This is the first in a series of tutorials on procedural generation with Rust.

Procedural generation is a technique which allows content to be created programmatically, rather than everything in a game being specifically placed by a designer. Procedural generation doesn't mean completely randomised, rather randomised elements are used as long as they make sense.

This tutorial will show how to create a tilemap-based level with rooms connected by straight corridors, using Rust. We'll also cover how to use seeds to reproduce specific layouts and serialise the output into JSON. The rooms will be placed at random within the level, and corridors are drawn horizontally and vertically to connect the centres of the rooms.

The final code can be found on Github.

Setup

You'll need to install Rust - this tutorial uses version 1.27.0 . Once installed, create a binary project with Cargo:

cargo new dungeon --bin

Once created, change into the new folder and run the project to check everything's ok:

cd dungeon cargo run

After compiling, the project should print out "Hello world!" - this is the default boilerplate for projects set up with Cargo.

Create the board

The first step is to create the tilemap which will keep track of empty space and rooms in our level. In src/main.rs we'll create a struct to hold this data:

#[derive(Debug)] struct Level { width : i32 , height : i32 , board : Vec < Vec < i32 >> } impl Level { fn new ( width : i32 , height : i32 ) -> Self { let mut board = Vec :: new ( ) ; for _ in 0 .. height { let row = vec! [ 0 ; width as usize ] ; board . push ( row ) ; } Level { width , height , board } } } fn main ( ) { println! ( "Hello, world!" ) ; let level = Level :: new ( 10 , 8 ) ; println! ( "{:?}" , level ) ; }

When run, this will give you the "Hello world!" phrase, followed by the level, which at the moment is just loads and loads of zeros:

Hello , world! Level { width : 10 , height : 8 , board : [ [ 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 ] , [ 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 ] , [ 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 ] , [ 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 ] , [ 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 ] , [ 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 ] , [ 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 ] , [ 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 ] ] }

The Level struct is pretty basic for now:

#[derive(Debug)] struct Level { width : i32 , height : i32 , board : Vec < Vec < i32 >> }

It contains width and height values, which mark the size of the level. Our example is 10 tiles wide and 8 tiles high - if each tile is 16 pixels, this would make the map dimensions 768x600 pixels.

We're using a two-dimensional array (ie an array containing arrays) to represent the map ( board in the struct). Zero means an empty space, so when we initialise the map everything is empty; rooms and corridors will use ones when we add them. Each array inside board represents a row, and each entry in that array represents a position in that row. For instance, the co-ordinate (8, 6) would be board[6][8] in our struct - the y co-ordinate (6) becomes the first slice parameter to get the row array, then we use the x co-ordinate (8) to get the appropriate item.

You can also use a single-dimension array as the board - there are no nested arrays, so you can directly access each position on the board. This is faster than using a two-dimensional array, but comes at the cost of being slightly less clear, so we'll use the two-dimensional array for now.

We've also added a new function to the Level struct:

impl Level { fn new ( width : i32 , height : i32 ) -> Self { let mut board = Vec :: new ( ) ; for _ in 0 .. height { let row = vec! [ 0 ; width as usize ] ; board . push ( row ) ; } Level { width , height , board } } }

This sets the width and height properties of the struct, and creates a vector for each row:

let row = vec! [ 0 ; width as usize ] ;

Each row is set to contain width number of elements, all set to 0 ; all these rows are then added to the board vector and added to the Level struct. In Rust, vectors are growable arrays which adds a bit of overhead since they need to be able to resize. If we had a static size for the board, so we didn't have width and height in the Level struct, then we could use an array for the board instead of a Vector. Since we're dynamically creating the board size from the width and height, we'll need to use a vector instead.

Display

The #[derive(Debug)] lets us print out the contents of our level, but this is a bit of a mess at the moment with a single line of zeroes. To allow custom formatting, we need to derive the Display trait on Level so we can print out a nice map. The Display trait is pretty simple: we just need to provide a fmt function in an implementation block for our struct, and in the function we can print out whatever we like.

use std :: fmt ; struct Level { ... } impl Level { ... } impl fmt :: Display for Level { fn fmt ( & self , f : & mut fmt :: Formatter ) -> fmt :: Result { for row in 0 .. self . height as usize { for col in 0 .. self . width as usize { write! ( f , "{:?} " , self . board [ row ] [ col ] ) ? } write! ( f , "

" ) ? } Ok ( ( ) ) } } fn main ( ) { let level = Level :: new ( 10 , 8 ) ; println! ( "{}" , level ) ; }

In the fmt function, we're looping through each entry in the board and printing out the {:?} debug string, since each entry is an integer, along with a space, and for each row array we add a line break. Also notice that in main the println has changed from {:?} to {} - the former is for debug printing, and the latter uses our new Display formatting.

