lib.rs

use num::complex::Complex;

fn mandelbrot(px: i32, py: i32, width: i32, height: i32) -> i32 {
    let x = (px as f32) / (width  as f32) * 2.5 - 2.0;
    let y = (py as f32) / (height as f32) * 2.0 - 1.0;

    let c = Complex::new(x, y);
    let mut z = Complex::new(0.0, 0.0);
    let mut i = 0;

    while z.norm_sqr() < 4.0 {
        z = z * z + c;
        i += 1;
        if i == 300 { return 0; }
    }

    i
}

#[no_mangle]
pub unsafe extern "C" fn generate_image(buffer: *mut u8, width: i32, height: i32) {
    let data = std::slice::from_raw_parts_mut(buffer, (width * height * 4) as usize);
    let mut offs = 0;
    for y in 0..height {
        for x in 0..width {
            let c = mandelbrot(x, y, width, height);
            data[offs + 0] = (c * 31) as u8;
            data[offs + 1] = (c * 37) as u8;
            data[offs + 2] = (c * 41) as u8;
            data[offs + 3] = 255;
            offs += 4;
        }
    }
}