Scott Kim & Alexey Pajitnov
March 15, 1999
Game Developers Conference
These are presentation slides from an all-day tutorial given at the 1999 Game Developers Conference</A> in San Jose. This copy of the slides was taken from www.scottkim.com/articles. All screen shots are copyrighted by the respective game publishers.
Whether you are designing levels for an cartridge-based action puzzle game, creating puzzle templates for a CD-ROM puzzle anthology, adding puzzles to an adventure game, or designing an educational game, you need to know how to design good puzzles.
Mental challenge Marketable?
Easy to program Hard to invent?
Growing market Small market?
The good news is that puzzles appeal widely to both males and females of all ages. Although the current market is small, it is rapidly expanding, as computers become a mass market commodity and players demand familiar family games.
Examples: Pipe Dream, Honey Way, Lineman
Examples: Fool, Incred Machine, Puzzle Zone
Case Study: Jesse’s Strips
Case Study: Charlie Blast’s Territory
Case Study: Scott Kim’s Puzzle Box
Exercises: Idea Invention, Word SokobanOutline
We’ll start by surveying examples of outstanding puzzle games. Then Alexey and I will go into detail about some of our current projects. I’ll describe the eight steps in the puzzle design process. Finally we’ll split into groups of five people each and do projects.
What every puzzle designer should know
Here are four basic ways to categorize the types of possible puzzle games.
There are four types of play. Noninteractive experiences include books and movies. A Toy has no set goal. A Puzzle has a goal: find the solution. The goal of a Game is to beat another player. Each type of play builds on the previous type: a puzzle should first be a good toy.
Action puzzle games have time pressure and a way to fix mistakes. Story puzzle games have puzzles that advance the plot. Strategy puzzle games are based on multiplayer games. Construction puzzle games let you build something. Pure puzzle games are just puzzles.
Different people play puzzls for different reasons. Some see puzzles as metaphors for spiritual journeys. Puzzle fans like the challenge of finding the answer. Tetris and Solitaire players use puzzles as light distractions. People buy Disney titles for the familiar characters.
People who play puzzles tend to prefer one of three basic types: Word, Image or Logic puzzles. Each of these types of puzzle uses a different mode of thought. Of course some puzzles combine more than one mode. For instance, Hangman is a logical word game.
Here are some of our favorite puzzle games (other than ones we have designed). We chose examples that cover the full range of issues that arise in designing puzzle games.
Although Pipe Dream could be classified as an action puzzle game, at its heart it is a construction game. Other examples of constructive puzzles are: Lemmings, The Incredible Machine, Puyo-Puyo.
To make the concept of constructing a path more suitable for a computer game we restrict lines to a square grid.
Seven pieces is a magic number. Tetris has seven pieces. Psychologists have found the human short term memory can hold about seven things (plus or minus two). That is why 7-digit telephone numbers are so much easier to remember than 10-digit numbers.
So this is the concept.
To make a game, we need to specify these design elements.
Objects 4 corners, 2 lines, 1 cross
Rules Source of pieces: 5-cell stack
User interface Click to place; replace takes time
Scoring, levels Nothing specialPipe Dream (original)CONCEPT: Build a path from one cell to another using one-cell elements
For the original Pipe Dream, published by LucasFilm Games, these were the design decisions.
Objects 4 corners, 2 lines, 1 cross
Rules Sliding tiles
User interface Click to slide, restriction on drawn path
Scoring, levels Nothing specialPipe Dream (Microsoft bonus level) CONCEPT: Build a path from one cell to another using one-cell elements
But other games can be built based on the same concept. The Microsoft Entertainment Pack version of Pipe Dream includes a sliding tile variation as its bonus level. Quite a good game.
Pipe Dream (Lucasfilm bonus level)CONCEPT: Build a path from one cell to another using one-cell elements
The original Lucasfilm version includes a Tetris-like variation of Pipe Dream as its bonus level. Very hard game; it is almost impossible to construct paths of more than about five tiles.
Honey WayCONCEPT: Build a path from one cell to another using one-cell elements
For the Mind Aerobics daily puzzle on the Internet Gaming Zone, Alexey created a simpler game based on the same concept. The grid was changed from square to hexagonal, the player could build paths freely by drawing lines, and sources, crosses and obstacles were given.
The hexagonal grid suggested the theme: bees and honey.
The player tries to construct a line of honey from one honey blob to another by drawing lines from one cell to another.
The path must pass through every cell of the grid once, crossing over itself at the flowers in the directions indicated by the petals. Here is a complete solution. It looks complicated, but the hexagonal grid is actually more forgiving for path construction than a square grid.
