main.rs

use std::f32;

use num_complex::Complex;

// http://linas.org/art-gallery/escape/smooth.html
fn smooth_iter(i: u32, z: Complex<f32>) -> f32 {
    i as f32 - z.norm().ln().ln() / 2.0f32.ln()
}

// https://github.com/Nuke928/mandelbrot-opengl/blob/039fe9213c01992584f7b391da49bdeeb8d259e2/shader.glsl#L10-L16
fn map_to_color(t: f32) -> (u8, u8, u8) {
    let r = 9.0 * (1.0 - t) * t * t * t;
    let g = 15.0 * (1.0 - t) * (1.0 - t) * t * t;
    let b = 8.5 * (1.0 - t) * (1.0 - t) * (1.0 - t) * t;

    (
        (r * 255.0).min(255.0).floor() as u8,
        (g * 255.0).min(255.0).floor() as u8,
        (b * 255.0).min(255.0).floor() as u8,
    )
}

fn main() {
    let imgx = 2048;
    let imgy = 2048;

    let max_iter = 255;

    let scalex = 3.0 / imgx as f32;
    let scaley = 3.0 / imgy as f32;

    let mut imgbuf = image::ImageBuffer::new(imgx, imgy);

    for (x, y, pixel) in imgbuf.enumerate_pixels_mut() {
        let cx = x as f32 * scalex - 1.5;
        let cy = y as f32 * scaley - 1.5;

        let c = Complex::new(-0.4, 0.6);
        let mut z = Complex::new(cx, cy);

        let mut i = 0u32;
        while i < max_iter && z.norm() <= 2.0 {
            z = z * z + c;
            i += 1;
        }

        // let (r, g, b) = map_to_color(i as f32 / 255.0);

        let (r, g, b) = if i == max_iter {
            (0, 0, 0)
        } else {
            map_to_color(smooth_iter(i, z) / max_iter as f32)
        };

        *pixel = image::Rgb([r, g, b]);
    }

    imgbuf.save("fractal.png").unwrap();
}