Run this code, and the level should look a bit nicer:

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Room

Right, it looks nicer now, but is very boring. Let's do the fun bit, and add some rooms to our map!

Create src/room.rs and add the following:

pub struct Room { pub x : i32 , pub y : i32 , pub x2 : i32 , pub y2 : i32 , pub width : i32 , pub height : i32 , pub centre : ( i32 , i32 ) } impl Room { pub fn new ( x : i32 , y : i32 , width : i32 , height : i32 ) -> Self { Room { x , y , x2 : x + width , y2 : y + height , width , height , centre : ( x + ( width / 2 ) , y + ( height / 2 ) ) } } pub fn intersects ( & self , other : & Self ) -> bool { self . x <= other . x2 && self . x2 >= other . x && self . y <= other . y2 && self . y2 >= other . y } }

The Room struct contains the points of the room's rectangle, along with its' width, height and centre point. The new function saves us having to calculate the points and centre when we call it, and the intersects function will be used when placing rooms to make sure the rooms aren't overlapping.

Refactor Level

Before we start using Room , let's tidy up the Level struct. Create src/level.rs and move all the level-related code into it; update struct Level to pub struct level and fn new to pub fn new :

use std :: fmt ; pub struct Level { width : i32 , height : i32 , board : Vec < Vec < i32 >> } impl Level { pub fn new ( width : i32 , height : i32 ) -> Self { let mut board = Vec :: new ( ) ; for _ in 0 .. height { let row = vec! [ 0 ; width as usize ] ; board . push ( row ) ; } Level { width , height , board } } } impl fmt :: Display for Level { fn fmt ( & self , f : & mut fmt :: Formatter ) -> fmt :: Result { for row in 0 .. self . height as usize { for col in 0 .. self . width as usize { write! ( f , "{:?} " , self . board [ row ] [ col ] ) ? } write! ( f , "

" ) ? } Ok ( ( ) ) } }

The pub annotations allow the struct to be used in other files in our project, otherwise we'd have errors when trying to run the project.

Update main.rs to declare and use Level :

mod level ; use level :: Level ; fn main ( ) { let level = Level :: new ( 10 , 8 ) ; println! ( "{}" , level ) ; }

mod level declares the level module, then use level::Level imports the struct into the main file. Compile and run again to check that everthing's still working with cargo run - you should see the board again.

Let's actually add rooms now! First of all, we need to add the rand crate to our project; this provides random-number functionality which we can use to get different-sized rooms. In Cargo.toml , add rand = "0.5" under the [dependencies] :

# Cargo . toml [ dependencies ] rand = "0.5"

We now need to declare that we're using this crate in main.rs - at the top of the file, add extern crate rand; :

extern crate rand ; ...

And in level.rs we add a use statement so it gets imported:

use rand ; use rand :: prelude :: * ; use std :: fmt ; ...

Run cargo run - this will download and compile the rand crate, then print out exactly the same board as before. The use rand::prelude::* statement imports standard traits and functions from the rand crate - this is a shortcut to having to know exactly which imports you want and listing them all out.

We now need to add a vector to the level to track rooms - this will be used to make sure that no rooms overlap - and add a function which places them.

use std :: fmt ; use rand ; use rand :: prelude :: * ; use room :: Room ; pub struct Level { width : i32 , height : i32 , board : Vec < Vec < i32 >> , rooms : Vec < Room > } impl Level { pub fn new ( width : i32 , height : i32 ) -> Self { let mut board = Vec :: new ( ) ; for _ in 0 .. height { let row = vec! [ 0 ; width as usize ] ; board . push ( row ) ; } Level { width , height , board , rooms : Vec :: new ( ) } } pub fn place_rooms ( & mut self , rng : & mut StdRng ) { let mut rng = rand :: thread_rng ( ) ; let max_rooms = 10 ; let min_room_width = 4 ; let max_room_width = 8 ; let min_room_height = 5 ; let max_room_height = 12 ; for _ in 0 .. max_rooms { let mut x = rng . gen_range ( 0 , self . width ) ; let mut y = rng . gen_range ( 0 , self . height ) ; let width = rng . gen_range ( min_room_width , max_room_width ) ; let height = rng . gen_range ( min_room_height , max_room_height ) ; if x + width > self . width { x = self . width - width ; } if y + height > self . height { y = self . height - height ; } let mut collides = false ; let room = Room :: new ( x , y , width , height ) ; for other_room in & self . rooms { if room . intersects ( & other_room ) { collides = true ; break ; } } if ! collides { self . add_room ( & room ) ; } } } fn add_room ( & mut self , room : & Room ) { for row in 0 .. room . height { for col in 0 .. room . width { let y = ( room . y + row ) as usize ; let x = ( room . x + col ) as usize ; self . board [ y ] [ x ] = 1 ; } } self . rooms . push ( * room ) ; } } impl fmt :: Display for Level { fn fmt ( & self , f : & mut fmt :: Formatter ) -> fmt :: Result { for row in 0 .. self . height as usize { for col in 0 .. self . width as usize { write! ( f , "{:?} " , self . board [ row ] [ col ] ) ? } write! ( f , "

