From ab047cfb36d6dc94db2eaf669da566029ce049b7 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?IOhannes=20m=20zm=C3=B6lnig?=
 <zmoelnig@users.sourceforge.net>
Date: Tue, 25 Mar 2014 11:42:00 +0000
Subject: renamed HOWTO to 'pd-externals-HOWTO'

no longer language-specific names...

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+% format latexg -*- latex -*-
+
+\documentclass[12pt, a4paper,english,titlepage]{article}  
+
+%% HOWTO write an external for Pd
+%% Copyright (c) 2001-2014 by IOhannes m zmölnig
+%%
+%%  Permission is granted to copy, distribute and/or modify this document
+%%  under the terms of the GNU Free Documentation License, Version 1.2
+%%  or any later version published by the Free Software Foundation;
+%%  with no Invariant Sections, no Front-Cover Texts, and no Back-Cover
+%%  Texts.  A copy of the license is included in the LICENSE.txt file.
+
+\usepackage[utf8]{inputenc}
+
+\usepackage[T1]{fontenc}
+\usepackage[english]{babel}
+
+% add hypertext support (fine for latex2html)
+\usepackage{html}
+\usepackage{hyperref}
+
+% add landscape support (for rotating text through 90deg)
+\usepackage{lscape}
+
+\makeatletter
+\@ifpackageloaded{tex4ht}
+  {\let\iftexforht\@firstoftwo}
+  {\let\iftexforht\@secondoftwo}
+\makeatother
+
+\iftexforht{\newcommand\pdtilde{\textasciitilde}}{\newcommand\pdtilde{$\sim$}}
+
+\title{
+HOWTO \\
+write an External \\
+for {\em Pure Data}
+}
+
+\author{
+IOhannes m zmölnig \\
+\\
+\href{http://iem.at/}{institute of electronic music and acoustics}
+}
+
+%\date{}
+
+\begin{document}
+\maketitle
+
+\begin{abstract}
+Pd is a graphical real-time computer-music  system that follows the tradition of
+IRCAMs {\em ISPW-max}.
+
+Although plenty of functions are built into Pd,
+it is sometimes a pain or simply impossible to create a patch with a certain
+functionality out of the given primitives and combinations of these.
+
+Therefore, Pd can be extended with self made primitives (``objects'')
+that are written in complex programming-languages, like {\tt C/C++}. 
+
+This document aims to explain how to write such primitives in {\tt C},
+the popular language that was used to realize Pd.
+
+\iftexforht{You can download this HOWTO as \href{pd-externals-HOWTO.pdf}{pdf (English)}.}{}
+
+\end{abstract}
+
+
+\vfill
+\newpage
+
+\tableofcontents
+
+\vfill
+\newpage
+
+\section{definitions and prerequisites}
+Pd refers to the graphical real-time computer-music environment {\em Pure Data}
+by Miller~S.~Puckette.
+
+To fully understand this document, it is necessary to
+be acquainted with Pd and to 
+have a general understanding of programming techniques especially in {\tt C}.
+
+To write externals yourself, a {\tt C}-compiler that supports the
+{\tt ANSI-C}-Standard, like the {\em Gnu C-compiler} (gcc) on linux-systems or
+{\em Visual-C++} on windos-plattforms, will be necessary.
+
+\subsection{classes, instances, objects}
+Pd is written in the programming-language {\tt C}.
+Due to its graphical nature, Pd is a {\em object-oriented} system.
+Unfortunately {\tt C} does not support very well the use of classes.
+Thus the resulting source-code is not as elegant as {\tt C++}-code would be, for instance.
+
+In this document, the expression {\em class} refers to the realisation of a concept
+combining data and manipulators on this data.
+
+Concrete {\em instances of a class} are called {\em objects}.
+
+\subsection{internals, externals und libraries}
+
+To avoid confusion of ideas, the expressions {\em internal}, {\em external} and
+{\em library} should be explained here.
+
+\paragraph{Internal}
+An {\em internal} is a class that is built into Pd.
+Plenty of primitives, such as ``+'', ``pack'' or ``sig\pdtilde'' are {\em internals}.
+
+\paragraph{External}
+An {\em external} is a class that is not built into Pd but is loaded at runtime.
+Once loaded into Pd's memory, {\em externals} cannot be distinguished from
+{\em internals} any more.
+
+\paragraph{Library}
+A {\em library} is a collection of {\em externals} that are compiled into a 
+single binary-file.
+
+{\em Library}-files have to follow a system dependent naming convention:
+
+\begin{tabular}{c||c|c|c}
+library & linux&irix&Win32 \\
+\hline
+{\tt my\_lib}&{\tt  my\_lib.pd\_linux}&{\tt  my\_lib.pd\_irix}&
+{\tt  my\_lib.dll}\\
+\end{tabular}
+
+The simplest form of a {\em library} includes exactly one {\em external}
+bearing the same name as the {\em library}.
+
+Unlike {\em externals}, {\em libraries} can be imported by Pd with special operations.
+After a {\em library} has been imported,
+all included {\em externals} have been loaded into memory and are available as objects.
+
+Pd supports two modes to import {\em libraries}:
+
+\begin{itemize}
+\item via the command line-option ``{\tt -lib my\_lib}''
+\item by creating an object ``{\tt my\_lib}''
+\end{itemize}
+
+The first method loads a {\em library} when Pd is started.
+This method is preferably used for {\em libraries} that contain several {\em externals}.
+
+The other method should be used for {\em libraries} that contain exactly
+one {\em external} bearing the same name.
+Pd checks first, whether a class named ``my\_lib'' is already loaded.
+If this is not the case\footnote{
+If a class ``my\_lib'' is already existent, an object ``my\_lib'' will be instantiated
+and the procedure is done. 
+Thus, no {\em library} has been loaded.
+Therefore no {\em library} that is named like an already used class-name like, say, ``abs'',
+can be loaded.}, all paths are searched for a file called
+``{\tt my\_lib.pd\_linux}''\footnote{or another system-dependent filename-extensions (s.a.)}.
+If such file is found, all included {\em externals} are loaded into memory by calling a
+routine \verb+my_lib_setup()+.
+After loading, a class ``my\_lib'' is (again) looked for as a (newly loaded) {\em external}.
+If so, an instance of this class is created, else the instantiation fails and an error is
+printed.
+Anyhow, all {\em external}-classes declared in the {\em library} are loaded by now.
+
+
+\section{my first external: {\tt helloworld}}
+Usually the first attempt learning a programming-language is a ``hello world''-application.
+
+In our case, an object class should be created, that prints the line ``hello world!!'' to
+the standard error every time it is triggered with a ``bang''-message.
+
+
+
+\subsection{the interface to Pd}
+To write a Pd-external a well-defined interface is needed.
+This is provided in the header-file ``m\_pd.h''.
+
+\begin{verbatim}
+#include "m_pd.h"
+\end{verbatim}
+
+\subsection{a class and its data space}
+First a new class has to be prepared and the data space for this class has to be defined.
+
+\begin{verbatim}
+static t_class *helloworld_class;
+
+typedef struct _helloworld {
+  t_object  x_obj;
+} t_helloworld;
+\end{verbatim}
+
+\verb+hello_worldclass+ is going to be a pointer to the new class.
+
+The structure \verb+t_helloworld+ (of the type \verb+_helloworld+) is
+the data space of the class.
+
+An absolutely necessary element of the data space is a variable of the type
+\verb+t_object+, which is used to store internal object-properties like
+the graphical presentation of the object or data about inlets and outlets.
+
+\verb+t_object+ has to be the first entry in the structure !
+
+Because a simple ``hello world''-application needs no variables,
+the structure is empty apart from the \verb+t_object+.
+
+
+\subsection{method space}
+Apart from the data space, a class needs a set of manipulators (methods) to
+manipulate the data with.
+
+If a message is sent to an instance of our class, a method is called.
+These methods are the interfaces to the message system of Pd.
+On principal they have no return argument and are therefore of the
+type \verb+void+.
+
+\begin{verbatim}
+void helloworld_bang(t_helloworld *x)
+{
+  post("Hello world !!");
+}
+\end{verbatim}
+
+
+This method has an argument of the type \verb+t_helloworld+,
+which would enable us to manipulate the data space.
+
+Since we only want to output ``Hello world!''
