Project 2: CS61BYoG


This section will be for any details we believe were not clear enough in the original spec. It is placed at the top for better visibility.


In Project 2, you will create an engine for generating explorable worlds, which for lack of a better word we will call a “game”. This is a large design project that will require you and one partner to work through every stage of development from ideation to presentation. The goal of this project is to teach you how to handle a larger piece of code with little starter code in the hopes of emulating something like a product development cycle. In accordance with this, the grading of this project will be different from other projects. Since there is no notion of “the correct answer” when it comes to game design and implementation, you will be assessed much like a performance review you might receive at an internship or job in addition to a very general autograder. While this means you will be graded slightly subjectively, we promise to be pretty nice bosses and will respect you as any boss should respect their hard working employees. Please talk to us if you feel the grading scheme feels unfair.

A video playlist discussing tips for working on this project can be found at this link. Slides for these videos can be found at this link.

There are several key deadlines for this assignment:

Now on to the assignment spec!


Your task for the next 3 weeks is to design and implement a 2D tile-based game. By “tile-based”, we mean the world for your game will consist of a 2D grid of tiles. By “game” we mean that the player will be able to walk around and interact with the world. Your game will have an overhead perspective. As an example of a much more sophisticated game than you will build, the NES game “Zelda II” is (sometimes) a tile based overhead game:


The game you build can either use graphical tiles (as shown above), or it can use text based tiles, like the game shown below:


We will provide a tile rendering engine, a small set of starter tiles, and the headers for a few required methods that must be implemented for your game and that will be used by the autograder. The project will have two major deadlines. By the first deadline, you should be able to generate random worlds that meet the criteria below. By the second deadline, a player should be able to explore and interact with the world.

The major goal of this project is to give you a chance to attempt to manage the enormous complexity that comes with building a large system. Be warned: The game you build probably isn’t going to be fun! Three weeks is simply not enough time, particularly for novice programmers. However, we do hope you will find it to be a fulfilling project, and the worlds you generate might even be beautiful.

Skeleton Code Structure

The skeleton code contains two key packages that you’ll be using: byog.TileEngine and byog.Core. byog.TileEngine provides some basic methods for rendering, as well as basic code structure for tiles, and contains:

IMPORTANT NOTE: Do NOT change’s charcter field or character() method as it may lead to bad autograder results.

The other package byog.Core contains everything unrelated to tiles. We recommend that you put all of your game code in this package, though this not required. The byog.Core package comes with the following classes:

byog.Core.Game provides two methods for playing your game. The first is public TETile[][] playWithInputString(String input). This method takes as input a series of keyboard inputs, and returns a 2D TETile array representing the state of the universe after processing all the key presses provided in input (described below). The second is public void playWithKeyboard(). This method takes input from the keyboard, and draws the result of each keypress to the screen.

The game engine makes heavy use of StdDraw. You may need to consult the API specification for StdDraw at some points in the project, which can be found here.

Phase 1: World Generation

As mentioned above, the first goal of the project will be to write a world generator. The requirements for your world are listed below:

As an example of a world that meets all of these requirements (click for higher resolution), see the image below. In this image, # represents walls, a dot represents floors, and there is also one golden colored wall segment that represents a locked door. All unused spaces are left blank.


Once you’ve completed lab 5, you can start working on your world generation algorithm without reading or understanding the rest of the spec.

It is very likely that you will end up throwing away your first world generation algorithm. This is normal! In real world systems, it is common to build several completely new versions before getting something you’re happy with. The room generation algorithm above was my 3rd one, and was ultimately much simpler than either of my first two.

You’re welcome to search the web for cool world generation algorithms. You should not copy and paste code from existing games, but you’re welcome to draw inspiration from code on the web. Make sure to cite your sources using @source tags. You can also try playing existing 2D tile based games for inspiration. Brogue is an example of a particularly elegant, beautiful game. Dwarf Fortress is an example of an incredibly byzantine, absurdly complex world generation engine.