" ) ? } Ok ( ( ) ) } }

You'll notice that the self.rooms.push(*room) throws an error - this is because we only have a reference to room (ie it's passed to add_room as &Room ) so we can't move the struct itself into our rooms array. We could change the parameter to remove the borrow (ie fn add_room(&mut self, room: Room) ), but this will make things a bit hairy later on when we need to use the room data again. Instead, we can derive the Copy trait on Room so that the rooms vector has a copy of the room instead of the original struct:

#[derive(Clone, Copy)] pub struct Room { ... }

The Copy trait requires the Clone trait to be satisfied, so we add both to the room.

Finally, we need to actually call our new function - update main to place rooms:

extern crate rand ; mod room ; mod level ; use level :: Level ; fn main ( ) { let mut level = Level :: new ( 48 , 40 ) ; level . place_rooms ( ) ; println! ( "{}" , level ) ; }

When run, we now have rooms!

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 0 0 0 0 0 0 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 0 0 0 0 0 0 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 0 0 0 0 0 0 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 0 0 0 0 0 0 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 0 0 0 0 0 0 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 0 0 0 0 0 0 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 0 0 0 0 0 0 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 0 0 0 0 0 0 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 0 0 0 0 0 0 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 1 1 1 1 0 0 0 0 0 0 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 0 0 0 0 0 0 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 0 0 0 0 0 0 1 1 1 1 1 1 0 0 0 0 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 0 0 0 0 0 0 1 1 1 1 1 1 0 0 0 0 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 0 1 1 1 1 1 1 0 0 0 0 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 0 1 1 1 1 1 1 0 0 0 0 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Seedable

If you run the programme several times, you'll notice that the layout changes each time. When using procedural generation, it's nice to have reproducible output so you can re-use levels you like. The way we do this is by using a seedable random number generator, which will produce the same random numbers when given the same initial value. This means that every time we use the same seed, we'll get the same level out, which is how things like the Spelunky daily challenges work - everyone gets the same seed which generates the same levels.

The rand crate provides this functionality, so we all we need to do is change where the type of random number generator, and make sure we use the same one throughout the code.

I've found the SeedableRng provided by the rand crate to be a bit picky in what it accepts as a seed, so we'll add a couple of crates to help create a seed in the correct format.

In Cargo.toml, add sha2 and arrayref crates:

# Cargo . toml [ dependencies ] arrayref = "0.3.4" rand = "0.5" sha2 = "0.7.1"

SeedableRng requires an array of 32 u8 items, so these crates will help us turn a string of text into the appropriate format. Sha2 provides hash functions, so we can use this to turn a string of any length into a string 64 characters long; arrayref provides a macro to turn a string's bytes into the format required by SeedableRng because it can't accept String::as_bytes directly.

In main.rs , we need to declare the crates and use them, then set up the hash to pass into the random number generator:

extern crate rand ; extern crate sha2 ; #[macro_use] extern crate arrayref ; mod room ; mod level ; use sha2 :: { Sha256 , Digest } ; use rand :: prelude :: * ; use level :: Level ; fn create_hash ( text : & str ) -> String { let mut hasher = Sha256 :: default ( ) ; hasher . input ( text . as_bytes ( ) ) ; format! ( "{:x}" , hasher . result ( ) ) } fn main ( ) { let hash = create_hash ( "manuelneuersweeperkeeper" ) ; let seed = array_ref! ( hash . as_bytes ( ) , 0 , 32 ) ; let mut rng : StdRng = SeedableRng :: from_seed ( * seed ) ; let mut level = Level :: new ( 48 , 40 ) ; level . place_rooms ( & mut rng ) ; println! ( "{}" , level ) ; }

And then tweak level.rs so place_rooms takes rng as a parameter

use std :: fmt ; use rand :: prelude :: * ; use room :: Room ; pub fn place_rooms ( & mut self , rng : & mut StdRng ) { let max_rooms = 10 ; let min_room_width = 4 ; let max_room_width = 8 ; ...

Run the project again - cargo run - Cargo will download the crates then compile the project. You should now see the same map every time you run the project - try changing the hash string for different maps.