+(and, by the way, our data space is quite sparse),
+we renounce a manipulation.
+
+The command \verb+post(char *c,...)+ sends a string to the standard error.
+A carriage return is added automatically.
+Apart from this, the \verb+post+-command works like the {\tt C}-command \verb+printf()+.
+
+\subsection{generation of a new class}
+To generate a new class, information of the data space and the method space of this class,
+have to be passed to Pd when a library is loaded.
+
+On loading a new library ``my\_lib'',
+Pd tries to call a function ``my\_lib\_setup()''.
+This function (or functions called by it) 
+declares the new classes and their properties.
+It is only called once, when the library is loaded.
+If the function-call fails (e.g., because no function of the specified name is present)
+no external of the library will be loaded.
+
+\begin{verbatim}
+void helloworld_setup(void)
+{
+  helloworld_class = class_new(gensym("helloworld"),
+        (t_newmethod)helloworld_new,
+        0, sizeof(t_helloworld),
+        CLASS_DEFAULT, 0);
+
+  class_addbang(helloworld_class, helloworld_bang);
+}
+\end{verbatim}
+
+\paragraph{class\_new}
+
+The function \verb+class_new+ creates a new class and returns a pointer to this prototype.
+
+The first argument is the symbolic name of the class.
+
+The next two arguments define the constructor and destructor of the class.
+
+Whenever a class object is created in a Pd-patch,
+the class-constructor \verb+(t_newmethod)helloworld_new+ instantiates the object
+and initialises the data space.
+
+Whenever an object is destroyed
+(either by closing the containing patch or by deleting the object from the patch)
+the destructor frees the dynamically reserved memory.
+The allocated memory for the static data space is automatically reserved and freed.
+
+Therefore we do not have to provide a destructor in this example, the argument
+is set to ``0''.
+
+To enable Pd to reserve and free enough memory for the static data space,
+the size of the data structure has to be passed as the fourth argument.
+
+The fifth argument has influence on the graphical representation of the class objects.
+The default-value is \verb+CLASS_DEFAULT+ or simply ``0''.
+
+The remaining arguments define the arguments of an object and its type.
+
+Up to six numeric and symbolic object-arguments can be defined via
+\verb+A_DEFFLOAT+ and \verb+A_DEFSYMBOL+.
+If more arguments are to be passed to the object
+or if the order of atom types should by more flexible, 
+\verb+A_GIMME+ can be used for passing an arbitrary list of atoms.
+
+The list of object-arguments is terminated by ``0''.
+In this example we have no object-arguments at all for the class.
+
+\paragraph{class\_addbang}
+We still have to add a method space to the class.
+
+\verb+class_addbang+ adds a method for a ``bang''-message to the class that is
+defined in the first argument.
+The added method is defined in the second argument.
+
+
+\subsection{constructor: instantiation of an object}
+Each time, an object is created in a Pd-patch, the
+constructor that is defined with the \verb+class_new+-command,
+generates a new instance of the class.
+
+The constructor has to be of type \verb+void *+.
+
+\begin{verbatim}
+void *helloworld_new(void)
+{
+  t_helloworld *x = (t_helloworld *)pd_new(helloworld_class);
+
+  return (void *)x;
+}
+\end{verbatim}
+
+
+The arguments of the constructor-method depend on the object-arguments
+defined with \verb+class_new+.
+
+\begin{tabular}{l|l}
+\verb+class_new+-argument&constructor-argument\\
+\hline
+\verb+A_DEFFLOAT+&\verb+t_floatarg f+ \\
+\verb+A_DEFSYMBOL+&\verb+t_symbol *s+ \\
+\verb+A_GIMME+&\verb+t_symbol *s, int argc, t_atom *argv+
+\end{tabular}
+
+Because there are no object-arguments for our ``hello world''-class,
+the constructor has anon too.
+
+The function \verb+pd_new+ reserves memory for the data space,
+initialises the variables that are internal to the object and
+returns a pointer to the data space.
+
+The type-cast to the data space is necessary.
+
+Normally, the constructor would initialise the object-variables.
+However, since we have none, this is not necessary.
+
+
+The constructor has to return a pointer to the instantiated data space.
+
+\subsection{the code: \tt helloworld}
+
+\begin{verbatim}
+#include "m_pd.h"
+
+static t_class *helloworld_class;
+
+typedef struct _helloworld {
+  t_object  x_obj;
+} t_helloworld;
+
+void helloworld_bang(t_helloworld *x)
+{
+  post("Hello world !!");
+}
+
+void *helloworld_new(void)
+{
+  t_helloworld *x = (t_helloworld *)pd_new(helloworld_class);
+
+  return (void *)x;
+}
+
+void helloworld_setup(void) {
+  helloworld_class = class_new(gensym("helloworld"),
+        (t_newmethod)helloworld_new,
+        0, sizeof(t_helloworld),
+        CLASS_DEFAULT, 0);
+  class_addbang(helloworld_class, helloworld_bang);
+}
+\end{verbatim}
+
+
+\section{a simple external: {\tt counter}}
+
+Now we want to realize a simple counter as an external.
+A ``bang''-trigger outputs the counter-value on the outlet and
+afterwards increases the counter-value by 1.
+
+This class is similar to the previous one,
+but the data space is extended by a variable ``counter'' and the
+result is written as a message to an outlet instead of 
+a string to the standard error.
+
+\subsection{object-variables}
+Of course, a counter needs a state-variable to store the actual counter-value.
+
+State-variables that belong to class instances belong to the data space.
+
+\begin{verbatim}
+typedef struct _counter {
+  t_object  x_obj;
+  t_int i_count;
+} t_counter;
+\end{verbatim}
+
+The integer variable \verb+i_count+ stores the counter-value.
+
+\subsection{object-arguments}
+It is quite useful for a counter, if a initial value can be defined by the user.
+Therefore this initial value should be passed to the object at creation-time.
+
+\begin{verbatim}
+void counter_setup(void) {
+  counter_class = class_new(gensym("counter"),
+        (t_newmethod)counter_new,
+        0, sizeof(t_counter),
+        CLASS_DEFAULT,
+        A_DEFFLOAT, 0);
+
+  class_addbang(counter_class, counter_bang);
+}
+\end{verbatim}
+
+So we have an additional argument in the function \verb+class_new+:
+\verb+A_DEFFLOAT+ tells Pd, that the object needs one argument of the 
+type \verb+t_floatarg+.
+If no argument is passed, this will default to ``0''.
+
+\subsection{constructor}
+The constructor has some new tasks.
+On the one hand, a variable value has to be initialised,
+on the other hand, an outlet for the object has to be created.
+
+\begin{verbatim}
+void *counter_new(t_floatarg f)
+{
+  t_counter *x = (t_counter *)pd_new(counter_class);
+
+  x->i_count=f;
+  outlet_new(&x->x_obj, &s_float);
+
+  return (void *)x;
+}
+\end{verbatim}
+
+The constructor-method has one argument of type \verb+t_floatarg+ as declared
+in the setup-routine by \verb+class_new+.
+This argument is used to initialise the counter.
+
+A new outlet is created with the function \verb+outlet_new+.
+The first argument is a pointer to the interna of the object
+the new outlet is created for.
+
+The second argument is a symbolic description of the outlet-type.
+Since out counter should output numeric values it is of type ``float''.
+
+\verb+outlet_new+ returns a pointer to the new outlet and saves this very pointer
+in the \verb+t_object+-variable \verb+x_obj.ob_outlet+.
+If only one outlet is used, the pointer need not additionally be stored in the data space.
+If more than one outlets are used, the pointers have to be stored in the data space,
+because the \verb+t_object+-variable can only hold one outlet pointer.
+
+\subsection{the counter method}
+When triggered, the counter value should be sent to the outlet
+and afterwards be incremented by 1.
+
+\begin{verbatim}
+void counter_bang(t_counter *x)
+{
+  t_float f=x->i_count;
+  x->i_count++;
+  outlet_float(x->x_obj.ob_outlet, f);
+}
+\end{verbatim}
+
+The function \verb+outlet_float+ sends a floating-point-value (second argument) to the outlet
+that is specified by the first argument.
+
+We first store the counter in a floating point-buffer.
+Afterwards the counter is incremented and not before that the buffer variable is sent 
+to the outlet.
