perx.rs

use std::f32::consts::PI;
use std::io::{BufferedWriter, stdout};
use std::rand::{Rng, StdRng};

struct Vec2 {
    x: f32,
    y: f32,
}

fn lerp(a: f32, b: f32, v: f32) -> f32 { a * (1.0 - v) + b * v }

fn smooth(v: f32) -> f32 { v * v * (3.0 - 2.0 * v) }

fn random_gradient<R: Rng>(r: &mut R) -> Vec2 {
    let v = PI * 2.0 * r.gen();
    Vec2 { x: v.cos(), y: v.sin() }
}

fn gradient(orig: Vec2, grad: Vec2, p: Vec2) -> f32 {
    (p.x - orig.x) * grad.x + (p.y - orig.y) * grad.y
}

struct Noise2DContext {
    rgradients: [Vec2, ..256],
    permutations: [u16, ..256],
}

impl Noise2DContext {
    fn new() -> Noise2DContext {
        let mut rng = StdRng::new();

        let mut rgradients = [Vec2 { x: 0.0, y: 0.0 }, ..256];
        for i in range(0, 256) { rgradients[i] = random_gradient(&mut rng); }

        let mut permutations = [0, ..256];
        for i in range(0u16, 256) { permutations[i] = i; }
        rng.shuffle_mut(permutations);

        Noise2DContext { rgradients: rgradients, permutations: permutations }
    }

    fn get_gradient(&self, x: i32, y: i32) -> Vec2 {
        let idx = self.permutations[x & 255] + self.permutations[y & 255];
        self.rgradients[idx & 255]
    }

    fn get_gradients(&self, x: f32, y: f32) -> ([Vec2, ..4], [Vec2, ..4]) {
        let x0f = x.floor();
        let y0f = y.floor();
        let x1f = x0f + 1.0;
        let y1f = y0f + 1.0;

        let x0 = x0f as i32;
        let y0 = y0f as i32;
        let x1 = x0 + 1;
        let y1 = y0 + 1;

        ([self.get_gradient(x0, y0), self.get_gradient(x1, y0),
          self.get_gradient(x0, y1), self.get_gradient(x1, y1)],
         [Vec2 { x: x0f, y: y0f }, Vec2 { x: x1f, y: y0f },
          Vec2 { x: x0f, y: y1f }, Vec2 { x: x1f, y: y1f }])
    }

    fn get(&self, x: f32, y: f32) -> f32 {
        let p = Vec2 {x: x, y: y};
        let (gradients, origins) = self.get_gradients(x, y);

        let v0 = gradient(origins[0], gradients[0], p);
        let v1 = gradient(origins[1], gradients[1], p);
        let v2 = gradient(origins[2], gradients[2], p);
        let v3 = gradient(origins[3], gradients[3], p);

        let fx = smooth(x - origins[0].x);
        let vx0 = lerp(v0, v1, fx);
        let vx1 = lerp(v2, v3, fx);
        let fy = smooth(y - origins[0].y);

        lerp(vx0, vx1, fy)
    }
}

fn main() {
    let symbols = [' ', '░', '▒', '▓', '█', '█'];
    let mut pixels = [0f32, ..256*256];
    let n2d = Noise2DContext::new();

    for _ in range(0, 100) {
        for y in range(0, 256) {
            for x in range(0, 256) {
                let v = n2d.get(x as f32 * 0.1, y as f32 * 0.1);
                pixels[y*256+x] = v * 0.5 + 0.5;
            }
        }
    }

    let mut out = BufferedWriter::new(stdout());
    for y in range(0, 256) {
        for x in range(0, 256) {
            let idx = (pixels[y*256+x] / 0.2) as uint;
            let _ = out.write_char(symbols[idx]);
        }
        let _ = out.write_char('\n');
    }
    let _ = out.flush();
}