OpenMusic

Visual Programming | Computer-Assisted Composition

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Instantiating Objects

Instantiation

An instance is an exemplar of a class of objects. Instantiation is the process of creating an instance of a class using a factory box.

Factory Slots

A factory box has a number of slots, represented by inputs and outputs. Once values are assigned to the slots or parameters of a factory box, it can be evaluated to produce an instance[1], an exemplar of a class.

Note that the value of a factory box can also be defined via its editor.

First Input / Output : “Self”

The first input / output of a factory box is usually called “self”. It stands for the object itself.

A “self” input can be connected to :

Reciprocally, the evaluation of a “self” output, or its connection to another box returns the computed object itself.

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Automatic Object Conversions

When compatibility allows it, OM automatic converts objects of a diferent type and creates an instance of the relevant class.

A chord can be created from a note, but a note cannot be created from a
chord.

A chord can be created from a note, but a note cannot be created from a chord.

Manipulating Objects via the “Self” Input

The merger function builds a chord-sequence, or chord-seq[4] , out of two other chord-sequences given as arguments[5].

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The two initial chord-seqs are locked to preserve their value. Conversely, the box that is to be evaluated isn’t locked, to take the result of the upstream computation into account.

Protecting a Box

Evaluation

To evaluate a box, select it and press v .

Its value is computed, and the result of the “self” output, that is, the internal representation of the resulting instance[1] is displayed in the Listener.

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About Evaluation

Tip : Reinitializing a Box

To reset a box to its default state, press SHIFT + i .

Other Inputs / Outputs : Object Parameters

Parameters (Slots)

The other inputs and outputs represent the various parameters (also called class slots[2]), used for defining an instance.

Inputs and outputs respectively address the same parameters - and follow the same ordering.

A note box has five inlets and outlets, a "self", and four other inlets,
which correspond to the usual musical features or parameters of a note :
midicents – pitch –, velocity – dynamics –, duration, midi
channel.

A note box has five inlets and outlets, a “self”, and four other inlets, which correspond to the usual musical features or parameters of a note : midicents - pitch -, velocity - dynamics -, duration, midi channel.

To get information about the qualities of a slot, keep pressing Cmd while overing the mouse over an input or output.

Setting Input Values

Building a chord with two of its parameters : a list of pitches (6000
6800) for C4 and G#4, and a list of note velocities – dynamics – (100
50).

Building a chord with two of its parameters : a list of pitches (6000 6800) for C4 and G#4, and a list of note velocities - dynamics - (100 50).

Input values must be specified to define an object. Several parameters can be set or connected at a time. If no value is specified, the default value of the input is applied.

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Setting Box Inputs Values, Using a Box’s Editor

Conflict : Setting the “Self” Input and Other Attributes

An object can be created directly from the “self” input value, and from the other input parameters. By convention, “self” has priority over the other inputs, whose values are ignored.

Different values have been assigned to the "self" and "pitch" inputs. The
value of the "self" input is applied for the
instantiation.

Different values have been assigned to the “self” and “pitch” inputs. The value of the “self” input is applied for the instantiation.

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Getting Output Values

The different outlets of an object can be used for reading the values of its attributes. Outputs can be connected as parameters to other factory or function box inputs.

To evaluate the value of an output, Cmd click on it. The whole box is evaluated and a specific instance of the class is created.

The second input represents the pitch value of a note box.

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References :

  1. Instance

An actual object created at runtime, out of a given class. In OM, more specifically, an object created when evaluating a factory box. An instance can be saved as a global variable.

SHIFT click on an outlet - especially the first outlet representing the self, the whole object - of a factory box to materialize an instance.

  1. Slot

In object oriented programming, a slot represents and attribute of a class. For instance, the class “note” in OM has 4 slots : pitch, duration, velocity, and MIDI channel.

  1. Class

A category of objects sharing common properties - characteristics and behaviour. A class specifies the internal structure and behaviour of an object. In OM, it is represented in a patch by a factory box that can produce an instance of a class.

See also : Object, Instance

  1. Chord-Seq

OM name of a chord sequence. By extension, a note sequence, since a single note can be considered a chord.

  1. Argument

An argument represents a parameter upon which a function operates. For instance, the (om+ x y) function has two arguments : x and y.

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