd>
<dt>result-to</dt>
<dd>
Optional. The name of a variable or control value in which
to store the value returned by the function.
</dd>
</dl>
<h2 id="call-glyph"><call-glyph></h2>
<p>
The <call-glyph> element causes code for the whole of a
glyph program to be compiled and inserted, in the manner of a
macro. Like <call-macro>, <call-glyph> can contain
<with-param> elements, passing values to the glyph
program. For a detailed account of its use, see the chapter on
<a href="functions.html#glyph">functions, macros and glyph
programs</a>.
</p>
<h3>Content</h3>
<p>
If the glyph being called has one or more <param>
elements, one or more <with-param>
elements. <param-set> elements are not permitted here.
</p>
<h3>Attribute</h3>
<dl>
<dt>ps-name</dt>
<dd>
Required. Must match the <tt>ps-name</tt> attribute of the
<glyph> element being called.
</dd>
</dl>
<h2 id="call-macro"><call-macro></h2>
<p>
Causes a macro to be compiled and its code inserted at the
present location.
</p>
<pre>
<call-macro name="lc-vert-stem-with-serif">
<with-param name="anchor" value="left-left"/>
<with-param name="distance-from-anchor" value="hn-width"/>
<with-param name="stem-a" value="right-right"/>
<with-param name="serif-a" value="right-serif-right"/>
<with-param name="stem-b" value="right-left"/>
<with-param name="serif-b" value="right-serif-left"/>
</call-macro></pre>
<h3>Content</h3>
<p>
Either one or more <with-param> elements, one for each
parameter defined in the <macro> element, or several
<param-set> elements if the macro is to be compiled and
inserted at this place more than once. <with-param> may
be omitted for each <param> element with a
<tt>value</tt> attribute.
</p>
<h3>Attribute</h3>
<dl>
<dt>name</dt>
<dd>
Required. The name of the macro to call.
</dd>
</dl>
<h2 id="call-param"><call-param></h2>
<p>
This element may be used within a <glyph> or
<macro> element containing <param> elements. It
will cause to be executed a snippet of code passed into a
called <glyph> or <macro> via a <with-param>
element. For details, see the <a
href="functions.html#callable">"Callable Parameters"</a>
section of <a href="functions">Functions, Macros and Glyph
Programs</a>.
</p>
<h3>Content</h3>
<p>None.</p>
<h3>Attribute</h3>
<dl>
<dt>name</dt>
<dd>
Required. The name of the <param> to call.
</dd>
</dl>
<h2 id="ceiling"><ceiling></h2>
<p>Yields the smallest integer greater than or equal to
<tt>value</tt>.</p>
<h3>Content</h3>
<p>None.</p>
<h3>Attributes</h3>
<dl>
<dt>value</dt>
<dd>
Required, except when <ceiling> is the child of a
<formula>. Any value or expression. The value to operate on.
</dd>
<dt>result-to</dt>
<dd>
Optional; not allowed when <ceiling> is the child of a
<formula>. If <tt>result-to</tt> is omitted where
allowed, Xgridfit attempts to write the result to
<tt>value</tt>. If <tt>value</tt> cannot be written to, the
compiler issues a warning and the result is left on the
stack.
</dd>
</dl>
<h2 id="command"><command></h2>
<p>
Causes any TrueType instruction (except the PUSHB and PUSHW
instructions) to be inserted at this place in the output.
<tt>name</tt> is the name of the command; <tt>modifier</tt>,
is simply copied into brackets after the instruction that is
generated. This element
</p>
<pre>
<command name="MIRP" modifier="10110"/></pre>
<p>
is compiled to "MIRP[10110]". The <tt>modifier</tt> attribute
lacks portability, since it is copied in literally. A better
solution is to use <modifier> elements within the
<command> element, thus:
</p>
<pre>
<command name="MIRP">
<modifier type="rp0" value="yes"/>
<modifier type="minimum-distance" value="no"/>
<modifier type="round" value="no"/>
<modifier type="color" value="black"/>
</command></pre>
<p>
Though verbose, this style allows Xgridfit to check the input
code and has the potential to allow Xgridfit to vary the
syntax of its output. (Since Xgridfit now produces scripts
only for FontForge, the latter capability is not exploited.)
</p>
<h3>Content</h3>
<p>
One or more <a href="#modifier"><modifier></a> elements,
if required by the instruction and if the <tt>modifier</tt>
attribute is not used.
</p>
<h3>Attributes</h3>
<dl>
<dt>name</dt>
<dd>
Required. The name of the TrueType instruction to be
output. The compiler checks this against a list of
instructions.
</dd>
<dt>modifier</dt>
<dd>
A modifier string to be inserted <i>literatim</i> in the
TrueType instruction. For example, if <tt>command</tt> is
"MIRP" and <tt>modifier</tt> is "rnd", then
<tt>MIRP[rnd]</tt> is output.
</dd>
</dl>
<h2 id="compile-if"><compile-if></h2>
<p>
Code within <compile-if> is compiled only if the
<tt>test</tt> attribute evaluates to true (non-zero). The
compiler must be able to evaluate <tt>test</tt> at compile
time: thus it may contain only constants, number literals,
control value indexes and a few operators (<tt>+ - = !=
&gt; &lt; &gt;= &lt;= or and not</tt>).
</p>
<p>
Here is a simple example of <compile-if>:
</p>
<pre>
<compile-if test="bold-italic">
<delta>
<delta-set size="3" distance="-2">
<point num="pt"/>
</delta-set>
</delta>
</compile-if></pre>
<p>
The delta is compiled and inserted in the output code only if
<tt>bold-italic</tt> (a global constant) is non-zero.
</p>
<p>
The <compile-if> element may also contain an
<else> element, which must come last. If <tt>test</tt>
evaluates to false (zero), the code contained in <else>
is compiled.
</p>
<h3>Content</h3>
<p>
Programming to be conditionally compiled.
</p>
<h3>Attribute</h3>
<dl>
<dt>test</dt>
<dd>
Required. Any value or expression that can be resolved to a
number at compile time. If it evaluates as true (non-zero),
the content of this element is compiled.
</dd>
</dl>
<h2 id="constant"><constant></h2>
<p>
A constant is a named number. The <tt>value</tt> can be an
integer, either of the two kinds of fixed-point number
(e.g. "2.3" for a distance on the grid or "1.0v" for a
component of a vector), or the name of another constant, in
which case it creates an alias for that constant. It can also
be a simple expression (usually addition or subtraction)
based on another constant:
</p>
<pre>
<constant name="bottom-left" value="3"/>
<constant name="bottom" value="bottom-left"/>
<constant name="bottom-right" value="bottom + 4"/></pre>
<p>
Constants can be referenced just about anywhere that numbers
are called for. To refer to a constant belonging to another
glyph program, use the glyph's <tt>ps-name</tt> followed by a
slash and the name of the constant, e.g.
</p>
<pre>
<point num="macron/bottom"/></pre>
<p>
This is useful when instructing composite glyphs.
</p>
<p>
Constants can be declared at the beginning of a <glyph>
program, or as a child of the <xgridfit> element.
</p>
<h3>Content</h3>
<p>None.</p>
<h3>Attributes</h3>
<dl>
<dt>name</dt>
<dd>
Required. A name: any sequence of letters, numbers, hyphens,
periods; no spaces permitted. Other elements can refer to
the constant by this name.
</dd>
<dt>value</dt>
<dd>
Required. A number or simple expression. It should be
possible to resolve this attribute to a number at compile
time.
</dd>
</dl>
<h2 id="contour"><contour></h2>
<p>
Specifies a contour to be shifted by a <shift>
instruction.
</p>
<h3>Content</h3>
<p>None.</p>
<h3>Attributes</h3>
<dl>
<dt>num</dt>
<dd>
Required. A number or simple expression, the number of the
contour. It should be possible to resolve this attribute to
a number at compile time.
</dd>
<dt>zone</dt>
<dd>
Optional. Possible values are "glyph" and "twilight."
Include the attribute <tt>zone="twilight"</tt> if this
contour is in the twilight zone; otherwise the compiler will
assume that it is in the glyph zone.
</dd>
</dl>
<h2 id="control-values"><control-value></h2>
<p>
The font's Control Value Table is built from the
<control-value> elements. Each <control-value> has an
<tt>name</tt> (which must be unique) and a numerical value. The
index of the <control-value> is generated by Xgridfit, and
no attempt should be made to predict it: Xgridfit instructions
should use only the names of <control-value>s, though the
index may be derived and used at run time.
</p>
<pre>
<control-value name="curved-char-bottom" value="-25"/>
<control-value name="lc-x-height" value="850"/>
<control-value name="lc-descender-depth" value="-555"/>
<control-value name="lc-ascender-height" value="1485"/></pre>
<h3>Content</h3>
<p>None.</p>
<h3>Attributes</h3>
<dl>
<dt>name</dt>
<dd>
Required. A name: any sequence of letters, numbers, hyphens,
periods; no spaces permitted.
</dd>
<dt>value</dt>
<dd>
Required. A number in font units (the units of the grid on
which the font was designed, normally 100 units per em or
2048 units per em).
</dd>
<dt>index</dt>
<dd>
Optional, and consulted only in merge-mode. Specifies how to
determine a control-value's index. "Auto" (the default)
means that if a control-value with this one's <tt>value</tt>
is found in the font, it should be re-used; otherwise this
control value should be appended to the end of the
control-value table. "Append" means that the control-value
should always be appended to the end of the control-value
table. A number specifies the index at which the
control-value should be placed. If the <tt>value</tt> of
this control-value is different from the value of that of
the control-value at that index in the existing font, the
control-value is updated.
</dd>
</dl>
<h2 id="control-value-delta"><control-value-delta></h2>
<p>
The <control-value-delta> element works like the
<delta> element, but operates on the Control Value Table
rather than on a point. It should normally be invoked in the
<pre-program>. Each <delta-set> inside a
control-value-delta element must have <tt>cv</tt>,
<tt>size</tt> and <tt>distance</tt> attributes, but it may not
contain a point.
</p>
<p>
The setting of the vectors has no effect on the
<control-value-delta>. Rather, the <delta-set>
specifies an amount to add to or subtract from the value
stored there.
</p>
<pre>
<control-value-delta>
<delta-set cv="pq-char-width" size="6" distance="-8"/>
<delta-set cv="pq-char-width" size="9" distance="-8"/>
</control-value-delta></pre>
<h3>Content</h3>
<p>
One or more <delta-set> elements.
</p>
<h3>Attributes</h3>
<p>None.</p>
<h2 id="control-value-index"><control-value-index></h2>
<p>
Assigns the index of a control value to a variable. Use this
if you need to get such an index for any reason, since the
<set-equal> instruction yields the value, not the index,
of a control value.
</p>
<h3>Content</h3>
<p>None.</p>
<h3>Attributes</h3>
<dl>
<dt>value</dt>
<dd>
Required. The name of the control value whose index you want
to retrieve. No other kind of value is recognized here.
</dd>
<dt>result-to</dt>
<dd>
Required. The name of a <variable> in which to store
the index of the control value.. Only a variable is
permitted here--not, for example, the name of another
control value.
</dd>
</dl>
<h2 id="default-el"><default></h2>
<p>
This element, which may appear as a child of <xgridfit>,
declares a default value. If the type is "minimum-distance,"
"control-value-cut-in," "single-width," "single-width-cut-in,"
"delta-base," "delta-shift" or "round-state," Xgridfit also
inserts code in the prep program to set a font-wide default in
the TrueType engine. Another way of setting these defaults is
simply to include elements that set these values in the
<pre-program>, and the effect is the same. If you want
the TrueType engine to reject all attempts to set defaults
(that is, if you want to use only the defaults that are
standard for TrueType), include this:
</p>
<pre>
<default type="use-truetype-defaults" value="yes"/></pre>
<p>
In addition to TrueType defaults, stored in the font file,
this element controls several defaults that govern how
Xgridfit operates.
</p>
<h3>Content</h3>
<p>None.</p>
<h3>Attributes</h3>
<dl>
<dt>type</dt>
<dd>
Required. Must be one of the following: "minimum-distance",
"control-value-cut-in", "single-width",
"single-width-cut-in", "delta-base", "delta-shift",
"delta-break", "max-twilight-points", "max-storage",
"legacy-storage", "max-stack", "use-truetype-defaults",
"round-state", "function-base", "init-graphics", "color",
"delete-all", "combine-prep", "auto-instr", "auto-hint",
"cv-num-in-compile". For details about the meanings of these
types, see <a href="graphics.html">The Graphics State and
Xgridfit Defaults</a> and <a
href="merge-mode.html">Merge-mode</a>.
</dd>
<dt>value</dt>
<dd>
Required. For permissible values, see <a
href="graphics.html">The Graphics State and Xgridfit
Defaults</a>.
</dd>
</dl>
<h2 id="delta"><delta></h2>
<p>
A delta instruction moves points at particular sizes. The
<delta> element may contain any number of
<delta-set> elements, each one specifying a point to
move, a size at which to move it, and a distance to move it.
</p>
<p>
The direction of the move is determined by the current setting
of the freedom vector. The available specifications are fuzzy
as to the details. You will experience no surprises when the
vectors are set to x or y; you may experiment with the vectors
set at other angles.
</p>
<p>
When the first element of a <delta> is a <point>,
that point is the default, which every <delta-set>
element will move unless it contains its own
<point>. These two <delta> elements are
equivalent:
</p>
<pre>
<delta>
<delta-set size="3" distance="8">
<point num="p1"/>
</delta-set>
<delta-set size="4" distance="8">
<point num="p1"/>
</delta-set>
</delta>
<delta>
<point num="p1"/>
<delta-set size="3" distance="8"/>
<delta-set size="4" distance="8"/>
</delta></pre>
<p>
Note that a <move> element may contain <delta>
elements. When a <delta-set> element inside one of these
<delta> elements lacks a <point>, it operates on
the point moved by the parent <move>.
</p>
<h3>Content</h3>
<p>
An optional <point> element, followed by one or more
<delta-set> elements.
