veloren/world/src/structure.rs

use vek::*;

pub struct StructureGen2d {
    seed: u32,
    freq: u32,
    spread: u32,
}

impl StructureGen2d {
    pub fn new(seed: u32, freq: u32, spread: u32) -> Self {
        Self { seed, freq, spread }
    }

    fn random(&self, seed: u32, pos: Vec2<i32>) -> u32 {
        let pos = pos.map(|e| (e * 13 + (1 << 31)) as u32);

        let next = (self.seed + seed)
            .wrapping_mul(0x168E3D1F)
            .wrapping_add(0xDEADBEAD);
        let next = next
            .rotate_left(13)
            .wrapping_mul(133227)
            .wrapping_add(pos.x);
        let next = next.rotate_left(13).wrapping_mul(318912) ^ 0x42133742;
        let next = next
            .rotate_left(13)
            .wrapping_mul(938219)
            .wrapping_add(pos.y);
        let next = next.rotate_left(13).wrapping_mul(313322) ^ 0xDEADBEEF;
        let next = next.rotate_left(13).wrapping_mul(929009) ^ 0xFF329DE3;
        let next = next.rotate_left(13).wrapping_mul(422671) ^ 0x42892942;
        next
    }

    pub fn sample(&self, sample_pos: Vec2<i32>) -> [(Vec2<i32>, u32); 9] {
        let mut samples = [(Vec2::zero(), 0); 9];

        let sample_closest = sample_pos.map(|e| e - e.rem_euclid(self.freq as i32));

        for i in 0..3 {
            for j in 0..3 {
                let center = sample_closest
                    + Vec2::new(i, j).map(|e| e as i32 - 1) * self.freq as i32
                    + self.freq as i32 / 2;
                samples[i * 3 + j] = (
                    center
                        + Vec2::new(
                            (self.random(1, center) % (self.spread * 2)) as i32
                                - self.spread as i32,
                            (self.random(2, center) % (self.spread * 2)) as i32
                                - self.spread as i32,
                        ),
                    self.random(3, center),
                );
            }
        }

        samples
    }
}