+
+What appears to be unnecessary on the first glance, makes sense after further
+inspection:
+The buffer variable has been realized as \verb+t_float+,
+since \verb+outlet_float+ expects a floating point-value and a typecast is
+inevitable.
+
+If the counter value was sent to the outlet before being incremented,
+this could result in an unwanted (though well defined) behaviour:
+If the counter-outlet directly triggered its own inlet,
+the counter-method would be called although the counter value was not yet incremented.
+Normally this is not what we want.
+
+The same (correct) result could of course be obtained with a single line,
+but this  would obscure the {\em reentrant}-problem.
+
+\subsection{the code: \tt counter}
+
+\begin{verbatim}
+#include "m_pd.h"
+
+static t_class *counter_class;
+
+typedef struct _counter {
+  t_object  x_obj;
+  t_int i_count;
+} t_counter;
+
+void counter_bang(t_counter *x)
+{
+  t_float f=x->i_count;
+  x->i_count++;
+  outlet_float(x->x_obj.ob_outlet, f);
+}
+
+void *counter_new(t_floatarg f)
+{
+  t_counter *x = (t_counter *)pd_new(counter_class);
+
+  x->i_count=f;
+  outlet_new(&x->x_obj, &s_float);
+
+  return (void *)x;
+}
+
+void counter_setup(void) {
+  counter_class = class_new(gensym("counter"),
+        (t_newmethod)counter_new,
+        0, sizeof(t_counter),
+        CLASS_DEFAULT,
+        A_DEFFLOAT, 0);
+
+  class_addbang(counter_class, counter_bang);
+}
+\end{verbatim}
+
+
+\section{a complex external: \tt counter}
+
+The simple counter of the previous chapter can easily be extended to more complexity.
+It might be quite useful to be able to reset the counter to an initial value,
+to set upper and lower boundaries and to control the step-width.
+Each overrun should send a ``bang''-Message to a second outlet and reset the counter to
+the initial value.
+
+\subsection{extended data space}
+
+\begin{verbatim}
+typedef struct _counter {
+  t_object  x_obj;
+  t_int i_count;
+  t_float step;
+  t_int i_down, i_up;
+  t_outlet *f_out, *b_out;
+} t_counter;
+\end{verbatim}
+
+The data space has been extended to hold variables for step width and 
+upper and lower boundaries.
+Furthermore pointers for two outlets have been added.
+
+\subsection{extension of the class}
+The new class objects should have methods for different messages,
+like ``set'' and ``reset''.
+Therefore the method space has to be extended too.
+
+\begin{verbatim}
+  counter_class = class_new(gensym("counter"),
+        (t_newmethod)counter_new,
+        0, sizeof(t_counter),
+        CLASS_DEFAULT, 
+        A_GIMME, 0);
+\end{verbatim}
+
+The class generator \verb+class_new+ has been extended by the argument \verb+A_GIMME+.
+This enables a dynamic number of arguments to be passed at the instantiation of the object.
+
+\begin{verbatim}
+  class_addmethod(counter_class,
+        (t_method)counter_reset,
+        gensym("reset"), 0);
+\end{verbatim}
+
+\verb+class_addmethod+ adds a method for an arbitrary selector to an class.
+
+The first argument is the class the method (second argument) will be added to.
+
+The third argument is the symbolic selector that should be associated with the method.
+
+The remaining ``0''-terminated arguments describe the list of atoms that
+follows the selector.
+
+\begin{verbatim}
+  class_addmethod(counter_class,
+        (t_method)counter_set, gensym("set"),
+        A_DEFFLOAT, 0);
+  class_addmethod(counter_class,
+        (t_method)counter_bound, gensym("bound"),
+        A_DEFFLOAT, A_DEFFLOAT, 0);
+\end{verbatim}
+
+A method for ``set'' followed by a numerical value is added,
+as well as a method for the selector ``bound'' followed by two numerical values.
+
+\begin{verbatim}
+  class_sethelpsymbol(counter_class, gensym("help-counter"));
+\end{verbatim}
+
+If a Pd-object is right-clicked, a help-patch describing the object-class can be opened.
+By default, this patch is located in the directory ``{\em doc/5.reference/}'' and
+is named like the symbolic class name.
+
+An alternative help-patch can be defined with the 
+\verb+class_sethelpsymbol+-command.
+
+\subsection{construction of in- and outlets}
+
+When creating the object, several arguments should be passed by the user.
+
+\begin{verbatim}
+void *counter_new(t_symbol *s, int argc, t_atom *argv)
+\end{verbatim}
+Because of the declaration of arguments in the \verb+class_new+-function
+with \verb+A_GIMME+,
+the constructor has following arguments:
+
+\begin{tabular}{c|l}
+\verb+t_symbol *s+ & the symbolic name,\\
+& that was used for object creation \\
+\verb+int argc+ & the number of arguments passed to the object\\
+\verb+t_atom *argv+ & a pointer to a list of {\tt argc} atoms
+\end{tabular}
+
+\begin{verbatim}
+  t_float f1=0, f2=0;
+
+  x->step=1;
+  switch(argc){
+  default:
+  case 3:
+    x->step=atom_getfloat(argv+2);
+  case 2:
+    f2=atom_getfloat(argv+1);
+  case 1:
+    f1=atom_getfloat(argv);
+    break;
+  case 0:
+    break;
+  }
+  if (argc<2)f2=f1;
+  x->i_down = (f1<f2)?f1:f2;
+  x->i_up   = (f1>f2)?f1:f2;
+
+  x->i_count=x->i_down;
+\end{verbatim}
+
+If three arguments are passed, these should be the {\em lower boundary},
+the {\em upper boundary} and the {\em step width}.
+
+If only two arguments are passed, the step-width defaults to ``1''.
+If only one argument is passed, this should be the {\em initial value} of the counter with
+step-width of ``1''.
+
+\begin{verbatim}
+  inlet_new(&x->x_obj, &x->x_obj.ob_pd,
+        gensym("list"), gensym("bound"));
+\end{verbatim}
+
+The function \verb+inlet_new+ creates a new ``active'' inlet.
+``Active'' means, that a class-method is called each time
+a message is sent to an ``active'' inlet.
+
+Due to the software-architecture, the first inlet is always ``active''.
+
+The first two arguments of the \verb+inlet_new+-function are
+pointers to the interna of the object and to the graphical presentation of the object.
+
+The symbolic selector that is specified by the third argument is to be
+substituted by another symbolic selector (fourth argument) for this inlet.
+
+Because of this substitution of selectors,
+a message on a certain right inlet can be treated as a message with 
+a certain selector on the leftmost inlet.
+
+This means:
+\begin{itemize}
+\item The substituting selector has to be declared by \verb+class_addmethod+
+in the setup-routine.
+\item It is possible to simulate a certain right inlet, by sending a message with
+this inlet's selector to the leftmost inlet.
+\item It is not possible to add methods for more than one selector to a right inlet.
+Particularly it is not possible to add a universal method for arbitrary selectors to 
+a right inlet.
+\end{itemize}
+
+\begin{verbatim}
+  floatinlet_new(&x->x_obj, &x->step);
+\end{verbatim}
+\verb+floatinlet_new+ generates a new ``passive'' inlet for numerical values.
+``Passive'' inlets allow parts of the data space-memory to be written directly 
+from outside.
+Therefore it is not possible to check for illegal inputs.
+
+The first argument is a pointer to the internal infrastructure of the object.
+The second argument is the address in the data space-memory,
+where other objects can write too.
+
+``Passive'' inlets can be created for pointers, symbolic or
+numerical (floating point\footnote{
+That's why the {\tt step}-width of the class\/data space is realized as {\tt t\_float}.})
+values.
+
+
+\begin{verbatim}
+  x->f_out = outlet_new(&x->x_obj, &s_float);
+  x->b_out = outlet_new(&x->x_obj, &s_bang);
+\end{verbatim}
+
+The pointers returned by \verb+outlet_new+ have to be saved in the class\/data space
+to be used later by the outlet-routines.
+
+The order of the generation of inlets and outlets is important,
+since it corresponds to the order of inlets and outlets in the
+graphical representation of the object.
+
+\subsection{extended method space}
+
+The method for the ``bang''-message has to full fill the more complex tasks.