Dangerous bees complicate some of the puzzles.
LinemanCONCEPT: Build any cyclic pathusing one-cell elements
Lineman, from the Russian Six Pack (Interplay) uses the same seven objects but different rules. Pieces appear directly on the playing field and can only be rotated, not moved. The goal is construct loops, which collapse, not paths from one place to another. Excellent game.
Three games, Three genres
Here are other puzzle games that demonstrate some of the design challenges in other puzzle game genres.
Created solely by Cliff Johnson in the 80s, The Fool’s Errand is an integrated work of art. Each puzzle links with a tarot card and story segment. The bold silhouette art style looks good on a small screen. Each puzzle unlocks part of a larger unifying “meta-puzzle”.
The Incredible Machine (TIM) is the best construction puzzle game. There are three important design decisions. Decision 1: allow the player to build things. SimCity, shown above, allows construction, but does not give the player a fixed goal and is thus a toy, not a puzzle.
Decision 2. No realtime decision making. In contrast, Lemmings, shown above, requires players to solve the puzzle by repositioning lemmings while they are walking around. In The Incredible Machine, building and running machines happen in separate modes.
Decision 3: Player authoring. In contrast, Marble Drop, shown here, has separate build and run modes, but does not allow the player to construct original puzzles. Instead, all the puzzles come preconstructed, which allows Marble Drop to have beautifully rendered screens.
In The Incredible Machine, players can build their own puzzles in a separate freeform construction mode, separate from puzzle mode. The goal of this particular puzzle is to get all balls into all the aquariums using a motley collection of ropes, pulleys, ramps and other devices.
The designers of TIM did a brilliant job of including a broad range of play elements that all interact with one another within a rich physics model, while keeping the user interface simple and obvious.
The Puzzle Zone on America Online [editor’s note: now on boxerjam.com] is a good example of an online puzzle. Following the model of newspaper puzzles, Puzzle Zone delivers four new puzzles every day. The puzzles add new twists to familiar word games.
Flexicon, shown above, is a twist on a crossword puzzle. The problem with crossword puzzles on computer is that the screen is too small to hold a large puzzle. The solution here is to save space by overlapping four rectangular regions, only one of which is visible at a time.
Strip Search adds new twists to the familiar word search.: The theme here — Joes — was inspired by the topical event of Joe Dimaggio’s death. Found words appear in order of length, giving the player a hint. When all words are found, the leftover letters form a witty phrase.
Finally, the Puzzle Zone also includes elements that build community and encourage players to keep coming back: message boards, high score boards, and a place to buy branded merchandise.
The puzzles in Puzzle Zone are somewhat mundane and obvious, but that is not a bad thing. By using familiar puzzle types, the Puzzle Zone lowers the barrier to entry. Furthermore, word games require very little data to be downloaded, so play is snappy.
Recent design experience with 3 aha’s
Jesse’s Strips, designed by Alexey Pajitnov, is one of a number of image-based puzzles from Pandora’s Box, a forthcoming title from Microsoft.
One of the members of the Pandora’s Box team suggested the concept.
The problem with long skinny pieces, however...
The playing field is too messy
I considered many possible solutions before hitting on the idea of spreading the pieces across several different pages.
To make multiple pages and repeat the picture in progress on each of them, distributing the pieces.
This was the first Aha.
Player does not understand what happens when the pages switch
But this insight raised another problem...
To emphasize certain color for the picture on each page; to do the same with the pieces on the page.
Which in turn required a second Aha.
We need to move the pieces from page to page now and User Interface become too complicated
The final insight was motivated by wanting to keep the user interface simple. Instead of separate commands to rotate pieces and changes pages...
To move the piece to the next page together with the 90 degrees rotation.
The two things happen together. This is a good example of how the difficulties in realizing a particular puzzle concept can guide the designer toward novel solutions. [Editor’s note: the final published version in Pandora’s Box works differently.]
Adding action to a classic computer puzzle game
Charlie Blast’s Territory is a game for the Nintendo 64 published by Kemco. Kemco hired Realtime Associates to develop the game; they in turn hired Scott to assist in game design and level design for the puzzles. This example highlights some of the techniques he used in level design.
Charlie Blast is based on the classic puzzle game Sokoban, which is one of the most widely copied computer games. It has simple rules that are easy to program, yet has deep gameplay. It works well on low-resolution displays with simple arrow controls, such as GameBoy.
