A set of extension methods for System.Random to mimic the behaviour of UnityEngine.Random

RandomExtensions.cs

using UnityEngine;
using Random = System.Random;

public static class RandomExtensions
{
    public static Vector2 NextOnUnitCircle(this Random random)
    
        var angle = random.NextSingle(0, 360f) * Mathf.Deg2Rad;
        var x = Mathf.Cos(angle);
        var y = Mathf.Sin(angle);
        return new Vector2(x, y);
    }

    public static Vector3 NextOnUnitSphere(this Random random)
    {
        var angle = random.NextSingle(0, 360f) * Mathf.Deg2Rad;
        var z = random.NextSingle(-1f, 1f);
        var mp = Mathf.Sqrt(1 - z * z);
        var x = mp * Mathf.Cos(angle);
        var y = mp * Mathf.Sin(angle);
        return new Vector3(x, y, z);
    }

    public static Vector3 NextInsideUnitSphere(this Random random)
    {
        return random.NextOnUnitSphere() * random.NextSingle();
    }

    public static Vector2 NextInsideUnitCircle(this Random random)
    {
        return random.NextOnUnitCircle() * random.NextSingle();
    }

    public static Quaternion NextRotation(this Random random)
    {
        var x = random.NextSingle(0f, 360f);
        var y = random.NextSingle(0f, 360f);
        var z = random.NextSingle(0f, 360f);
        return Quaternion.Euler(x, y, z);
    }

    public static Quaternion NextRotationUniform(this Random random)
    {
        float normal, w, x, y, z;

        do
        {
            w = random.NextSingle(-1f, 1f);
            x = random.NextSingle(-1f, 1f);
            y = random.NextSingle(-1f, 1f);
            z = random.NextSingle(-1f, 1f);
            normal = w * w + x * x + y * y + z * z;
        }
        while (normal > 1f || normal == 0f);

        normal = Mathf.Sqrt(normal);
        return new Quaternion(x / normal, y / normal, z / normal, w / normal);
    }

    public static float NextSingle(this Random random, float min = 0f, float max = 1f)
    {
        return Mathf.Lerp(min, max, (float) random.NextDouble());
    }

    public static Color NextColorHsv(this Random random)
    {
        return random.NextColorHsv(0f, 1f, 0f, 1f, 0f, 1f, 1f, 1f);
    }

    public static Color NextColorHsv(this Random random, float minHue, float maxHue)
    {
        return random.NextColorHsv(minHue, maxHue, 0f, 1f, 0f, 1f, 1f, 1f);
    }

    public static Color NextColorHsv(
        this Random random,
        float minHue,
        float maxHue,
        float minSaturation,
        float maxSaturation)
    {
        return random.NextColorHsv(minHue, maxHue, minSaturation, maxSaturation, 0f, 1f, 1f, 1f);
    }

    public static Color NextColorHsv(
        this Random random,
        float minHue,
        float maxHue,
        float minSaturation,
        float maxSaturation,
        float minValue,
        float maxValue)
    {
        return random.NextColorHsv(minHue, maxHue, minSaturation, maxSaturation, minValue, maxValue, 1f, 1f);
    }

    public static Color NextColorHsv(
        this Random random,
        float minHue,
        float maxHue,
        float minSaturation,
        float maxSaturation,
        float minValue,
        float maxValue,
        float minAlpha,
        float maxAlpha)
    {
        var h = Mathf.Lerp(minHue, maxHue, random.NextSingle());
        var s = Mathf.Lerp(minSaturation, maxSaturation, random.NextSingle());
        var v = Mathf.Lerp(minValue, maxValue, random.NextSingle());
        var color = Color.HSVToRGB(h, s, v, true);
        color.a = Mathf.Lerp(minAlpha, maxAlpha, random.NextSingle());
        return color;
    }
}