</p>
<h3>Attributes</h3>
<dl>
<dt>compile-if</dt>
<dd>
Optional. Any value or expression that can be resolved to a
number at compile time. If true (non-zero), the
<delta> element is compiled; otherwise the compiler
passes it over.
</dd>
</dl>
<h2 id="delta-set"><delta-set></h2>
<p>
The <delta-set> element encapsulates the essential
information about a single delta move or adjustment: the
resolution at which to apply the delta, the magnitude of the
adjustment, and the point or control value that will be
affected.
</p>
<p>
The resolution is determined by the <tt>size</tt> attribute,
which can be a number from 0 to 47. It is added to the value
set by the <set-delta-base> or <with-delta-base>
instruction to obtain the resolution (in pixels per em or
"ppem") at which the move should take place. The default delta
base is 9; if you don't change it, a <tt>size</tt> of "0"
means 9 ppem, "9" means 18 ppem, and so forth up to "47,"
which means 56 ppem.
</p>
<p>
The <tt>distance</tt> attribute is the distance to shift the
point along the freedom vector, or the amount to add to or
subtract from the control value. Legal values are from -8 to 8
(excluding 0). When moving points, negative numbers shift
against the direction of the freedom vector (generally down or
left) and positive numbers shift in the direction of the
freedom vector.
</p>
<p>
The default unit by which pixels are moved and control values
adjusted is 1/8 pixel. The unit is controlled by means of the
<set-delta-shift> or the <with-delta-shift>
instruction.
</p>
<p>
A <delta-set> that is the child of a <delta> will
normally contain a single <point>. However, the
<point> may be omitted in either of two circumstances:
First, when the <delta> is the child of a <move>
element, the <point>, when not specified, is implicitly
the <point> that is the child of the parent
<move>. Second, when the first child element of the
<delta> is <point>, that point will be moved by
any <delta-set> that lacks a child <point>. A
<delta-set> that is the child of a
<control-value-delta> element may not contain a
<point>, but it must have a <tt>cv</tt> attribute.
</p>
<p>
All attribute values in a <delta-set> and a child
<point> must be capable of being resolved to numerical
values at compile time. Variables and function parameters are
not permitted.
</p>
<h3>Content</h3>
<p>
When the <delta-set> is the child of a <delta>
element, it may contain a <point>; this is the point to
move. It <i>must</i> contain a <point> when it the
parent <delta> is not the child of a <move> and
the first child of the <delta> is not a
<point>. When the <delta-set> is the child of
<control-value-delta> it has no content.
</p>
<h3>Attributes</h3>
<dl>
<dt>cv</dt>
<dd>
Required when the <delta-set> is the child of
<control-value-delta>. The name of the control value
to adjust.
</dd>
<dt>size</dt>
<dd>
Required. An integer from 0 to 47. The resolution at which
to move the point or adjust the control value, as explained
above.
</dd>
<dt>distance</dt>
<dd>
Required. An integer from -8 to 8, excluding 0. The distance
to move the point or the amount to adjust the control value,
as explained above.
</dd>
</dl>
<h2 id="diagonal-stem"><diagonal-stem></h2>
<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 <align> 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-distance</tt>
attribute. At the end of this instruction the minimum distance
is 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 <diagonal-stem> instructions together,
enclose them in a <tt><with-round-state round="no"></tt> element to
turn off rounding beforehand
and on again afterwards. In this case, do not include the <tt>round</tt>
attribute with the <diagonal-stem> 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 <line> 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>
<pre>
<with-minimum-distance value="diag-min-dist">
<with-round-state round="no">
<diagonal-stem distance="cap-thick-diag" save-vectors="yes">
<line ref="left-diag-left-line"/>
<line ref="left-diag-right-line"/>
</diagonal-stem>
<diagonal-stem distance="cap-thin-diag" save-vectors="yes">
<line ref="right-diag-right-line"/>
<line ref="right-diag-left-line"/>
</diagonal-stem>
</with-round-state>
</with-minimum-distance></pre>
<h3>Content</h3>
<p>
Two <line> elements, the second to be made parallel to
the first. Optionally, one or two <align> elements, the
first containing points to be aligned with the first line and
the second with the second line.
</p>
<h3>Attributes</h3>
<dl>
<dt>distance</dt>
<dd>
Required. The name of a control value which determines the
distance to place the second line from the first.
</dd>
<dt>round</dt>
<dd>
Optional. The value may be "yes" or "no", the name of a
standard or custom round state, or any number or expression
to use as an input for SROUND. If the value is anything but
"no", rounding is used.
</dd>
<dt>cut-in</dt>
<dd>
Optional. The value may be "yes" or "no"; the default is
"yes". Determines whether to use the control value cut-in.
</dd>
<dt>min-distance</dt>
<dd>
Optional. The value may be "yes" or "no" or any value or
expression to be used to set the minimum distance for this
operation.
</dd>
<dt>color</dt>
<dd>
Optional. Permitted values are "black", "white" and
"gray". The default is "black." The kind of distance between
the points of the two <line> elements.
</dd>
<dt>freedom-vector</dt>
<dd>
Optional. The value may be "yes" or "no"; the default is
"no". Determines whether to set the freedom vector to the
same angle as the projection vector.
</dd>
<dt>save-vectors</dt>
<dd>
Optional. The value may be "yes" or "no"; the default is
"no". If "yes", both the projection vector and the freedom
vector are guaranteed to be the same after this intruction
as they were before.
</dd>
</dl>
<h2 id="disable-instructions"><disable-instructions></h2>
<p>
Disables the instructions associated with glyphs. The
TrueType specification does not say that instructions in the
<pre-program> are disabled: presumably they are
not. This instruction is available only in the
<pre-program>.
</p>
<h3>Content</h3>
<p>None.</p>
<h3>Attributes</h3>
<p>None.</p>
<h2 id="divide"><divide></h2>
<p>Divides <tt>dividend</tt> by <tt>divisor</tt>. If
<tt>result-to</tt> is not specified, Xgridfit attempts to
write the result to <tt>dividend</tt>.</p>
<h3>Content</h3>
<p>None.</p>
<h3>Attributes</h3>
<dl>
<dt>dividend</dt>
<dd>
Required, except when <divide> is a child of the
<formula> element. Any value or expression. The number
to be divided.
</dd>
<dt>divisor</dt>
<dd>
Required, except when <divide> is a child of the
<formula> element. Any value or expression. The number
by which the dividend is to be divided.
</dd>
<dt>result-to</dt>
<dd>
Optional; not allowed when <divide> is the child of a
<formula>. The name of a variable or control value in
which to store the result. In a <formula> element the
result can be passed automatically to the next arithmetic
element; otherwise, if this attribute is missing, the
compiler tries to store the result in
<tt>dividend</tt>. Failing that, it issues a warning and
leaves the result on the stack.
</dd>
</dl>
<h2 id="else-el"><else></h2>
<p>
Provides the "else" clause for an <a
href="#if-el"><if></a> or <a
href="#compile-if"><compile-if></a> element. The
<else> must be the last child of the parent element.
</p>
<h3>Content</h3>
<p>
Programming to be conditionally compiled.
</p>
<h3>Attributes</h3>
<p>None.</p>
<h2 id="enable-instructions"><enable-instructions></h2>
<p>
Enables the instructions associated with glyphs. This
instruction is available only in the <pre-program>.
</p>
<h3>Content</h3>
<p>None.</p>
<h3>Attributes</h3>
<p>None.</p>
<h2 id="entry"><entry></h2>
<p>
An entry in the <a href="#ps-private">PostScript private
dictionary</a>.
</p>
<h3>Content</h3>
<p>None.</p>
<h3>Attributes</h3>
<dl>
<dt>name</dt>
<dd>
Required. The name of the entry.
</dd>
<dt>value</dt>
<dd>
Required. The value of the entry. Usually this is a
space-delimited list of numbers; for BlueFuzz it must be an
integer.
</dd>
</dl>
<h2 id="flip-on"><flip-off><br/><flip-on></h2>
<p>
"Flips" a range of points so that they all become either
on-line points or off-line points. The <flip-off> and
<flip-on> elements must contain a single <range>
element. The range operated upon always runs from the lowest
point to the highest.
</p>
<h3>Content</h3>
<p>
One <range> element.
</p>
<h3>Attributes</h3>
<p>None.</p>
<h2 id="floor"><floor></h2>
<p>Yields the greatest integer less than or equal to <tt>value</tt>,
which is either an integer representing 64ths of a pixel or
a fixed-point number. The returned value, if looked at as
an integer, is either zero or a multiple of 64.</p>
<h3>Content</h3>
<p>None.</p>
<h3>Attributes</h3>
<dl>
<dt>value</dt>
<dd>
Required, except when <floor> is the child of a
<formula>. Any value or expression. The value to operate on.
</dd>
<dt>result-to</dt>
<dd>
Optional; not allowed when <floor> is the child of a
<formula>. The name of a variable or control value in
which to store the result. If <tt>result-to</tt> is omitted
where allowed, Xgridfit attempts to write the result to
<tt>value</tt>. If <tt>value</tt> cannot be written to, the
compiler issues a warning and the result is left on the
stack.
</dd>
</dl>
<h2 id="formula"><formula></h2>
<p>A formula is a block containing arithmetical instruction
elements. Within the <formula> the behavior of these
elements is modified slightly: when a <tt>result-to</tt> attribute is
missing, they do not attempt to write their result back to
one of the values passed to them, but rather leave it on the
stack, thus making it available to the following instruction
element. Further, while Xgridfit normally issues a warning
when an arithmetic element takes a value from the stack or
leaves a result on the stack, within a formula this is the
expected behavior and so the warning is suppressed. The
instructions within the formula should be chained, the
result of one operation being used as an argument for the
following one; this results in tight code being generated.
Example:</p>
<pre>
<formula result-to="minimum-distance">
<round value="lc-vert-stem"/>
<multiply value2="0.8"/>
</formula></pre>
<p>This rounds the control-value "lc-vert-stem," multiplies it by
0.8, and sets the minimum distance in the graphics state to
the result. The original entry in the control-value table is
unchanged. By contrast, if this <round> element were
not the child of a <formula>, the result would be
written back to the control-value table.</p>
<h3>Content</h3>
<p>
A sequence of elements that perform arithmetic: set-equal,
add, subtract, divide, multiply, absolute, negate, floor,
ceiling, minimum, maximum, round, no-round,
control-value-index.
</p>
<h3>Attributes</h3>
<dl>
<dt>result-to</dt>
<dd>
Optional. The name of a variable or control value in which
to store the result. If there is no <tt>result-to</tt>
attribute, the compiler issues a warning and the result is
left on the stack.
</dd>
</dl>
<h2 id="functions"><function></h2>
<p>
The <function> element is used to define
functions. Functions are called by name using the <a
href="#call-function"><call-function></a>
element. Normally Xgridfit takes care of indexing functions
and making sure the right number is used to call them.
</p>
<p>
A function may also have a <tt>num</tt> attribute: this is
used to define the function in the fpgm table and ensures that
any legacy programming can continue to call older functions by
number. Xgridfit assigns a number automatically to any
function that lacks a <tt>num</tt> attribute.
</p>
<p>
A function that returns a value must have the attribute
<tt>return="yes"</tt>; within such a function an instruction
may assign a value to the special variable "return". The
return value must be a single number; lines, vectors, and
other structures consisting of two or more numbers cannot be
returned.
</p>
<p>
A <function> may contain any number of <param>
elements and any number of <variable> elements, followed
by programming.
</p>
<pre>
<function name="lc-standard-serif">
<!-- Regulates vertical distances within a serif -->
<param name="base"/>
<param name="bottom-left"/>
<param name="bottom-right"/>
<param name="top-left"/>
<param name="top-right"/>
<with-vectors axis="y">
<mdap>
<point num="base"/>
</mdap>
<mirp distance="lc-serif-height" set-rp0="yes">
<point num="top-left"/>
</mirp>
<align>
<point num="top-right"/>
</align>
<mirp distance="lc-serif-height" set-rp0="yes">
<point num="bottom-left"/>
</mirp>
<align>
<point num="bottom-right"/>
</align>
</with-vectors>
</function></pre>
<p>
You may define <a
href="functions.html#function-variant">function variants</a>,
that is, alternative versions of a function to be used at
certain sizes or resolutions. To do so, simply include one or
more <a href="#function-variant"><variant></a> elements
as the last children of the <function> element.
</p>
<h3>Content</h3>
<p>
First optional <param> elements; next optional
<variable> and <alias> elements (in any order);
then elements containing programming to be executed by
default; finally optional <variant> elements defining
versions of the function to be used if the <tt>test</tt>
attribute of the <variant> element evaluates as true
(non-zero) when the <pre-program> is run.
</p>
<h3>Attributes</h3>
<dl>
<dt>name</dt>
<dd>
Required. A name: any sequence of letters, numbers, hyphens,
periods; no spaces permitted. The name of this function.
</dd>
<dt>xml:id</dt>
<dd>
Optional. A valid XML ID, i.e. any sequence of letters,
numbers, hyphens, periods; no spaces permitted; and unique
within the program. This ID may be used if a function is
imported into a file using XInclude.
</dd>
<dt>num</dt>
<dd>
Optional. A non-negative integer (zero or greater). See
above for its use. If your program contains functions with
<tt>num</tt> attributes, it should not contain a
<legacy-functions> element.
</dd>
<dt>return</dt>
<dd>
Optional. Permitted values are "yes" and "no"; "no" is the
default. If "yes", the function may return a value by
assigning a value to the special "return" variable.
</dd>
</dl>
<h2 id="get-coordinate"><get-coordinate></h2>
<p>
Gets the coordinate of a point, measured along the current
projection vector. If the projection vector is set to
<tt>x</tt>, for example, the result will be the horizontal
distance of the point from the grid origin (0,0). The
<tt>result-to</tt> attribute may be the name of a variable, a
control value, or a graphics state variable.