Full listing

main.rs

extern crate rand ; extern crate sha2 ; #[macro_use] extern crate arrayref ; mod room ; mod level ; use sha2 :: { Sha256 , Digest } ; use rand :: prelude :: * ; use level :: Level ; fn create_hash ( text : & str ) -> String { let mut hasher = Sha256 :: default ( ) ; hasher . input ( text . as_bytes ( ) ) ; format! ( "{:x}" , hasher . result ( ) ) } fn main ( ) { let hash = create_hash ( "manuelneuersweeperkeeper" ) ; let seed = array_ref! ( hash . as_bytes ( ) , 0 , 32 ) ; let mut rng : StdRng = SeedableRng :: from_seed ( * seed ) ; let mut level = Level :: new ( 48 , 40 ) ; level . place_rooms ( & mut rng ) ; println! ( "{}" , level ) ; }

level.rs

use std :: fmt ; use rand :: prelude :: * ; use room :: Room ; pub struct Level { width : i32 , height : i32 , board : Vec < Vec < i32 >> , rooms : Vec < Room > } impl Level { pub fn new ( width : i32 , height : i32 ) -> Self { let mut board = Vec :: new ( ) ; for _ in 0 .. height { let row = vec! [ 0 ; width as usize ] ; board . push ( row ) ; } Level { width , height , board , rooms : Vec :: new ( ) } } pub fn place_rooms ( & mut self , rng : & mut StdRng ) { let max_rooms = 10 ; let min_room_width = 4 ; let max_room_width = 8 ; let min_room_height = 5 ; let max_room_height = 12 ; for _ in 0 .. max_rooms { let mut x = rng . gen_range ( 0 , self . width ) ; let mut y = rng . gen_range ( 0 , self . height ) ; let width = rng . gen_range ( min_room_width , max_room_width ) ; let height = rng . gen_range ( min_room_height , max_room_height ) ; if x + width > self . width { x = self . width - width ; } if y + height > self . height { y = self . height - height ; } let mut collides = false ; let room = Room :: new ( x , y , width , height ) ; for other_room in & self . rooms { if room . intersects ( & other_room ) { collides = true ; break ; } } if ! collides { self . add_room ( & room ) ; } } } fn add_room ( & mut self , room : & Room ) { for row in 0 .. room . height { for col in 0 .. room . width { let y = ( room . y + row ) as usize ; let x = ( room . x + col ) as usize ; self . board [ y ] [ x ] = 1 ; } } self . rooms . push ( * room ) ; } } impl fmt :: Display for Level { fn fmt ( & self , f : & mut fmt :: Formatter ) -> fmt :: Result { for row in 0 .. self . height as usize { for col in 0 .. self . width as usize { write! ( f , "{:?} " , self . board [ row ] [ col ] ) ? } write! ( f , "

" ) ? } Ok ( ( ) ) } }

room.rs

#[derive(Clone, Copy)] pub struct Room { pub x : i32 , pub y : i32 , pub x2 : i32 , pub y2 : i32 , pub width : i32 , pub height : i32 , pub centre : ( i32 , i32 ) } impl Room { pub fn new ( x : i32 , y : i32 , width : i32 , height : i32 ) -> Self { Room { x , y , x2 : x + width , y2 : y + height , width , height , centre : ( x + ( width / 2 ) , y + ( height / 2 ) ) } } pub fn intersects ( & self , other : & Self ) -> bool { self . x <= other . x2 && self . x2 >= other . x && self . y <= other . y2 && self . y2 >= other . y } }

Refactor using Enums

At the moment, we've got a few magic numbers floating around - 0 for empty spaces, and 1 for rooms, so before we add more of them with corridors, let's tidy those up. We'll create an enum for tile types which we'll use instead of numbers, and implement the Display trait so they still show up as zeroes and ones. Even though we only have two types of tiles at the moment, using an enum makes it easy to extend - we could add doors or pits of lava - and see which tile is being used in each function.

In level.rs , create a new Tile enum:

#[derive(Clone)] pub enum Tile { Empty , Walkable } impl fmt :: Display for Tile { fn fmt ( & self , f : & mut fmt :: Formatter ) -> fmt :: Result { match self { Tile :: Empty => write! ( f , "0" ) , Tile :: Walkable => write! ( f , "1" ) } } }

We define two variations in the Tile enum, Empty and Walkable which will represent empty areas and rooms/corridors respectively. The Display trait simply checks which tile variation is currently being printed, then prints a string of "0" or "1" - this will mean we can drop this replacement in and see the same map as before.

Update the Level implementation to use the enum:

pub struct Level { width : i32 , height : i32 , board : Vec < Vec < Tile >> , rooms : Vec < Room > } impl Level { pub fn new ( width : i32 , height : i32 ) -> Self { let mut board = Vec :: new ( ) ; for _ in 0 .. height { let row = vec! [ Tile :: Empty ; width as usize ] ; board . push ( row ) ; } Level { width , height , board , rooms : Vec :: new ( ) } } fn add_room ( & mut self , room : & Room ) { for row in 0 .. room . height { for col in 0 .. room . width { let y = ( room . y + row ) as usize ; let x = ( room . x + col ) as usize ; self . board [ y ] [ x ] = Tile :: Walkable ; } } self . rooms . push ( * room ) ; } ... } impl fmt :: Display for Level { fn fmt ( & self , f : & mut fmt :: Formatter ) -> fmt :: Result { for row in 0 .. self . height as usize { for col in 0 .. self . width as usize { write! ( f , "{} " , self . board [ row ] [ col ] ) ? } write! ( f , "

" ) ? } Ok ( ( ) ) } }

Run cargo run again - you should see the same output. Right, on to the corridors!

