Version: 2020.2
LanguageEnglish
  • C#

Random

class in UnityEngine

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Implemented in:UnityEngine.CoreModule

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Description

Easily generate random data for games.

This static class provides several easy game-oriented ways of generating pseudorandom numbers.

The generator is an Xorshift 128 algorithm, based on the paper Xorshift RNGs by George Marsaglia. It is statically initialized with a high-entropy seed from the operating system, and stored in native memory where it will survive domain reloads. This means that the generator is seeded exactly once on process start, and after that is left entirely under script control.

For more details on the seed, including how to manage it yourself, see InitState. To learn how to save and restore the state of Random, see state.

Versus System.Random

This class has the same name as the .NET Framework class System.Random and serves a similar purpose, but differs in some key ways:

Static vs instanced
UnityEngine.Random is a static class, and so its state is globally shared. Getting random numbers is easy, because there is no need to new an instance and manage its storage. However, static state is problematic when working with threads or jobs (the generator will error if used outside the main thread), or if multiple independent random number generators are required. In those cases, managing instances of System.Random would be a better option.

Float upper bounds are inclusive
All properties and methods in UnityEngine.Random that work with or derive work from float-based randomness (for example value or ColorHSV) will use an inclusive upper bound. This means that it is possible, though as rare as any other given value, for the max to be randomly returned. In contrast, System.Random.NextDouble() has an exclusive maximum, and will never return the maximum value, but only a number slightly below it.

Performance
Methods in UnityEngine.Random have been measured to be between 20% and 40% faster than their equivalents in System.Random.

Name resolution ambiguity
Because the classes share the name Random, it can be easy to get a CS0104 "ambiguous reference" compiler error if the System and UnityEngine namespaces are both brought in via using. To disambiguate, either use an alias using Random = UnityEngine.Random;, fully-qualify the typename e.g. UnityEngine.Random.InitState(123);, or eliminate the using System and fully-qualify or alias types from that namespace instead.

Static Properties

insideUnitCircleReturns a random point inside or on a circle with radius 1.0 (Read Only).
insideUnitSphereReturns a random point inside or on a sphere with radius 1.0 (Read Only).
onUnitSphereReturns a random point on the surface of a sphere with radius 1.0 (Read Only).
rotationReturns a random rotation (Read Only).
rotationUniformReturns a random rotation with uniform distribution (Read Only).
stateGets or sets the full internal state of the random number generator.
valueReturns a random float within [0.0..1.0] (range is inclusive) (Read Only).

Static Methods

ColorHSVGenerates a random color from HSV and alpha ranges.
InitStateInitializes the random number generator state with a seed.
RangeReturns a random float within [minInclusive..maxInclusive] (range is inclusive).
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