+
+\begin{verbatim}
+void counter_bang(t_counter *x)
+{
+  t_float f=x->i_count;
+  t_int step = x->step;
+  x->i_count+=step;
+  if (x->i_down-x->i_up) {
+    if ((step>0) && (x->i_count > x->i_up)) {
+      x->i_count = x->i_down;
+      outlet_bang(x->b_out);
+    } else if (x->i_count < x->i_down) {
+      x->i_count = x->i_up;
+      outlet_bang(x->b_out);
+    }
+  }
+  outlet_float(x->f_out, f);
+}
+\end{verbatim}
+
+Each outlet is identified by the \verb+outlet_...+-functions via the
+pointer to this outlets.
+
+The remaining methods still have to be implemented:
+
+\begin{verbatim}
+void counter_reset(t_counter *x)
+{
+  x->i_count = x->i_down;
+}
+
+void counter_set(t_counter *x, t_floatarg f)
+{
+  x->i_count = f;
+}
+
+void counter_bound(t_counter *x, t_floatarg f1, t_floatarg f2)
+{
+  x->i_down = (f1<f2)?f1:f2;
+  x->i_up   = (f1>f2)?f1:f2;
+}
+\end{verbatim}
+
+\subsection{the code: \tt counter}
+
+\begin{verbatim}
+#include "m_pd.h"
+
+static t_class *counter_class;
+
+typedef struct _counter {
+  t_object  x_obj;
+  t_int i_count;
+  t_float step;
+  t_int i_down, i_up;
+  t_outlet *f_out, *b_out;
+} t_counter;
+
+void counter_bang(t_counter *x)
+{
+  t_float f=x->i_count;
+  t_int step = x->step;
+  x->i_count+=step;
+
+  if (x->i_down-x->i_up) {
+    if ((step>0) && (x->i_count > x->i_up)) {
+      x->i_count = x->i_down;
+      outlet_bang(x->b_out);
+    } else if (x->i_count < x->i_down) {
+      x->i_count = x->i_up;
+      outlet_bang(x->b_out);
+    }
+  }
+
+  outlet_float(x->f_out, f);
+}
+
+void counter_reset(t_counter *x)
+{
+  x->i_count = x->i_down;
+}
+
+void counter_set(t_counter *x, t_floatarg f)
+{
+  x->i_count = f;
+}
+
+void counter_bound(t_counter *x, t_floatarg f1, t_floatarg f2)
+{
+  x->i_down = (f1<f2)?f1:f2;
+  x->i_up   = (f1>f2)?f1:f2;
+}
+
+void *counter_new(t_symbol *s, int argc, t_atom *argv)
+{
+  t_counter *x = (t_counter *)pd_new(counter_class);
+  t_float f1=0, f2=0;
+
+  x->step=1;
+  switch(argc){
+  default:
+  case 3:
+    x->step=atom_getfloat(argv+2);
+  case 2:
+    f2=atom_getfloat(argv+1);
+  case 1:
+    f1=atom_getfloat(argv);
+    break;
+  case 0:
+    break;
+  }
+  if (argc<2)f2=f1;
+
+  x->i_down = (f1<f2)?f1:f2;
+  x->i_up   = (f1>f2)?f1:f2;
+
+  x->i_count=x->i_down;
+
+  inlet_new(&x->x_obj, &x->x_obj.ob_pd,
+        gensym("list"), gensym("bound"));
+  floatinlet_new(&x->x_obj, &x->step);
+
+  x->f_out = outlet_new(&x->x_obj, &s_float);
+  x->b_out = outlet_new(&x->x_obj, &s_bang);
+
+  return (void *)x;
+}
+
+void counter_setup(void) {
+  counter_class = class_new(gensym("counter"),
+        (t_newmethod)counter_new,
+        0, sizeof(t_counter),
+        CLASS_DEFAULT, 
+        A_GIMME, 0);
+
+  class_addbang  (counter_class, counter_bang);
+  class_addmethod(counter_class,
+        (t_method)counter_reset, gensym("reset"), 0);
+  class_addmethod(counter_class, 
+        (t_method)counter_set, gensym("set"),
+        A_DEFFLOAT, 0);
+  class_addmethod(counter_class,
+        (t_method)counter_bound, gensym("bound"),
+        A_DEFFLOAT, A_DEFFLOAT, 0);
+
+  class_sethelpsymbol(counter_class, gensym("help-counter"));
+}
+\end{verbatim}
+
+
+\section{a signal-external: {\tt pan\pdtilde}}
+Signal classes are normal Pd-classes, that offer additional methods for signals.
+
+
+All methods and concepts that can be realized with normal object classes can
+therefore be realized with signal classes too.
+
+Per agreement, the symbolic names of signal classes end with a tilde \pdtilde.
+
+The class ``pan\pdtilde'' shall demonstrate, how signal classes are written.
+
+A signal on the left inlet is mixed with a signal on the second inlet.
+The mixing-factor between 0 and 1 is defined via a \verb+t_float+-message
+on a third inlet.
+
+\subsection{variables of a signal class}
+Since a signal-class is only an extended normal class,
+there are no principal differences between the data spaces.
+
+\begin{verbatim}
+typedef struct _pan_tilde {
+  t_object x_obj;
+
+  t_sample f_pan;
+  t_float  f;
+
+  t_inlet *x_in2;
+  t_inlet *x_in3;
+
+  t_outlet*x_out;
+
+} t_pan_tilde;
+\end{verbatim}
+
+Only one variable \verb+f_pan+ for the {\em mixing-factor} of the panning-function is needed.
+
+The other variable \verb+f+ is needed whenever a signal-inlet is needed too.
+If no signal but only a float-message is present at a signal-inlet, this
+variable is used to automatically convert the float to signal.
+
+Finally, we have the members \verb+x_in2+, \verb+x_in3+ and \verb+x_out+,
+which are needed to store handles to the various extra inlets (resp. outlets) of the object.
+
+\subsection{signal-classes}
+
+\begin{verbatim}
+void pan_tilde_setup(void) {
+  pan_tilde_class = class_new(gensym("pan~"),
+        (t_newmethod)pan_tilde_new,
+        (t_method)pan_tilde_free,
+        sizeof(t_pan_tilde),
+        CLASS_DEFAULT, 
+        A_DEFFLOAT, 0);
+
+  class_addmethod(pan_tilde_class,
+        (t_method)pan_tilde_dsp, gensym("dsp"), 0);
+  CLASS_MAINSIGNALIN(pan_tilde_class, t_pan_tilde, f);
+}
+\end{verbatim}
+
+Something has changed with the \verb+class_new+ function: 
+the third argument specifies a ``free-method'' (aka {\em destructor}), which is called whenever an instance of the object
+is to be deleted (just like the ``new-method'' is called whenever an instance is to be created).
+In the prior examples this was set to \verb+0+ (meaning: we don't care),
+but in this example we have to clean up some ressources when we don't need them any more.
+
+More interestingly, a method for signal-processing has to be provided by each signal class.
+
+Whenever Pd's audio engine is started, a message with the selector ``dsp''
+is sent to each object.
+Each class that has a method for the ``dsp''-message is recognised as signal class.
+
+Signal classes that want to provide signal-inlets have to
+declare this via the \verb+CLASS_MAINSIGNALIN+-macro.
+This enables signals at the first (default) inlet.
+If more than one signal-inlet is needed, they have to be created explicitly
+in the constructor-method.
+
+Inlets that are declared as signal-inlets cannot provide
+methods for \verb+t_float+-messages any longer.
+
+The first argument of the macro is a pointer to the signal class.
+The second argument is the type of the class's data space.
+
+The last argument is a dummy-variable out of the data space that is needed
+to replace non-existing signal at the signal-inlet(s) with \verb+t_float+-messages.
+
+\subsection{construction of signal-inlets and -outlets}
+
+\begin{verbatim}
+void *pan_tilde_new(t_floatarg f)
+{
+  t_pan_tilde *x = (t_pan_tilde *)pd_new(pan_tilde_class);
+
+  x->f_pan = f;
+
+  x->x_in2 = inlet_new(&x->x_obj, &x->x_obj.ob_pd, &s_signal, &s_signal);
+  x->x_in3 = floatinlet_new (&x->x_obj, &x->f_pan);
+
+  x->x_out = outlet_new(&x->x_obj, &s_signal);
+
+  return (void *)x;
+}
+\end{verbatim}
+
+Additional signal-inlets are added like other inlets with the routine \verb+inlet_new+.
