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use crate::math::{self, scale_shift};
use crate::noise_fns::{MultiFractal, NoiseFn, Perlin, Seedable};
/// Noise function that outputs ridged-multifractal noise.
///
/// This noise function, heavily based on the fBm-noise function, generates
/// ridged-multifractal noise. Ridged-multifractal noise is generated in much
/// the same way as fBm noise, except the output of each octave is modified by
/// an absolute-value function. Modifying the octave values in this way
/// produces ridge-like formations.
///
/// The values output from this function will usually range from -1.0 to 1.0 with
/// default values for the parameters, but there are no guarantees that all
/// output values will exist within this range. If the parameters are modified
/// from their defaults, then the output will need to be scaled to remain in
/// the [-1,1] range.
///
/// Ridged-multifractal noise is often used to generate craggy mountainous
/// terrain or marble-like textures.
#[derive(Clone, Debug)]
pub struct RidgedMulti {
/// Total number of frequency octaves to generate the noise with.
///
/// The number of octaves control the _amount of detail_ in the noise
/// function. Adding more octaves increases the detail, with the drawback
/// of increasing the calculation time.
pub octaves: usize,
/// The number of cycles per unit length that the noise function outputs.
pub frequency: f64,
/// A multiplier that determines how quickly the frequency increases for
/// each successive octave in the noise function.
///
/// The frequency of each successive octave is equal to the product of the
/// previous octave's frequency and the lacunarity value.
///
/// A lacunarity of 2.0 results in the frequency doubling every octave. For
/// almost all cases, 2.0 is a good value to use.
pub lacunarity: f64,
/// A multiplier that determines how quickly the amplitudes diminish for
/// each successive octave in the noise function.
///
/// The amplitude of each successive octave is equal to the product of the
/// previous octave's amplitude and the persistence value. Increasing the
/// persistence produces "rougher" noise.
pub persistence: f64,
/// The attenuation to apply to the weight on each octave. This reduces
/// the strength of each successive octave, making their respective
/// ridges smaller. The default attenuation is 2.0, making each octave
/// half the height of the previous.
pub attenuation: f64,
seed: u32,
sources: Vec<Perlin>,
}
impl RidgedMulti {
pub const DEFAULT_SEED: u32 = 0;
pub const DEFAULT_OCTAVE_COUNT: usize = 6;
pub const DEFAULT_FREQUENCY: f64 = 1.0;
pub const DEFAULT_LACUNARITY: f64 = std::f64::consts::PI * 2.0 / 3.0;
pub const DEFAULT_PERSISTENCE: f64 = 1.0;
pub const DEFAULT_ATTENUATION: f64 = 2.0;
pub const MAX_OCTAVES: usize = 32;
pub fn new() -> Self {
Self {
seed: Self::DEFAULT_SEED,
octaves: Self::DEFAULT_OCTAVE_COUNT,
frequency: Self::DEFAULT_FREQUENCY,
lacunarity: Self::DEFAULT_LACUNARITY,
persistence: Self::DEFAULT_PERSISTENCE,
attenuation: Self::DEFAULT_ATTENUATION,
sources: super::build_sources(Self::DEFAULT_SEED, Self::DEFAULT_OCTAVE_COUNT),
}
}
pub fn set_attenuation(self, attenuation: f64) -> Self {
Self {
attenuation,
..self
}
}
}
impl Default for RidgedMulti {
fn default() -> Self {
Self::new()
}
}
impl MultiFractal for RidgedMulti {
fn set_octaves(self, mut octaves: usize) -> Self {
if self.octaves == octaves {
return self;
}
octaves = math::clamp(octaves, 1, Self::MAX_OCTAVES);
Self {
octaves,
sources: super::build_sources(self.seed, octaves),
..self
}
}
fn set_frequency(self, frequency: f64) -> Self {
Self { frequency, ..self }
}
fn set_lacunarity(self, lacunarity: f64) -> Self {
Self { lacunarity, ..self }
}
fn set_persistence(self, persistence: f64) -> Self {
Self {
persistence,
..self
}
}
}
impl Seedable for RidgedMulti {
fn set_seed(self, seed: u32) -> Self {
if self.seed == seed {
return self;
}
Self {
seed,
sources: super::build_sources(seed, self.octaves),
..self
}
}
fn seed(&self) -> u32 {
self.seed
}
}
/// 2-dimensional `RidgedMulti` noise
impl NoiseFn<[f64; 2]> for RidgedMulti {
fn get(&self, mut point: [f64; 2]) -> f64 {
let mut result = 0.0;
let mut weight = 1.0;
point = math::mul2(point, self.frequency);
for x in 0..self.octaves {
// Get the value.
