随机数生成

许多游戏依靠随机性来实现核心游戏机制. 本页将指导你了解常见的随机性类型, 以及如何在Godot中实现它们.

在简要概述生成随机数的实用函数之后，你将学习如何从数组、字典中获取随机元素，以及如何在 GDScript 中使用噪点生成器。最后，我们将了解加密安全的随机数生成以及它与典型随机数生成的区别。

备注

计算机不能产生“真正的”随机数。相反，它们依赖伪随机数生成器（PRNG）。

Godot内部使用`PCG Family <https://www.pcg-random.org/>`__ of 伪随机数生成器。

全局作用域 vs RandomNumberGenerator 类

Godot 提供了两种生成随机数的方式：通过全局作用域方法或使用 RandomNumberGenerator 类。

全局作用域方法更容易设置，但不能提供太多控制。

RandomNumberGenerator需要使用更多代码，但允许建立多个实例，每个实例都有自己的种子和状态。

本教程使用全局作用域方法, 只存在于RandomNumberGenerator类中的方法除外.

randomize() 方法

备注

自Godot 4.0以来，当项目启动时，随机种子会自动设置为随机值。这意味着你不再需要在 _ready() 中调用 randomize() 来确保项目运行的结果是随机的。但是，如果你想使用特定的种子编号，或者使用不同的方法生成它，你仍然可以使用 randomize()。

在全局作用域中，你可以找到一个 randomize() 方法。该方法应该在你的项目开始初始化随机种子时只调用一次。多次调用它是不必要的，且可能会对性能产生负面影响。

把它放在你的主场景脚本的 _ready() 方法中是个不错的选择：

GDScriptC#

func _ready():
    randomize()

你也可以使用 seed() 设置固定的随机种子。这样做会在运行过程中为你提供确定性的结果：

GDScriptC#

func _ready():
    seed(12345)
    # To use a string as a seed, you can hash it to a number.
    seed("Hello world".hash())

当使用RandomNumberGenerator类时，应该在实例上调用 randomize() ，因为它有自己的种子:

GDScriptC#

var random = RandomNumberGenerator.new()
random.randomize()

获得一个随机数

让我们来看看Godot中最常用的一些生成随机数的函数和方法.

The function randi() returns a random number between 0 and 2^32 - 1. Since the maximum value is huge, you most likely want to use the modulo operator (%) to bound the result between 0 and the denominator:

GDScriptC#

# Prints a random integer between 0 and 49.
print(randi() % 50)

# Prints a random integer between 10 and 60.
print(randi() % 51 + 10)

randf() 返回一个介于 0 和 1 之间的随机浮点数。在实现 加权随机概率 系统等时很有用。

randfn() returns a random floating-point number following a normal distribution. This means the returned value is more likely to be around the mean (0.0 by default), varying by the deviation (1.0 by default):

GDScriptC#

# Prints a random floating-point number from a normal distribution with a mean 0.0 and deviation 1.0.
print(randfn(0.0, 1.0))

randf_range() 接受两个参数 from 和 to，并返回一个介于 from 和 to 之间的随机浮点数：

GDScriptC#

# Prints a random floating-point number between -4 and 6.5.
print(randf_range(-4, 6.5))

randi_range() takes two arguments from and to, and returns a random integer between from and to:

GDScriptC#

# Prints a random integer between -10 and 10.
print(randi_range(-10, 10))

获取一个随机数组元素

We can use random integer generation to get a random element from an array, or use the Array.pick_random method to do it for us:

GDScriptC#

var _fruits = ["apple", "orange", "pear", "banana"]

func _ready():
    for i in range(100):
        # Pick 100 fruits randomly.
        print(get_fruit())

    for i in range(100):
        # Pick 100 fruits randomly, this time using the `Array.pick_random()`
        # helper method. This has the same behavior as `get_fruit()`.
        print(_fruits.pick_random())

func get_fruit():
    var random_fruit = _fruits[randi() % _fruits.size()]
    # Returns "apple", "orange", "pear", or "banana" every time the code runs.
    # We may get the same fruit multiple times in a row.
    return random_fruit

To prevent the same fruit from being picked more than once in a row, we can add more logic to the above method. In this case, we can't use Array.pick_random since it lacks a way to prevent repetition:

GDScriptC#

var _fruits = ["apple", "orange", "pear", "banana"]
var _last_fruit = ""


func _ready():
    # Pick 100 fruits randomly.
    for i in range(100):
        print(get_fruit())


func get_fruit():
    var random_fruit = _fruits[randi() % _fruits.size()]
    while random_fruit == _last_fruit:
        # The last fruit was picked. Try again until we get a different fruit.
        random_fruit = _fruits[randi() % _fruits.size()]

    # Note: if the random element to pick is passed by reference,
    # such as an array or dictionary,
    # use `_last_fruit = random_fruit.duplicate()` instead.
    _last_fruit = random_fruit

    # Returns "apple", "orange", "pear", or "banana" every time the code runs.
    # The function will never return the same fruit more than once in a row.
    return random_fruit

这种方法可以让随机数生成的感觉不那么重复. 不过, 它仍然不能防止结果在有限的一组值之间 "乒乓反复". 为了防止这种情况, 请使用 shuffle bag 模式来代替.