+The last two arguments are references to the symbolic selector ``signal''
+in the lookup-table.
+
+Signal-outlets are also created like normal (message-)outlets,
+by setting the outlet-selector to ``signal''.
+
+The newly created inlets/outlets are ``user-allocated'' data.
+Pd will keep track of all the ressources it automatically creates (like the default inlet),
+and will eventually free these ressources once they are no longer needed.
+However, if we request an ``extra'' ressource (like the additional inlets/outlets in this example;
+or - more commonly - memory that is allocated via \verb+malloc+ or similar),
+we have to make sure ourselves, that these ressources are freed when no longer needed.
+If we fail to do so, we will invariably create a dreaded {\em memory leak}.
+
+Therefore, we store the ``handles'' to the newly created inlets/outlets as returned by the \verb+..._new+ routines
+for later use.
+
+
+\subsection{DSP-methods}
+Whenever Pd's audio engine is turned on,
+all signal-objects declare their perform-routines that are to be added to the DSP-tree.
+
+The ``dsp''-method has two arguments, the pointer to the class-data space, and 
+a pointer to an array of signals.
+
+The signals are arranged in the array in such way,
+that they are ordered in a clockwise way in the graphical representation of the
+object.\footnote{
+If both left and right in- and out-signals exist, this means:
+First is the leftmost in-signal followed by the right in-signals;
+after the right out-signals, finally there comes the leftmost out-signal.}
+
+\begin{verbatim}
+void pan_tilde_dsp(t_pan_tilde *x, t_signal **sp)
+{
+  dsp_add(pan_tilde_perform, 5, x,
+          sp[0]->s_vec, sp[1]->s_vec, sp[2]->s_vec, sp[0]->s_n);
+}
+\end{verbatim}
+
+\verb+dsp_add+ adds a {\em perform}-routine (as declared in the first argument)
+to the DSP-tree.
+
+The second argument is the number of the following pointers to diverse variables.
+Which pointers to which variables are passed is not limited.
+
+Here, sp[0] is the first in-signal, sp[1] represents the second in-signal and
+sp[3] points to the out-signal.
+
+The structure \verb+t_signal+ contains a pointer to the
+its signal-vector \verb+().s_vec+ (an array of samples of type  \verb+t_sample+),
+and the length of this signal-vector \verb+().s_n+.
+
+Since all signal vectors of a patch (not including it's sub-patches) are of the same length,
+it is sufficient to get the length of one of these vectors.
+
+\subsection{perform-routine}
+The perform-routine is the DSP-heart of each signal class.
+
+A pointer to an integer-array is passed to it.
+This array contains the pointers, that were passed via \verb+dsp_add+,
+which must be casted back to their real type.
+
+The perform-routine has to return a pointer to integer,
+that points to the address behind the stored pointers of the routine.
+This means, that the return argument equals the
+argument of the perform-routine plus
+the number of pointer variables (as declared as the second argument
+of \verb+dsp_add+) plus one.
+
+\begin{verbatim}
+t_int *pan_tilde_perform(t_int *w)
+{
+  t_pan_tilde *x = (t_pan_tilde *)(w[1]);
+  t_sample  *in1 =    (t_sample *)(w[2]);
+  t_sample  *in2 =    (t_sample *)(w[3]);
+  t_sample  *out =    (t_sample *)(w[4]);
+  int          n =           (int)(w[5]);
+
+  t_sample f_pan = (x->f_pan<0)?0.0:(x->f_pan>1)?1.0:x->f_pan;
+
+  while (n--) *out++ = (*in1++)*(1-f_pan)+(*in2++)*f_pan;
+
+  return (w+6);
+}
+\end{verbatim}
+
+Each sample of the signal vectors is read and manipulated in the \verb+while+-loop.
+
+
+Optimisation of the DSP-tree tries to avoid unnecessary copy-operations.
+Therefore it is possible, that in- and out-signal are located
+at the same address in the memory.
+In this case, the programmer has to be careful not to write into the out-signal
+before having read the in-signal to avoid overwriting data that is not yet saved.
+
+\subsection{destructor}
+
+\begin{verbatim}
+void pan_tilde_free(t_pan_tilde *x)
+{
+  inlet_free(x->x_in2);
+  inlet_free(x->x_in3);
+  outlet_free(x->x_out);
+}
+\end{verbatim}
+
+The object has some dynamically allocated ressources,
+namely the additional inlets and outlets we created in the constructor.
+
+Since Pd doesn't track dynamically allocated ressources for us,
+we have to free them manually in the ``free-method'' (aka: destructor).
+We do so by calling \verb+inlet_free+ (resp. \verb+outlet_free+) on the handles to
+our additional iolets.
+
+Note that we do not need to free the default first outlet.
+As it is created automatically by Pd, it is also freed automatically.
+
+\subsection{the code: \tt pan\pdtilde}
+
+\begin{verbatim}
+#include "m_pd.h"
+
+static t_class *pan_tilde_class;
+
+typedef struct _pan_tilde {
+  t_object  x_obj;
+  t_sample f_pan;
+  t_sample f;
+
+  t_inlet *x_in2;
+  t_inlet *x_in3;
+  t_outlet*x_out;
+} t_pan_tilde;
+
+t_int *pan_tilde_perform(t_int *w)
+{
+  t_pan_tilde *x = (t_pan_tilde *)(w[1]);
+  t_sample  *in1 =    (t_sample *)(w[2]);
+  t_sample  *in2 =    (t_sample *)(w[3]);
+  t_sample  *out =    (t_sample *)(w[4]);
+  int          n =           (int)(w[5]);
+  t_sample f_pan = (x->f_pan<0)?0.0:(x->f_pan>1)?1.0:x->f_pan;
+
+  while (n--) *out++ = (*in1++)*(1-f_pan)+(*in2++)*f_pan;
+
+  return (w+6);
+}
+
+void pan_tilde_dsp(t_pan_tilde *x, t_signal **sp)
+{
+  dsp_add(pan_tilde_perform, 5, x,
+          sp[0]->s_vec, sp[1]->s_vec, sp[2]->s_vec, sp[0]->s_n);
+}
+
+void pan_tilde_free(t_pan_tilde *x)
+{
+  inlet_free(x->x_in2);
+  inlet_free(x->x_in3);
+  outlet_free(x->x_out);
+}
+
+void *pan_tilde_new(t_floatarg f)
+{
+  t_pan_tilde *x = (t_pan_tilde *)pd_new(pan_tilde_class);
+
+  x->f_pan = f;
+  
+  x->x_in2=inlet_new(&x->x_obj, &x->x_obj.ob_pd, &s_signal, &s_signal);
+  x->x_in3=floatinlet_new (&x->x_obj, &x->f_pan);
+  x->x_out=outlet_new(&x->x_obj, &s_signal);
+
+  return (void *)x;
+}
+
+void pan_tilde_setup(void) {
+  pan_tilde_class = class_new(gensym("pan~"),
+        (t_newmethod)pan_tilde_new,
+        0, sizeof(t_pan_tilde),
+        CLASS_DEFAULT, 
+        A_DEFFLOAT, 0);
+
+  class_addmethod(pan_tilde_class,
+        (t_method)pan_tilde_dsp, gensym("dsp"), 0);
+  CLASS_MAINSIGNALIN(pan_tilde_class, t_pan_tilde, f);
+}
+\end{verbatim}
+
+\vfill
+\newpage
+\begin{appendix}
+
+\section{Pd's message-system}
+Non-audio-data are distributed via a message-system.
+Each message consists of a ``selector'' and a list of atoms.
+
+\subsection{atoms}
+
+There are three kinds of atoms:
+\begin{itemize}
+\item {\em A\_FLOAT}: a numerical value (floating point)
+\item {\em A\_SYMBOL}: a symbolic value (string)
+\item {\em A\_POINTER}: a pointer
+\end{itemize}
+
+Numerical values are always floating point-values (\verb+t_float+),
+even if they could be displayed as integer values.
+
+Each symbol is stored in a lookup-table for reasons of performance.
+The command \verb+gensym+ looks up a string in the lookup-table and
+returns the address of the symbol.