Corridors

Let's connect our rooms together so it's more of a useful dungeon. The procedure for adding corridors is going to be very basic - we'll loop through all the rooms in the level, and connect the centre point of each pair with vertical and horizontal lines.

To make the corridor functions a bit more readable, we'll change the Room struct's centre from a tuple into a struct - this will allow us to name the centre point's co-ordinates so we can access them via centre.x / centre.y rather than centre.0 / centre.1 .

#[derive(Debug, Clone, Copy)] pub struct Point { pub x : i32 , pub y : i32 } #[derive(Clone, Copy)] pub struct Room { ... pub centre : Point } impl Room { pub fn new ( x : i32 , y : i32 , width : i32 , height : i32 ) -> Self { Room { ... centre : Point { x : x + ( width / 2 ) , y : y + ( height / 2 ) } } } ...

That's the last bit of refactoring for now, promise! Right, update the Level impl block in level.rs with three functions:

... impl Level { ... pub fn place_corridors ( & mut self , rng : & mut StdRng ) { for i in 0 .. ( self . rooms . len ( ) - 1 ) { let room = self . rooms [ i ] ; let other = self . rooms [ i + 1 ] ; match rng . gen_range ( 0 , 2 ) { 0 => { match room . centre . x <= other . centre . x { true => self . horz_corridor ( room . centre . x , other . centre . x , room . centre . y ) , false => self . horz_corridor ( other . centre . x , room . centre . x , room . centre . y ) } match room . centre . y <= other . centre . y { true => self . vert_corridor ( room . centre . y , other . centre . y , other . centre . x ) , false => self . vert_corridor ( other . centre . y , room . centre . y , other . centre . x ) } } _ => { match room . centre . y <= other . centre . y { true => self . vert_corridor ( room . centre . y , other . centre . y , other . centre . x ) , false => self . vert_corridor ( other . centre . y , room . centre . y , other . centre . x ) } match room . centre . x <= other . centre . x { true => self . horz_corridor ( room . centre . x , other . centre . x , room . centre . y ) , false => self . horz_corridor ( other . centre . x , room . centre . x , room . centre . y ) } } } } } fn horz_corridor ( & mut self , start_x : i32 , end_x : i32 , y : i32 ) { for col in start_x .. end_x + 1 { self . level . board [ y as usize ] [ col as usize ] = Tile :: Walkable ; } } fn vert_corridor ( & mut self , start_y : i32 , end_y : i32 , x : i32 ) { for row in start_y .. end_y + 1 { self . level . board [ row as usize ] [ x as usize ] = Tile :: Walkable ; } } }

and update main.rs to call place_corridors :

... fn main ( ) { let hash = create_hash ( "manuelneuersweeperkeeper" ) ; let seed = array_ref! ( hash . as_bytes ( ) , 0 , 32 ) ; let mut rng : StdRng = SeedableRng :: from_seed ( * seed ) ; let mut level = Level :: new ( 48 , 40 ) ; level . place_rooms ( & mut rng ) ; level . place_corridors ( & mut rng ) ; println! ( "{}" , level ) ; }

If you run the project again, you'll see we've connected the rooms with corridors.

Corridor placement

Let's go into a bit more detail about the corridor placement.

pub fn place_corridors ( & mut self , rng : & mut StdRng ) { for i in 0 .. ( self . rooms . len ( ) - 1 ) { let room = self . rooms [ i ] ; let other = self . rooms [ i + 1 ] ;

As with the place_rooms function, we pass in the seeded random number generator so that the placement is repeatable with the same seed. We then start going through each room that's been placed in the level as a pair, starting with the first and second. The next loop will pick the second and third, then the third and fourth, and so on; once we get to the second-to-last and last then that's the final loop. This means that the last room won't connect with the first room - this could be changed by checking if we're at the last element then using the first room as other .

match rng . gen_range ( 0 , 2 ) { 0 => { } , _ => { } , }

Next, we decide whether to start with a horizontal or vertical corridor between rooms. This adds a bit of variety to the corridors, since we don't want every corridor to always start horizontally. The range is between 0 and 2 since gen_range includes the lower bound (0) but excludes the upper (2), and we want a fifty-fifty split.

The horz_corridor and vert_corridor are very simple functions - they simply create a straight line of walkable tiles between two points. The line goes from the centre point of the first room all the way to the centre point of the next room, at which point the opposite corridor function is called to join the corridors together. The room.centre.x <= other.centre.x checks before the corridor function calls are because ranges in Rust - 0..x - will only work with positive numbers, so we need to make sure the first parameter is the room with the smallest centre co-ordinate ( x or y depending on whether its horizontal or vertical).

