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<html>
<head>
<title>Developer's Guide: The class Protocols</title>
</head>
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<TD ALIGN="left"><A HREF="devguide-13.html">The class HierarchyNode
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<TD ALIGN="center"><A HREF="devguide-9.html">The Document and Graphics Classes</A></TD>
<TD ALIGN="right"><A HREF="devguide-15.html">The class Selectable</A></TD>
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<H2><FONT face="Helvetica,Arial"><A NAME="N1"></A>The class <A NAME="N2"></A><tt>Protocols</tt></font></H2>
<P>While sharing a common interface, the various types of graphics objects
provide a variety of additional capabilities and interfaces. The class
<tt>Protocols</tt> defines some flags that indicate the presence of certain
standard extensions. These flags are boolean class variables with names
of the form `<CODE>is_</CODE>*' or `<CODE>has_</CODE>*'. By default all of these flags
are false. Derived classes are expected to set the appropriate flags.</P>
<P>The standard flags are:
<DL>
<DT><B><CODE>has_properties</CODE></B><DD>
<P>True, iff object can have properties. If true, the object must
implement the methods
<tt>AddStyle</tt>,
<tt>Properties</tt>,
<tt>SetProperties</tt>,
<tt>ObjectChanged</tt> and
<tt>ObjectRemoved</tt>. </P>
<P>The class <A HREF="devguide-16.html#N2"><tt>Primitive</tt></A> provides this interface.</P>
<DT><B><CODE>has_fill</CODE></B><DD>
<P>True, iff object can have fill properties. If true,
<CODE>has_properties</CODE> must also be true. In addition, the object
must implement the method <tt>Filled</tt> and the method
<tt>SetProperties</tt> must accept the fill properties.</P>
<P>The class <A HREF="devguide-16.html#N2"><tt>Primitive</tt></A> provides this interface.</P>
<DT><B><CODE>has_line</CODE></B><DD>
<P>True, iff object can have line properties. If true,
<CODE>has_properties</CODE> must also be true. In addition, the object
must implement the method <tt>LineWidth</tt> and the
method <tt>SetProperties</tt> must accept the line
properties.</P>
<P>The class <A HREF="devguide-16.html#N2"><tt>Primitive</tt></A> provides this interface.</P>
<DT><B><CODE>has_font</CODE></B><DD>
<P>True, iff object can have a font. If true, <CODE>has_properties</CODE>
must also be true. In addition, the method <tt>SetProperties</tt> must accept the font properties.</P>
<DT><B><CODE>is_Bezier</CODE></B><DD>
<DT><B><CODE>is_Rectangle</CODE></B><DD>
<DT><B><CODE>is_Ellipse</CODE></B><DD>
<DT><B><CODE>is_Text</CODE></B><DD>
<DT><B><CODE>is_Image</CODE></B><DD>
<DT><B><CODE>is_Eps</CODE></B><DD>
<P>Indicate the type of object.</P>
<DT><B><CODE>is_Compound</CODE></B><DD>
<P>True, iff the object is a compound object.</P>
<DT><B><CODE>is_Group</CODE></B><DD>
<P>True, iff the object is a group. A group is a compound object. A
group object can be <EM>ungrouped</EM>, that is, the user can issue
a command that replaces the group with its children, which
become direct children of the group's parent. To this end, a
group must provide the method <tt>Ungroup</tt>. (see the
document method <tt>UngroupSelected</tt>)</P>
<DT><B><CODE>is_Blend</CODE></B><DD>
<P>True, iff the object is a blend group.</P>
<DT><B><CODE>is_curve</CODE></B><DD>
<P>True, iff the object can be converted to a <tt>PolyBezier</tt> object. If true, the object must implement
the methods <A HREF="devguide-11.html#N6"><tt>AsBezier</tt></A> and <tt>Paths</tt>.</P>
<P>Sketch treats the PolyBezier as a kind of `common denominator'
for blending. For instance, if you try to blend a rectangle and
an ellipse, both are converted to beziers and the beziers are
blended.</P>
<DT><B><CODE>is_clip</CODE></B><DD>
<P>True, iff the object may be used as a clip mask. If true, the
methods <A HREF="devguide-15.html#N5"><tt>Hit</tt></A> and <A HREF="devguide-11.html#N9"><tt>DrawShape</tt></A> must
accept an additional boolean parameter <CODE>clip</CODE> indicating
whether the object is used as a clip mask.</P>
</DL>
</P>
<HR NOSHADE>
<TABLE WIDTH="100%">
<TR>
<TD ALIGN="left"><A HREF="devguide-13.html">The class HierarchyNode
</A></TD>
<TD ALIGN="center"><A HREF="devguide-9.html">The Document and Graphics Classes</A></TD>
<TD ALIGN="right"><A HREF="devguide-15.html">The class Selectable</A></TD>
</TR>
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