+If the string is not yet to be found in the table,
+a new symbol is added.
+
+Atoms of type {\em A\_POINTER} are not very important (for simple externals). 
+
+The type of an atom \verb+a+ is stored in the structure-element \verb+a.a_type+.
+
+\subsection{selectors}
+The selector is a symbol that defines the type of a message.
+There are five predefined selectors:
+\begin{itemize}
+\item ``{\tt bang}'' labels a trigger event.
+A ``bang''-message consists only of the selector and contains no lists of atoms.
+\item ``{\tt float}'' labels a numerical value.
+The list of a ``float''-Message contains one single atom of type {\em A\_FLOAT}
+\item ``{\tt symbol}'' labels a symbolic value.
+The list of a ``symbol''-Message contains one single atom of type {\em A\_SYMBOL}
+\item ``{\tt pointer}'' labels a pointer value.
+The list of a ``pointer''-Message contains one single atom of type {\em A\_POINTER}
+\item ``{\tt list}'' labels a list of one or more atoms of arbitrary type.
+\end{itemize}
+
+Since the symbols for these selectors are used quite often,
+their address in the lookup-table can be queried directly,
+without having to use \verb+gensym+:
+
+\begin{tabular}{l||l|l}
+selector&lookup-routine&lookup-address\\
+\hline
+\tt bang &\verb+gensym("bang")+ & \verb+&s_bang+ \\
+\tt float &\verb+gensym("float")+ & \verb+&s_float+ \\
+\tt symbol &\verb+gensym("symbol")+ & \verb+&s_symbol+ \\
+\tt pointer &\verb+gensym("pointer")+ & \verb+&s_pointer+ \\
+\tt list &\verb+gensym("list")+ & \verb+&s_list+ \\
+--- (signal) &\verb+gensym("signal")+&\verb+&s_symbol+
+\end{tabular}
+
+Other selectors can be used as well.
+The receiving class has to provide a method for a specifique selector
+or for ``anything'', which is any arbitrary selector.
+
+Messages that have no explicit selector and start with a numerical value,
+are recognised automatically either as ``float''-message (only one atom) or as
+``list''-message (several atoms).
+
+For example, messages ``\verb+12.429+'' and ``\verb+float 12.429+'' are identical.
+Likewise, the messages ``\verb+list 1 for you+'' is identical to ``\verb+1 for you+''.
+
+\section{Pd-types}
+Since Pd is used on several platforms,
+many ordinary types of variables, like \verb|int|, are re-defined.
+To write portable code, it is reasonable to use types provided by Pd.
+
+Apart from this there are many predefined types,
+that should make the life of the programmer simpler.
+
+Generally, Pd-types start with \verb|t_|.
+
+\begin{tabular}{c|l}
+Pd-type & description \\
+\hline\hline
+\verb+t_atom+& atom \\
+\verb+t_float+ & floating point value\\
+\verb+t_symbol+ & symbol \\
+\verb+t_gpointer+ & pointer (to graphical objects) \\
+\hline
+\verb+t_int+ & integer value \\
+\verb+t_signal+ & structure of a signal \\
+\verb+t_sample+ & audio signal-value (floating point)\\
+\verb+t_outlet+ & outlet of an object \\
+\verb+t_inlet+ & inlet of an object \\
+\verb+t_object+ & object-interna \\
+\hline
+\verb+t_class+ & a Pd-class \\
+\verb+t_method+ & class-method \\
+\verb+t_newmethod+ & pointer to a constructor (new-routine) \\
+\end{tabular}
+
+
+\section{important functions in ``m\_pd.h''}
+
+\subsection{functions: atoms}
+
+\subsubsection{SETFLOAT}
+\begin{verbatim}
+SETFLOAT(atom, f)
+\end{verbatim}
+This macro sets the type of \verb+atom+ to \verb+A_FLOAT+
+and stores the numerical value \verb+f+ in this atom.
+
+\subsubsection{SETSYMBOL}
+\begin{verbatim}
+SETSYMBOL(atom, s)
+\end{verbatim}
+This macro sets the type of \verb+atom+ to \verb+A_SYMBOL+
+and stores the symbolic pointer \verb+s+ in this atom.
+
+\subsubsection{SETPOINTER}
+\begin{verbatim}
+SETPOINTER(atom, pt)
+\end{verbatim}
+This macro sets the type of \verb+atom+ to \verb+A_POINTER+
+and stores the pointer \verb+pt+ in this atom.
+
+\subsubsection{atom\_getfloat}
+\begin{verbatim}
+t_float atom_getfloat(t_atom *a);
+\end{verbatim}
+If the type of the atom \verb+a+ is \verb+A_FLOAT+,
+the numerical value of this atom else ``0.0'' is returned.
+
+\subsubsection{atom\_getfloatarg}
+\begin{verbatim}
+t_float atom_getfloatarg(int which, int argc, t_atom *argv)
+\end{verbatim}
+If the type of the atom -- that is found at in the atom-list
+\verb+argv+ with the length \verb+argc+ at the place \verb+which+ --
+is \verb+A_FLOAT+, the numerical value of this atom else ``0.0'' is returned.
+
+\subsubsection{atom\_getint}
+\begin{verbatim}
+t_int atom_getint(t_atom *a);
+\end{verbatim}
+If the type of the atom \verb+a+ is \verb+A_FLOAT+,
+its numerical value is returned as integer else ``0'' is returned.
+
+\subsubsection{atom\_getsymbol}
+\begin{verbatim}
+t_symbol atom_getsymbol(t_atom *a);
+\end{verbatim}
+If the type of the atom \verb+a+ is \verb+A_SYMBOL+,
+a pointer to this symbol is returned, else a null-pointer ``0'' is returned.
+
+\subsubsection{atom\_gensym}
+\begin{verbatim}
+t_symbol *atom_gensym(t_atom *a);
+\end{verbatim}
+If the type of the atom \verb+a+ is \verb+A_SYMBOL+,
+a pointer to this symbol is returned.
+
+Atoms of a different type, are ``reasonably'' converted into a string.
+This string is -- on demand -- inserted into the symbol-table.
+A pointer to this symbol is returned.
+
+\subsubsection{atom\_string}
+\begin{verbatim}
+void atom_string(t_atom *a, char *buf, unsigned int bufsize);
+\end{verbatim}
+Converts an atom \verb+a+ into a {\tt C}-string \verb+buf+.
+The memory to this char-Buffer has to be reserved manually and
+its length has to be declared in \verb+bufsize+.
+
+\subsubsection{gensym}
+\begin{verbatim}
+t_symbol *gensym(char *s);
+\end{verbatim}
+Checks, whether the C-string \verb+*s+ has already been inserted into the symbol-table.
+If no entry exists, it is created.
+A pointer to the symbol is returned.
+
+\subsection{functions: classes}
+\subsubsection{class\_new}
+\begin{verbatim}
+t_class *class_new(t_symbol *name,
+        t_newmethod newmethod, t_method freemethod,
+        size_t size, int flags,
+        t_atomtype arg1, ...);
+\end{verbatim}
+Generates a class with the symbolic name \verb+name+.
+\verb+newmethod+ is the constructor that creates an instance of the class and
+returns a pointer to this instance.
+
+If memory is reserved dynamically, this memory has to be freed by the
+destructor-method \verb+freemethod+ (without any return argument),
+when the object is destroyed.
+
+\verb+size+  is the static size of the class-data space,
+that is returned by \verb+sizeof(t_mydata)+.
+
+\verb+flags+ define the presentation of the graphical object.
+A (more or less arbitrary) combination of following objects is possible:
+
+\begin{tabular}{l|l}
+flag&description\\
+\hline
+\verb+CLASS_DEFAULT+ & a normal object with one inlet \\
+\verb+CLASS_PD+ & \em object (without graphical presentation) \\
+\verb+CLASS_GOBJ+ & \em pure graphical object (like arrays, graphs,...)\\
+\verb+CLASS_PATCHABLE+ & \em a normal object (with one inlet) \\
+\verb+CLASS_NOINLET+ & the default inlet is suppressed \\
+\end{tabular}
+
+Flags the description of which is printed in {\em italic}
+are of small importance for writing externals.
+
+The remaining arguments \verb+arg1,...+ define the
+types of object-arguments passed at the creation of a class-object.
