游戏开发中的Random随机函数

Unity C# (CPU)

System.Random

var rand = new Random();
rand.Next();                    // 非负整数

rand.NextSingle();              // 0-1 float
rand.Sample();                  // 0-1 float
rand.Next(Int32 x);             // 小于x的非负整数
rand.Next(Int32, Int32);
rand.NextBytes(Byte[]);
rand.NextBytes(Span<Byte>);
rand.NextDouble();
rand.NextInt64();
rand.NextInt64(Int64);
rand.NextInt64(Int64, Int64);

UnityEngine.Random

• 线程不安全
• 不能在Job System非主线程中使用
• https://docs.unity3d.com/ScriptReference/Random.html

Range

• Range(float minInclusive, float maxInclusive)
• Range(int minInclusive, int maxExclusive)

Seed

int seed = 123;
Random.InitState(seed);
float rand = Random.value;

Color

• Random.ColorHSV()
• Random.ColorHSV(float hueMin, float hueMax)

Vector

• Random.insideUnitCircle
• Random.insideUnitSphere
• Random.onUnitSphere

Quaternion

• Random.rotation
• Random.rotationUniform

Unity.Mathematics.Random

• 线程安全
• 支持Job System线程中使用
• 第一次使用next，seed一样，结果一样(determinism|伪随机)
• Mathematics.Random
• ECS Tutorials

    NextFloat();
    NextFloat(Single);
    NextFloat(Single, Single);
    NextFloat2();
    NextFloat2(float2);
    NextFloat2(float2, float2);
    NextFloat2Direction();
    NextFloat3();
    NextFloat3(float3);
    NextFloat3(float3, float3);
    NextFloat3Direction();
...

public void Execute(int index)
{
    Random rand = Random.CreateFromIndex((uint)index);
    Result[index] = rand.NextFloat(0, 100);
}

XOR Shift Random

• ToyPathTracer
  • https://github.com/aras-p/ToyPathTracer/blob/main/Unity/Assets/Maths.cs
• https://www.reedbeta.com/blog/quick-and-easy-gpu-random-numbers-in-d3d11/
• https://www.reedbeta.com/blog/hash-functions-for-gpu-rendering/
• https://gist.github.com/septagon/e04204d4cdd59a6c028c70de59bd62b7
• https://zhuanlan.zhihu.com/p/326270572

  static uint XorShift32(ref uint state)
  {
      uint x = state;
      x ^= x << 13;
      x ^= x >> 17;
      x ^= x << 15;
      state = x;
      return x;
  }
  
  public static float RandomFloat01(ref uint state)
  {
      return (XorShift32(ref state) & 0xFFFFFF) / 16777216.0f;
  }
  
  public static float3 RandomInUnitDisk(ref uint state)
  {
      float3 p;
      do
      {
          p = 2.0f * new float3(RandomFloat01(ref state), RandomFloat01(ref state), 0) - new float3(1, 1, 0);
      } while (lengthsq(p) >= 1.0);
      return p;
  }
  
  public static float3 RandomInUnitSphere(ref uint state)
  {
      float3 p;
      do
      {
          p = 2.0f * new float3(RandomFloat01(ref state), RandomFloat01(ref state), RandomFloat01(ref state)) - new float3(1, 1, 1);
      } while (lengthsq(p) >= 1.0);
      return p;
  }
  
  public static float3 RandomUnitVector(ref uint state)
  {
      float z = RandomFloat01(ref state) * 2.0f - 1.0f;
      float a = RandomFloat01(ref state) * 2.0f * kPI;
      float r = sqrt(1.0f - z * z);
      float x, y;
      sincos(a, out x, out y);
      return new float3(r * x, r* y, z);
  }

Unreal

Houdini