godot-docs/classes/class_randomnumbergenerator.rst

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.. _class_RandomNumberGenerator:

RandomNumberGenerator
=====================

**Inherits:** :ref:`RefCounted<class_RefCounted>` **<** :ref:`Object<class_Object>`

A class for generating pseudo-random numbers.

.. rst-class:: classref-introduction-group

Description
-----------

RandomNumberGenerator is a class for generating pseudo-random numbers. It currently uses `PCG32 <https://www.pcg-random.org/>`__.

\ **Note:** The underlying algorithm is an implementation detail. As a result, it should not be depended upon for reproducible random streams across Godot versions.

To generate a random float number (within a given range) based on a time-dependant seed:

::

    var rng = RandomNumberGenerator.new()
    func _ready():
        var my_random_number = rng.randf_range(-10.0, 10.0)

\ **Note:** The default values of :ref:`seed<class_RandomNumberGenerator_property_seed>` and :ref:`state<class_RandomNumberGenerator_property_state>` properties are pseudo-random, and change when calling :ref:`randomize<class_RandomNumberGenerator_method_randomize>`. The ``0`` value documented here is a placeholder, and not the actual default seed.

.. rst-class:: classref-introduction-group

Tutorials
---------

- :doc:`Random number generation <../tutorials/math/random_number_generation>`

.. rst-class:: classref-reftable-group

Properties
----------

.. table::
   :widths: auto

   +-----------------------+----------------------------------------------------------+-------+
   | :ref:`int<class_int>` | :ref:`seed<class_RandomNumberGenerator_property_seed>`   | ``0`` |
   +-----------------------+----------------------------------------------------------+-------+
   | :ref:`int<class_int>` | :ref:`state<class_RandomNumberGenerator_property_state>` | ``0`` |
   +-----------------------+----------------------------------------------------------+-------+

.. rst-class:: classref-reftable-group

Methods
-------

.. table::
   :widths: auto

   +---------------------------+--------------------------------------------------------------------------------------------------------------------------------------------------+
   | :ref:`float<class_float>` | :ref:`randf<class_RandomNumberGenerator_method_randf>` **(** **)**                                                                               |
   +---------------------------+--------------------------------------------------------------------------------------------------------------------------------------------------+
   | :ref:`float<class_float>` | :ref:`randf_range<class_RandomNumberGenerator_method_randf_range>` **(** :ref:`float<class_float>` from, :ref:`float<class_float>` to **)**      |
   +---------------------------+--------------------------------------------------------------------------------------------------------------------------------------------------+
   | :ref:`float<class_float>` | :ref:`randfn<class_RandomNumberGenerator_method_randfn>` **(** :ref:`float<class_float>` mean=0.0, :ref:`float<class_float>` deviation=1.0 **)** |
   +---------------------------+--------------------------------------------------------------------------------------------------------------------------------------------------+
   | :ref:`int<class_int>`     | :ref:`randi<class_RandomNumberGenerator_method_randi>` **(** **)**                                                                               |
   +---------------------------+--------------------------------------------------------------------------------------------------------------------------------------------------+
   | :ref:`int<class_int>`     | :ref:`randi_range<class_RandomNumberGenerator_method_randi_range>` **(** :ref:`int<class_int>` from, :ref:`int<class_int>` to **)**              |
   +---------------------------+--------------------------------------------------------------------------------------------------------------------------------------------------+
   | void                      | :ref:`randomize<class_RandomNumberGenerator_method_randomize>` **(** **)**                                                                       |
   +---------------------------+--------------------------------------------------------------------------------------------------------------------------------------------------+

.. rst-class:: classref-section-separator

----

.. rst-class:: classref-descriptions-group

Property Descriptions
---------------------

.. _class_RandomNumberGenerator_property_seed:

.. rst-class:: classref-property

:ref:`int<class_int>` **seed** = ``0``

.. rst-class:: classref-property-setget

- void **set_seed** **(** :ref:`int<class_int>` value **)**
- :ref:`int<class_int>` **get_seed** **(** **)**

Initializes the random number generator state based on the given seed value. A given seed will give a reproducible sequence of pseudo-random numbers.

\ **Note:** The RNG does not have an avalanche effect, and can output similar random streams given similar seeds. Consider using a hash function to improve your seed quality if they're sourced externally.