</p>
<pre>
<get-coordinate result-to="v">
<point num="p"/>
</get-coordinate></pre>
<p>
Most of the time it will be more convenient to use one of the
"coord" operators in an <a
href="expressions.html">expression</a>.
</p>
<h3>Content</h3>
<p>
The <point> to get the coordinate of.
</p>
<h3>Attributes</h3>
<dl>
<dt>grid-fitted</dt>
<dd>
Optional. Permitted values are "yes" and "no"; the default
is "yes". Whether to use the point's current (grid-fitted)
position or its original position (before grid-fitting).
</dd>
<dt>result-to</dt>
<dd>
Optional. The name of a variable or control value in which
to store the result. If there is no <tt>result-to</tt>
attribute, the compiler issues a warning and the result is
left on the stack.
</dd>
</dl>
<h2 id="getinfo"><getinfo></h2>
<p>
The <getinfo> element provides access to the TrueType
GETINFO instruction, which queries the TrueType engine about
the state of the current glyph, about the engine version, or
about whether ClearType is enabled. In general it is more
convenient to use Xgridfit's built-in <a
href="graphics.html#engine">graphics variables</a> to obtain
such information, but the <getinfo> element may be
useful to combine selectors in ways that Xgridfit does not
anticipate; and future versions of the TrueType may introduce
selectors that Xgridfit does not know about.
</p>
<p>
<getinfo> takes two attributes: <tt>selector</tt>
indicates which query or queries to submit to GETINFO. Its
value can be any number or expression; and note that the
relevant <a href="graphics.html#engine">graphics variables</a>
can be used here, and the value of these variables in this
context is the selector rather than the result of a GETINFO
query, as is the case elsewhere. Selectors for GETINFO can be
combined by ANDing them; this can be simulated in Xgridfit by
adding selectors together (since TrueType programming does not
have arithmetical AND). This query
</p>
<pre>
<getinfo result-to="v" selector="is-glyph-rotated + is-glyph-stretched"/></pre>
<p>
will return a non-zero (true) value if either condition is
true.
</p>
<p>
The second attribute, <tt>result-to</tt>, works like the same
attribute elsewhere: that is, it is a variable in which to
store the result of the query, and if it is omitted the
compiler issues a warning and the value is left on the top of
the stack.
</p>
<h3>Content</h3>
<p>None.</p>
<h3>Attributes</h3>
<dl>
<dt>selector</dt>
<dd>
One or more of the following, added together:
is-glyph-rotated, is-glyph-stretched, is-glyph-grayscale,
is-cleartype-enabled, is-compatible-width-enabled,
is-symmetrical-smoothing-enabled, is-BGR-order. Or, by
itself, is-glyph-transformed.
</dd>
<dt>result-to</dt>
<dd>
Optional. The name of a variable in which to store the
result. If there is no <tt>result-to</tt> attribute, the
compiler issues a warning and the result is left on the
stack.
</dd>
</dl>
<h2 id="glyph"><glyph></h2>
<p>
The <glyph> element contains instructions relating to an
individual glyph. Example:
</p>
<pre>
<glyph ps-name="sample-glyph">
<constant name="last" value="50"/>
. . .
<variable id="v"/>
<with-vectors axis="y">
<!-- programming here -->
</with-vectors>
<with-vectors axis="x">
<!-- more programming here -->
</with-vectors>
<interpolate-untouched-points/>
</glyph></pre>
<p>
To make a glyph program callable in the manner of a macro (see
<a href="#call-glyph"><call-glyph></a>), include one or
more <param> elements for key values. These should have
<tt>value</tt> attributes, since the glyph program will have
to be compiled and run even when it is not called.
</p>
<h3>Content</h3>
<p>
<param> elements (if any) must come first, followed by
<constant>, <range>, <set>, <line>,
<alias> and <variable> elements in any
order. Finally programming for the glyph.
</p>
<h3>Attributes</h3>
<dl>
<dt>ps-name</dt>
<dd>
Required. The PostScript name of the glyph. It must match
the PostScript name of the glyph in the font.
</dd>
<dt>xml:id</dt>
<dd>
Optional. A valid XML ID, i.e. any sequence of letters,
numbers, hyphens, periods; no spaces permitted; and unique
within the program. This ID may be used if a <glyph>
is imported into a file using XInclude.
</dd>
<dt>init-graphics</dt>
<dd>
Optional. Permitted values are "yes" and "no". This
attribute determines whether variables used by Xgridfit to
track the graphics state are initialized at the beginning of
the glyph program. Such initialization is not needed when
instructions are imported from another font. The default
value is normally "yes," but the default may be set with the
<tt>init-graphics</tt> <default> or with the -G option
for the <tt>xgridfit</tt> executable.
</dd>
</dl>
<h2 id="glyph-select"><glyph-select></h2>
<p>
Specifies a whitespace-delimited list of glyphs to compile,
ignoring all others. It is all right to keep this element in
the file when you don't need it: just empty it out. These are
valid:
</p>
<pre>
<glyph-select>a macron amacron</glyph-select>
<glyph-select></glyph-select></pre>
<p>
This element corresponds to the <tt>glyph-select</tt>
parameter and the <tt>-g</tt> command line option, either of
which will, if present, override the element.
</p>
<h3>Content</h3>
<p>
A whitespace-delimited list of ps-names of glyph elements.
</p>
<h3>Attributes</h3>
<p>None.</p>
<h2 id="if-el"><if></h2>
<p>
Contains instructions that are executed only if the expression
in the <tt>test</tt> attribute is true. If the test is false,
and an <else> element is the last child of this
<if>, the instructions in the <else> element are
executed. <if> elements may be nested.
</p>
<p>
The <tt>test</tt> attribute contains an expression, e.g.
</p>
<pre>
<if test="minimum-distance = 1p"></pre>
<p>
For more on expressions, see the <a
href="expressions.html">Expressions</a> section of this
documentation. In the TrueType language, where all data is
numeric, a non-zero value is considered true and zero false. So
the <tt>test</tt> attribute can be used to tell whether a
value is zero. This
</p>
<pre>
test="round(lc-vert-stem) != 0"</pre>
<p>
is equivalent to this:
</p>
<pre>
test="round(lc-vert-stem)"</pre>
<p>
The <if> element may contain an <else> clause,
which must come last.
</p>
<pre>
<if test="boolean-expression">
<!-- programming -->
<else>
<!-- alternative programming -->
</else>
</if></pre>
<h3>Content</h3>
<p>
Programming, followed optionally by an <else> element.
</p>
<h3>Attributes</h3>
<dl>
<dt>test</dt>
<dd>
Required. Any value or expression. The condition to test
for.
</dd>
</dl>
<h2 id="infile"><infile></h2>
<p>
Contains the name of a file to which TrueType instructions are
to be added. This may be either a FontForge source file (.sfd)
or a TrueType font (.ttf).
</p>
<pre>
<infile>MyFont.sfd</infile>
<outfile>MyFont.ttf</outfile></pre>
<h3>Content</h3>
<p>
The name of a file with extension <tt>.sfd</tt> or
<tt>.ttf</tt>.
</p>
<h3>Attributes</h3>
<p>None.</p>
<h2 id="interpolate"><interpolate></h2>
<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 <interpolate> element must contain at least one
point to interpolate. It may contain any number of
<point>s, <range>s and <set>s. Like most other elements
that move points, it may contain a <reference> element;
but this element must contain two <point>s, not just
one.
</p>
<p>
This instruction may be nested inside a <move> element
containing a reference point, in which case no reference
points are needed in the <interpolate> element: the
points it contains are automatically interpolated between the
<move> element's reference point and its moved point.
These two <interpolate> elements do the same thing:
</p>
<pre>
<interpolate>
<reference>
<point num="top"/>
<point num="bottom"/>
</reference>
<point num="bar-top-left"/>
</interpolate>
<move>
<reference>
<point num="bottom"/>
</reference>
<point num="top"/>
<interpolate>
<point num="bar-top-left"/>
</interpolate>
</move></pre>
<p>
If you want to round points after interpolating them, simply
include the attribute <tt>round="yes"</tt> on the
<interpolate> element. The points will be moved along the
freedom vector to the nearest rounded position. Note that this
has no effect on <range> or <set> elements. If you
want to use a round state other than the current one, use the
appropriate value for <tt>round</tt>:
</p>
<pre>
<interpolate round="to-half-grid">
<reference>
<point num="a"/>
<point num="b"/>
</reference>
<point num="c"/>
</interpolate></pre>
<h3>Content</h3>
<p>
An optional <reference> element (containing two
<point> elements), followed by one or more
<point>, <range> and <set> elements.
</p>
<h3>Attributes</h3>
<dl>
<dt>compile-if</dt>
<dd>
Optional. Any value or expression that can be resolved to a
number at compile time. This <interpolate> element is
compiled only if the <tt>compile-if</tt> attribute evaluates
as true (non-zero). If this attribute is not present, the
<interpolate> is compiled.
</dd>
<dt>round</dt>
<dd>
Optional. The value may be "yes" or "no", the name of a
standard or custom round state, or any number or expression
to use as an input for SROUND. If the value is anything but
"no", any points referred to by <point> elements (but
not <range> or <set> elements) are moved to the
nearest rounded position. Points are not rounded when this
attribute is not present.
</dd>
</dl>
<h2 id="interpolate-untouched-points"><interpolate-untouched-points></h2>
<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>
<h3>Content</h3>
<p>None.</p>
<h3>Attribute</h3>
<dl>
<dt>axis</dt>
<dd>
Optional. Permitted values are "x" and "y". Determines the
axis along which interpolation is performed. If this
attribute is omitted, interpolation is performed along both
x and y axes.
</dd>
</dl>
<h2 id="legacy-functions"><legacy-functions></h2>
<p>
Stores functions from a font that has been converted for use
with Xgridfit. Normally this should not be created or edited
by hand: see <a href="convert.html">Conversion</a> for further
details.
</p>
<h3>Content</h3>
<p>
Programming imported from an existing font: normally just
<command> and <push> elements.
</p>
<h3>Attributes</h3>
<dl>
<dt>max-function-defs</dt>
<dd>
Required. A positive integer (one or higher). One more than
the highest index of a functon defined in the
<legacy-functions> element. Normally this will be set
correctly by ttx2xgf, but the user should check it before
proceeding.
</dd>
</dl>
<h2 id="line"><line></h2>
<p>
A <line> is defined by its two end-points. These points
need not be adjacent.
</p>
<p>
When a <line> has a <tt>name</tt> attribute, another
<line> may refer to it by name. You may name the
<line> the first time you use it or declare it in a
<line> element among the declarations at the beginning
of a <glyph>. For example, if you declare the line
thus:
</p>
<pre>
<line name="line-2b">
<point num="b"/>
<point num="a"/>
</line></pre>
<p>then you can use an abbreviated form whenever you need it:</p>
<pre>
<set-freedom-vector>
<line ref="line-2b"/>
</set-freedom-vector></pre>
<p>
If both points that define a <line> are in the same
zone, you may use the optional <tt>zone</tt> attribute on the
<line> to indicate this. Most instructions that take a
<line> as an argument allow one point to be in one zone
and the other point in the other: in such cases place the
<tt>zone</tt> attributes on the <point>s. The exception
is the <move-point-to-intersection> instruction, which
requires that each of the two lines it takes as arguments be
entirely in a zone. For this instruction, place the
<tt>zone</tt> attributes on the <line>s, never on the
<point>s.
</p>
<h3>Content</h3>
<p>
Two <point> elements, one at each end of the line. These
are required if no <tt>ref</tt> attribute is present.
</p>
<h3>Attributes</h3>
<dl>
<dt>name</dt>
<dd>
Optional, but necessary if this <line> is referred to
elsewhere. A name: any sequence of letters, numbers,
hyphens, periods; no spaces permitted. Names this
<line>.
</dd>
<dt>ref</dt>
<dd>
Required if no <point> elements are present. A
reference to a named <line>.
</dd>
<dt>zone</dt>
<dd>
Optional. Permitted values are "twilight" and
"glyph". Include the attribute <tt>zone="twilight"</tt> if
both end-points of the line are in the twilight zone.
</dd>
</dl>
<h2 id="macros"><macro></h2>
<p>
A <a href="functions.html#macros">macro</a> is a stretch of
code that is compiled and inserted into the program stream
wherever a <call-macro> element is encountered. Macros
resemble functions in syntax: they begin with <param>
definitions followed by program code, which can access all
global variables and values (e.g. control values, graphics
variables, constants and variables declared as children of
<xgridfit>). Macros can be called from a
<function>, <pre-program> or <glyph>, and
variables and values local to these structures can be accessed
by passing them as parameters.
</p>
<p>
Macro parameters are fundamentally different from function
parameters. A function parameter is passed to the function on
the stack at run time; the macro parameter, on the other hand,
is swapped at compile time for the <tt>value</tt> parameter,
which is then evaluated as any value is evaluated at run
time. When passing variables or control values, there is no
rule governing whether they are passed to the macro by value
or by reference; rather, they are evaluated according to the
rule that governs evaluation of variables for the particular
instruction where they occur.
</p>
<h3>Content</h3>
<p>
Optional <param> elements, followed by optional
<alias> elements, and then by programming.
</p>
<h3>Attributes</h3>
<dl>
<dt>name</dt>
<dd>
Required. A name: any sequence of letters, numbers, hyphens,
periods; no spaces permitted. Names this <macro>.
</dd>
<dt>xml:id</dt>
<dd>
Optional. A valid XML ID, i.e. any sequence of letters,
numbers, hyphens, periods; no spaces permitted; and unique
within the program. This ID may be used if a <macro>
is imported into a file using XInclude.
</dd>
</dl>
<h2 id="maximum"><maximum></h2>
<p>Yields the greater of the two values <tt>value1</tt> and
<tt>value2</tt>.</p>
<pre>
<maximum value1="lc-vert-stem" value2="1p" result-to="lc-vert-stem"/></pre>
<h3>Content</h3>
<p>None.</p>
<h3>Attributes</h3>
<dl>
<dt>value1</dt>
<dd>
Required except when <maximum> is the child of a
<formula> element. Any value or expression.