+A maximum of six type checked arguments can be passed to an object.
+The list of argument-types are terminated by ``0''.
+
+Possible types of arguments are:
+
+\begin{tabular}{l|l}
+\verb+A_DEFFLOAT+ & a numerical value \\
+\verb+A_DEFSYMBOL+ & a symbolical value \\
+\verb+A_GIMME+ & a list of atoms of arbitrary length and types \\
+\end{tabular}
+
+If more than six arguments are to be passed,
+\verb+A_GIMME+ has to be used and a manual type-check has to be made.
+
+\subsubsection{class\_addmethod}
+\begin{verbatim}
+void class_addmethod(t_class *c, t_method fn, t_symbol *sel,
+    t_atomtype arg1, ...);
+\end{verbatim}
+Adds a method \verb+fn+ for a selector \verb+sel+ to a class \verb+c+.
+
+The remaining arguments \verb+arg1,...+ define the
+types of the list of atoms that follow the selector.
+A maximum of six type-checked arguments can be passed.
+If more than six arguments are to be passed,
+\verb+A_GIMME+ has to be used and a manual type-check has to be made.
+
+The list of arguments is terminated by ``0''.
+
+
+Possible types of arguments are:
+
+\begin{tabular}{l|l}
+\verb+A_DEFFLOAT+ & a numerical value \\
+\verb+A_DEFSYMBOL+ & a symbolical value \\
+\verb+A_POINTER+ & a pointer \\
+\verb+A_GIMME+ & a list of atoms of arbitrary length and types \\
+\end{tabular}
+
+\subsubsection{class\_addbang}
+\begin{verbatim}
+void class_addbang(t_class *c, t_method fn);
+\end{verbatim}
+Adds a method \verb+fn+ for ``bang''-messages to the class \verb+c+.
+
+The argument of the ``bang''-method is a pointer to the class-data space:
+
+\verb+void my_bang_method(t_mydata *x);+
+
+\subsubsection{class\_addfloat}
+\begin{verbatim}
+void class_addfloat(t_class *c, t_method fn);
+\end{verbatim}
+Adds a method \verb+fn+ for ``float''-messages to the class \verb+c+.
+
+The arguments of the ``float''-method is a pointer to the class-data space and
+a floating point-argument:
+
+\verb+void my_float_method(t_mydata *x, t_floatarg f);+
+
+\subsubsection{class\_addsymbol}
+\begin{verbatim}
+void class_addsymbol(t_class *c, t_method fn);
+\end{verbatim}
+Adds a method \verb+fn+ for ``symbol''-messages to the class \verb+c+.
+
+The arguments of the ``symbol''-method is a pointer to the class-data space and
+a pointer to the passed symbol:
+
+\verb+void my_symbol_method(t_mydata *x, t_symbol *s);+
+
+\subsubsection{class\_addpointer}
+\begin{verbatim}
+void class_addpointer(t_class *c, t_method fn);
+\end{verbatim}
+Adds a method \verb+fn+ for ``pointer''-messages to the class \verb+c+.
+
+The arguments of the ``pointer''-method is a pointer to the class-data space and
+a pointer to a pointer:
+
+\verb+void my_pointer_method(t_mydata *x, t_gpointer *pt);+
+
+\subsubsection{class\_addlist}
+\begin{verbatim}
+void class_addlist(t_class *c, t_method fn);
+\end{verbatim}
+Adds a method \verb+fn+ for ``list''-messages to the class \verb+c+.
+
+The arguments of the ``list''-method are -- apart from a pointer to the class-data space --
+a pointer to the selector-symbol (always \verb+&s_list+),
+the number of atoms and a pointer to the list of atoms:
+
+\verb+void my_list_method(t_mydata *x,+
+
+\verb+   t_symbol *s, int argc, t_atom *argv);+
+
+\subsubsection{class\_addanything}
+\begin{verbatim}
+void class_addanything(t_class *c, t_method fn);
+\end{verbatim}
+Adds a method \verb+fn+ for an arbitrary message to the class \verb+c+.
+
+The arguments of the anything-method are -- apart from a pointer to the class-data space --
+a pointer to the selector-symbol,
+the number of atoms and a pointer to the list of atoms:
+
+\verb+void my_any_method(t_mydata *x,+
+
+\verb+   t_symbol *s, int argc, t_atom *argv);+
+
+\subsubsection{class\_addcreator}
+\begin{verbatim}
+ void class_addcreator(t_newmethod newmethod, t_symbol *s, 
+    t_atomtype type1, ...);
+\end{verbatim}
+Adds a creator-symbol \verb+s+, alternative to the symbolic class name,
+to the constructor \verb+newmethod+.
+Thus, objects can be created either by their ``real'' class name or
+an alias-name (p.e. an abbreviation, like the internal ``float'' resp. ``f'').
+
+The ``0''-terminated list of types corresponds to that of \verb+class_new+.
+
+\subsubsection{class\_sethelpsymbol}
+\begin{verbatim}
+void class_sethelpsymbol(t_class *c, t_symbol *s);
+\end{verbatim}
+
+If a Pd-object is right-clicked, a help-patch for the corresponding object class
+can be opened.
+By default this is a patch with the symbolic class name in the
+directory ``{\em doc/5.reference/}''.
+
+The name of the help-patch for the class that is pointed to by \verb+c+
+is changed to the symbol \verb+s+.
+
+Therefore, several similar classes can share a single help-patch.
+
+Path-information is relative to the default help path {\em doc/5.reference/}.
+
+\subsubsection{pd\_new}
+\begin{verbatim}
+t_pd *pd_new(t_class *cls);
+\end{verbatim}
+Generates a new instance of the class \verb+cls+ and
+returns a pointer to this instance.
+
+\subsection{functions: inlets and outlets}
+All routines for inlets and outlets need a reference to the object-interna of
+the class-instance.
+When instantiating a new object,
+the necessary data space-variable of the \verb+t_object+-type is initialised.
+This variable has to be passed as the \verb+owner+-object to the
+various inlet- and outlet-routines.
+
+\subsubsection{inlet\_new}
+\begin{verbatim}
+t_inlet *inlet_new(t_object *owner, t_pd *dest,
+      t_symbol *s1, t_symbol *s2);
+\end{verbatim}
+Generates an additional ``active'' inlet for the object
+that is pointed at by \verb+owner+.
+Generally, \verb+dest+ points at ``\verb+owner.ob_pd+''.
+
+The selector \verb+s1+ at the new inlet is substituted by the selector \verb+s2+.
+
+If a message with selector \verb+s1+ appears at the new inlet,
+the class-method for the selector \verb+s2+ is called.
+
+This means
+\begin{itemize}
+\item The substituting selector has to be declared by \verb+class_addmethod+
+in the setup-routine.
+\item It is possible to simulate a certain right inlet, by sending a message with
+this inlet's selector to the leftmost inlet.
+
+Using an empty symbol (\verb+gensym("")+) as selector
+makes it impossible to address a right inlet via the leftmost one.
+
+\item It is not possible to add methods for more than one selector to a right inlet.
+Particularly it is not possible to add a universal method for arbitrary selectors to 
+a right inlet.
+\end{itemize}
+
+\subsubsection{floatinlet\_new}
+\begin{verbatim}
+t_inlet *floatinlet_new(t_object *owner, t_float *fp);
+\end{verbatim}
+Generates a new ``passive'' inlet for the object that is pointed at by \verb+owner+.
+This inlet enables numerical values to be written directly into the
+memory \verb+fp+, without calling a dedicated method.
+
+\subsubsection{symbolinlet\_new}
+\begin{verbatim}
+t_inlet *symbolinlet_new(t_object *owner, t_symbol **sp);
+\end{verbatim}
+Generates a new ``passive'' inlet for the object that is pointed at by \verb+owner+.
+This inlet enables symbolic values to be written directly into the
+memory \verb+*sp+, without calling a dedicated method.
+
+
+\subsubsection{pointerinlet\_new}
+\begin{verbatim}
+t_inlet *pointerinlet_new(t_object *owner, t_gpointer *gp);
+\end{verbatim}
+Generates a new ``passive'' inlet for the object that is pointed at by \verb+owner+.
+This inlet enables pointer to be written directly into the
+memory \verb+gp+, without calling a dedicated method.