let mut signal = self.sources[x].get(point);
// Make the ridges.
signal = signal.abs();
signal = 1.0 - signal;
// Square the signal to increase the sharpness of the ridges.
signal *= signal;
// Apply the weighting from the previous octave to the signal.
// Larger values have higher weights, producing sharp points along
// the ridges.
signal *= weight;
// Weight successive contributions by the previous signal.
weight = signal / self.attenuation;
// Clamp the weight to [0,1] to prevent the result from diverging.
weight = math::clamp(weight, 0.0, 1.0);
// Scale the amplitude appropriately for this frequency.
signal *= self.persistence.powi(x as i32);
// Add the signal to the result.
result += signal;
// Increase the frequency.
point = math::mul2(point, self.lacunarity);
}
// Scale and shift the result into the [-1,1] range
let scale = 2.0 - 0.5_f64.powi(self.octaves as i32 - 1);
scale_shift(result, 2.0 / scale)
}
}
/// 3-dimensional `RidgedMulti` noise
impl NoiseFn<[f64; 3]> for RidgedMulti {
fn get(&self, mut point: [f64; 3]) -> f64 {
let mut result = 0.0;
let mut weight = 1.0;
point = math::mul3(point, self.frequency);
for x in 0..self.octaves {
// Get the value.
let mut signal = self.sources[x].get(point);
// Make the ridges.
signal = signal.abs();
signal = 1.0 - signal;
// Square the signal to increase the sharpness of the ridges.
signal *= signal;
// Apply the weighting from the previous octave to the signal.
// Larger values have higher weights, producing sharp points along
// the ridges.
signal *= weight;
// Weight successive contributions by the previous signal.
weight = signal / self.attenuation;
// Clamp the weight to [0,1] to prevent the result from diverging.
weight = math::clamp(weight, 0.0, 1.0);
// Scale the amplitude appropriately for this frequency.
signal *= self.persistence.powi(x as i32);
// Add the signal to the result.
result += signal;
// Increase the frequency.
point = math::mul3(point, self.lacunarity);
}
// Scale and shift the result into the [-1,1] range
let scale = 2.0 - 0.5_f64.powi(self.octaves as i32 - 1);
scale_shift(result, 2.0 / scale)
}
}
/// 4-dimensional `RidgedMulti` noise
impl NoiseFn<[f64; 4]> for RidgedMulti {
fn get(&self, mut point: [f64; 4]) -> f64 {
let mut result = 0.0;
let mut weight = 1.0;
point = math::mul4(point, self.frequency);
for x in 0..self.octaves {
// Get the value.
let mut signal = self.sources[x].get(point);
// Make the ridges.
signal = signal.abs();
signal = 1.0 - signal;
// Square the signal to increase the sharpness of the ridges.
signal *= signal;
// Apply the weighting from the previous octave to the signal.
// Larger values have higher weights, producing sharp points along
// the ridges.
signal *= weight;
// Weight successive contributions by the previous signal.
weight = signal * self.attenuation;
// Clamp the weight to [0,1] to prevent the result from diverging.
weight = math::clamp(weight, 0.0, 1.0);
// Scale the amplitude appropriately for this frequency.
signal *= self.persistence.powi(x as i32);
// Add the signal to the result.
result += signal;
// Increase the frequency.
point = math::mul4(point, self.lacunarity);
}
// Scale and shift the result into the [-1,1] range
let scale = 2.0 - 0.5_f64.powi(self.octaves as i32 - 1);
scale_shift(result, 2.0 / scale)
}
}