</dd>
<dt>value2</dt>
<dd>
Required except when <maximum> is the child of a
<formula> element. Any value or expression.
</dd>
<dt>result-to</dt>
<dd>
Optional; not allowed when <maximum> is the child of a
<formula>. The name of a variable in which to store
the result. If <tt>result-to</tt> is omitted where allowed,
the compiler issues a warning and the result is left on the
stack.
</dd>
</dl>
<h2 id="mdap"><mdap></h2>
<p>Corresponds to the TrueType MDAP instruction. Normally
<move> is a better choice for moving points, but this
element is provided to facilitate low-level programming.</p>
<p>
This element rounds a point to the grid if the <tt>round</tt>
attribute is not <tt>no</tt>; otherwise it "touches" the point
(marks it as moved).
</p>
<pre>
<mdap>
<point num="p"/>
</mdap></pre>
<h3>Content</h3>
<p>
A single <point>.
</p>
<h3>Attributes</h3>
<dl>
<dt>round</dt>
<dd>
Optional. The value may be "yes" or "no", the name of a
standard or custom round state, or any number or expression
to use as an input for SROUND. The default value is "yes."
This attribute determines whether and how to round the
point.
</dd>
</dl>
<h2 id="mdrp"><mdrp></h2>
<p>Corresponds to the TrueType MDRP instruction. Normally
<move> is a better choice for moving points, but this
element is provided to facilitate low-level programming.</p>
<p>
This element will also take care of setting RP0 beforehand if
a reference point is supplied. If no reference point is
supplied, the current value of RP0 is used.
</p>
<pre>
<mdrp>
<reference>
<point num="r"/>
</reference>
<point num="p"/>
</mdrp></pre>
<h3>Content</h3>
<p>
An optional <reference> element (containing one point),
followed by a single <point>.
</p>
<h3>Attributes</h3>
<dl>
<dt>round</dt>
<dd>
Optional. The value may be "yes" or "no", the name of a
standard or custom round state, or any number or expression
to use as an input for SROUND. The default value is "yes."
This attribute determines whether and how to round the
distance between the reference point and the moved point.
</dd>
<dt>min-distance</dt>
<dd>
Optional. Permitted values are "yes" and "no". The default
is "yes." Whether or not to maintain a minimum distance
between the reference point and the moved point.
</dd>
<dt>set-rp0</dt>
<dd>
Optional. Permitted values are "yes" and "no". The default
is "no." Whether or not to set the RP0 pointer to the moved
point after the instruction is executed.
</dd>
<dt>color</dt>
<dd>
Optional. Permitted values are "black", "white" and
"gray". The default is "gray." The kind of distance between
the reference point and the moved point. This is used by
some TrueType engines to compensate for engine
characteristics.
</dd>
</dl>
<h2 id="measure-distance"><measure-distance></h2>
<p>
Measures the distance between two points and returns an
F26dot6 number. The measurement is performed along the
projection vector, and the result may be positive or negative
depending on the relationship of the distance to the direction
of the vector. Another way of putting it is that the order of
the two points in this instruction is significant; reverse
them and you reverse the sign of the result.
</p>
<pre>
<measure-distance result-to="v">
<point num="p1"/>
<point num="p2"/>
</measure-distance></pre>
<p>
Usually it will be more convenient to use the <tt>--</tt> or
<tt>---</tt> operator in an <a
href="expressions.html">expression</a>.
</p>
<h3>Content</h3>
<p>
Two <point> elements.
</p>
<h3>Attributes</h3>
<dl>
<dt>grid-fitted</dt>
<dd>
Optional. Permitted values are "yes" and "no"; the default
is "yes". Whether to use the point's current (grid-fitted)
position or its original position (before grid-fitting).
</dd>
<dt>result-to</dt>
<dd>
Optional. The name of a variable or control value in which
to store the result. If there is no <tt>result-to</tt>
attribute, the compiler issues a warning and the result is
left on the stack.
</dd>
</dl>
<h2 id="message"><message></h2>
<p>
The <message> element produces no TrueType code, but
rather causes a message to be output at compile-time via the
<xsl:message> element. This may help with debugging.
</p>
<h3>Content</h3>
<p>
Text of a message to be output.
</p>
<h3>Attributes</h3>
<p>None.</p>
<h2 id="miap"><miap></h2>
<p>Corresponds to the MIAP instruction. Normally
<move> is a better choice for moving points, but this
element is provided to facilitate low-level programming.</p>
<p>Positions a point a specified distance from the grid
origin.</p>
<h3>Content</h3>
<p>
A single point.
</p>
<h3>Attributes</h3>
<dl>
<dt>distance</dt>
<dd>
Required. The name of a control value.
</dd>
<dt>round</dt>
<dd>
Optional. The value may be "yes" or "no", the name of a
standard or custom round state, or any number or expression
to use as an input for SROUND. The default value is "yes."
This attribute determines whether and how to round the
distance between the reference point and the moved point.
</dd>
<dt>cut-in</dt>
<dd>
Optional. The value may be "yes" or "no". The default is
"yes." Whether to use the control value cut-in. If rounding
is used, this will always be <tt>yes</tt>, even if you set
it to <tt>no</tt>.
</dd>
</dl>
<h2 id="minimum"><minimum></h2>
<p>Yields the lesser of the two values <tt>value1</tt> and
<tt>value2</tt>.</p>
<pre>
<minimum value1="lc-vert-stem" value2="1p" result-to="lc-vert-stem"/></pre>
<h3>Content</h3>
<p>None.</p>
<h3>Attributes</h3>
<dl>
<dt>value1</dt>
<dd>
Required except when <minimum> is the child of a
<formula> element. Any value or expression.
</dd>
<dt>value2</dt>
<dd>
Required except when <minimum> is the child of a
<formula> element. Any value or expression.
</dd>
<dt>result-to</dt>
<dd>
Optional; not allowed when <minimum> is the child of a
<formula>. The name of a variable in which to store
the result. If <tt>result-to</tt> is omitted where allowed,
the compiler issues a warning and the result is left on the
stack.
</dd>
</dl>
<h2 id="mirp"><mirp></h2>
<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>
<pre>
<mirp distance="lc-x-height">
<reference>
<point num="p1"/>
</reference>
<point num="p2"/>
</mirp></pre>
<h3>Content</h3>
<p>
An optional <reference> element (containing one point),
followed by a single <point>.
</p>
<h4>Attributes</h4>
<dl>
<dt>distance</dt>
<dd>
Required. The name of a control value. Distance (from a
<control-value> element) relative to the reference
point (or to RP0 if that was set by a previous instruction).
</dd>
<dt>round</dt>
<dd>
Optional. The value may be "yes" or "no", the name of a
standard or custom round state, or any number or expression
to use as an input for SROUND. The default value is "yes."
This attribute determines whether and how to round the
distance between the reference point and the moved point.
</dd>
<dt>cut-in</dt>
<dd>
Optional. The value may be "yes" or "no". The default is
"yes." Whether to use the control value 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>
Optional. Permitted values are "yes" and "no". The default
is "yes." Whether or not to maintain a minimum distance
between the reference point and the moved point.
</dd>
<dt>set-rp0</dt>
<dd>
Optional. Permitted values are "yes" and "no". The default
is "no." Whether or not to set the RP0 pointer to the moved
point after the instruction is executed.
</dd>
<dt>color</dt>
<dd>
Optional. Permitted values are "black", "white" and
"gray". The default is "gray." The kind of distance between
the reference point and the moved point. This is used by
some TrueType engines to compensate for engine
characteristics.
</dd>
</dl>
<h2 id="modifier"><modifier></h2>
<p>
When used as the content of a <command> element,
controls one or two bits of the output instruction.
</p>
<h3>Content</h3>
<p>None.</p>
<h3>Attributes</h3>
<dl>
<dt>type</dt>
<dd>
Required. Must be one of the following: "set-rp0", "round",
"minimum-distance", "color", "grid-fitted", "to-line",
"axis", "ref-ptr". This determines which bits are affected.
</dd>
<dt>value</dt>
<dd>
Required. The possible values vary with the
<tt>type</tt>. For details and defaults, see the <a
href="low-level.html#command">"Low-Level Elements"</a>
section.
</dd>
</dl>
<h2 id="move"><move></h2>
<p>Moves a point and, optionally, aligns other points with it
or moves other points in relation to it. For details, see the section
on <a href="moves.html">moving points</a>.</p>
<h3>Content</h3>
<p>
An optional <reference> element containing one
<point>; then a required <point>. This may be
followed by any number of the following elements, in this
order:
</p>
<ul>
<li><delta></li>
<li><align>,
<interpolate>,
<shift> (in any order),</li>
<li><move></li>
<li><delta></li>
</ul>
<p>
The first group of <delta> element is executed before
the embedded <align>, <interpolate>, <shift>
and <move> elements; the second group is executed
afterwards. A <move> may contain <interpolate>
only if <reference> is present.
</p>
<h3>Attributes</h3>
<dl>
<dt>distance</dt>
<dd>
Optional. The name of a <control-value> 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>
Optional. 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, and the schema does not permit both to be
present.
</dd>
<dt>round</dt>
<dd>
Optional. The value may be "yes" or "no", the name of a
standard or custom round state, or any number or expression
to use as an input for SROUND. The default is "yes." Whether
and how to round the <tt>distance</tt> or
<tt>pixel-distance</tt>. "Yes" means round the distance
according to the current round state (to-grid, if you
haven't changed it). If you specify "no", no rounding is
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 defined
in the top level of the program (as a child of
<xgridfit>), 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 <move>
instructions use the same round state, it is more efficient
to enclose them in a <with-round-state> 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><with-round-state
round="no"></tt> and omit the <tt>round</tt> attribute
for the <move> 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 "yes", "no" or any value or
expression; the default value is "yes". If the value of this
attribute is <tt>no</tt>, the value of the <tt>round</tt>
attribute must also be "no". (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>
Optional. The value may be "yes" or "no" or any value or
expression to be used to set the minimum distance for this
operation. This attribute has an effect only when there is
a reference point.
</dd>
<dt>color</dt>
<dd>
Optional. Permitted values are "black", "white" and
"gray". The default is "gray." The kind of distance between
the reference point and the moved point. This is used by
some TrueType engines to compensate for engine
characteristics. This applies only when there is a reference
point.
</dd>
</dl>
<h2 id="move-point-to-intersection"><move-point-to-intersection></h2>
<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 <line> elements rather than the <tt>zone</tt>
attributes of the <point> elements that make up the
lines.</p>
<pre>
<move-point-to-intersection>
<point num="p"/>
<line>
<point num="l1p1"/>
<point num="l1p2"/>
</line>
<line>
<point num="l2p1"/>
<point num="l2p2"/>
</line>
</move-point-to-intersection></pre>
<h3>Content</h3>
<p>
A single <point> and two <line> elements.
</p>
<h3>Attributes</h3>
<p>None.</p>
<h2 id="multiply"><multiply></h2>
<p>Multiplies <tt>value1</tt> by <tt>value2</tt>. If there is no
<tt>result-to</tt> attribute, Xgridfit attempts to write the
result to <tt>value1</tt>.</p>
<pre>
<multiply value1="lc-vert-stem" value2="3.3" result-to="v"/></pre>
<h3>Content</h3>
<p>None.</p>
<h3>Attributes</h3>
<dl>
<dt>value1</dt>
<dd>
Required except when <multiply> is the child of a
<formula> element. Any value or expression.
</dd>
<dt>value2</dt>
<dd>
Required except when <multiply> is the child of a
<formula> element. Any value or expression.
</dd>
<dt>result-to</dt>
<dd>
Optional; not allowed when <multiply> is the child of
a <formula>. The name of a variable in which to store
the result. If <tt>result-to</tt> is omitted where allowed,
the compiler issues a warning and the result is left on the
stack.
</dd>
</dl>
<h2 id="negate"><negate></h2>
<p>
Converts positive to negative numbers; negative numbers stay
negative. If the <tt>result-to</tt> attribute is not present,
Xgridfit attempts to write the result back to
<tt>value</tt>. Failing that, it issues a warning and leaves
the result on the stack.
</p>
<pre>
<negate value="v"/></pre>
<h3>Content</h3>
<p>None.</p>
<h3>Attributes</h3>
<dl>
<dt>value</dt>
<dd>
Required, except when <negate> is the child of a
<formula>. Any value or expression. The value to operate on.
</dd>
<dt>result-to</dt>
<dd>
Optional; not allowed when <negate> is the child of a
<formula>. The name of a variable or control value in
which to store the result. If <tt>result-to</tt> is omitted
where allowed, and <tt>value</tt> is a variable or control
value, the result is written to <tt>value</tt>. If
<tt>value</tt> cannot be written to, the compiler issues a
warning and the result is left on the stack.
</dd>
</dl>
<h2 id="no-compile"><no-compile></h2>
<p>
This element, which must always be a child of
<xgridfit>, contains <glyph> elements (usually
imported via XInclude) which are visible for reference
purposes but not compiled. If a file <tt>MyFont-Basic.xgf</tt>
contains a glyph program with an opening tag that looks like
this:
</p>
<pre>
<glyph ps-name="a" xml:id="a"></pre>
<p>
then that glyph program can be made visible within another
file thus:
</p>
<pre>
<no-compile>
<xi:include href="MyFont-Basic.xgf#a"/>
</no-compile></pre>
<p>
Now the following <point> will compile correctly:
</p>
<pre>
<point num="a/top + another-num"</pre>
<p>
The glyph included in this way can also be compiled via
<call-glyph>:
</p>
<pre>
<call-glyph ps-name="a">
<with-param name="left-sidebearing" value="111"/>
</call-glyph></pre>
<p>
The <no-compile> element can be overridden with the
<glyph-select> element (<tt>glyph-select</tt> parameter
or <tt>-g</tt> option). This behavior may ease the testing of
programs for composite glyphs.
</p>
<h3>Content</h3>
<p>
One or more <glyph> elements; more typically,
<xi:include> elements importing <glyph> elements
from other files.
