terrain_forge/noise/
value.rs

1use super::NoiseSource;
2
3/// Value noise generator (interpolated random values at grid points)
4pub struct Value {
5    seed: u64,
6    frequency: f64,
7}
8
9impl Value {
10    pub fn new(seed: u64) -> Self {
11        Self {
12            seed,
13            frequency: 1.0,
14        }
15    }
16
17    pub fn with_frequency(mut self, frequency: f64) -> Self {
18        self.frequency = frequency;
19        self
20    }
21
22    // Hash to get random value at grid point
23    fn hash(&self, x: i32, y: i32) -> f64 {
24        let h = (x as u64)
25            .wrapping_mul(374761393)
26            .wrapping_add((y as u64).wrapping_mul(668265263))
27            .wrapping_add(self.seed);
28        let h = (h ^ (h >> 13)).wrapping_mul(1274126177);
29        // Convert to [-1, 1]
30        (h as i64 as f64) / (i64::MAX as f64)
31    }
32
33    fn lerp(a: f64, b: f64, t: f64) -> f64 {
34        a + t * (b - a)
35    }
36
37    fn smoothstep(t: f64) -> f64 {
38        t * t * (3.0 - 2.0 * t)
39    }
40}
41
42impl NoiseSource for Value {
43    fn sample(&self, x: f64, y: f64) -> f64 {
44        let x = x * self.frequency;
45        let y = y * self.frequency;
46
47        let x0 = x.floor() as i32;
48        let y0 = y.floor() as i32;
49
50        let dx = Self::smoothstep(x - x0 as f64);
51        let dy = Self::smoothstep(y - y0 as f64);
52
53        let v00 = self.hash(x0, y0);
54        let v10 = self.hash(x0 + 1, y0);
55        let v01 = self.hash(x0, y0 + 1);
56        let v11 = self.hash(x0 + 1, y0 + 1);
57
58        let vx0 = Self::lerp(v00, v10, dx);
59        let vx1 = Self::lerp(v01, v11, dx);
60
61        Self::lerp(vx0, vx1, dy)
62    }
63}
64
65#[cfg(test)]
66mod tests {
67    use super::*;
68
69    #[test]
70    fn value_deterministic() {
71        let noise = Value::new(12345);
72        assert_eq!(noise.sample(1.5, 2.5), noise.sample(1.5, 2.5));
73    }
74
75    #[test]
76    fn value_range() {
77        let noise = Value::new(42);
78        for i in 0..100 {
79            for j in 0..100 {
80                let v = noise.sample(i as f64 * 0.1, j as f64 * 0.1);
81                assert!((-1.0..=1.0).contains(&v), "Value {} out of range", v);
82            }
83        }
84    }
85}
terrain_forge/noise/value.rs

terrain_forge/noise/
value.rs