The Default Tileset and Tile Rendering Engine

The tile rendering engine we provide takes in a 2D array of TETile objects and draws it to the screen. Let’s call this TETile[][] world for now. world[0][0] corresponds to the bottom left tile of the world. The first coordinate is the x coordinate, e.g. world[9][0] refers to the tile 9 spaces over to the right from the bottom left tile. The second coordinate is the y coordinate, and the value increases as we move upwards, e.g. world[0][5] is 5 tiles up from the bottom left tile. All values should be non-null, i.e. make sure to fill them all in before calling renderFrame. Make sure you understand the orientation of the world grid! If you’re unsure, write short sample programs that draw to the grid to deepen your understanding. If you mix up x vs. y or up vs. down, you’re going to have an incredibly confusing time debugging.

We have provided a small set of default tiles in and these should serve as a good example of how to create TETile objects. We strongly recommend adding your own tiles as well.

The tile engine also supports graphical tiles! To use graphical tiles, simply provide the filename of the tile as the fifth argument to the TETile constructor. Images must be 16 x 16, and should ideally be in PNG format. There are a large number of open source tilesets available online for tile based games. Feel free to use these. Note: Your github accounts are set up to reject files other than .txt or .java files. We will not have access to your tiles when running your code. Make sure to keep your own copy of your project somewhere else other than Github if you want to keep a copy of your project with graphics for archival purposes. Graphical tiles are not required.

If you do not supply a filename or the file cannot be opened, then the tile engine will use the unicode character provided instead. This means that if someone else does not have the image file locally in the same location you specified, the game will still be playable but will use unicode characters instead of textures you chose.

The tile rendering engine relies on StdDraw. We recommend against using StdDraw commands like setXScale or setYScale unless you really know what you’re doing, as you may considerably alter or damage the a e s t h e t i c of the game otherwise.

Starting the Game

Your game must support both methods of starting it, one using the Core.Game.playWithKeyboard() method, and the other using the Core.Game.playWithInputSting(String s) method.

When your Core.Game.playWithKeyboard() method is run, your game must display a Main Menu that provides at LEAST the option to start a new game, load a previously saved game, and quit the game. The Main Menu should be navigable only using the keyboard, using N for “new game”, L for “load game”, and Q for quit. You may include additional options.


After pressing N for “new game”, the user should be prompted to enter a “random seed”, which is an integer of their choosing. This integer will be used to generate the world randomly (as described later and in lab 5). After the user has pressed the final number in their seed, they should press S to tell the game that they’ve entered the entire seed that they want.

The behavior of the “Load” command is described elsewhere in this specification.

If the game instead started with Core.Game.playWithInputString(), no menu should be displayed and nothing should be drawn to the screen. The game should otherwise process the given String as if a human player was pressing the given keys using the Core.Game.playWithKeyboard() method. For example, if we call Core.Game.playWithInputString("N3412S"), the game should generate a world with seed 3412 and return the generated 2D tile array.

We recommend that you do not implement Core.Game.playWithKeyboard() until you get to phase 2 of the project (interactivity), though you’re welcome to do so at anytime. It will be easier to test drive and debug your world generator by using playWithInputString instead.

If you want to allow the user to have additional options, e.g. the ability to pick attributes of their character, specify world generation parameters, etc., you should create additional options. For example, you might add a fourth option “S” to the main menu for “select creature and start new game” if you want the user to be able to pick what sort of creature to play as. These additional options may have arbitrary behavior of your choosing. The behavior of N, L, and Q must be exactly as described in the spec!

Phase 2: Interactivity

In the second phase of the game, you’ll add the ability for the user to actually play the game, and will also add user interface (UI) elements to your game to make it feel more immersive and informative.

The requirements for interactivity are as follows:

Optionally, you may also include game mechanics that allow the player to win or lose (see gold points below). Aside from these feature requirements, there will be a few technical requirements for your game, described in more detail below.

Game UI (User Interface) Appearance

After the user has entered a seed and pressed S, the game should start. The user interface of the game must include:

As an example of the bare minimum, the game below displays a grid of tiles and a HUD that displays the description of the tile under the mouse pointer (click image for higher resolution):


You may include additional features if you choose. In the example below (click image for higher resolution), as with the previous example, the mouse cursor is currently over a wall, so the HUD displays the text “wall” in the top right. However, this game’s HUD also provides the user with 5 hearts representing the player’s “health”. Note that this game does not meet the requirements of the spec above, as it is a large erratic cavernous space, as opposed to rooms connected by hallways.