</p>
<h3>Attributes</h3>
<p>None.</p>
<h2 id="no-round"><no-round></h2>
<p>
Like round, but without the rounding. That is, it may apply a
correction for the "color" of the distance, but it will not
round the distance. If the <tt>result-to</tt> attribute is not
present, Xgridfit attempts to write the result back to
<tt>value</tt>. Failing that, it issues a warning and leaves
the result on the stack.
</p>
<pre>
<no-round value="v1" color="black" result-to="v2"/></pre>
<h3>Content</h3>
<p>None.</p>
<h3>Attributes</h3>
<dl>
<dt>value</dt>
<dd>
Required, except when <no-round> is the child of a
<formula>. Any value or expression. A distance on the current
grid; the value to operate on.
</dd>
<dt>color</dt>
<dd>
Optional. Permitted values are "black", "white" and
"gray". The default is "gray." The kind of distance that the
<tt>value</tt> represents. This is used by some TrueType
engines to compensate for engine characteristics.
</dd>
<dt>result-to</dt>
<dd>
Optional; not allowed when <no-round> is the child of
a <formula>. The name of a variable or control value
in which to store the result. If <tt>result-to</tt> is
omitted where allowed, and <tt>value</tt> is a variable or
control value, the result is written to <tt>value</tt>. If
<tt>value</tt> cannot be written to, the compiler issues a
warning and the result is left on the stack.
</dd>
</dl>
<h2 id="no-warning"><no-warning></h2>
<p>
Inside a <no-warning></no-warning> block, warning
messages are suppressed. Use this if you find a particular
warning message annoying and you want to assure the compiler
that you know what you're doing.
</p>
<h3>Content</h3>
<p>
Programming of any kind.
</p>
<h3>Attributes</h3>
<p>None.</p>
<h2 id="outfile"><outfile></h2>
<p>
Contains the name of a file to write. If the filename ends
<tt>.sfd</tt> it is assumed that a FontForge source file is
desired, and the generated FontForge script ends with a "Save"
command. If the filename ends <tt>.ttf</tt> it is assumed that
a TrueType font is desired, and the generated FontForge script
ends with a "Generate" command. It is an error if the filename
has any other suffix.
</p>
<p>
The <tt>fmflags</tt> attribute indicates flags to pass to
FontForge when generating a TrueType font. It has no effect
when the <outfile> is a FontForge source file. For a
list of these flags, see the documentation for the <a
href="http://fontforge.sourceforge.net/scripting-alpha.html#G">Generate</a>
command. Probably the most likely to be used is "2048"
(generate old-style kern table).
</p>
<pre>
<infile>MyFont.sfd</infile>
<outfile fmflags="2048">MyFont.ttf</outfile></pre>
<h3>Content</h3>
<p>
The name of a file, with extension of either <tt>.sfd</tt> or
<tt>.ttf</tt>.
</p>
<h3>Attributes</h3>
<dl>
<dt>fmflags</dt>
<dd>
Optional. An integer. Flags to be passed to the FontForge
"Generate" command. This has no effect when Python output is
selected; instead, use <tt>pyflags</tt>.
</dd>
<dt>pyflags</dt>
<dd>
A list of flags for FontForge to use when it generates a
font. This is a space-separated list of tokens,
e.g. <tt>pyflags="old-kern ofm"</tt>. Possible tokens are:
afm, pfm, tfm, ofm, composites-in-afm, glyph-map-file,
short-post, apple, opentype, old-kern, dummy-dsig,
TeX-table, round, no-hints, omit-instructions,
PfEd-comments, PfEd-colors, PfEd-lookups, PfEd-guidelines,
PfEd-background, symbol. For the meanings of these, see the
section of the FontForge manual on <a
href="http://fontforge.sourceforge.net/python.html#f-generate">generating
fonts in Python scripts</a>.
</dd>
</dl>
<h2 id="outfile-base"><outfile-base></h2>
<p>
This element, which must be a child of <xgridfit>,
corresponds to the <tt>outfile-base</tt> parameter and the
<tt>-S</tt> option for the <tt>xgridfit</tt> shell script. If
present, it causes a separate file to be output for every
glyph that Xgridfit compiles. The name of the file is the
string supplied in this element, plus the <tt>ps-name</tt> of
the glyph, plus the extension .pe, .py or .debug. For example,
this element
</p>
<pre>
<outfile-base>Test</outfile-base></pre>
<p>
causes Xgridfit to output files with names like
<tt>Test_A.pe</tt> and <tt>Test_B.py</tt> (or
<tt>Test_A.py</tt> and <tt>Test_B.pe</tt> when Python output
is requested). Elements such as control values, functions and
the pre-program are output as usual in the default output
script or in a file specified with the -O option. Note that
this element also causes the output of <outfile> to be
saved in a separate script whose default name depends on
<outfile-base>. See <a
href="#outfile-script-name"><outfile-script-name></a> to
specify a different name for this separate file.
</p>
<p>
This feature depends on the presence of an extension element
that not every XSLT processor supports. Xsltproc, which
Xgridfit uses by default, does support it.
</p>
<h3>Content</h3>
<p>
A fragment of a file name, from which other file names are
built.
</p>
<h3>Attributes</h3>
<p>None.</p>
<h2 id="outfile-script-name"><outfile-script-name></h2>
<p>
When the <outfile-base> element is present or the
<tt>-S</tt> option is used, and the <outfile> element is
present or the <tt>-o</tt> option is used, Xgridfit outputs
the FontForge command that saves a font file or generates a
font in a separate script file. By default the filename for
this script is based on the outfile-base: for example, if the
-S parameter is <tt>MyFont</tt>, then the filename will be
<tt>MyFont_outfile.pe</tt> or <tt>MyFont_outfile.py</tt>. Use
the <outfile-script-name> element (or the <tt>-z</tt>
option) to specify a filename other than the default. This
element must be a child of <xgridfit>.
</p>
<p>
This element has no effect when the outfile-base is not
specified, and the glyph programs in a script are not being
saved separately.
</p>
<h3>Content</h3>
<p>
Name of a file containing the FontForge "Generate" or "Save"
command.
</p>
<h3>Attributes</h3>
<p>None.</p>
<h2 id="params"><param></h2>
<p>
A <param> element is a declaration that a value, a
structure or some code may be passed to the <function>,
<macro> or <glyph> that contains it by the "call"
element that calls it. The <param> elements should be
the first children of <function>, <macro> and
<glyph> elements.
</p>
<p>
In the case of a <function>, only a value (a single
number) may be passed. A <macro> or <glyph> is
much more flexible: <line>, <range>, <set>
and fragments of code may be passed. Within the <macro>
or <glyph>, the structures can be referenced via
<tt>ref</tt> attributes; code passed as a parameter can be
called via a <call-param> element.
</p>
<p>
A <param> may contain a default <tt>value</tt>--that is,
a value to be used in the event that the call element does not
pass a value. The <param> may also contain code to be
used when the call element does not pass code; but it may not
contain a <line>, <range> or <set>.
</p>
<h3>Content</h3>
<p>
Normally this element is empty; but a <param> intended
to pass code to a <macro> or <glyph> may contain
code to be used when the <call-macro> or
<call-glyph> element lacks a matching <with-param>
element.
</p>
<h3>Attributes</h3>
<dl>
<dt>name</dt>
<dd>
Required. A name: any sequence of letters, numbers, hyphens,
periods; no spaces permitted. The name of the <param>
is used both by the call element and by the code that
requires the value or item passed.
</dd>
<dt>value</dt>
<dd>
Optional. A default value.
</dd>
</dl>
<h2 id="param-set"><param-set></h2>
<p>
Contains a set of parameters (each encoded as a
<with-param> element) to be passed to a function or
macro. There may be more than one of these in a
<call-function> or <call-macro> element; and in
that case the function is called repeatedly (via LOOPCALL)
until the list of <param-set> elements is exhausted; or
the macro code is compiled and inserted repeatedly.
</p>
<h3>Content</h3>
<p>
One or more <with-param> elements.
</p>
<h3>Attribute</h3>
<dl>
<dt>opt</dt>
<dd>
Optional. If set to "yes," forces optimization in pushing function
parameters onto the stack. That is, instructs Xgridfit to
push all parameters with a single PUSHB command. Use this if
you are sure that all parameters can be determined by the
compiler (i.e. they are not determined at run-time) and that
they are all between 0 and 255, but Xgridfit is not
optimizing. If you get this wrong, that is, if you force
optimization when it really ought not to be used, incorrect
code will be generated and your glyph program will
fail. Still, it may be worth a try since the failure will
probably be obvious. Conversely, set this to "no" if
Xgridfit is incorrectly optimizing the parameters in a
function call. This probably won't happen, since Xgridfit
optimizes rather conservatively, but it's here just in case.
</dd>
</dl>
<h2 id="point"><point></h2>
<p>
The <point> element defines a point. It is used in all
instructions that manipulate or refer to points.
</p>
<h3>Content</h3>
<p>None.</p>
<h3>Attributes</h3>
<dl>
<dt>num</dt>
<dd>
Required. Any value or expression. The number of a point. To
refer to a point in a glyph other than the one whose glyph
program is currently running (as you may have occasion to do
when instructing composite glyphs), use the syntax "g/p",
where g is the ps-name of the other glyph, and p is the
point being referred to (it must be the name of a
<constant> declared in the other glyph).
</dd>
<dt>zone</dt>
<dd>
Optional. Permitted values are "twilight" and "glyph". The
zone that contains this point. Instructions will take note
of this attribute, when present, and adjust the zone
pointers appropriately. The glyph zone is always the default
zone. When a point is in the glyph zone it is generally
redundant to include an attribute <tt>zone="glyph"</tt>, and
doing so may also cause unnecessary (though harmless) code
to be generated. N.B. For instructions that deal with lists
of points, include the zone attribute only in the first.
</dd>
</dl>
<h2 id="pre-program"><pre-program></h2>
<p>
The prep table (or CVT program) is made from the
<pre-program> element. It contains instructions that are
executed before a font is rasterized, or whenever it is about
to be rasterized in a new size. A typical thing to do in the
<pre-program> is to adjust control values, e.g. rounding
or applying deltas to them. Another is to set defaults: an
instruction that assigns a value to a graphic variable sets a
default when it is executed in the <pre-program>. For
example, if executed in the <pre-program> this
instruction:
</p>
<pre>
<set-minimum-distance value="0.9"></pre>
<p>
ensures that the minimum-distance graphics variable is always
0.9 pixels at the beginning of any glyph program.
</p>
<p>
The <pre-program> element must be present in a complete
Xgridfit program, even if it is empty.
</p>
<h3>Content</h3>
<p>
One or more optional <variable> and <alias>
elements, followed by optional programming.
</p>
<h3>Attribute</h3>
<dl>
<dt>xml:id</dt>
<dd>
Optional. A valid XML ID, i.e. any sequence of letters,
numbers, hyphens, periods; no spaces permitted; and unique
within the program. This ID may be used if the
<pre-program> is imported into a file using XInclude.
</dd>
</dl>
<h2 id="ps-private"><ps-private></h2>
<p>
Provides access to the font's private PostScript
dictionary. This dictionary is not included in a TrueType
font, but it does provide crucial information to the FontForge
auto-hinter; and the FontForge auto-instructor, in turn,
depends on the presence of PostScript-style hints. For
details, see <a href="merge-mode.html">Merge-mode</a>.
</p>
<h3>Content</h3>
<p>
One or more <entry> elements, each supplying the name
and value of an entry in the PostScript private
dictionary. For example:
</p>
<pre>
<ps-private>
<entry name="BlueValues" value="-33 -2 856 873 1358 1385"/>
<entry name="OtherBlues" value="-578 -553"/>
<entry name="BlueFuzz" value="0"/>
</ps-private>
</pre>
<h2 id="push"><push></h2>
<p>
The <push> element does the work of the various PUSHB
and PUSHW instructions, and it can generate the code to move
any value (e.g. a variable or control-value) onto the
stack. It may be used in combination with <command> to
insert low-level TrueType commands into your Xgridfit
programming in a portable way. Its content is a
whitespace-delmited list of numbers, identifiers and
expressions. These are valid Xgridfit <push>
instructions:
</p>
<pre>
<push>2 5 89 67</push>
<push>
left
right
lc-vertical-stem
-1
</push>
<push> 0.58p 2.0 to-grid </push>
<push>1 (top + 3) 512</push></pre>
<p>
It is essential that all expressions containing whitespace be
enclosed in parentheses.
</p>
<h3>Content</h3>
<p>
A space-delimited list of values and expressions.
</p>
<h3>Attributes</h3>
<p>None.</p>
<h2 id="range"><range></h2>
<p>
A <range> is a collection of contiguous points defined
by its end-points. It can be used in any instruction that
operates on more than one point: <shift>, <align>,
<interpolate>, <shift-absolute>,
<toggle-points>. The order of points in the
<range> is not significant. Example:
</p>
<pre>
<align>
<reference>
<point num="bottom"/>
</reference>
<range>
<point num="bottom - 2"/>
<point num="bottom + 2"/>
</range>
</align></pre>
<p>
If "bottom" is point 17, the <range> begins with 15 and
ends with 19. But any reference point in the parent element of
the <range> is excluded from the <range>, so this
<range> actually represents points 15, 16, 18 and
19. The same is true of implicit reference points supplied by
a <move> element that is the parent of the parent of the
<range>:
</p>
<pre>
<move>
<point num="bottom"/>
<align>
<range>
<point num="bottom - 2"/>
<point num="bottom + 2"/>
</range>
</align>
</move></pre>
<p>
Here the points in the <range> are aligned with "bottom"
after it has been moved by the <move> instruction; but
"bottom" itself is not part of the <range>. The code
above is functionally identical to this:
</p>
<pre>
<move>
<point num="bottom"/>
<align>
<point num="bottom - 2"/>
<point num="bottom - 1"/>
<point num="bottom + 1"/>
<point num="bottom + 2"/>
</align>
</move></pre>
<p>
The latter generates more efficient code than the example with
the <range>, but the <range> is more flexible,
since its endpoints, its size, and the points to be excluded
need not be known until run-time. This makes the <range>
ideal for use in functions.
