You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: heightmap_visualization.rs
    path of file: ./repos/veloren/world/examples
    
    the code of the file until where you have to start completion: use image::{
    codecs::png::{CompressionType, FilterType, PngEncoder},
    ImageBuffer, ImageEncoder,
};
use rayon::ThreadPoolBuilder;
use std::{fs::File, io::Write};
use vek::*;
use veloren_world::{
    sim::{FileOpts, WorldOpts, DEFAULT_WORLD_MAP},
    Land, World,
};

fn grey_from_scalar(lo: f32, hi: f32, x: f32) -> [u8; 3] {
    let y = (x - lo) / (hi - lo);
    let z = (y * 255.0) as u8;
    [z, z, z]
}

fn grey_from_scalar_thresh(k: f32) -> impl Fn(f32, f32, f32) -> [u8; 3] {
    move |lo: f32, hi: f32, x: f32| -> [u8; 3] {
        let y = (x - lo) / (hi - lo);
        let y = if y > k {
            let mut y = y;
            // y \in [K, 1.0]
            y -= k;
            // y \in [0.0, 1.0-k]
            y *= 0.5 / (1.0 - k);
            // y \in [0.0, 0.50]
            y + 0.5
        } else {
            0.0
        };
        let z = (y * 255.0) as u8;
        [z, z, z]
    }
}

fn rgb_from_scalar(lo: f32, hi: f32, x: f32) -> [u8; 3] {
    let (lo, hi, x) = if lo < 0.0 {
        (0.0, hi - lo, x - lo)
    } else {
        (lo, hi, x)
    };
    let mid = (hi - lo) / 2.0;
    let r = 0;
    let g = if x < mid {
        0
    } else {
        // x \in [mid, hi]
        let mut g = x - mid;
        // g \in [0, hi-mid]
        g /= hi - mid;
        // g \in [0, 1]
        g *= 255.0;
        // g \in [0, 255]
        g as u8
    };
    let b = if x >= mid {
        255 - ((x - mid) / mid * 255.0) as u8
    } else {
        // x \in [0, mid]
        let mut b = x / mid;
        // b \in [0, 1]
        b *= 255.0;
        // b \in [0, 255]
        b as u8
    };
    [r, g, b]
}

fn image_from_function<F: FnMut(u32, u32) -> [u8; 3]>(
    name: &str,
    width: u32,
    height: u32,
    mut f: F,
) {
    let mut heightmap: ImageBuffer<image
    
fn main() {
    common_frontend::init_stdout(None);
    let pool = ThreadPoolBuilder::new().build().unwrap();
    println!("Loading world");
    let (world, _index) = World::generate(
        59686,
        WorldOpts {
            seed_elements: true,
            world_file: FileOpts::LoadAsset(DEFAULT_WORLD_MAP.into()),
            calendar: None,
        },
        &pool,
        &|_| {},
    );
    println!("Loaded world");

    let land = Land::from_sim(world.sim());
    image_with_autorange("heightmap.png", 1024, 1024, rgb_from_scalar, |x, y| {
        land.get_alt_approx(Vec2::new(x as i32 * 32, y as i32 * 32))
    });
    image_with_autorange(
        "heightmap_big.png",
        1024 * 4,
        1024 * 4,
        rgb_from_scalar,
        |x, y| land.get_alt_approx(Vec2::new(x as i32 * 8, y as i32 * 8)),
    );
    image_with_autorange("heightmap_dx.png", 1024, 1024, grey_from_scalar, |x, y| {
        let mut v = 0.0;
        for i in -1i32..=1 {
            for j in -1i32..=1 {
                let sobel = (2 - i.abs()) * (-j);
                v += sobel as f32
                    * land.get_alt_approx(Vec2::new((x as i32 + i) * 32, (y as i32 + j) * 32));
            }
        }
        v
    });
    image_with_autorange("heightmap_dy.png", 1024, 1024, grey_from_scalar, |x, y| {
        let mut v = 0.0;
        for i in -1i32..=1 {
            for j in -1i32..=1 {
                let sobel = (2 - j.abs()) * (-i);
                v += sobel as f32
                    * land.get_alt_approx(Vec2::new((x as i32 + i) * 32, (y as i32 + j) * 32));
            }
        }
        v
    });
    image_with_autorange(
        "heightmap_magnitude.png",
        1024,
        1024,
        grey_from_scalar,
        |x, y| {
            let mut dx = 0.0;
            for i in -1i32..=1 {
                for j in -1i32..=1 {
                    let sobel = (2 - i.abs()) * (-j);
                    dx += sobel as f32
                        * land.get_alt_approx(Vec2::new((x as i32 + i) * 32, (y as i32 + j) * 32));
                }
            }
            let mut dy = 0.0;
            for i in -1i32..=1 {
                for j in -1i32..=1 {
                    let sobel = (2 - j.abs()) * (-i);
                    dy += sobel as f32
                        * land.get_alt_approx(Vec2::new((x as i32 + i) * 32, (y as i32 + j) * 32));
                }
            }
            (dx * dx + dy * dy).sqrt()
        },
    );
    if false {
        for i in 1..=100 {
            #[rustfmt::skip]
            // convert -delay 10 -loop 0 -dispose previous heightmap_delta_{001..100}.png heightmap_thresholds.gif
            // convert -delay 20 -loop 0 -dispose previous $(seq 1 3 100 | xargs printf "heightmap_delta_%03d.png ") heightmap_thresholds.gif
            image_with_autorange(
                &format!("heightmap_delta_{:03}.png", i),
                1024,
                1024,
                grey_from_scalar_thresh(i as f32 * 0.01),
                |x, y| {
                    let mut v = 0.0;
                    for i in -1i32..=1 {
                        for j in -1i32..=1 {
                            let tmp = if i == 0 && j == 0 {
                                1.0
                            } else if (i + j).abs() == 1 {
                                -0.25
                            } else {
                                0.0
                            };
                            v += tmp as f32
                                * land.get_alt_approx(Vec2::new(
                                    (x as i32 + i) * 32,
                                    (y as i32 + j) * 32,
                                ));
                        }
                    }
                    v
                },
            );
        }
    }
    image_with_autorange(
        "heightmap_max5.png",
        1024,
        1024,
        grey_from_scalar_thresh(0.95),
        |x, y| {
            let mut v = -f32::INFINITY;
            for i in -2i32..=2 {
                for j in -2i32..=2 {
                    if i != 0 || j != 0 {
                        v =
                            v.max(land.get_alt_approx(Vec2::new(
                                (x as i32 + i) * 32,
                                (y as i32 + j) * 32,
                            )));
                    }
                }
            }
            land.get_alt_approx(Vec2::new(x as i32 * 32, y as i32 * 32)) / v
        },
    );
}