获取一个随机字典值

我们也可以将数组的类似逻辑应用于字典:

GDScriptC#

var _metals = {
    "copper": {"quantity": 50, "price": 50},
    "silver": {"quantity": 20, "price": 150},
    "gold": {"quantity": 3, "price": 500},
}


func _ready():
    for i in range(20):
        print(get_metal())


func get_metal():
    var random_metal = _metals.values()[randi() % metals.size()]
    # Returns a random metal value dictionary every time the code runs.
    # The same metal may be selected multiple times in succession.
    return random_metal

加权随机概率

randf() 方法返回一个介于 0.0 和 1.0 之间的浮点数。我们可以使用它来创建“加权”概率，其中不同的结果具有不同的可能性：

GDScriptC#

func _ready():
    for i in range(100):
        print(get_item_rarity())


func get_item_rarity():
    var random_float = randf()

    if random_float < 0.8:
        # 80% chance of being returned.
        return "Common"
    elif random_float < 0.95:
        # 15% chance of being returned.
        return "Uncommon"
    else:
        # 5% chance of being returned.
        return "Rare"

You can also get a weighted random index using the rand_weighted() method on a RandomNumberGenerator instance. This returns a random integer between 0 and the size of the array that is passed as a parameter. Each value in the array is a floating-point number that represents the relative likelihood that it will be returned as an index. A higher value means the value is more likely to be returned as an index, while a value of 0 means it will never be returned as an index.

For example, if [0.5, 1, 1, 2] is passed as a parameter, then the method is twice as likely to return 3 (the index of the value 2) and twice as unlikely to return 0 (the index of the value 0.5) compared to the indices 1 and 2.

Since the returned value matches the array's size, it can be used as an index to get a value from another array as follows:

GDScriptC#

# Prints a random element using the weighted index that is returned by `rand_weighted()`.
# Here, "apple" will be returned twice as rarely as "orange" and "pear".
# "banana" is twice as common as "orange" and "pear", and four times as common as "apple".
var fruits = ["apple", "orange", "pear", "banana"]
var probabilities = [0.5, 1, 1, 2];

var random = RandomNumberGenerator.new()
print(fruits[random.rand_weighted(probabilities)])

使用 shuffle bag 达到“更好”随机性

以上面同样的例子为例, 我们希望随机挑选水果. 然而, 每次选择水果时依靠随机数生成会导致分布不那么 均匀 . 如果玩家足够幸运(或不幸), 他们可能会连续三次或更多次得到相同的水果.

You can accomplish this using the shuffle bag pattern. It works by removing an element from the array after choosing it. After multiple selections, the array ends up empty. When that happens, you reinitialize it to its default value:

GDScriptC#

var _fruits = ["apple", "orange", "pear", "banana"]
# A copy of the fruits array so we can restore the original value into `fruits`.
var _fruits_full = []


func _ready():
    _fruits_full = _fruits.duplicate()
    _fruits.shuffle()

    for i in 100:
        print(get_fruit())


func get_fruit():
    if _fruits.is_empty():
        # Fill the fruits array again and shuffle it.
        _fruits = _fruits_full.duplicate()
        _fruits.shuffle()

    # Get a random fruit, since we shuffled the array,
    # and remove it from the `_fruits` array.
    var random_fruit = _fruits.pop_front()
    # Returns "apple", "orange", "pear", or "banana" every time the code runs, removing it from the array.
    # When all fruit are removed, it refills the array.
    return random_fruit

在运行上面的代码时, 仍有可能连续两次得到同一个水果. 我们摘下一个水果时, 它将不再是一个可能的返回值, 但除非数组现在是空的. 当数组为空时, 此时我们将其重置回默认值, 这样就导致了能再次获得相同的水果, 但只有这一次.

随机噪音

当你需要一个 缓慢 根据输入而变化的值时, 上面显示的随机数生成方式就显示出了它们的局限性. 这里的输入可以是位置, 时间或其他任何东西.

为了实现这一点，你可以使用随机噪声函数。噪声函数在程序式生成中特别受欢迎，可用于生成逼真的地形。Godot 为此提供了 FastNoiseLite，它支持 1D、2D 和 3D 噪声。以下是 1D 噪声的示例：

GDScriptC#

var _noise = FastNoiseLite.new()

func _ready():
    # Configure the FastNoiseLite instance.
    _noise.noise_type = FastNoiseLite.NoiseType.TYPE_SIMPLEX_SMOOTH
    _noise.seed = randi()
    _noise.fractal_octaves = 4
    _noise.frequency = 1.0 / 20.0

    for i in 100:
        # Prints a slowly-changing series of floating-point numbers
        # between -1.0 and 1.0.
        print(_noise.get_noise_1d(i))

密码安全的伪随机数生成器

目前为止提到的方法都无法实现密码安全的伪随机数生成（CSPRNG）。这对于游戏而言没有问题，但是对于涉及加密、认证、签名的场景就显得捉襟见肘。

Godot 为此提供了 Crypto 类。这个类可以执行非对称密钥加密、解密、签名和验证，也可以生成密码安全的随机字节块、RSA 密钥、HMAC 摘要、自签名的 X509Certificate。

CSPRNG 的缺点是它比标准伪随机数的生成慢得多。其 API 的使用也不太方便。因此，游戏机制应避免使用 CSPRNG。

使用 Crypto 类生成 0 到 2^32-1（含）之间的 2 个随机整数的示例：

var crypto := Crypto.new()
# Request as many bytes as you need, but try to minimize the amount
# of separate requests to improve performance.
# Each 32-bit integer requires 4 bytes, so we request 8 bytes.
var byte_array := crypto.generate_random_bytes(8)

# Use the ``decode_u32()`` method from PackedByteArray to decode a 32-bit unsigned integer
# from the beginning of `byte_array`. This method doesn't modify `byte_array`.
var random_int_1 := byte_array.decode_u32(0)
# Do the same as above, but with an offset of 4 bytes since we've already decoded
# the first 4 bytes previously.
var random_int_2 := byte_array.decode_u32(4)

prints("Random integers:", random_int_1, random_int_2)

参见

请参阅 PackedByteArray 的文档，了解可用于将生成的字节解码为各种类型的数据（如整数或浮点）的其他方法。