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<title>Callback</title>
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<h3>
NAME</h3>
Snack_AddCallback, Snack_RemoveCallback, Snack_ExecCallbacks - track changes
to Snack sound objects
<h3>
SYNOPSIS</h3>
#include <snack.h>
<br><b>Snack_AddCallback</b>(sound, procedure, clientData)
<br><b>Snack_RemoveCallback</b>(sound, id)
<br><b>Snack_ExecCallbacks</b>(sound, flag)
<h3>
ARGUMENTS</h3>
Sound *sound (in)
<br> Sound object to attach the callback to.
<br>updateProc *procedure (in)
<br> Procedure to invoke when the sound data changes.
<br>ClientData *clientData (in)
<br> Arbitrary one-word value to pass to <i>procedure</i>.
<br>int id (in)
<br> Unique identifer for the callback.
<br>int flag (in)
<br> Flag which specifies how the sound changed.
<h3>
DESCRIPTION</h3>
<b>Snack_AddCallback</b> adds a callback <i>procedure</i> to <i>sound</i>,
that will be called whenever its content changes. It returns an <i>id</i>
number that can be used by <b>Snack_RemoveCallback</b> to remove the callback.
The <i>clientData</i> parameter to <i>procedure</i> is a copy of the <i>clientData</i>
argument given to <b>Snack_AddCallback</b> when
<br>the callback was created. Typically, <i>clientData</i> points to a
data structure containing application-specific
<br>information about what to do in <i>procedure</i>.
<br>
<b>Snack_ExecCallbacks</b> is used in sub-commands so that changes
to a sound can be tracked for example Snack´s canvas item types.
The <i>flag</i> specifies whether all sound data has changed (SNACK_NEW_SOUND)
or if new data has been appended (SNACK_MORE_DATA).
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