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<H1><A NAME="SECTION00870000000000000000"></A>
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<A NAME="sect4.encapsulation"></A>
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<BR>
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Encapsulation in Pd
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</H1>
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<P>
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The examples for this chapter will use Pd's
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<A NAME="4703"></A><I>encapsulation</I>
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mechanism, which permits the building of patches that
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may be reused any number of times. One or more object boxes in a Pd patch may
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be
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<A NAME="4705"></A>
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<I>subpatches</I>,
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which are separate patches encapsulated inside the boxes. These come in
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two types:
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<I>one-off subpatches</I> and
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<A NAME="4708"></A><A NAME="4709"></A><I>abstractions</I>.
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In either case the subpatch appears as an object box in another patch,
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called the
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<A NAME="4711"></A><I>parent</I>.
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<P>
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If you type ``pd" or ``pd my-name" into an object box, this creates a one-off
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subpatch. The contents of the subpatch are saved as part of the parent patch,
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in one file. If you make several copies of a subpatch you may change them
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individually. On the other hand, you can invoke an abstraction by typing into
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the box the name of a Pd patch saved to a file (without the ``.pd" extension).
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In this situation Pd will read that file into the subpatch. In this way,
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changes to the file propagate everywhere the abstraction is invoked.
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<P>
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A subpatch (either one-off or abstraction) may have inlets and outlets that
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appear on the box in the parent patch. This is specified using the following
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objects:
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<P>
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<BR><!-- MATH
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$\fbox{ $ \mathrm{inlet} $}$
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-->
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<IMG
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WIDTH="50" HEIGHT="41" ALIGN="MIDDLE" BORDER="0"
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SRC="img374.png"
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ALT="\fbox{ $ \mathrm{inlet} $}">,
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<!-- MATH
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$\fbox{ $ \mathrm{inlet}\sim $}$
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-->
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<IMG
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WIDTH="67" HEIGHT="41" ALIGN="MIDDLE" BORDER="0"
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SRC="img375.png"
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ALT="\fbox{ $ \mathrm{inlet}\sim $}">:
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<A NAME="4903"></A><A NAME="4904"></A>create inlets for the object box containing the subpatch. The
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<TT>inlet~</TT> version creates an inlet for audio signals, whereas
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<TT>inlet</TT> creates one for control streams. In either case, whatever
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comes to the inlet of the box in the parent patch comes out of the
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<TT>inlet</TT> or <TT>inlet~</TT> object in the subpatch.
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<P>
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<BR><!-- MATH
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$\fbox{ $\mathrm{outlet}$\ }$
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-->
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<IMG
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WIDTH="65" HEIGHT="41" ALIGN="MIDDLE" BORDER="0"
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SRC="img376.png"
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ALT="\fbox{ $\mathrm{outlet}$\ }">,
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<!-- MATH
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$\fbox{ $\mathrm{outlet}\sim$\ }$
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-->
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<IMG
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WIDTH="82" HEIGHT="41" ALIGN="MIDDLE" BORDER="0"
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SRC="img377.png"
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ALT="\fbox{ $\mathrm{outlet}\sim$\ }">:
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<A NAME="4905"></A><A NAME="4906"></A>Corresponding objects for output from subpatches.
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<P>
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Pd provides an argument-passing mechanism so that you can parametrize different
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invocations of an abstraction. If in an object box you type ``$1",
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it is expanded to mean ``the first creation argument in my box on the
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parent patch", and similarly for ``$2" and so on. The text in
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an object box is interpreted at the time the box is created, unlike the
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text in a message box. In message boxes, the same ``$1" means ``the
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first argument of the message I just received" and is interpreted whenever
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a new message comes in.
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<P>
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An example of an abstraction, using inlets, outlets, and parametrization, is
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shown in Figure <A HREF="#fig04.11">4.11</A>. In part (a), a patch invokes
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<TT>plusminus</TT> in an object box, with a creation argument equal to 5. The number 8 is fed to
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the <TT>plusminus</TT> object, and out comes the sum and difference of 8
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and 5.
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<P>
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<DIV ALIGN="CENTER"><A NAME="fig04.11"></A><A NAME="4885"></A>
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<TABLE>
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<CAPTION ALIGN="BOTTOM"><STRONG>Figure 4.11:</STRONG>
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Pd's abstraction mechanism: (a) invoking the abstraction,
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<TT>plusminus</TT> with 5 as a creation argument; (b) the contents of the
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file,
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``plusminus.pd".</CAPTION>
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<TR><TD><IMG
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WIDTH="353" HEIGHT="134" BORDER="0"
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SRC="img378.png"
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ALT="\begin{figure}\psfig{file=figs/fig04.11.ps}\end{figure}"></TD></TR>
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</TABLE>
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</DIV>
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<P>
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The <TT>plusminus</TT> object is not defined by Pd, but is rather defined
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by the patch residing in the file named ``plusminus.pd". This patch is shown
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in part (b) of the figure. The one <TT>inlet</TT> and
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two <TT>outlet</TT> objects correspond to the inlets and outlets of
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the <TT>plusminus</TT> object. The two ``$1" arguments (to the
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<TT>+</TT> and <TT>-</TT> objects) are replaced by 5 (the creation argument of the
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<TT>plusminus</TT> object).
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<P>
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We have already seen one abstraction in the examples: the <TT>output~</TT> object introduced in Figure <A HREF="node16.html#fig01.10">1.10</A> (Page <A HREF="node16.html#fig01.10"><IMG ALIGN="BOTTOM" BORDER="1" ALT="[*]"
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SRC="crossref.png"></A>). That
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example also shows that an abstraction may display controls as part of its box
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on the parent patch; see the Pd documentation for a description of this
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feature.
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<P>
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<ADDRESS>
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Miller Puckette
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2006-12-30
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