</p>
<p>
All the points in a <range> must be in the same zone,
determined by the optional <tt>zone</tt> attribute on the
<range> element. Any <tt>zone</tt> attributes on the
<point>s within the <range> are ignored.
</p>
<h3>Content</h3>
<p>
Two <point> elements. These are required if no
<tt>ref</tt> attribute is present.
</p>
<h3>Attributes</h3>
<dl>
<dt>name</dt>
<dd>
Optional, but necessary if this <range> is referred to
elsewhere. A name: any sequence of letters, numbers,
hyphens, periods; no spaces permitted. Names this
<range>.
</dd>
<dt>ref</dt>
<dd>
Required if no <point> elements are present. A
reference to a named <range>.
</dd>
<dt>zone</dt>
<dd>
Optional. Permitted values are "twilight" and
"glyph".
</dd>
</dl>
<h2 id="restore-default"><restore-default></h2>
<p>
To reset any of the graphics variables tracked by Xgridfit to
its default value (that is, the value set by your Xgridfit
program via a <default> element or by setting it in the
<pre-program>--failing that, the TrueType default), use
the <restore-default> element. Use the value
<tt>all</tt> to reset <em>all</em> graphics variables,
including the freedom and projection vectors and the auto-flip
state, which Xgridfit does not track. The <tt>all</tt> option
sets these last to their TrueType defaults: the x axis for the
vectors and "on" for auto-flip.
</p>
<pre>
<restore-default name="minimum-distance"/></pre>
<h3>Content</h3>
<p>None.</p>
<h3>Attribute</h3>
<dl>
<dt>name</dt>
<dd>
The name of the graphics variable to restore to its
default value. Possible values are "minimum-distance",
"control-value-cut-in", "single-width",
"single-width-cut-in", "delta-base", "delta-shift",
"round-state", "all".
</dd>
</dl>
<h2 id="reference"><reference></h2>
<p>
In any instruction that can position a point or other
structure with reference to one or more points, the
<reference> element holds the reference point(s). This
element generally contains precisely one point, but when it is
the child of an <interpolate> element it must contain
two points. In the following example, point p2 is moved
relative to point p1:
</p>
<pre>
<move>
<reference>
<point num="p1"/>
</reference>
<point num="p2"/>
</move></pre>
<h3>Content</h3>
<p>
A single <point>. When the <reference> element is
the child of <interpolate>, two points.
</p>
<h3>Attributes</h3>
<p>None.</p>
<h2 id="round"><round></h2>
<p>
Rounds a number representing a distance according to the
current round state, applies whatever correction is
appropriate for the "color" of the distance, and returns the
result.
</p>
<pre><round value="lc-vert-stem" color="black" result-to="new-cvt"/></pre>
<h3>Content</h3>
<p>None</p>
<h3>Attributes</h3>
<dl>
<dt>value</dt>
<dd>
Required, except when the child of <formula>. Any
value or expression, understood as a distance on the current
grid. This is the number to round.
</dd>
<dt>color</dt>
<dd>
Optional. Permitted values are "black", "white" and
"gray". The default is "gray." The kind of distance that the
<tt>value</tt> represents. This is used by some TrueType
engines to compensate for engine characteristics.
</dd>
<dt>result-to</dt>
<dd>
Optional; not allowed when <round> is the child of a
<formula>. The name of a variable or control value in
which to store the result. If <tt>result-to</tt> is omitted
where allowed, and <tt>value</tt> is a variable or control
value, the result is written to <tt>value</tt>. If
<tt>value</tt> cannot be written to, the compiler issues a
warning and the result is left on the stack.
</dd>
</dl>
<h2 id="round-state"><round-state></h2>
<p>
Declares a custom round state whose name can be passed to
<set-round-state>, <with-round-state>, or any
element that takes a <tt>round</tt> attribute. For an
explanation of the <tt>period</tt>, <tt>phase</tt> and
<tt>threshold</tt> attributes, see "<a
href="round.html">Rounding</a>." Note that only a limited number
of values is permitted for each of these attributes. This
element is permitted only at the top level of a program, as a
child of <xgridfit>.
</p>
<pre>
<round-state name="my-round" period="two-pixel"
phase="three-quarters"
threshold="three-quarters"/></pre>
<h3>Content</h3>
<p>None.</p>
<h3>Attributes</h3>
<dl>
<dt>name</dt>
<dd>
Required. A name: any sequence of letters, numbers, hyphens,
periods; no spaces permitted. This is the name under which
the program may refer to this round state.
</dd>
<dt>period</dt>
<dd>
Required. One of the following: "half-pixel", "one-pixel",
"two-pixel".
</dd>
<dt>phase</dt>
<dd>
Required. One of the following: "zero", "one-quarter",
"one-half", "three-quarters".
</dd>
<dt>threshold</dt>
<dd>
Required. One of the following: "period-minus-one",
"minus-three-eighths", "minus-one-quarter",
"minus-one-eighth", "zero", "one-eighth", "one-quarter",
"three-eighths", "one-half", "five-eighths",
"three-quarters", "seven-eighths", "one", "nine-eighths",
"five-quarters", "eleven-eighths".
</dd>
</dl>
<h2 id="set"><set></h2>
<p>
A <set> is an arbitrary collection of points, defined by
the <point> elements contained in the <set>
element. The <set> can be used by any element that
accepts a collection of points: <align>,
<interpolate>, <shift>, <shift-absolute>,
<toggle-points>.
</p>
<p>
A <set> can be used only in a <glyph> program, or
it can be referenced in a <macro> called by a
<glyph> program. The name of a <set> can be passed
to a macro as a parameter, and a <set> can be the
content of a <with-param> element.
</p>
<p>
Xgridfit must be able to resolve the <tt>num</tt> attributes
of all <point>s in a <set> at compile time. It is
an error to attempt to reference a variable in a <set>.
</p>
<p>
When a <set> is used in an element that has reference
points, either explicitly via the <reference> element
or implicitly via an enclosing <move> element, any
reference points repeated in the set are excluded. This works
only when the <reference> points can be resolved at
compile time.
</p>
<p>
A <set> may be preferable to a <range> when all
point numbers are known at compile time and the range is
short, including perhaps three or four points. The code
generated by Xgridfit on encountering a <set> is less
flexible, but vastly more efficient than that generated on
encountering a <range>.
</p>
<p>
A <set> may be defined thus among the declarations at
the beginning of a <glyph>:
</p>
<pre>
<set name="bar-bottom-left-corner">
<point num="bar-bottom-left"/>
<point num="bar-bottom-left + 1"/>
<point num="bar-bottom-left + 2"/>
</set>
<set name="bar-bottom-right-corner">
<point num="bar-bottom-right"/>
<point num="bar-bottom-right - 1"/>
<point num="bar-bottom-right - 2"/>
</set></pre>
<p>
It can then be referenced whenever needed:
</p>
<pre>
<move distance="cap-horz-stem">
<reference>
<point num="bar-top-left"/>
</reference>
<point num="bar-bottom-left"/>
<shift>
<set ref="bar-bottom-left-corner"/>
<set ref="bar-bottom-right-corner"/>
</shift>
</move></pre>
<h3>Content</h3>
<p>
One or more <point> elements. These are required if no
<tt>ref</tt> element is present.
</p>
<h3>Attributes</h3>
<dl>
<dt>name</dt>
<dd>
Optional, but necessary if this <set> is referred to
elsewhere. A name: any sequence of letters, numbers,
hyphens, periods; no spaces permitted. Names this
<set>.
</dd>
<dt>ref</dt>
<dd>
Required if no <point> elements are present. A
reference to a named <set>.
</dd>
<dt>zone</dt>
<dd>
Optional. Permitted values are "twilight" and
"glyph".
</dd>
</dl>
<h2 id="set-auto-flip"><set-auto-flip></h2>
<p>
When "on" (the default setting), the TrueType engine
automatically adjusts the signs of control values when
executing MIRP and MIAP instructions. This works very well, so
there is rarely a reason to set this to "off."
</p>
<h3>Content</h3>
<p>None.</p>
<h3>Attribute</h3>
<dl>
<dt>value</dt>
<dd>
Required. Permitted values are "on" and "off".
</dd>
</dl>
<h2 id="set-control-value"><set-control-value><br/>
<with-control-value></h2>
<p>
You can assign a value to a control value anywhere: in the
<pre-program>, a <function>, or a <glyph>
program. The value you assign can be either in font units (the
units of the grid on which you designed the font) or in pixel
units (the grid on which the glyph is now being
rasterized). To specify which, include the attribute
<tt>unit="font"</tt> or <tt>unit="pixel"</tt> ("font" is the
default). You must specify the name of the control value with
the <tt>name</tt> attribute and the value (an integer in font
units or an "F26Dot6" number in pixel units) with the
<tt>value</tt> attribute.
</p>
<p>
You can use <set-control-value> to make a control value
<a href="cvt.html#local">simulate a local variable</a>.
</p>
<p>
Use <with-control-value>, which takes attributes exactly
like those of <set-control-value>, to assign a control
value to be used only within the <with-control-value>
element. After this element, the value will be the same as it
was before.
</p>
<pre>
<set-control-value name="myval" unit="font" value="850"/>
<set-control-value name="otherval" unit="pixel"
value="control-value(otherval) * 2"/>
<with-projection-vector axis="y">
<set-control-value name="myval" unit="pixel"
value="point(a) --- point(b)"/>
</with-projection-vector></pre>
<h3>Content</h3>
<p>
None for <set-control-value>; <with-control-value>
contains programming of any kind.
</p>
<h3>Attributes</h3>
<dl>
<dt>name</dt>
<dd>
Required. The name of the control value to set.
</dd>
<dt>value</dt>
<dd>
Required. Any value or expression. The value to write to the
control value.
</dd>
<dt>unit</dt>
<dd>
Optional. Permitted values are "font" and "pixel"; the
default is "font". Whether the value is in font units or
pixel units.
</dd>
</dl>
<h2 id="set-control-value-cut-in"><set-control-value-cut-in><br/>
<with-control-value-cut-in></h2>
<p>
The <tt>value</tt> is a <a
href="types.html#grid-distance">distance on the grid</a>. If
the difference between a distance from a
<control-value> element and the original distance is
greater than this, the original distance is used. The effect
is generally to use the <control-value> distance at low
resolutions and the original distance at high
resolutions. This can be used to promote evenness at small
sizes, where a 1-pixel difference between the width of (say) p
and b can look bad. The default value is 17/16: that is,
1.0625p or 68.
</p>
<pre>
<set-control-value-cut-in value="1.1"/></pre>
<h3>Content</h3>
<p>
<set-control-value-cut-in> has no content;
<with-control-value-cut-in> contains programming.
</p>
<h3>Attribute</h3>
<dl>
<dt>value</dt>
<dd>
Required. Any value or expression. This is the new control
value cut-in.
</dd>
</dl>
<h2 id="set-coordinate"><set-coordinate></h2>
<p>Moves a point 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 <move> with the <tt>pixel-distance</tt> attribute.</p>
<h3>Content</h3>
<p>
A <point> to move.
</p>
<h3>Attribute</h3>
<dl>
<dt>coordinate</dt>
<dd>
Required. Any value or expression. This is the new
coordinate of the point.
</dd>
</dl>
<h2 id="set-delta-base"><set-delta-base><br/><with-delta-base></h2>
<p>
Sets the number that is added to the "size" attribute of a
<delta-set> element to get the resolution at which an
adjustment should take place. The default value is 9, and that
rarely needs to be changed.
</p>
<pre>
<with-delta-base value="56">
<delta>
<delta-set size="12" distance="-8">
<point num="p"/>
</delta-set>
</delta>
</with-delta-base></pre>
<h3>Content</h3>
<p>
<set-delta-base> has no content; <with-delta-base>
contains programming.
</p>
<h3>Attribute</h3>
<dl>
<dt>value</dt>
<dd>
Required. Any value or expression. This is the new delta
base.
</dd>
</dl>
<h2 id="set-delta-shift"><set-delta-shift><br/><with-delta-shift></h2>
<p>
The unit by which a delta instruction shifts a point. If the
unit is "2," the smallest shift is half a pixel; if "4," it is
a quarter of a pixel; if "8" (the default) it is one eighth,
and so on.
</p>
<pre>
<set-delta-shift value="32"/></pre>
<h3>Content</h3>
<p>
<set-delta-shift> has no content;
<with-delta-shift> contains programming.
</p>
<h3>Attribute</h3>
<dl>
<dt>units-per-pixel</dt>
<dd>
Required. These values are permitted: "2", "4", "8", "16",
"32", "64".
</dd>
</dl>
<h2 id="set-dropout-control"><set-dropout-control></h2>
<p>
Sets up dropout control. The <tt>threshold</tt> is a number
between 0 and 254 in pixels per em. The <tt>flags</tt>
attribute is a number that tells how to set up dropout control
relative to the threshold. Here are the flags as explained in
the <a
href="http://developer.apple.com/textfonts/TTRefMan/RM05/Chap5.html#SCANCTRL">Apple
TrueType Reference</a>:
</p>
<ul>
<li>
<i>1. Set dropout control to TRUE if other conditions do not block
and ppem is less than or equal to the threshold value.</i>
</li>
<li>
<i>2. Set dropout control to TRUE if other conditions do not block
and the glyph is rotated.</i>
</li>
<li>
<i>4. Set dropout control to TRUE if other conditions do not block
and the glyph is stretched.</i>
</li>
<li>
<i>8. Set dropout control to FALSE unless ppem is less than or
equal to the threshold value.</i>
</li>
<li>
<i>16. Set dropout control to FALSE unless the glyph is rotated.</i>
</li>
<li>
<i>32. Set dropout control to FALSE unless the glyph is stretched.</i>
</li>
</ul>
<p>
Note that, for the sake of simplicity, the numbers used here
are different from those implied in the Apple TrueType
Reference. Xgridfit adjusts them before passing them to the
TrueType engine.