\ **Note:** Setting this property produces a side effect of changing the internal :ref:`state<class_RandomNumberGenerator_property_state>`, so make sure to initialize the seed *before* modifying the :ref:`state<class_RandomNumberGenerator_property_state>`:

::

    var rng = RandomNumberGenerator.new()
    rng.seed = hash("Godot")
    rng.state = 100 # Restore to some previously saved state.

.. rst-class:: classref-item-separator

----

.. _class_RandomNumberGenerator_property_state:

.. rst-class:: classref-property

:ref:`int<class_int>` **state** = ``0``

.. rst-class:: classref-property-setget

- void **set_state** **(** :ref:`int<class_int>` value **)**
- :ref:`int<class_int>` **get_state** **(** **)**

The current state of the random number generator. Save and restore this property to restore the generator to a previous state:

::

    var rng = RandomNumberGenerator.new()
    print(rng.randf())
    var saved_state = rng.state # Store current state.
    print(rng.randf()) # Advance internal state.
    rng.state = saved_state # Restore the state.
    print(rng.randf()) # Prints the same value as in previous.

\ **Note:** Do not set state to arbitrary values, since the random number generator requires the state to have certain qualities to behave properly. It should only be set to values that came from the state property itself. To initialize the random number generator with arbitrary input, use :ref:`seed<class_RandomNumberGenerator_property_seed>` instead.

.. rst-class:: classref-section-separator

----

.. rst-class:: classref-descriptions-group

Method Descriptions
-------------------

.. _class_RandomNumberGenerator_method_randf:

.. rst-class:: classref-method

:ref:`float<class_float>` **randf** **(** **)**

Returns a pseudo-random float between ``0.0`` and ``1.0`` (inclusive).

.. rst-class:: classref-item-separator

----

.. _class_RandomNumberGenerator_method_randf_range:

.. rst-class:: classref-method

:ref:`float<class_float>` **randf_range** **(** :ref:`float<class_float>` from, :ref:`float<class_float>` to **)**

Returns a pseudo-random float between ``from`` and ``to`` (inclusive).

.. rst-class:: classref-item-separator

----

.. _class_RandomNumberGenerator_method_randfn:

.. rst-class:: classref-method

:ref:`float<class_float>` **randfn** **(** :ref:`float<class_float>` mean=0.0, :ref:`float<class_float>` deviation=1.0 **)**

Returns a `normally-distributed <https://en.wikipedia.org/wiki/Normal_distribution>`__ pseudo-random number, using Box-Muller transform with the specified ``mean`` and a standard ``deviation``. This is also called Gaussian distribution.

.. rst-class:: classref-item-separator

----

.. _class_RandomNumberGenerator_method_randi:

.. rst-class:: classref-method

:ref:`int<class_int>` **randi** **(** **)**

Returns a pseudo-random 32-bit unsigned integer between ``0`` and ``4294967295`` (inclusive).

.. rst-class:: classref-item-separator

----

.. _class_RandomNumberGenerator_method_randi_range:

.. rst-class:: classref-method

:ref:`int<class_int>` **randi_range** **(** :ref:`int<class_int>` from, :ref:`int<class_int>` to **)**

Returns a pseudo-random 32-bit signed integer between ``from`` and ``to`` (inclusive).

.. rst-class:: classref-item-separator

----

.. _class_RandomNumberGenerator_method_randomize:

.. rst-class:: classref-method

void **randomize** **(** **)**

Setups a time-based seed to for this **RandomNumberGenerator** instance. Unlike the :ref:`@GlobalScope<class_@GlobalScope>` random number generation functions, different **RandomNumberGenerator** instances can use different seeds.

.. |virtual| replace:: :abbr:`virtual (This method should typically be overridden by the user to have any effect.)`
.. |const| replace:: :abbr:`const (This method has no side effects. It doesn't modify any of the instance's member variables.)`
.. |vararg| replace:: :abbr:`vararg (This method accepts any number of arguments after the ones described here.)`
.. |constructor| replace:: :abbr:`constructor (This method is used to construct a type.)`
.. |static| replace:: :abbr:`static (This method doesn't need an instance to be called, so it can be called directly using the class name.)`
.. |operator| replace:: :abbr:`operator (This method describes a valid operator to use with this type as left-hand operand.)`