Running the project again should now give you a map with several rooms connected with corridors!

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JSON

We can print the map out in the console, but it's not much use there. We can convert the level into JSON so it can be exported and used in a game using serde .

In Cargo.toml , add serde , serde_json and serde_derive :

# Cargo . toml [ dependencies ] arrayref = "0.3.4" rand = "0.5" sha2 = "0.7.1" serde = "1.0.68" serde_derive = "1.0.68" serde_json = "1.0.22"

serde is a serialisation and deserialisation crate which contains the core functions, while serde_json is specifically for converting JSON data. serde_derive is an incredibly useful crate which allows most Rust data structures to be automatically converted by deriving the Serialize or Deserialize traits.

In main.rs , import the crates:

#[macro_use] extern crate serde_derive ; extern crate serde ; extern crate serde_json ; ...

Then we need to derive Serialize on our structs so we can convert the level into JSON.

... #[derive(Clone, Serialize)] pub enum Tile { ... } ... #[derive(Serialize)] pub struct Level { ...

#[derive(Debug, Clone, Copy, Serialize)] pub struct Point { pub x : i32 , pub y : i32 } #[derive(Clone, Copy, Serialize)] pub struct Room { ...

We have to add Serialize to all the structs used by Level to be able to serialise it completely: Tile and Room are used directly in Level , and Point is used in Room . If you leave one of those out, you'll see an error message complaining that the Serialize trait is not satisfied, so you should be able to track down everything you need to mark as serialisable. Primitive types, like i32, are already implemented in serde, so we don't need to do anything extra with the level's width or height properties.

Once this is done, update main.rs again to actually serialise the level and print it out:

fn main ( ) { let hash = create_hash ( "manuelneuersweeperkeeper" ) ; let seed = array_ref! ( hash . as_bytes ( ) , 0 , 32 ) ; let mut rng : StdRng = SeedableRng :: from_seed ( * seed ) ; let mut level = Level :: new ( 48 , 40 ) ; level . place_rooms ( & mut rng ) ; level . place_corridors ( & mut rng ) ; let serialised = serde_json :: to_string ( & level ) . unwrap ( ) ; println! ( "{:?}" , serialised ) ; }

Run the project again, and...

" { \"width\" : 48 , \"height\" : 40 , \"board\" : [ [ \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" ] , [ \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Walkable\" , \"Walkable\" , \"Walkable\" , \"Walkable\" , \"Walkable\" , \"Walkable\" , \"Walkable\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , \"Empty\" , ... snip ... ] ] , \ "rooms\":[{\"x\":35,\"y\":25,\"x2\":42,\"y2\":32,\"width\":7,\"height\":7,\"centre\":{\"x\":38,\"y\":28}},{\"x\":32,\"y\":13,\"x2\":38,\"y2\":20,\"width\":6,\"height\":7,\"centre\":{\"x\":35,\"y\":16}},{\"x\":1,\"y\":21,\"x2\":7,\"y2\":29,\"width\":6,\"height\":8,\"centre\":{\"x\":4,\"y\":25}},{\"x\":15,\"y\":1,\"x2\":22,\"y2\":10,\"width\":7,\"height\":9,\"centre\":{\"x\":18,\"y\":5}},{\"x\":14,\"y\":15,\"x2\":20,\"y2\":25,\"width\":6,\"height\":10,\"centre\":{\"x\":17,\"y\":20}}]}"

Right. Not quite what we had in mind.

Custom serialisation

The default serialisation for the Tile enum is just using a string, in this case "Empty" or "Walkable", which is far from readable. However, it's easy enough to create our own custom serialisation with Serde - all we need to do is implement it for Tile like we already have with Display, and then we can output whatever we like as JSON.

In level.rs , remove the Serialize derive tag from Tile , then add a new implementation block:

use serde :: { Serialize , Serializer } ; #[derive(Clone)] pub enum Tile { Empty , Walkable } impl Serialize for Tile { fn serialize < S > ( & self , serializer : S ) -> Result < S :: Ok , S :: Error > where S : Serializer { match self { Tile :: Empty => serializer . serialize_i32 ( 0 ) , Tile :: Walkable => serializer . serialize_i32 ( 1 ) } } } ...

The serialize function has quite a complicated-looking method signature:

fn serialize < S > ( & self , serializer : S ) -> Result < S :: Ok , S :: Error > where S : Serializer {

S is a serialiser of any format - Serde can be for JSON or a number of other formats - so this implementation block is generic: you should be able to add other serialisations without having to change this code. The code in the function is very similar to Tile's Display implementation: we check the type of the Tile enum, then return a serialised i32 , either zero or one, depending on the enum value.

Run the project again, and this time the serialised output should look much nicer!