</p>
<p>
To turn off dropout control, set both <tt>threshold</tt> and
<tt>flags</tt> to zero.
</p>
<h3>Content</h3>
<p>None.</p>
<h3>Attributes</h3>
<dl>
<dt>threshold</dt>
<dd>
Required.
</dd>
<dt>flags</dt>
<dd>
Required.
</dd>
</dl>
<h2 id="set-dropout-type"><set-dropout-type></h2>
<p>
Sets dropout type. The <a
href="http://www.microsoft.com/typography/otspec/ttinst.htm">Microsoft
TrueType Reference</a> describes the action of the possible
values as follows:
</p>
<ul>
<li>
<i>if n=0 rules 1 and 2, and 3 are invoked (dropout control
scan conversion including stubs)</i>
</li>
<li>
<i>if n=1 rules 1, 2 and 4 are invoked (dropout control scan
conversion excluding stubs)</i>
</li>
<li>
<i>if n=2 rules 1 and 2 only are invoked (fast scan conversion;
dropout control turned off)</i>
</li>
<li>
<i>if n=3 same as n = 2</i>
</li>
<li>
<i>if n = 4 rules 1, 2, and 5 are invoked (smart dropout
control scan conversion including stubs)</i>
</li>
<li>
<i>if n = 5 rules 1, 2, and 6 are invoked (smart dropout
control scan conversion excluding stubs)</i>
</li>
<li>
<i>if n = 6 same as n = 2</i>
</li>
<li>
<i>if n = 7 same as n = 2</i>
</li>
</ul>
<p>
<i>The scan conversion rules are shown here:</i>
</p>
<dl>
<dt>Rule 1</dt>
<dd>
If a pixel’s center falls within the glyph outline, that
pixel is turned on.
</dd>
<dt>Rule 2</dt>
<dd>
If a contour falls exactly on a pixel’s center, that pixel is turned on.
</dd>
<dt>Rule 3</dt>
<dd>
If a scan line between two adjacent pixel centers (either
vertical or horizontal) is intersected by both an
on-Transition contour and an off-Transition contour and
neither of the pixels was already turned on by rules 1 and
2, turn on the left-most pixel (horizontal scan line) or the
bottom-most pixel (vertical scan line). This is “Simple”
dropout control.
</dd>
<dt>Rule 4</dt>
<dd>
Apply Rule 3 only if the two contours continue to intersect
other scan lines in both directions. That is, do not turn on
pixels for ‘stubs.’ The scanline segments that form a square
with the intersected scan line segment are examined to
verify that they are intersected by two contours. It is
possible that these could be different contours than the
ones intersecting the dropout scan line segment. This is
very unlikely but may have to be controlled with
grid-fitting in some exotic glyphs.
</dd>
<dt>Rule 5</dt>
<dd>
If a scan line between two adjacent pixel centers (either
vertical or horizontal) is intersected by both an
on-Transition contour and an off-Transition contour and
neither of the pixels was already turned on by rules 1 and
2, turn on the pixel which is closer to the midpoint between
the on-Transition contour and off-Transition contour. This
is “Smart” dropout control.
</dd>
<dt>Rule 6</dt>
<dd>
Apply Rule 5 only if the two contours continue to intersect
other scan lines in both directions. That is, do not turn on
pixels for ‘stubs.’
</dd>
</dl>
<h3>Content</h3>
<p>None.</p>
<h3>Attribute</h3>
<dl>
<dt>value</dt>
<dd>
Required. Possible values are from "0" to "7," with meanings
as described above.
</dd>
</dl>
<h2 id="set-dual-projection-vector"><set-dual-projection-vector></h2>
<p>
Like <set-projection-vector>, but the dual projection
vector can be set only from a line, and it uses the original
positions in the outline of the points that constitute the
line rather than their current positions (assuming they have
moved).
</p>
<p>
The dual projection vector is not used by every instruction:
just by <interpolate>, <get-coordinate>,
<measure-distance>, <mirp>, <mdrp>, and
<move> (only when a "relative-to" point is
present). This vector lasts only until a new projection vector
is set; then it gets canceled.
</p>
<p>
One or both points in the line may be in the twilight zone.
See the explanation for <set-vectors>.
</p>
<pre>
<with-projection-vector>
<set-dual-projection-vector to-line="orthogonal">
<line ref="line-a"/>
</set-dual-projection-vector>
<!-- programming here; then the end of the with-projection-vector
block returns the dual projection vector to its former value. -->
</with-projection-vector></pre>
<h3>Content</h3>
<p>
One <line>.
</p>
<h3>Attributes</h3>
<dl>
<dt>to-line</dt>
<dd>
Optional. Possible values are "orthogonal" and "parallel";
the default is "parallel". Determines whether the dual
projection vector will be orthogonal or parallel to the
<line> from which it is set.
</dd>
</dl>
<h2 id="set-equal"><set-equal></h2>
<p>Set <tt>target</tt> (variable, control value, or any of the
graphics state variables that Xgridfit can write to) equal
to <tt>source</tt>, which can be an expression or any number
type that Xgridfit can handle.</p>
<pre>
<!-- This is the equivalent of a := b; in C. -->
<set-equal target="a" source="b"/></pre>
<h3>Content</h3>
<p>None.</p>
<h3>Attributes</h3>
<dl>
<dt>source</dt>
<dd>
Required. Any value or expression.
</dd>
<dt>target</dt>
<dd>
Required. The name of a variable, control value or graphics
variable to write to.
</dd>
</dl>
<h2 id="set-freedom-vector"><set-freedom-vector><br/>
<with-freedom-vector></h2>
<p>
Just like <a href="#set-vectors"><set-vectors></a>, but
sets only the freedom vector.
</p>
<h2 id="set-minimum-distance"><set-minimum-distance><br/>
<with-minimum-distance></h2>
<p>
The minimum-distance property is used by several instructions
when the "min-distance" attribute is "yes." The default
minimum distance is one pixel (1.0, 1p, 64), but can be set to
another value here.
</p>
<pre>
<with-minimum-distance value="0.85">
<!-- The distance between p1 and p2 must be at least 0.85 pixel. -->
<move round="no">
<reference>
<point num="p1"/>
</reference>
<point num="p2"/>
</move>
</with-minimum-distance></pre>
<h3>Content</h3>
<p>
<set-minimum-distance> has no content;
<with-minimum-distance> contains programming.
</p>
<h3>Attributes</h3>
<dl>
<dt>value</dt>
<dd>
Required. Any value or expression. This is the new minimum
distance.
</dd>
</dl>
<h2 id="set-projection-vector"><set-projection-vector><br/>
<with-projection-vector></h2>
<p>
Just like <a href="#set-vectors"><set-vectors></a>, but
sets only the projection vector.
</p>
<h2 id="set-round-state"><set-round-state><br/>
<with-round-state></h2>
<p>
Sets the round state. If the <tt>round</tt> attribute matches
the name of a <round-state>, that round state is
used. If not, one of TrueType's prefabricated round states may
be used:
</p>
<ul>
<li>to-grid</li>
<li>to-half-grid</li>
<li>to-double-grid</li>
<li>up-to-grid</li>
<li>down-to-grid</li>
</ul>
<p>
If the <tt>round</tt> attribute is not one of these, and not
the name of one of the custom round-states, Xgridfit tries to
resolve it as a number, constant, variable or function
parameter and use that as an argument to SROUND. You had
better know what you're doing if you intend to use a raw
number in this way; it is safer, more intelligible and just as
effective to supply a custom <a
href="#round-state"><round-state></a> element.
</p>
<p>
The distinction between the element beginning with "set" and
the one beginning with "with" is the same as it is for the <a
href="vectors.html#vect-inst">vector-setting elements</a>:
briefly, the round state set by the "set" element affects the
instructions that follow it; the round state set by the "with"
instruction affects only the instructions that it contains.
</p>
<p>
Xgridfit generates instructions that keep track of the round
state (since the TrueType engine provides no way to read it),
but it may lose track if Xgridfit instructions are not used
exclusively.
</p>
<pre>
<with-round-state round="to-half-grid">
<move>
<point num="v-point"/>
</move>
</with-round-state></pre>
<h3>Content</h3>
<p>
<set-round-state> has no content;
<with-round-state> contains programming.
</p>
<h3>Attributes</h3>
<dl>
<dt>round</dt>
<dd>
Required. The name or a standard or custom round state; any
value or expression. This is the new round state.
</dd>
</dl>
<h2 id="set-single-width"><set-single-width><br/>
<with-single-width></h2>
<p>
The size of the single width, in FUnits, i.e. the units of the
grid the font was designed on (usually 2048 or 1000 units per
em). Presumably this width is converted to the current grid,
and it is that converted value that the single-width cut-in is
compared to.
</p>
<h3>Content</h3>
<p>
<set-single-width> has no content;
<with-single-width> contains programming.
</p>
<h3>Attributes</h3>
<dl>
<dt>value</dt>
<dd>
Required. Any value or expression, interpreted as font
units. This is the new single width.
</dd>
</dl>
<h2 id="set-single-width-cut-in"><set-single-width-cut-in><br/>
<with-single-width-cut-in></h2>
<p>
When the <mirp> or <mdrp> instruction is used, or
when <move> is used relative to a point, a single width
(determined by <set-single-width> or
<with-single-width>) may be used rather than a control
value or the original distance if this condition is met: the
absolute (either positive or negative) difference between the
original outline and the single width is less than the
single-width cut-in. The relevant distances are in pixels.
</p>
<p>
The single width feature appears to be used rarely.
</p>
<h3>Content</h3>
<p>
<set-single-width-cut-in> has no content;
<with-single-width-cut-in> contains programming.
</p>
<h3>Attributes</h3>
<dl>
<dt>value</dt>
<dd>
Required. Any value or expression. This is the new
single-width cut-in.
</dd>
</dl>
<h2 id="set-vectors"><set-vectors><br/><with-vectors></h2>
<p>
Sets both the projection vector and the freedom vector to the
same value. They can be set to "x" or "y" via the
<tt>axis</tt> attribute; to a line by including a line element
as the content of the <set-vectors> element or the first
child of the <with-vectors> element; or by passing "raw"
values via the <tt>x-component</tt> and <tt>y-component</tt>
attributes.
</p>
<p>
Xgridfit looks first for an <tt>axis</tt> attribute, next for
a <line>, and finally for <tt>x-component</tt> and
<tt>y-component</tt> attributes (neither is used unless both
are present). If it finds none of these and the present
element is <with-vectors>, Xgridfit simply stores the
present vectors on the stack and restores them at the end of
the block. If the present element is <set-vectors>,
Xgridfit prints a warning and attempts to find "raw" vector
values on the stack.
</p>
<p>
The "raw" values passed in via <tt>x-component</tt> and
<tt>y-component</tt> are constrained in ways that make them
difficult to calculate, at least in a TrueType program, but
the <tt>x-component/y-component</tt> method is useful to
restore values that have been saved via
<store-projection-vector> or
<store-freedom-vector>. For example, to copy one vector
to another, you can do this:
</p>
<pre>
<variable name="x-comp"/>
<variable name="y-comp"/>
<store-freedom-vector x-component="x-comp" y-component="y-comp"/>
<set-projection-vector x-component="x-comp" y-component="y-comp"/></pre>
<p>
But because of the way these instructions can leave values on
the stack and take them from the stack again, this is easier
and more efficient:
</p>
<pre>
<no-warning>
<store-freedom-vector/>
<set-projection-vector/>
</no-warning></pre>
<p>
When setting vectors to a line, one or both points in the line
can be in the twilight zone. You can include a <tt>zone</tt>
attribute in the <line> element or one in either or both
<point> elements. Include a <tt>zone</tt> attribute in
the <line> element if both points are in the twilight
zone. This is the same as including an attribute
<tt>zone="twilight"</tt> in both points. If only one point is
in the twilight zone, include the <tt>zone</tt> attribute for
that point.
</p>
<p>
Here are several examples:
</p>
<pre>
<with-vectors axis="x">
<!-- programming that moves points horizontally. -->
</with-vectors>
<with-vectors to-line="orthogonal">
<line ref="diagonal-line"/>
<!-- programming that moves points along a line orthogonal to
diagonal-line. -->
</with-vectors>
<set-vectors to-line="parallel">
<line ref="diagonal-line"/>
</set-vectors>
<!-- Subsequent programming will move points along a line parallel
to diagonal-line. --></pre>
<h3>Content</h3>
<p>
<set-vectors> has no content if an <tt>axis</tt>
attribute or the <tt>x-coordinate</tt> and
<tt>y-coordinate</tt> attributes are present; otherwise it may
contain a <line> element. <with-vectors> works
the same way, but also contains programming.
</p>
<h3>Attributes</h3>
<dl>
<dt>axis</dt>
<dd>
Optional, and incompatible with other attributes. Possible
values are "x" and "y".
</dd>
<dt>to-line</dt>
<dd>
Optional, and permitted only when a <line> is
present. Possible values are "orthogonal" and "parallel";
the default is "parallel". Determines whether the vectors
will be orthogonal or parallel to the <line> from
which they are set.
</dd>
<dt>x-component, y-component</dt>
<dd>
Optional, but if one of these attributes is present, the
other must be as well. Not permitted with other attributes
or when a <line> is present.
</dd>
</dl>
<h2 id="shift"><shift></h2>
<p>Shifts one or more points, ranges, sets, 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 <move> or
<mdrp> for that).</p>
<p>The <shift> element may contain points, ranges, sets,
contours and zones in any combination and order. The following
is perfectly correct:</p>
<pre>
<shift>
<reference>
<point num="ref-pt"/>
</reference>
<point num="move-pt-1"/>
<range ref="move-rg-1"/>
<contour num="0"/>
<point num="move-pt-2"/>
<range ref="move-rg-2"/>
</shift></pre>
<p>
But note that all the points are shifted first, then all the
ranges or sets, then all the contours, and finally any zones. The
order of child elements in the <shift> element is not
significant.
