terrain_forge/noise/
simplex.rs

1use super::NoiseSource;
2
3/// Simplex noise - faster than Perlin with fewer directional artifacts
4pub struct Simplex {
5    seed: u64,
6    frequency: f64,
7}
8
9impl Simplex {
10    const F2: f64 = 0.3660254037844386; // (sqrt(3) - 1) / 2
11    const G2: f64 = 0.21132486540518713; // (3 - sqrt(3)) / 6
12
13    pub fn new(seed: u64) -> Self {
14        Self {
15            seed,
16            frequency: 1.0,
17        }
18    }
19
20    pub fn with_frequency(mut self, frequency: f64) -> Self {
21        self.frequency = frequency;
22        self
23    }
24
25    fn hash(&self, x: i32, y: i32) -> usize {
26        let h = (x as u64)
27            .wrapping_mul(374761393)
28            .wrapping_add((y as u64).wrapping_mul(668265263))
29            .wrapping_add(self.seed);
30        (h ^ (h >> 13)).wrapping_mul(1274126177) as usize % 12
31    }
32
33    fn grad(hash: usize, x: f64, y: f64) -> f64 {
34        const GRAD: [(f64, f64); 12] = [
35            (1.0, 1.0),
36            (-1.0, 1.0),
37            (1.0, -1.0),
38            (-1.0, -1.0),
39            (1.0, 0.0),
40            (-1.0, 0.0),
41            (0.0, 1.0),
42            (0.0, -1.0),
43            (1.0, 1.0),
44            (-1.0, 1.0),
45            (1.0, -1.0),
46            (-1.0, -1.0),
47        ];
48        let (gx, gy) = GRAD[hash];
49        gx * x + gy * y
50    }
51}
52
53impl NoiseSource for Simplex {
54    fn sample(&self, x: f64, y: f64) -> f64 {
55        let x = x * self.frequency;
56        let y = y * self.frequency;
57
58        let s = (x + y) * Self::F2;
59        let i = (x + s).floor() as i32;
60        let j = (y + s).floor() as i32;
61
62        let t = (i + j) as f64 * Self::G2;
63        let x0 = x - (i as f64 - t);
64        let y0 = y - (j as f64 - t);
65
66        let (i1, j1) = if x0 > y0 { (1, 0) } else { (0, 1) };
67
68        let x1 = x0 - i1 as f64 + Self::G2;
69        let y1 = y0 - j1 as f64 + Self::G2;
70        let x2 = x0 - 1.0 + 2.0 * Self::G2;
71        let y2 = y0 - 1.0 + 2.0 * Self::G2;
72
73        let mut n = 0.0;
74        for &(dx, dy, di, dj) in &[(x0, y0, 0, 0), (x1, y1, i1, j1), (x2, y2, 1, 1)] {
75            let t = 0.5 - dx * dx - dy * dy;
76            if t > 0.0 {
77                let t2 = t * t;
78                n += t2 * t2 * Self::grad(self.hash(i + di, j + dj), dx, dy);
79            }
80        }
81        70.0 * n
82    }
83}
84
85#[cfg(test)]
86mod tests {
87    use super::*;
88
89    #[test]
90    fn simplex_deterministic() {
91        let noise = Simplex::new(12345);
92        assert_eq!(noise.sample(1.5, 2.5), noise.sample(1.5, 2.5));
93    }
94
95    #[test]
96    fn simplex_range() {
97        let noise = Simplex::new(42);
98        for i in 0..50 {
99            for j in 0..50 {
100                let v = noise.sample(i as f64 * 0.1, j as f64 * 0.1);
101                assert!((-1.0..=1.0).contains(&v), "Value {} out of range", v);
102            }
103        }
104    }
105}
terrain_forge/noise/simplex.rs

terrain_forge/noise/
simplex.rs