One of the most common ways to create a new game is to change an existing game. Here are some ways to change Sokoban.
For Charlie Blast’s Territory Kemco decided to pump up the 3D action elements of the game by using 3D perspective, moving camera, animated main character (Charlie Blast), and adding action elements.
We added common action game features like jumping, moving platforms, moving spikes, and a multiplayer competitive mode. We did not include damage points, because that would have shifted the emphasis of gameplay too far in the direction of dexterity, not puzzle solving.
Features like bombs, blocks and breakaway tiles add depth and variety to the underlying Sokoban game. Of course features interact with each other. TNT crates and blocks were introduced specifically to complement the jumping ability.
Here’s how bombs work. A 1 bomb blows up itself. A 2 bomb also blows up the four adjacent squares. A 3 bomb blows up a larger diamond region. The detonator and TNT act like a 2 bomb. You can light pm;u a detonator, and you can jump only over TNT.
The goal of every puzzle is to arrange the bombs so that when Charlie lights the detonator, it triggers a chain reaction that blows up all the bombs. Suppose Charlie lights the detonator in this configuration. Which bombs will not blow up?
Here’s the answer. The only bombs that don’t blow up are the 1 bomb at right, which is too far away from a 2 bomb, and the 2 and TNT bombs in the lower left, which touch another 2 bomb diagonally.
The bulk of my time was spent designing the 60 levels, structured as 6 ramps of 10 puzzles each. Puzzles within a ramp start easy and get harder. Each ramp has a different visual theme and emphasizes a different mix of features, to keep the game from getting too repetitive.
I used many different strategies for coming up with ideas for levels, so that there would be a wide variety of puzzle types. Here are six of my strategies. Following are examples of how I used each strategy to design a particular level.
#17 Run Like Crazy
Some puzzles are structured as a linear sequence of events. For this puzzle, Î started by drawing a board that wraps a long narrow corridor into a small space.
#17 Run Like Crazy
This puzzle features an autodetonator, shown in red here, which blows up automatically in a preset amount of time unless you touch it to reset it. The basic drama of this puzzle is that you must run to the autodetonator, then push it back a long way so it blows up a bomb.
#17 Run Like Crazy
I then compounded the puzzle by adding obstacles along the three legs of the journey. Moving spikes that raise and lower out of the game cause you to have to wait a bit before you can get to the autodetonator -- frustrating when you have to get there quickly.
#17 Run Like Crazy
Next you must push the autodetonator onto a moving platform that travels slowly to the right, then push it off. Again, timing is critical if you are to execute this move before the autodetonator blows up.
#17 Run Like Crazy
I added one more spike in the right leg of the journey..
#17 Run Like Crazy
Finally there is the end game. One bombs only blow up themselves, so the ending position must be an autodetonator surrounded by one bombs. Because two of the 1 bombs are against walls they cannot be pushed away from, there is only one possible ending position.
#48 Ice Rink. Initial pattern.
Another way to invent a puzzle is to start with a pretty pattern, then try playing it. Here are three opening positions I considered for the puzzle Ice Rink. They look similar, but behave very differently. You cannot stop moving on ice until you hit a wall or reach solid ground.
#49 Diamond. Initial pattern.
Here are three patterns I considered for a puzzle called Diamond, which features a patch of ice surrounded by solid ground. After drawing the opening patterns I played them to see if they could be solved. If they were not solvable, I then had to decide how to modify the pattern.
#60 The… Final pattern.
For the final puzzle I decided to aim for a pretty final position that would spell the word “End”. This is what I originally hoped for..
#60 The… Initial pattern.
The actual final puzzle required many modifications to the boards and pieces to make sure that the puzzle only had one solution. Shown here is the final beginning position.
#57 Pinball. Overall picture.
One of the features of Charlie Blast is bumpers, which rebound bombs pushed into them. Bumpers reminded me of pinball bumpers, so I built this puzzle to look like a pinball machine, complete with a moving beltway for returning a queue of balls into play.
#16 Long Haul
Some puzzles create distinct moods. Long haul, for instance, creates a frantic suspenseful mood as you must run further and further away from an autodetonator with a very short fuse in order to reposition bombs that are further and further away.
#16 Long Haul
It is easy to see that the autodetonator and 1 bomb cannot move, so the solution must be to create a chain of 3 bombs reaching from one end to the other.
#16 Long Haul
Or is it really that easy? A bit of analysis will show that the previous solution cannot be achieved, so a modified chain like this is necessary.