</p>
<p>
If you want to move points to the nearest rounded position
after the shift, include a <tt>round</tt> attribute. This
works exactly like the <tt>round</tt> attribute on the <a
href="#interpolate"><interpolate></a> element.
</p>
<h3>Content</h3>
<p>
Any number of <point>, <range>, <set>,
<contour> and <zone> elements, in any order.
</p>
<h3>Attributes</h3>
<dl>
<dt>compile-if</dt>
<dd>
Optional. If present, the <shift> element is compiled
only if this attribute evaluates as true (non-zero) at
compile time.
</dd>
<dt>round</dt>
<dd>
Optional. Possible values are "yes", "no", one of the
standard or custom round states, or any value or expression
yielding a number to pass to SROUND. The default value is
"no", since by default no rounding is done on the
<point>s contained in a <shift> element.
</dd>
<dt>reference-ptr</dt>
<dd>
Optional. Possible values are "1" and "2". This determines
which reference pointer (RP1 or RP2) to use. Normally
Xgridfit decides which pointer is appropriate in the
context; otherwise RP1 is used.
</dd>
</dl>
<h2 id="shift-absolute"><shift-absolute></h2>
<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 <shift-absolute> element must contain at
least one point to shift: that is, a <range>,
<set> or <point> element. It may contain any
number of <point>s, <range>s and <set>s.
</p>
<h3>Content</h3>
<p>
Any combination of <range>, <set> and <point>
elements in any order.
</p>
<h3>Attributes</h3>
<dl>
<dt>pixel-distance</dt>
<dd>
Required. Any value or expression, understood as a distance
on the grid.
</dd>
</dl>
<h2 id="srp"><srp></h2>
<p>
Does the work of SRP0, SRP1, SRP2. But it should rarely be
necessary to set the reference pointers explicitly.
</p>
<h3>Content</h3>
<p>
One <point> element; the reference pointer is set to
point to this.
</p>
<h3>Attribute</h3>
<dl>
<dt>whichpointer</dt>
<dd>
Required. The reference pointer to set. Possible values are
"0", "1" and "2".
</dd>
</dl>
<h2 id="store-projection-vector"><store-projection-vector><br/>
<store-freedom-vector></h2>
<p>
These instructions store a vector as two numbers, an
x-component and a y-component. The <tt>x-component</tt> and
<tt>y-component</tt> attributes, if given, must be identifiers
for variables:
</p>
<pre>
<store-projection-vector x-component="vx" y-component="vy"/></pre>
<p>
If these attributes are not given, a warning is printed and
the values are left on the stack, where they will be picked up
correctly by a following <tt>set</tt> instruction. For
example, this code sets the projection vector to be the same
as the freedom vector:
</p>
<pre>
<store-freedom-vector/>
<set-projection-vector/></pre>
<p>
Note that a <tt>with</tt> block will not pick up the
components of a vector from the stack.
</p>
<h3>Content</h3>
<p>None.</p>
<h3>Attributes</h3>
<dl>
<dt>x-component, y-component</dt>
<dd>
Optional, but if one attribute is present the other must be
as well. The names of variables in which to store the
components of the vector. If these attributes are not
present, the compiler displays a warning and the values are
left on the stack.
</dd>
</dl>
<h2 id="subtract"><subtract></h2>
<p>Subtracts <tt>minuend - subtrahend</tt>. If <tt>result-to</tt> is not
specified, Xgridfit attempts to write the result to
<tt>minuend</tt>.</p>
<h3>Content</h3>
<p>None.</p>
<h3>Attributes</h3>
<dl>
<dt>minuend</dt>
<dd>
Required, except when <subtract> is the child of a
<formula>. Any value or expression. The value to
subtract from.
</dd>
<dt>subtrahend</dt>
<dd>
Required, except when <subtract> is the child of a
<formula>. Any value or expression. The value to
subtract from the minuend.
</dd>
<dt>result-to</dt>
<dd>
Optional; not allowed when
<subtract> is the child of a <formula>. The
name of a variable of control value in which to store
the result of this operation. If <tt>result-to</tt> is
omitted where allowed, and <tt>minuend</tt> is a variable or
control value, the result is written to <tt>minuend</tt>. If
<tt>minuend</tt> cannot be written to, the compiler issues a
warning and the result is left on the stack.
</dd>
</dl>
<h2 id="szp"><szp></h2>
<p>
Does the work of SZP0, SZP1, SZP2. But these should rarely be
needed (use the zone attributes of the point element instead).
</p>
<h3>Content</h3>
<p>None.</p>
<h3>Attributes</h3>
<dl>
<dt>zone</dt>
<dd>
Required. Possible values are "twilight" and "glyph". The
zone to set the zone pointer to.
</dd>
<dt>whichpointer</dt>
<dd>
Required. Possible values are "0", "1" and "2". Identifies
the pointer to set.
</dd>
</dl>
<h2 id="toggle-points"><toggle-points></h2>
<p>
Any of the points that are on-line become off-line, and any
that are off-line become on-line. The <toggle-points>
element must contain at least one point to toggle: that is, a
<range>, <set> or <point> element. It may
contain any number of <point>s, <set>s and
<range>s.
</p>
<h3>Content</h3>
<p>
One or more <point>, <set> and <range>
elements.
</p>
<h3>Attributes</h3>
<p>None.</p>
<h2 id="to-stack"><to-stack></h2>
<p>
The <to-stack> element moves a single value onto the
stack. This can be any kind of value or expression, e.g. a
number literal, variable, control value or graphics variable.
Use <push> instead when more than one value needs to be
placed on the stack.
</p>
<h3>Content</h3>
<p>
A single value or expression.
</p>
<h3>Attributes</h3>
<p>None.</p>
<h2 id="untouch"><untouch></h2>
<p>A point that has been moved is "touched." This
untouches it so that it will be affected by
the <interpolate-untouched-points> instruction.</p>
<h3>Content</h3>
<p>
One <point> element.
</p>
<h3>Attributes</h3>
<p>None.</p>
<h2 id="variables"><variable></h2>
<p>
Variables are spaces in the TrueType Storage Area. They are
declared in <variable> elements; Xgridfit takes care of
indexing the Storage Area.
</p>
<pre>
<variable name="var-name"/></pre>
<p>
Most variables are local to a glyph program, function or
pre-program. Variable declarations may come among the
declarations at the beginning of a <glyph> program;
after <param> elements in a <function>, and at the
beginning of the <pre-program>. A global variable may be
declared anywhere in the top level of the program, as a child
of <xgridfit> (it is good form to group variable
declarations together); a value may be assigned to a global
variable in the <pre-program> and read by code in any
<glyph> or <function> or elsewhere in the
<pre-program>.
</p>
<p>
Variables must be written to before they can be read from.
(Some versions of Freetype initialize them to zero, but the
Microsoft rasterizer yields an error if a variable is read
before it is written.) Local variables may be initialized with
a <tt>value</tt> attribute in the declaration.
</p>
<p>
A variable is named via its <tt>name</tt> attribute. This must
be unique in the file in the case of a global variable, but in
the case of local variables unique only in the <glyph>
program or <function>. Several names are reserved and
should be avoided when naming variables and constants, since
they belong to pre-defined variables and constants:
</p>
<ul>
<li>Current size (all read-only):
<ul>
<li>pixels-per-em</li>
<li>point-size</li>
</ul>
</li>
<li>Values of the round-state variable (constants):
<ul>
<li>to-grid</li>
<li>to-half-grid</li>
<li>to-double-grid</li>
<li>down-to-grid</li>
<li>up-to-grid</li>
<li>no</li>
<li>custom</li>
</ul>
</li>
<li>Graphics variables:
<p>
Writing to these changes the graphics state. The "default"
variables can be written to only in the
<pre-program>. Trying to write to them elsewhere
produces a compile error. Actually, it is never necessary to
write to a "default" variable since writing to one of the
other variables in the <pre-program> automatically
writes to the "default" variable as well. So treat the
"default" variables as read-only variables.
</p>
<ul>
<li>round-state (can be written to only via
<set-round-state> and
<with-round-state>)</li>
<li>custom-round-state
(can be written to only via <set-round-state> and
<with-round-state>)</li>
<li>minimum-distance</li>
<li>minimum-distance-default</li>
<li>control-value-cut-in</li>
<li>control-value-cut-in-default</li>
<li>single-width</li>
<li>single-width-default</li>
<li>single-width-cut-in</li>
<li>single-width-cut-in-default</li>
<li>delta-base delta-base-default</li>
<li>delta-shift delta-shift-default</li>
</ul>
</li>
</ul>
<h3>Content</h3>
<p>None.</p>
<h3>Attributes</h3>
<dl>
<dt>name</dt>
<dd>
Required. A name: any sequence of letters, numbers, hyphens,
periods; no spaces permitted. The name of this variable.
</dd>
<dt>value</dt>
<dd>
Optional. Any value or expression. A value with which to
initialize the variable.
</dd>
</dl>
<h2 id="function-variant"><variant></h2>
<p>
A <variant> is an alternative version of a function to
be used at certain sizes or resolutions. Include one or more
<variant> elements as the last children of any
<function> element. For further explanation, see the
section on <a
href="functions.html#function-variant">functions</a>.
</p>
<h3>Content</h3>
<p>
Programming. <param> and <variable> elements are
not permitted; the <variant> must use those of the
parent <function>.
</p>
<h3>Attribute</h3>
<dl>
<dt>test</dt>
<dd>
Required. Any value or expression. The variant is used if
this attribute evaluates as true (non-zero) when the
<pre-program> is run.
</dd>
</dl>
<h2><with-control-value></h2>
<p>
See <a href="#set-control-value"><set-control-value></a>
</p>
<h2><with-control-value-cut-in></h2>
<p>
See <a href="#set-control-value-cut-in"><set-control-value-cut-in></a>
</p>
<h2><with-delta-base></h2>
<p>
See <a href="#set-delta-base"><set-delta-base></a>
</p>
<h2><with-delta-shift></h2>
<p>
See <a href="#set-delta-shift"><set-delta-shift></a>
</p>
<h2><with-freedom-vector></h2>
<p>
See <a href="#set-freedom-vector"><set-freedom-vector></a>
</p>
<h2><with-minimum-distance></h2>
<p>
See <a href="#set-minimum-distance"><set-minimum-distance></a>
</p>
<h2 id="with-param"><with-param></h2>
<p>
Defines a value to be passed to a function, macro or glyph program. The
<tt>value</tt> may be any of the value-types that Xgridfit
handles. Note that all values are resolved to numbers before a
call to a function takes place: Xgridfit does not pass
parameters to functions by reference. A result of this is
that if a variable or control value is passed to a function,
these things cannot be written to.
</p>
<p>
In general there will be a <with-param> element for
every <param> element that appears in the function or
macro being called. However, a <with-param> element may
be omitted if the matching <param> contains a default
<tt>value</tt>.
</p>
<p>
The order of <with-param> elements in a
<param-set>, <call-function>, <call-macro>
or <call-glyph> element is not significant.
</p>
<p>
If the <with-param> element is part of a call to a
macro, the value passed can be a <set>, <range> or
<line>. The <tt>name</tt> of such a structure can be
passed via the <tt>value</tt> attribute, or the structure
itself can be passed as the child of <with-param>. When
<with-param> contains a <set>, <range> or
<line>, the <tt>value</tt> attribute is optional.
</p>
<p>
Programming can also be passed via a <with-param>
element, and in this case too the <tt>value</tt> attribute is
optional.
</p>
<h3>Content</h3>
<p>
Usually none, but if the call is to a <macro> or
<glyph>, the element can contain a <range>,
<set> or <line>, or a fragment of programming.
</p>
<h3>Attributes</h3>
<dl>
<dt>name</dt>
<dd>
Required. A name: any sequence of letters, numbers, hyphens,
periods; no spaces permitted. This must match the name of
<param> in the <function>, <macro> or
<glyph> being called.
</dd>
<dt>value</dt>
<dd>
Required except when content is present. Any value or
expression. The value to pass as a parameter.
</dd>
</dl>
<h2><with-projection-vector></h2>
<p>
See <a href="#set-projection-vector"><set-projection-vector></a>
</p>
<h2><with-round-state></h2>
<p>
See <a href="#set-round-state"><set-round-state></a>
</p>
<h2><with-single-width></h2>
<p>
See <a href="#set-single-width"><set-single-width></a>
</p>
<h2><with-single-width-cut-in></h2>
<p>
See <a href="#set-single-width-cut-in"><set-single-width-cut-in></a>
</p>
<h2><with-vectors></h2>
<p>
See <a href="#set-vectors"><set-vectors></a>
</p>
<h2 id="xgridfit-el"><xgridfit></h2>
<p>
The root element of an Xgridfit program file.
</p>
<h3>Namespace declaration</h3>
<p>
This element must contain the namespace declaration
xmlns="http://xgridfit.sourceforge.net/Xgridfit2".
</p>
<h3>Content</h3>
<p>
One at most of these: <glyph-select>, <infile>,
<outfile>, <outfile-base>,
<outfile-script-name>, <no-compile>,
<legacy-functions>, <pre-program>. Any number of
these: <constant>, <alias>, <variable>,
<round-state>, <default>, <control-value>,
<function>, <macro>, <glyph>,
<xi.include>.
</p>
<h3>Attribute</h3>
<dl>
<dt>xml:id</dt>
<dd>
Optional. A valid XML ID, i.e. any sequence of letters,
numbers, hyphens, periods; no spaces permitted; and unique
within the program. This ID may be used if the
<xgridfit> element is imported into a file using
XInclude.
</dd>
</dl>
<h2 id="zone"><zone></h2>
<p>
A zone to be shifted by a <shift> instruction.
</p>
<h3>Content</h3>
<p>None.</p>
<h3>Attribute</h3>
<dl>
<dt>zone</dt>
<dd>
Required. Must be "twilight" or "glyph".
</dd>
</dl>
</div>
</body>
</html>
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