" { \"width\" : 48 , \"height\" : 40 , \"board\" : [ [ 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 ] [ 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 1 , 1 , 1 , 1 , 1 , 1 , 1 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 ] , [ 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 1 , 1 , 1 , 1 , 1 , 1 , 1 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 ] , [ 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 1 , 1 , 1 , 1 , 1 , 1 , 1 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 ] , [ 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 1 , 1 , 1 , 1 , 1 , 1 , 1 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 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\"centre\" : { \"x\" : 38 , \"y\" : 28 } } , { \"x\" : 32 , \"y\" : 13 , \"x2\" : 38 , \"y2\" : 20 , \"width\" : 6 , \"height\" : 7 , \"centre\" : { \"x\" : 35 , \"y\" : 16 } } , { \"x\" : 1 , \"y\" : 21 , \"x2\" : 7 , \"y2\" : 29 , \"width\" : 6 , \"height\" : 8 , \"centre\" : { \"x\" : 4 , \"y\" : 25 } } , { \"x\" : 15 , \"y\" : 1 , \"x2\" : 22 , \"y2\" : 10 , \"width\" : 7 , \"height\" : 9 , \"centre\" : { \"x\" : 18 , \"y\" : 5 } } , { \"x\" : 14 , \"y\" : 15 , \"x2\" : 20 , \"y2\" : 25 , \"width\" : 6 , \"height\" : 10 , \"centre\" : { \"x\" : 17 , \"y\" : 20 } } ] } "

Changing hashes

At the moment, to create a new map we have to change the string we're using to create the hash in main.rs , then recompile the entire project and run it: quite a slow process. Instead, let's allow a string to be passed to the programme at runtime so we can create new levels without having to re-compile the project every time.

In main.rs , update the main function to read command-line arguments:

... use rand :: distributions :: Alphanumeric ; ... fn main ( ) { let hash = match std :: env :: args ( ) . nth ( 1 ) { Some ( text ) => create_hash ( & text ) , None => create_hash ( & thread_rng ( ) . sample_iter ( & Alphanumeric ) . take ( 32 ) . collect :: < String > ( ) ) } ; let seed = array_ref! ( hash . as_bytes ( ) , 0 , 32 ) ; let mut rng : StdRng = SeedableRng :: from_seed ( * seed ) ; let mut level = Level :: new ( 48 , 40 ) ; level . place_rooms ( & mut rng ) ; level . place_corridors ( & mut rng ) ; println! ( "{}" , level ) ; let serialised = serde_json :: to_string ( & level ) . unwrap ( ) ; println! ( "{:?}" , serialised ) ; }

hash is now replaced with a match : std::env::args::nth(1) tries to read the second argument to the programme and if it exists, passes it to the create_hash function. (The second argument is used since the first is the name of the programme). If no argument was passed, we create a random thirty-two character string and pass that to create_hash ; whichever path is taken, we set the result back to hash which is then used as the seed.

Now, if you run the project and pass "manuelneuersweeperkeeper", you should see the same output as before:

cargo run manuelneuersweeperkeeper

If you just run cargo run then a random string is created and used instead, and you get a different map every time. However, if you like one of the maps it creates, there's no way to re-use the seed because firstly, we don't know what the random seed was, and secondly, there's no way to pass a seed without it being hashed.

Save hash

Let's update the Level struct so we can keep track of the seed used to create the level - that way, when we print the serialised JSON, we can easily retrieve the seed so we can re-create a level.

In level.rs we need to add a property to store the hash, then update the new function and pass the hash in where we create the level in main.rs .

... #[derive(Serialize)] pub struct Level { width : i32 , height : i32 , board : Vec < Vec < Tile >> , rooms : Vec < Room > , hash : String } impl Level { pub fn new ( width : i32 , height : i32 , hash : & String ) -> Self { let mut board = Vec :: new ( ) ; for _ in 0 .. height { let row = vec! [ Tile :: Empty ; width as usize ] ; board . push ( row ) ; } Level { width , height , board , rooms : Vec :: new ( ) , hash : hash . clone ( ) } } ...

... fn main ( ) { let hash = match std :: env :: args ( ) . nth ( 1 ) { Some ( text ) => create_hash ( & text ) , None => create_hash ( & thread_rng ( ) . sample_iter ( & Alphanumeric ) . take ( 32 ) . collect :: < String > ( ) ) } ; let seed = array_ref! ( hash . as_bytes ( ) , 0 , 32 ) ; let mut rng : StdRng = SeedableRng :: from_seed ( * seed ) ; let mut level = Level :: new ( 48 , 40 , & hash ) ; level . place_rooms ( & mut rng ) ; level . place_corridors ( & mut rng ) ; println! ( "{}" , level ) ; let serialised = serde_json :: to_string ( & level ) . unwrap ( ) ; println! ( "{:?}" , serialised ) ; }