As an example, the game below (click image for higher resolution) uses the GUI to list additional valid key presses, and provides more verbose information when the user mouses-over a tile (“You see grass-like fungus.”). The image shown below is a professional game, yours isn’t expect to look anywhere near as good.


For information about how to specify the location of the HUD, see the initialize(int width, int height, int xOffset, int yOffset) method of TERenderer or see lab 6.

Game UI Behavior

When the game begins, the user must be in control of some sort of entity that is displayed in the world. The user must be able to move up, left, down, and right using the W, A, S, and D keys, respectively. These keys may also do additional things, e.g. pushing objects. You may include additional keys in your game. The user may not interact with the world using mouse clicks, e.g. no clicking to allow movement.

The game must behave pseudorandomly. That is, given a certain seed, the same set of key presses must yield the exact same results!

In addition to movement keys, if the user enters “:Q”, the game should quit and save. The description of the saving (and loading) function is described in the next section. This command must immediately quit and save, and should require no further keypresses to complete, e.g. do not ask them if they are sure before quitting. We will call this single action of quitting and saving at the same time “quit/saving”.

This project uses StdDraw to handle user input. This results in a couple of important limitations:

Because of the requirement that your game must be playable from a String, your game cannot make use of real time, i.e. your game cannot have any mechanic which depends on a certain amount of time passing in real life, since that would not be captured in an input string and would not lead to deterministic behavior when using that string vs. playing at the keyboard. Keeping track of the number of turns that have elapsed is a perfectly reasonable mechanic,and might be an interesting thing to include in your game, e.g. maybe the game grows steadily darker in color with each step. You’re welcome to include other key presses like allowing the player to press space bar in order to move forwards one time step.

Saving and Loading

Sometimes, you’ll be playing a game, and you suddenly notice that it’s time to go to 61B lecture. For times like those, being able to save your progress and load it later is very handy. Your game must have the ability to save the game while playing and load the game in the exact state of the most recent save after quitting and opening the game back up.

Within a running Java program, we use variables to store and load values. However, to be able to quit the game (kill the program), and then load it back up, we need to have memory that’s a bit more persistent. This means you must save any information that is relevant to the state of the game concretely in a file somewhere you would be able to find when the game is opened again. The technique to accomplish this will be up to you, but we recommend looking into the Java interface Serializable, which is the easiest approach.

When the user restarts Game.main and presses L, the game should into exactly the same state as it was before the game was terminated. This state includes the state of the random number generator! More on this in the next section.

Playing With Input Strings and Phase 2

Your Core.Game.playWithInputString(String s) must be able to handle input strings that include movement

For example, the string “N543SWWWWAA” corresponds to the user starting a game with the seed 543, then moving up four times, then left twice. If we called Core.Game.playWithInputString("N543SWWWWAA"), your game would return a TETile[][] representing the world EXACTLY as it would be if we’d used playWithKeyboard and typed these keys in manually. Since the game must be deterministic given a seed and a string of inputs, this will allow players to replay exactly what happened in their game for a given sequence of inputs. This will also be handy for testing out your code, as well as for our autograder.

Core.Game.playWithInputString(String s) must also be able to handle saving and loading in a replay string, e.g. “N25SDDWD:Q” would correspond to starting a new game with seed 25, then moving right, right, up, right, then quit/saving. The method would then return the 2D TETile[][] array at the time of save. If we then started the game with the replay string “LDDDD”, we’d reload the game we just saved, move right four times, then return the 2D TETile[][] array after the fourth move.

Your game should not change in any way between saves, i.e. the same exact TETile[][] should be returned by the last call to playWithInputString for all of the following scenarios:

we then called playWithInputString with input “L:Q”, we’d expect the exact same world state to be saved and returned as TETile[][] as with the previous call where we provided “LDDDD”.

You do not need to worry about replay strings that contain multiple saves, i.e. “N5SDD:QD:QDD:Q” is not considered a valid replay string, since the game should have terminated before the second :Q. You do not need to worry about invalid replay strings, i.e. you can assume that every replay string provided by the autograder starts with either “N#S” or “L”, where # represents the user entered seed.

The return value of the playWithInputString method should not depend on whether the input string ends with :Q or not. The only difference is whether your game saves or not as a side effect of the method.

