Multiplayer Interactive-Fiction Game-Design Blog

Exceptional physics

20 August 2005

by Mike Rozak

Two abstractions of "physics" are used in games:

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  Universal physics - Universal physics allows players to perform actions that work "properly" everywhere in the game universe.
  
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    Example A: A character can swing a sword and attack monsters, doing damage to them. With enough damage, a monster dies. Likewise, a character can swing a bread-stick and do damage to the monster, although not as much. Alternatively, a character can attack a door with a sword and eventually destroy the door.
    
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    Example B: If the player has a shovel, they can dig any place in the game. If they dig in soft dirt, they dig more quickly than in stone, but they can still dig in stone. Furthermore, if they have a banana, they can use it like a shovel, except that it doesn't dig very well and it wears out quickly.
    
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  Exceptional physics - Physics handled by exceptions allows a large variety of actions, but each action is limited to specific certain places and objects.
  
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    Example A: A character can attack a monster with a sword. Attacking the monster with a bread-stick won't work because bread-sticks are food items. Attacking a door with a sword won't work either because doors are not monsters.
    
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    Example B: If the player has a shovel, they can only dig in a few places in the game, usually in areas where digging produces results. If they try to dig with a banana (which is not a shovel), they get nowhere.
    

Each abstraction of physics has advantages and disadvantages...

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  Universal physics
  
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    Once a player learns that he can perform the action (usually introduced in the game's tutorial) he knows he can do it anywhere.
    
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    Because it takes so much development time (and 3D modelling and animation) to allow an action to work predictably everywhere, games based on universal physics tend to emphasise a few actions and discard the rest. For example: "Platformers" allow players to run and jump, nothing else. First-person shooters let players run, jump, and shoot, nothing else. Ultimately, the limited set of actions results in scenarios where players do the same thing over and over, but with slight variations.
    
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    3D worlds seems to work well with universal physics, probably because 3D models can automatically be placed (and sometimes generated), while automatically generated text is uninteresting.

    Example: Drawing a character digging in the sand is same code as drawing the character digging in rock. Generating the speech is more troublesome, since (ideally) the sand's narration should be "You easily dig 3 foot hole in the sand." while the rock's would (ideally) be "With much effort you manage to chip the top layer of rock away." Since these sentences don't lend themselves to automatic generation, text-based worlds with universal physics often display "You dig N feet down," instead; This poorly-worded text weakens the experience.

    
    
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  Exceptional physics
  
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    Players are often uncertain where actions will work, or what they work on. Or, an action that a player thinks is logical isn't actually programmed into the physics. Known as the "guess the verb problem" in adventure games, this is a very frustrating experience for players. It breaks the immersion and forces players to get into the mind of the game designer and figure out what the game designer expects players to do.
    
    The "guess the verb" problem can be alleviated by listing the actions the player can perform. However, once the player knows the list of possibilities, the game shifts from one of problem solving into one where the player tries out all the different actions to see what affect they have. This happens in a Choose Your Own Adventure books, where fun comes from the exploration of alternate timelines, not the problem solving.

    Alternatively, the designer can anticipate the most popular combination of verbs and nouns, allowing doors to be attacked by swords, or digging to work even in places where it yields no real results. Unfortunately, the number of combinations, which grow exponentially, rapidly become very expensive to develop and test.

    
    
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    Exceptional physics is cheaper to implement (in text) than universal physics, so games with exceptional physics allow players to perform lots of different actions. In one room, characters might dig a hole, while in another they climb walls, and in a third they sew a shirt.
    
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    Textual worlds seem to work well with exceptional physics, probably because creating exceptions in 3D worlds requires extra artwork and animation.

    Example: The models, animation, and sound for "digging a hole" might take six man months. Climbing walls and sewing a shirt are each another six. Management gets irritated when such an expensive animation is only used once, so 3D worlds tend to reuse animations and consequently, they emphasise universal physics. Conversely, writing a few lines of text to describe hole digging, wall climbing, or sewing only takes a few minutes.

    
    

Single-player CRPGs vs. multi-player MMORPGs

Producing a matrix of games that emphasise universal vs. exceptional physics, and single vs. multiple player clarifies some of the common game categories:

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  A single-player game with universal physics is a FPS (first-person shooter) or a CRPG. The key difference between a FPS and a CRPG is the duration of the game (CRPGs are longer) and how much of the character's in-game skill is derived from the player's dexterity vs. a persistent character (FPS rely more on player dexterity, CRPGs have persistent characters.)
  
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  A multi-player game with universal physics is a multiplayer FPS (like Halo 2) or a MMORPG. Again, multiplayer FPSs are shorter and require more dexterity than a MMORPG.
  
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  A single-player game with exceptional physics is an adventure game or a Choose Your Own Adventure book. CYOA books list all the choices, while adventure games try to minimise "guess the verb" problems through good design. Adventure games and CYOA books don't usually have persistent characters, although Tunnels & Trolls' solitaire adventures do.
  
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  A multi-player game with exceptional physics exists in some older text MUDs (like MUD II). Uru Live was an attempt at a multiplayer, graphical adventure game, but it failed. A multiplayer CYOA book doesn't make much sense because only one player can chose the path, while other other players must tag along for the ride.
  

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   For a problem/challenge to be interesting to the player, it must be carefully balanced so that it isn't too easy nor too difficult. Because the player's own skill needs to affect his rate of success, this usually means the player must apply some thought/strategy to the problem to increase his chance of success. (In the case of FPS, dexterity is also required.)
   