Now when we run the project, the level prints out the hash used to create the level:

{ "width" : 48 , "height" : 40 , "board" : [ [ 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 ] , [ 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 1 , 1 , 1 , 1 , 1 , 1 , 1 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 ] , [ 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 1 , 1 , 1 , 1 , 1 , 1 , 1 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 ] , [ 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 1 , 1 , 1 , 1 , 1 , 1 , 1 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 ] , [ 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 1 , 1 , 1 , 1 , 1 , 1 , 1 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 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"y" : 28 } } , { "x" : 32 , "y" : 13 , "x2" : 38 , "y2" : 20 , "width" : 6 , "height" : 7 , "centre" : { "x" : 35 , "y" : 16 } } , { "x" : 1 , "y" : 21 , "x2" : 7 , "y2" : 29 , "width" : 6 , "height" : 8 , "centre" : { "x" : 4 , "y" : 25 } } , { "x" : 15 , "y" : 1 , "x2" : 22 , "y2" : 10 , "width" : 7 , "height" : 9 , "centre" : { "x" : 18 , "y" : 5 } } , { "x" : 14 , "y" : 15 , "x2" : 20 , "y2" : 25 , "width" : 6 , "height" : 10 , "centre" : { "x" : 17 , "y" : 20 } } ] , "hash" : "e8edd254c4ffece9f4937b4f1bae4ef6aec4124f86eee0c09428afac036cef47" }

However, we still don't have a way to pass a seed we already have in to our programme, such as when we use a randomised string. Rather than use positional arguments - so assuming the first argument is going to be a string to hash - let's use a crate to parse command line arguments.

Parse arguments with Clap

Clap is a handy crate which handles reading and parsing arguments to your programme. Add clap = "2.32.0" to Cargo.toml :

# Cargo . toml ... [ dependencies ] arrayref = "0.3.4" clap = "2.32.0" rand = "0.5" sha2 = "0.7.1" serde = "1.0.68" serde_derive = "1.0.68" serde_json = "1.0.22"

then update main.rs to handle arguments:

extern crate clap ; use clap :: { App , Arg } ; ... fn main ( ) { let matches = App :: new ( "Dungeon" ) . version ( "1.0" ) . author ( "James Baum <@whostolemyhat>" ) . arg ( Arg :: with_name ( "text" ) . short ( "t" ) . long ( "text" ) . takes_value ( true ) . help ( "A string to hash and use as a seed" ) ) . arg ( Arg :: with_name ( "seed" ) . short ( "s" ) . long ( "seed" ) . takes_value ( true ) . help ( "An existing seed. Must be 32 characters" ) ) . get_matches ( ) ; let seed : String = match matches . value_of ( "seed" ) { Some ( text ) => { if text . chars ( ) . count ( ) < 32 { panic! ( "Seed must be 32 characters long. Use -t option to create a new seed." ) } text . to_string ( ) } , None => { match matches . value_of ( "text" ) { Some ( text ) => create_hash ( & text ) , None => create_hash ( & thread_rng ( ) . sample_iter ( & Alphanumeric ) . take ( 32 ) . collect :: < String > ( ) ) } } } ; let seed_u8 = array_ref! ( seed . as_bytes ( ) , 0 , 32 ) ; let mut rng : StdRng = SeedableRng :: from_seed ( * seed_u8 ) ; let mut level = Level :: new ( 48 , 40 , & seed ) ; level . place_rooms ( & mut rng ) ; level . place_corridors ( & mut rng ) ; let serialised = serde_json :: to_string ( & level ) . unwrap ( ) ; println! ( "{}" , serialised ) ; }

Compile and run the project with cargo run - you should see the level created with a random seed (eg 8c8f397f8ce594a8669617c6ab347f5778b973d33df2977d1334803de715f753 ). You can now use that seed and pass it to your programme to re-create the level with the -s flag:

cargo run -- -s 8c8f397f8ce594a8669617c6ab347f5778b973d33df2977d1334803de715f753 , and you should see the same level.

If you want to pass text as before, then use the -t flag: cargo run -- -t manuelneuersweeperkeeper .

Note the double dash in the run command ( -- ) - this is only used when running with Cargo, otherwise your arguments would be passed to Cargo and not your programme. When using the compiled output, you don't need the extra dashes: levelgen -s 8c8f397f8ce594a8669617c6ab347f5778b973d33df2977d1334803de715f753 .

With Clap, you could also set up other parameters to be read in, such as the board size or number of rooms. These parameters would have to be the same every time if you wanted to re-create a level.

The end

That's it! There are a few things you could play around with, such as the size or number of rooms in a level, or whether to use certain types of corridors, or even unit tests since Rust makes that really easy!. In the next part, we'll cover using the JSON output to draw the maps, and also look at different algorithms to place and join rooms.

The final code can be found on Github.