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< H1 > < A ID = "SECTION00870000000000000000" > < / A >
< A ID = "sect4.encapsulation" > < / A >
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< BR >
Encapsulation in Pd
< / H1 >
< P >
The examples for this chapter will use Pd's
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< A ID = "4703" > < / A > < I > encapsulation< / I >
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mechanism, which permits the building of patches that
may be reused any number of times. One or more object boxes in a Pd patch may
be
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< A ID = "4705" > < / A >
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< I > subpatches< / I > ,
which are separate patches encapsulated inside the boxes. These come in
two types:
< I > one-off subpatches< / I > and
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< A ID = "4708" > < / A > < A ID = "4709" > < / A > < I > abstractions< / I > .
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In either case the subpatch appears as an object box in another patch,
called the
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< A ID = "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,
in one file. If you make several copies of a subpatch you may change them
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,
changes to the file propagate everywhere the abstraction is invoked.
< P >
A subpatch (either one-off or abstraction) may have inlets and outlets that
appear on the box in the parent patch. This is specified using the following
objects:
< P >
< BR > <!-- MATH
$\fbox{ $ \mathrm{inlet} $}$
-->
< IMG
WIDTH="50" HEIGHT="41" ALIGN="MIDDLE" BORDER="0"
SRC="img374.png"
ALT="\fbox{ $ \mathrm{inlet} $}">,
<!-- MATH
$\fbox{ $ \mathrm{inlet}\sim $}$
-->
< IMG
WIDTH="67" HEIGHT="41" ALIGN="MIDDLE" BORDER="0"
SRC="img375.png"
ALT="\fbox{ $ \mathrm{inlet}\sim $}">:
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< A ID = "4903" > < / A > < A ID = "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
< TT > inlet< / TT > creates one for control streams. In either case, whatever
comes to the inlet of the box in the parent patch comes out of the
< TT > inlet< / TT > or < TT > inlet~< / TT > object in the subpatch.
< P >
< BR > <!-- MATH
$\fbox{ $\mathrm{outlet}$\ }$
-->
< IMG
WIDTH="65" HEIGHT="41" ALIGN="MIDDLE" BORDER="0"
SRC="img376.png"
ALT="\fbox{ $\mathrm{outlet}$\ }">,
<!-- MATH
$\fbox{ $\mathrm{outlet}\sim$\ }$
-->
< IMG
WIDTH="82" HEIGHT="41" ALIGN="MIDDLE" BORDER="0"
SRC="img377.png"
ALT="\fbox{ $\mathrm{outlet}\sim$\ }">:
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< A ID = "4905" > < / A > < A ID = "4906" > < / A > Corresponding objects for output from subpatches.
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< P >
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",
it is expanded to mean "the first creation argument in my box on the
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
a new message comes in.
< P >
An example of an abstraction, using inlets, outlets, and parametrization, is
shown in Figure < A HREF = "#fig04.11" > 4.11< / A > . In part (a), a patch invokes
< TT > plusminus< / TT > in an object box, with a creation argument equal to 5. The number 8 is fed to
the < TT > plusminus< / TT > object, and out comes the sum and difference of 8
and 5.
< P >
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< DIV ALIGN = "CENTER" > < A ID = "fig04.11" > < / A > < A ID = "4885" > < / A >
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< TABLE >
< CAPTION ALIGN = "BOTTOM" > < STRONG > Figure 4.11:< / STRONG >
Pd's abstraction mechanism: (a) invoking the abstraction,
< TT > plusminus< / TT > with 5 as a creation argument; (b) the contents of the
file,
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"plusminus.pd".< / CAPTION >
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< TR > < TD > < IMG
WIDTH="353" HEIGHT="134" BORDER="0"
SRC="img378.png"
ALT="\begin{figure}\psfig{file=figs/fig04.11.ps}\end{figure}">< / TD > < / TR >
< / TABLE >
< / DIV >
< P >
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
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
< TT > plusminus< / TT > object).
< P >
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
on the parent patch; see the Pd documentation for a description of this
feature.
< P >
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Miller Puckette
2006-12-30
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