Puzzle designers often mine mathematics for ideas. Shown above is a puzzle based on the mathematical idea of a tour. The goal is to draw a closed path that visits every square once, using all the red lines. The unique solution is shown at right.
I decided to make a puzzle for Charlie Blast that used the idea of a tour. Suppose the tiles above are all breakaway tiles, which means you can only step on them once. How would you push all three one bombs off the bottom edge of the square? One solution is shown at right.
After a bit of work I came up with this more difficult tour puzzle. The goal is to push all three 1 bombs off the bottom edge of the square by walking a single path. The unique solution requires that you visit every square exactly once.
Here’s the final puzzle. The purple electric bombs act like 2 bombs, except if one electric bomb blows up, the other also blows up. Since the electric bomb along the bottom edge cannot be pushed up toward the 1 bombs, the three 1 bombs must be pushed down to surround it.
#30 Moving Ground
Another strategy is to exploit a feature. Shown above are two states of the same board, built entirely of moving platforms. The tall rectangles move left and right, while the wide rectangles move up and down. The green arrows show how the 2 bomb could be pushed.
#30 Moving Ground
Here is the final puzzle. The ground at the bottom is stable, while the ground at the top is moving. The goal is clear: build a chain of bombs between the immovable detonator at left and 1 bomb at right. But getting there requires a hair-raising ride around the platforms.
#30 Moving Ground
This puzzle is easier to analyze if we collapse time and push all the platforms together so all adjacencies are present at the once. The green arrows show all paths that bombs can follow as they move around the platforms. Removing the dead ends, we discover the loop at right.
Finally, puzzles can trick you into pursuing the wrong line of reasoning. For the puzzle Tadpole, I started by observing that a puzzle involving a 2 bomb, detonator and six 1 bombs must end with the 2 bomb and detonator surrounded by the 1 bombs.
With that analysis in mind, this puzzle appears to be simple: push the autodetonator into the pocket, seal the opening with a 1 bomb, then sit back and watch the fireworks.
By adding a couple of spikes I gave the puzzle a new wrinkle.
Now you can only push the autodetonator as far as shown above by the green line. You cannot push the autodetonator any further because the spikes prevent you from getting to the square to the right of the final position of the autodetonator.
The real solution requires that you rebuild the entire hexagonal pattern of 1 bombs up and to the right one square.
To complete the puzzle, I added some blocks and breakaway tiles.. These complications add difficulty to the puzzle, but are not integral to the central theme of the puzzle.
Creating a monthly puzzle for a children’s web site
The second case studies a monthly puzzle called Scott Kim’s Puzzle Box, which Scott created for the kid’s online service Juniornet. This example highlights issues in designing puzzles for the web.
Juniornet is an online service that gives kids a safe, fun, rewarding, and ad-free experience. Content comes from such well known brands as Highlights and Weekly Reader. Subscribers receive a CD-ROM, with more frequently updated content streamed across the internet.
My feature on Juniornet is an original content area called Scott Kim’s Puzzle Box, which delivers.a new collection of puzzles every month. The type of puzzle changes from month to month. Players can create their own puzzles, some of which are posted on the site.
Producing a rich puzzle experience on a monthly schedule posed several design challenges..
“Things Picked Up”
The puzzles are adapted from existing puzzles. For instance, the April puzzle is based on Hiroimono, a popular puzzle from Japan traditionally played with Go stones.
To make Hiroimono friendlier to kids I embodied the rules in the characters of a dog that is eating pet treats, and a cat that prevents the dog from backing up in the direction it came. Even with words, kids could be attracted to the game and have a sense of what it is about.
In order to keep production costs reasonable, I planned a modular structure that would allow most of the site to stay the same from month to month. These basic features are always the same.
4 TEMPLATES/YEAR, 3 VARIATIONS EACH
The type of puzzle changes every month. But instead of creating 12 different puzzle engines, I create only 4 engines for the year, then reuse each engine 3 times with minor variations.
15 MONTHLY PUZZLES, 24 KID’S PUZZLES
Every month I deliver 15 puzzles that I created, and 24 puzzles that kids create.
Production is structured so that the most difficult pieces to build change the least often. Templates change only once every three months. The monthly template variations require only art changes. Finally, puzzle specification requires only compact text files.
Players can create and submit their own puzzles. In order to keep puzzle creation kid friendly, I chose puzzles that are relatively easy to author. And I require that players solve their puzzles before submitting them, so I don’t receive puzzles that don’t work.
In eight easy steps
Now that we’ve seen two very different examples, what can we say about puzzle design in general?