Ambition Score

20 points of your project score will be based on features of your choosing, which we call your “ambition score”. The big idea is that beyond the base requirements of this project, we want you to try and polish your product a bit more and add some cool features. Below is a list of features worth a total of 200 points. This “ambition” category is only worth 20 points, i.e. if you do 30 points worth, you do not get extra credit. However, feel free to add as many feature as you’d like if you have the time and inclination.

Your game must still meet the basic requirements described above! For example, if you allow the user to use mouse clicks, the game should still allow keyboard based movement!

This list is by no means comphrehensive of all the things you could do to satisfy Ambition points! If you have another idea for how you want to make your game really cool, fill out this form to submit your idea and how many points you think it should be worth. You will get confirmation if your idea is approved and it may be added to the Ambition list above as well. If you have multiple ideas, please fill out the form once per addition. We will link a list of approved ideas below this line as we approve them. You’re welcome to use these approved ideas as well.

Requirements Summary

A list of the requirements and restrictions on your game. Please note that this section does not substitute reading the entire spec since there are a lot of details which are not captured here.

Gold Points

For gold points, you should make it possible to win or lose your game, and along the way, you should also introduce 3 “creative mechanics”. Mechanics refer to the underlying ways the game is controlled and how outcomes are calculated. The mechanics of a game make up the rulebook for the game and determine what can and cannot happen. Interesting games often have interesting mechanics and interactions that lead to a large variety of game states. For gold points, we are requiring at least 3 “creative mechanics”.

We leave it up to you to define creative mechanics. We aren’t going to police this closely, so creative mechanics will be on the honor system.

After adding your mechanics as well as your win/loss conditions, create a public youtube showcasing your game, including its creative mechanics and win/loss conditions, and submit a link using [this form (link TBA)]. It is not necessary for you to able to actually win your own game, i.e. it’s OK if your game is really hard.


Autograder points: 120 points.

Lab demo: 80 points.

Gold points: 12 gold points.

Lab Demo Checkoff Script

In the hopes of keeping this process as transparent as possible, click here for the exact script the TA or tutor will use when checking your project. By the end of the demo, you should be able to determine exactly what points you received and will have an opportunity to demonstrate any feature which was not checked off during the demo but exists in your project. Note that while some of these features are a bit subjective, this demo is meant to give you a chance to defend your work and was chosen over having us grade it locked behind doors with no input from you. We will respect the amount of work you put into your project and you should have a discussion with us if you believe we are not grading you fairly.

Office Hours

Due to the open-ended nature of this project, it will be hard for the course staff to help you debug your project in the same way that they can for other projects. As a result, we will be implementing the following procedure regarding receiving help during office hours in order to be able to allot an adequate enough time for those that attend.


Q: I want to make a game that’s about exploring the outdoors or caves or something like that, not a bunch of rooms. What should I do? A: That’s fine, you can just use the seed to create a starter house for your character that they can freely exit.

Q: Can I make a world that supports scrolling or multiple levels (i.e. stairs)? A: Sure. In this case, playWitInputString should return only the part of the world that is visible on the screen at the time that the last character in the replay string is entered.

Q: Can I add the ability for players to customize their character before starting a game? A: Yes, but you’ll need to create a fourth main menu option. Your game must support exactly the API described in this spec, i.e. “N23123S” must always start a game with the seed 23123, and must not ask for any additional input from the player.

Q: I’m getting two standard draw windows instead of one. How do I avoid having two StdDraw windows? A:Make sure you’re importing edu.princeton.cs.introcs.StdDraw instead of import edu.princeton.cs.algs4.StdDraw.

Q: Why is the phase 1 autograder saying “Could not initialize class edu.princeton.cs.introcs.StdDraw”? A: Somewhere in your code, your playWithInputString method tries to use the StdDraw class which is not allowed. For example if you call TERenderer.initialize(), you are using StdDraw. No StdDraw window should open when you call playWithInputString. We’ve seen some students whose code only opens a StdDraw window for some seeds, so look very carefully.

Q: The autograder is getting a NumberFormatException caused by Integer.parseInt. A: The Random class takes long as input, so the seeds we provide are too big to fit into an int. You need to use the Long class instead to parse the seed.