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Last active Aug 10, 2022
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Perlin noise in Python
"""Perlin noise implementation."""
# Licensed under ISC
from itertools import product
import math
import random
def smoothstep(t):
"""Smooth curve with a zero derivative at 0 and 1, making it useful for
return t * t * (3. - 2. * t)
def lerp(t, a, b):
"""Linear interpolation between a and b, given a fraction t."""
return a + t * (b - a)
class PerlinNoiseFactory(object):
"""Callable that produces Perlin noise for an arbitrary point in an
arbitrary number of dimensions. The underlying grid is aligned with the
There is no limit to the coordinates used; new gradients are generated on
the fly as necessary.
def __init__(self, dimension, octaves=1, tile=(), unbias=False):
"""Create a new Perlin noise factory in the given number of dimensions,
which should be an integer and at least 1.
More octaves create a foggier and more-detailed noise pattern. More
than 4 octaves is rather excessive.
``tile`` can be used to make a seamlessly tiling pattern. For example:
pnf = PerlinNoiseFactory(2, tile=(0, 3))
This will produce noise that tiles every 3 units vertically, but never
tiles horizontally.
If ``unbias`` is true, the smoothstep function will be applied to the
output before returning it, to counteract some of Perlin noise's
significant bias towards the center of its output range.
self.dimension = dimension
self.octaves = octaves
self.tile = tile + (0,) * dimension
self.unbias = unbias
# For n dimensions, the range of Perlin noise is ±sqrt(n)/2; multiply
# by this to scale to ±1
self.scale_factor = 2 * dimension ** -0.5
self.gradient = {}
def _generate_gradient(self):
# Generate a random unit vector at each grid point -- this is the
# "gradient" vector, in that the grid tile slopes towards it
# 1 dimension is special, since the only unit vector is trivial;
# instead, use a slope between -1 and 1
if self.dimension == 1:
return (random.uniform(-1, 1),)
# Generate a random point on the surface of the unit n-hypersphere;
# this is the same as a random unit vector in n dimensions. Thanks
# to:
# Pick n normal random variables with stddev 1
random_point = [random.gauss(0, 1) for _ in range(self.dimension)]
# Then scale the result to a unit vector
scale = sum(n * n for n in random_point) ** -0.5
return tuple(coord * scale for coord in random_point)
def get_plain_noise(self, *point):
"""Get plain noise for a single point, without taking into account
either octaves or tiling.
if len(point) != self.dimension:
raise ValueError("Expected {} values, got {}".format(
self.dimension, len(point)))
# Build a list of the (min, max) bounds in each dimension
grid_coords = []
for coord in point:
min_coord = math.floor(coord)
max_coord = min_coord + 1
grid_coords.append((min_coord, max_coord))
# Compute the dot product of each gradient vector and the point's
# distance from the corresponding grid point. This gives you each
# gradient's "influence" on the chosen point.
dots = []
for grid_point in product(*grid_coords):
if grid_point not in self.gradient:
self.gradient[grid_point] = self._generate_gradient()
gradient = self.gradient[grid_point]
dot = 0
for i in range(self.dimension):
dot += gradient[i] * (point[i] - grid_point[i])
# Interpolate all those dot products together. The interpolation is
# done with smoothstep to smooth out the slope as you pass from one
# grid cell into the next.
# Due to the way product() works, dot products are ordered such that
# the last dimension alternates: (..., min), (..., max), etc. So we
# can interpolate adjacent pairs to "collapse" that last dimension. Then
# the results will alternate in their second-to-last dimension, and so
# forth, until we only have a single value left.
dim = self.dimension
while len(dots) > 1:
dim -= 1
s = smoothstep(point[dim] - grid_coords[dim][0])
next_dots = []
while dots:
next_dots.append(lerp(s, dots.pop(0), dots.pop(0)))
dots = next_dots
return dots[0] * self.scale_factor
def __call__(self, *point):
"""Get the value of this Perlin noise function at the given point. The
number of values given should match the number of dimensions.
ret = 0
for o in range(self.octaves):
o2 = 1 << o
new_point = []
for i, coord in enumerate(point):
coord *= o2
if self.tile[i]:
coord %= self.tile[i] * o2
ret += self.get_plain_noise(*new_point) / o2
# Need to scale n back down since adding all those extra octaves has
# probably expanded it beyond ±1
# 1 octave: ±1
# 2 octaves: ±1½
# 3 octaves: ±1¾
ret /= 2 - 2 ** (1 - self.octaves)
if self.unbias:
# The output of the plain Perlin noise algorithm has a fairly
# strong bias towards the center due to the central limit theorem
# -- in fact the top and bottom 1/8 virtually never happen. That's
# a quarter of our entire output range! If only we had a function
# in [0..1] that could introduce a bias towards the endpoints...
r = (ret + 1) / 2
# Doing it this many times is a completely made-up heuristic.
for _ in range(int(self.octaves / 2 + 0.5)):
r = smoothstep(r)
ret = r * 2 - 1
return ret
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xavriley commented Apr 21, 2020

Original blog post with instructions and explanation is here

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KaufNation commented Jun 24, 2020

Is this O(1) to calculate any random location on the continuous curve, or is this O(n)?

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Crowkk commented May 15, 2021

Correct me if I'm wrong but there is an inconsistency in this snipet:

    for grid_point in product(*grid_coords):
        if grid_point not in self.gradient:
            self.gradient[grid_point] = self._generate_gradient()
        gradient = self.gradient[grid_point]

        dot = 0
        for i in range(self.dimension):
            dot += gradient[i] * (point[i] - grid_point[i])

When you call self.gradient[grid_point] (say grid_point = [2,3]) you are calling the gradient at row 2 and column 3; But in "position" space it is actually the reverse: the second row is on y = 2 and third col at x = 3 so when you make (point[i] - grid_point[i]) you're calculating the wrong difference because it is reversed. It should be grid_point[::-1][i] at least for 2D;

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somePythonProgrammer commented Dec 4, 2021

This code is very useful for terrain generation. I'll try using it in my game!

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