3. Construction Set
Here are the steps in designing any puzzle game. The first four steps sharpen the concept into a design specification; the last four steps bring the concept into reality.
Where do ideas come from? Here are six ways to get inspired. First, you can look to a previous game. Tetris was inspired by a noncomputer game called pentaminoes, and in turn inspired Welltris and other Tetris spinoffs.
1. Enable nonphysical moves (Tetris)
2. Algorithmic hint, create, analyze, enemy
3. Enforce the rules (Sokoban)
4. Undo, record moves (Solitaire)
5. Structure the experience (Lemmings)
6. Instruction (Chess)
7. Bells and whistles (Battle Chess)
8. Online play (NY Times crossword)
If you are going to put a puzzle on computer, there should be some gain. Many computer puzzle games do things that could never be done in a physical puzzle. But even if the puzzle is physically possible, there are many other ways the computer can enhance gameplay.
Endorfun was inspired by the play mechanism of a colored cube rolling on a square grid.
Like songs, puzzles can be inspired by real life. Stephen Sondheim: A good clue can give you all the pleasures of being duped that a mystery story can. It has surface innocence, surprise, the revelation of a concealed meaning, and the catharsis of solution.
Story puzzle games like Myst are built around story line, character, setting, and mood.
The story game Obsidian started as a series of concept sketches for characters and environments. Story and puzzles came later.
The second step is to whittle the concept down to manageable size. Say we wanted to make a puzzle based on the tricky core skill of parking a car in a crowded lot. We eliminate irrelevant details and make pieces uniform by conforming them to a square grid.
Rule designer: tweak rules
Level designer: build levels
Player: build levels3. Construction Set
The only way to test a puzzle concept works is to play it. So the next step is to build a construction set that makes it easy to build puzzles of a certain type. Sometimes a paper prototype is adequate. Once the rules are set, other people can use the construction set to build levels.
Now it is time to write a detailed design specification. Most puzzle game specs will describe puzzles in terms of board, pieces, moves and goals. In addition a design spec may also cover the user interface, scoring, story, art, sound and other aspects of production.
Schematically, a puzzle challenges the player to get from a problem to a solution.
But of course the path is never simple. Every puzzle requires that the player make choices, some of which lead to dead ends.
Puzzles in a game have a larger situation that gives the puzzle meaning. Applying the solution lets you move forward in the game.
Good puzzles have require insight. The insight above is to walk around the outside of the maze. Obscure insights, however, feel unfair.
The only way to find out whether a puzzle is fun is to watch someone play it. Often a puzzle you think is easy will turn out to be hard, or vice versa. Sometimes players will find simpler solutions. Or you will realize that the puzzle needs some other improvement.
Next you must put the levels into sequence. Linear is simplest, but can get tiring. A better organization is the sawtooth, which keeps going back to easy puzzles, or to give players freedom to play puzzles out of order. Metapuzzles motivate players to complete the whole game.
You also need to think about the transitions between puzzles. Whenever the player moves from one place to another in your game, there is an opportunity to lose the player’s interest. How can you bridge these gaps?
Finally there are all the matters of presentation that turn an abstract puzzle into something people can see, hear and touch. I won’t go into detail on production for puzzle games.
Inventing ideas for puzzles based on today’s headlines
The class divided up into teams of people each. Each team invented an idea for a puzzle game based on a story or ad in today’s San Jose Mercury News. Finally the groups pitched their ideas to the whole class.
Like most of the puzzles this is a character-driven action game that has been turned into a puzzle game by putting it onto a grid and turning real time action into turn based strategy.
A dynamic allocation puzzle. Prisoners are arriving at a jail. Allocate them to cells while avoiding certain bad combinations, such as an escape artist plus someone who has a key. Shuffling prisoners between cells takes time.
A clever idea that falls naturally out of a real situation. Irregularly shaped cubicles made of square modules are to be fit within a floor of a building. Additionally, every cubicle must have a clear path from its door to a building entrance.
A story about homeless Barbie inspired the most ideas. Get Barbie Home had Barbie wandering through the back streets of a city. Bust Out Barbie required chain smoking Malibu Barbie use Fashion Barbie’s hairspray to fashion a homemade bomb and stage a jail break.
into a word game
Next, groups were asked to invent a game that combined Sokoban with some sort of word game, then pitch the game to the group. The ideas were surprisingly varied, and several were sufficiently developed to be implementable.
Creating levels for a new variation of Sokoban
As part of the Sokoban Word Game exercise, groups invented three levels of their games. Some of the levels were completely drawn out, others were just titles or concepts.