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   In a game with persistent characters, the designers must ensure that when the player's character reaches a problem/challenge, the character's abilities and power will be well matched against the problem, whether it's a monster, trap, or lock to be picked. If the character is too weak, the player will never be able to solve the problem, no matter how much strategy is used. If the character is too strong, strategy is unnecessary, there's no challenge, and the game is no longer fun.

   CRPGs deal with the balance issue by ensuring that experience points (which increase a character's abilities and skills) are doled out such that the character's level will be appropriate for the challenge when he reaches it. This demands a finite supply of experience points.

   MMORPGs must continually respawn monsters so that every player will get his chance at a kill, which means there is an infinite supply of monsters, and consequently, and infinite supply of experience points. Hence, MMORPGs can't guarantee that a character's level will be appropriate to the challenge.

   Work-arounds exist: MMORPGs can offer rewards appropriate to the character's level. A more powerful character won't find the lower-level rewards beneficial, so he won't (theoretically) undertake the challenge. In reality, many players find it much easier to attack weaker monsters (and get fewer rewards more easily) than to challenge level-appropriate monsters.

   
   
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   In a game with multiple players, scenario balance is impossible. If a single player can't get past a challenge, he just waits until more players reach the challenge, and they all tackle it together. Alternatively, the player can call in his friends when needed. Of course, the treasure will have to be divided amongst all the players. This isn't a problem since MMORPG monsters respawn every minute, and the players can just re-kill the same monster until everyone has the desired loot.

   Work arounds exist: MMORPGs with instanced dungeons don't respawn the boss monster, who happens to have the best rewards. Players that wish to acquire the boss monster's loot multiple times must work through the entire instance each time.

   
   
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   Even if all these problems are solved, multiplayer games often become competitive. Competitive players (a significant portion of the MMORPG population) will read walkthroughs to make their life easier. Any problem that has a fixed solution/strategy will appear on the walkthroughs, eliminating the challenge for competitive players and unbalancing the game.
   
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   Consequently, a multiplayer universal-physics game cannot produce challenging scenarios for players. The challenge of a MMORPG is not the game; The challenge comes from dealing with the other players in the game.
   

What happens when a single-player adventure game is turned into a multiplayer adventure game? The problems that appear when a single-player universal-physics game is turned into a multiplayer game might also appear; The game's challenge might simply disappear, and fun along with it.

Two basic types of challenges present themselves in exceptional-physics worlds:

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  Puzzles - The player must figure out the one solution to a puzzle.

  If the designer has enough time, the puzzles might even allow several solutions. One urban legend describes a physics test which asked, "You want to know how tall a building is. All you have is a lantern and short length of rope. How can you use the lantern and rope to find the building's height?" The "correct" solution (I think) is to carry the lantern to the top of the building and use it to cast a shadow on the ground, allowing you to easily measure the height on the ground using the rope. Other more creative solutions involve giving the lantern to the doorman if he's willing to tell you the height of the building, or to drop the lantern from the roof and measure how long it takes to fall. A designer with enough time/money might allow for all these solutions. However, due to the cost of designing many solutions, single-solution puzzles are much more common.

  
  
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  Menu of choices - Games sometime present a menu of choices in an attempt to avoid the "guess the verb" problem. Games that do this ultimately encourage players to replay the game to see how different choices affect the experience.

  This is handy... Worlds based on universal physics save money by having players kill the same monster (with variations) over and over again, repeatedly jump over objects, etc. Worlds based on exceptional physics cannot expect a player to solve the same puzzle over and over again. Menus are are replayable content, though, and can be used to reduce production costs.

  
  

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  The skill of a player's character should, at most, act like a gate to determine if the problem can be solved. If the player's character doesn't have the necessary skill, the player must return later when his character has levelled up. However, a character skill that is significantly higher than the minimum won't make the puzzle any easier to solve.

  For example: A "salesmanship" skill of 5 might be required to convince the doorman to divulge the height of the building in exchange for the lantern. A higher skill shouldn't make the puzzle any easier to solve. If it did, the player would simply level up on easier fare (grinding) and breeze through the more difficult puzzles, just like they do in a MMORPG.

  However, if the game hands out a finite amount of experience points, then a higher skill level could make the puzzle easier. Finite XP requires the player to make trade-offs between being good at "salesmanship" or "swimming". Being a good salesman might make the tower puzzle easier, but result in a poor swimming skill that makes escaping the crocodiles more difficult.
  

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  While puzzles and menus can require a minimum number of players to complete, players shouldn't be able to bypass the problem-solving element by rounding up an army of players.

  Or, if players use an army, only a limited number of them get the reward, and the rest are unable to replay the scenario. You will need to warn the players ahead of time that there won't be enough reward to go around, and that they'll be blocked out from future attempts at the puzzle. (You can apply this approach to universal-physics games also.)

  
  
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  If a menu of choices is provided, the choices should produce different but equal outcomes, although an occasional "you died and have been resurrected" is okay. If players realise that one outcome in every menu tends to be vastly superior to the other outcomes, they won't be able to help themselves and will look in the walkthroughs. Single-player CYOA games have the same problem with unbalanced choices. However, in a single-player game, players can reload their character before the choice was made and replay. Reloading isn't possible in a multiplayer game, so players are more cautious.
  
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  The game can't be competitive. If it is, competitive players will readily download the puzzle solutions from the web, rapidly increase their level, and use their ill-gotten power to lord over players that didn't cheat.