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Signal Marshallers

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Functions to adapt C structures to native calling convention.

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<refsect2>
<title>What are Signal Marshallers?</title>
<para>
Marshals are functions which all have the same prototype:
they take a #GtkObject, a #GtkSignalFunc, a #gpointer,
and an array of argument values.
The functions are names gtk_marshall_RETURNTYPE__PARAMTYPE1_PARAMTYPE2....
</para>
<para>
They then call a native function:  the GtkObject is the first
parameter passed in.  The arguments are passed in the native
calling convention:  chars, shorts, ints, longs may be packed
on the stack, or tucked in registers:  it doesn't matter
because the same calling convention will be generated
inside the gtkmarshal code as is expected where you define
your handlers.
</para>
<para>
So the function named:
<programlisting>
gtk_marshal_BOOL__POINTER_INT_INT_UINT(GtkObject*, GtkSignalFunc, gpointer, GtkArg*);
</programlisting>
will call the #GtkSignalFunc assuming it was a function with signature:
<programlisting>
gboolean sigfunc(gpointer,gint,gint,guint);
</programlisting>
</para>
</refsect2>
<refsect2>
<title>Writing Custom Marshals</title>
<para>
Marshals are primarily used as arguments to gtk_signal_new().
Sometimes, you may find that a marshaller you need isn't available
in the standard list.  Then you have to write your own.
</para>
<para>
If you wish to define a signal with a new type of argument list.
Suppose you want 2 pointers and 2 integers.
You would write:
<programlisting>
typedef int (*GtkSignal_INT__POINTER_POINTER_INT_INT)(
			gpointer, gpointer, gint, gint
);

void marshal_INT__POINTER_POINTER_INT_INT(GtkObject*    object,
					   GtkSignalFunc func,
					   gpointer      func_data,
                                           GtkArg*       args)
{
	GtkSignal_NONE__POINTER_POINTER_INT_INT rfunc;
	gint* return_val;
	return_val = GTK_RETLOC_INT(args[4]);
	rfunc = (GtkSignal_INT__POINTER_POINTER_INT_INT)func;
	*return_val = (*rfunc)(object,
                               GTK_VALUE_POINTER(args[0]),
                               GTK_VALUE_POINTER(args[1]),
                               GTK_VALUE_INT(args[2]),
                               GTK_VALUE_INT(args[3]),
                               func_data);
}
</programlisting>
</para>

<!-- ##### SECTION See_Also ##### -->
<para>
<variablelist>

<varlistentry>
<term>#GtkSignal</term>
<listitem><para>The signal handling functions (of which marshallers are 
really an implementation detail).</para></listitem>
</varlistentry>

</variablelist>
</para>

<!-- ##### MACRO gtk_signal_default_marshaller ##### -->
<para>
A marshaller that returns void and takes no extra parameters.
</para>



