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use bevy::prelude::*; |
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|
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use crate::world::hash2; |
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|
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#[derive(Clone, Copy, Debug)] |
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pub struct Noise { |
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seed: u32, |
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} |
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|
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impl Noise { |
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pub fn new(seed: u32) -> Self { |
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Self { seed } |
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} |
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|
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fn gradient(&self, cell: IVec2) -> Vec2 { |
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let h = hash2( |
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(cell.x as u32).wrapping_add(self.seed.wrapping_mul(0x632B_E5AB)), |
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(cell.y as u32) ^ self.seed.rotate_left(16), |
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); |
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Vec2::from_angle(h as f32 / u32::MAX as f32 * std::f32::consts::TAU) |
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} |
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|
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pub fn sample(&self, p: Vec2) -> f32 { |
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let cell = p.floor(); |
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let f = p - cell; |
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let cell = cell.as_ivec2(); |
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let corner = |offset: IVec2| self.gradient(cell + offset).dot(f - offset.as_vec2()); |
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let u = f * f * f * (f * (f * 6.0 - 15.0) + 10.0); |
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let bottom = corner(IVec2::new(0, 0)).lerp(corner(IVec2::new(1, 0)), u.x); |
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let top = corner(IVec2::new(0, 1)).lerp(corner(IVec2::new(1, 1)), u.x); |
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(bottom.lerp(top, u.y) * std::f32::consts::SQRT_2).clamp(-1.0, 1.0) |
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} |
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|
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pub fn fbm(&self, p: Vec2, octaves: u32) -> f32 { |
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let (mut sum, mut amplitude, mut frequency, mut total) = (0.0, 1.0, 1.0, 0.0); |
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for octave in 0..octaves { |
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let layer = Noise::new(self.seed.wrapping_add(octave)); |
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sum += layer.sample(p * frequency) * amplitude; |
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total += amplitude; |
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amplitude *= 0.5; |
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frequency *= 2.0; |
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} |
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sum / total |
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} |
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} |
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|
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#[cfg(test)] |
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mod tests { |
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use super::*; |
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|
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fn grid() -> impl Iterator<Item = Vec2> { |
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(0..40).flat_map(|y| (0..40).map(move |x| Vec2::new(x as f32 * 0.37, y as f32 * 0.29))) |
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} |
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|
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#[test] |
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fn noise_is_deterministic_per_seed() { |
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let (a, b, c) = (Noise::new(3), Noise::new(3), Noise::new(4)); |
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assert!(grid().all(|p| a.fbm(p, 4) == b.fbm(p, 4))); |
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assert!(grid().any(|p| a.fbm(p, 4) != c.fbm(p, 4))); |
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} |
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|
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#[test] |
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fn noise_stays_in_range() { |
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let noise = Noise::new(9); |
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assert!(grid().all(|p| (-1.0..=1.0).contains(&noise.sample(p)))); |
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assert!(grid().all(|p| (-1.0..=1.0).contains(&noise.fbm(p, 5)))); |
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} |
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|
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#[test] |
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fn noise_is_zero_on_lattice_points() { |
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let noise = Noise::new(1); |
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assert_eq!(noise.sample(Vec2::new(5.0, -3.0)), 0.0); |
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} |
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|
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|
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#[test] |
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fn noise_is_continuous() { |
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let noise = Noise::new(5); |
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for p in grid() { |
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let d = (noise.sample(p) - noise.sample(p + Vec2::splat(0.001))).abs(); |
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assert!(d < 0.01, "jump of {d} at {p}"); |
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} |
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} |
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|
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#[test] |
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fn negative_coordinates_work() { |
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let noise = Noise::new(2); |
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let values: Vec<f32> = (0..20) |
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.map(|i| noise.sample(Vec2::new(-i as f32 * 0.7 - 0.3, -2.4))) |
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.collect(); |
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assert!(values.iter().any(|v| *v != 0.0)); |
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} |
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} |