+
+\subsubsection{outlet\_new}
+\begin{verbatim}
+t_outlet *outlet_new(t_object *owner, t_symbol *s);
+\end{verbatim}
+Generates a new outlet for the object that is pointed at by \verb+owner+.
+The Symbol \verb+s+ indicates the type of the outlet.
+
+\begin{tabular}{c|l||l}
+symbol & symbol-address & outlet-type \\
+\hline\hline
+``bang'' & \verb+&s_bang+ & message (bang)\\
+``float'' & \verb+&s_float+ & message (float)\\
+``symbol'' & \verb+&s_symbol+ & message (symbol) \\
+``pointer'' & \verb+&s_gpointer+ & message (pointer)\\
+``list'' & \verb+&s_list+ & message (list) \\
+--- & 0 & message \\
+\hline
+``signal'' & \verb+&s_signal+ & signal \\
+\end{tabular}
+
+There are no real differences between outlets of the various message-types.
+At any rate, it makes code more easily readable,
+if the use of outlet is shown at creation-time.
+For outlets for any messages a null-pointer is used.
+Signal-outlet must be declared with \verb+&s_signal+.
+
+Variables if the type \verb+t_object+ provide pointer to one outlet.
+Whenever a new outlet is generated, its address is stored in the
+object variable \verb+(*owner).ob_outlet+.
+
+If more than one message-outlet is needed,
+the outlet-pointers that are returned by \verb+outlet_new+ 
+have to be stored manually in the data space
+to address the given outlets.
+
+\subsubsection{outlet\_bang}
+\begin{verbatim}
+void outlet_bang(t_outlet *x);
+\end{verbatim}
+Outputs a ``bang''-message at the outlet specified by \verb+x+.
+
+\subsubsection{outlet\_float}
+\begin{verbatim}
+void outlet_float(t_outlet *x, t_float f);
+\end{verbatim}
+Outputs a ``float''-message with the numeric value \verb+f+
+at the outlet specified by \verb+x+.
+
+\subsubsection{outlet\_symbol}
+\begin{verbatim}
+void outlet_symbol(t_outlet *x, t_symbol *s);
+\end{verbatim}
+Outputs a ``symbol''-message with the symbolic value \verb+s+
+at the outlet specified by \verb+x+.
+
+\subsubsection{outlet\_pointer}
+\begin{verbatim}
+void outlet_pointer(t_outlet *x, t_gpointer *gp);
+\end{verbatim}
+Outputs a ``pointer''-message with the pointer \verb+gp+
+at the outlet specified by \verb+x+.
+
+\subsubsection{outlet\_list}
+\begin{verbatim}
+void outlet_list(t_outlet *x,
+                 t_symbol *s, int argc, t_atom *argv);
+\end{verbatim}
+Outputs a ``list''-message at the outlet specified by \verb+x+.
+The list contains \verb+argc+ atoms.
+\verb+argv+ points to the first element of the atom-list.
+
+Independent of the symbol \verb+s+, the selector ``list'' will precede
+the list.
+
+To make the code more readable,
+\verb+s+ should point to the symbol list
+(either via \verb+gensym("list")+ or via \verb+&s_list+)
+
+\subsubsection{outlet\_anything}
+\begin{verbatim}
+void outlet_anything(t_outlet *x,
+                     t_symbol *s, int argc, t_atom *argv);
+\end{verbatim}
+Outputs a message at the outlet specified by \verb+x+.
+
+The message-selector is specified with \verb+s+.
+It is followed by \verb+argc+ atoms.
+\verb+argv+ points to the first element of the atom-list.
+
+\subsection{functions: DSP}
+If a class should provide methods for digital signal-processing,
+a method for the selector ``dsp'' (followed by no atoms)
+has to be added to this class
+
+Whenever Pd's audio engine is started,
+all objects that provide a ``dsp''-method are identified as instances of signal classes.
+
+\paragraph{DSP-method}
+
+\begin{verbatim}
+void my_dsp_method(t_mydata *x, t_signal **sp)
+\end{verbatim}
+
+In the ``dsp''-method a class method for signal-processing
+is added to the DSP-tree by the function \verb+dsp_add+.
+
+Apart from the data space \verb+x+ of the object,
+an array of signals is passed.
+The signals in the array are arranged in such a way,
+that they can be read in the graphical representation of the object
+clockwisely.
+
+In case there are both two in- and out-signals, this means:
+
+\begin{tabular}{c|r}
+pointer & to signal \\
+\hline\hline
+sp[0] & left in-signal \\
+sp[1] & right in-signal \\
+sp[2] & right out-signal \\
+sp[3] & left out-signal \\
+\end{tabular}
+
+The signal structure contains apart from other things:
+
+\begin{tabular}{c|l}
+structure-element & description \\
+\hline
+\verb+s_n+ & length of the signal vector \\
+\verb+s_vec+ & pointer to the signal vector \\
+\end{tabular}
+
+The signal vector is an array of samples of type  \verb+t_sample+.
+
+\paragraph{perform-routine}
+\begin{verbatim}
+t_int *my_perform_routine(t_int *w)
+\end{verbatim}
+
+
+A pointer \verb+w+ to an array (of integer) is passed to
+the perform-routine that is inserted into the DSP-tree by \verb+class_add+.
+
+In this array the pointers that are passed via \verb+dsp_add+ are stored.
+These pointers have to be casted back to their original type.
+
+The first pointer is stored at \verb+w[1]+ !!!
+
+The perform-routine has to return a pointer to integer,
+that points directly behind the memory, where the object's pointers are stored.
+This means, that the return-argument equals the routine's argument \verb+w+
+plus the number of used pointers
+(as defined in the second argument of \verb+dsp_add+) plus one.
+
+\subsubsection{CLASS\_MAINSIGNALIN}
+\begin{verbatim}
+CLASS_MAINSIGNALIN(<class_name>, <class_data>, <f>);
+\end{verbatim}
+The macro \verb+CLASS_MAINSIGNALIN+ declares,
+that the class will use signal-inlets.
+
+The first macro-argument is a pointer to the signal-class.
+The second argument is the type of the class-data space.
+The third argument is a (dummy-)floating point-variable of the data space,
+that is needed to automatically convert ``float''-messages into signals
+if no signal is present at the signal-inlet.
+
+No ``float''-methods can be used for signal-inlets, that are created this way.
+
+\subsubsection{dsp\_add}
+\begin{verbatim}
+void dsp_add(t_perfroutine f, int n, ...);
+\end{verbatim}
+Adds the perform-routine \verb+f+ to the DSP-tree.
+The perform-routine is called at each DSP-cycle.
+
+The second argument\verb+n+ defines the number of following pointer-arguments 
+
+Which pointers to which data are passes is not limited.
+Generally, pointers to the data space of the object and to the
+signal-vectors are reasonable.
+The length of the signal-vectors should also be passed to manipulate signals effectively.
+
+\subsubsection{sys\_getsr}
+\begin{verbatim}
+float sys_getsr(void);
+\end{verbatim}
+Returns the sampler ate of the system.
+
+\subsection{functions: memory}
+\subsubsection{getbytes}
+\begin{verbatim}
+void *getbytes(size_t nbytes);
+\end{verbatim}
+Reserves \verb+nbytes+ bytes and returns a pointer to the allocated memory.
+
+\subsubsection{copybytes}
+\begin{verbatim}
+void *copybytes(void *src, size_t nbytes);
+\end{verbatim}
+Copies \verb+nbytes+ bytes from \verb+*src+ into a newly allocated memory.
+The address of this memory is returned.
+
+\subsubsection{freebytes}
+\begin{verbatim}
+void freebytes(void *x, size_t nbytes);
+\end{verbatim}
+Frees \verb+nbytes+ bytes at address \verb+*x+.
+
+\subsection{functions: output}
+\subsubsection{post}
+\begin{verbatim}
+void post(char *fmt, ...);
+\end{verbatim}
+
+Writes a {\tt C}-string to the standard error (shell).
+
+\subsubsection{error}
+\begin{verbatim}
+void error(char *fmt, ...);
+\end{verbatim}
+
+Writes a {\tt C}-string as an error-message to the standard error (shell).
+
+The object that has output the error-message is marked and
+can be identified via the Pd-menu {\em Find->Find last error}.
+
+\end{appendix}
+
+\end{document} 
+
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