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Read January 21, 2006, 05:29:53 AM #0

The Gaping Wolf Rules

original topic here Cached by Google for your pleasure Smiley

To save all that hassle though, here they are reproduced:

Thought they'd be worth a few moments of your time Wink

1. Each enemy type should have the same movement pattern. Never, ever re-use an enemy sprite with a different pattern as it will confuse the player. At least change the color.

2. Enemies should appear from varied places all over the screen, but not so varied as to confuse the player. It's good to define certain spots where enemies will commonly appear, and make sure the enemies spawned at those are reachable with any kind of weaponry the player might have.

3. Rear-moving enemies (the kind that move bottom-to-top, or "against the grain") are REALLY cheap unless you give the player advanced warning.

4. Enemies should move in chains, usually based upon arcs. Splines of any sort are good for this.

5. Difficulty levels should alter enemy patterns or their placement within the level, or outright add/remove enemies. Just making the enemies stronger is the cheap way out.

6. There should be no gaps in the action, unless you intentionally want to give the player a few moments to relax. (After, say, an intense slew of enemies.) The game must flow at all times, or the illusion of flying at high speed is lost.

7. Variety! Even if you want to keep the number of enemies low per level, you should stagger waves of different types of enemies. If you can help it, use a unique set of enemies per level.

8. No looping! It will immediately obvious to the player that you are repeating a section.

9. Keep the levels short, but full of life and variety. Most shooters have fairly short levels, less than 2-3 minutes running time. Anything longer than that, and you start to risk player boredom.

10. Balance powerups carefully! You must make sure to give the player enough firepower to survive what you are throwing at him/her.

11. Weight collision detection FOR the player but AGAINST the enemies. In other words, the hit-box that surrounds the player's ship should be at least as big as the sprite itself, or preferrably smaller. However, enemy hit-boxes should always be at least as big as the enemy sprite or, again, preferrably larger. This lets the player have "brushes with death" and not feel quite so cheated. (Plus it gives them more wiggle room when the screen is filled with bullets.)

12. Enemy bullets should generally follow a pattern; Think of it as a moving, deadly puzzle for the player to solve. If all enemies always fire directly at the player with absolute machine-perfect aim the game will be very frustrating and monotonous.

13. Bullets or objects that can harm the player must be visually distinguishable from the background. Make sure there is a high contrast ratio between enemies, their bullets, and the background/effects. This also applies to collectable items, such as powerups.

14. Boss fights; This mirrors rule #12. The boss fights should be a puzzle for the player to work out. It can be as simple as figuring out where to "shoot the core," or it could involve triggering other events that lead to the boss's destruction. Just make sure all of these are fairly obvious, the same goes for bullets striking parts of the boss that are damageable or not.

Well, I've wrestled with reality for 35 years, Doctor, and I'm happy to state I finally won out over it.
Read January 21, 2006, 06:47:11 AM #1

Re: The Gaping Wolf Rules

In a similar vein, here's a thread on GD.net, and here's a great post form that thread by ToohrVyk.

I can give you some examples of enemy AI routines I used in Darklaga (a vertical shoot'em up, see my signature), as well as the design behind them. To understand how to make a game difficult, you have to understand how the player reacts to obstacles. In shoot'em up games, difficulty comes from the following causes:

  • Reflex-based obstacles require good hand-eye coordination and the ability to react in a split second. Examples are very fast shots or speeding suicide bombers.
  • Tactics-based obstacles require more concentration, because they are crafted in such a way that blind reflexes will not work. Examples are player position during intricate boss attacks, or choosing the order in which to kill the enemies.
  • Strategy-based obstacles usually involve the choice of weapons, or the use of smart bombs.

The common denominator to all these obstacles is the one and only player resource: concentration time. A given player can only concentrate on a fixed amount of entities and concepts in a given time duration.

An isolated entity (a ship, a bullet), no matter how dangerous, should never require large amounts of skill to overcome, because this is simply not fun for the player: acquiring the required skill can only happen when fighting that entity, which means the player will fail a large amount of times. However, the interaction of several entities creates another kind of difficulty: since the player can only handle a limited amount of entities at a given time, player skill will come from the ability to decide which entites are worth concentrating on, and which are not. Difficulty will then come from interesting ways in which entites can be made to interact in order to surprise or puzzle the player.


The human brain has several innate abilities that allow it to handle large amounts of entites. The most important of these is clustering: if several entities are similar enough in their aspect and (simple) behavior, then the brain will be able to handle all of them at the same time as if there was only one. This has several implications on the difficulty of several situations:

  • Shots that move in the same direction are easier to manage than shots fired in random directions.
  • Shots that come from the same point are easier to manage than shots fired from several different points.
  • Enemies that are far away from each other cannot be easily concentrated on.
  • Differences in movement speed, as well as complex non-rectilinear movement, increase the difficulty of managing entitites. However, if all entitites move exactly the same way (even if it is complex), then the effect is lessened a great deal.
  • Colour-coding helps isolate movements. By having all shots that move in a given direction have a certain colour, the player will dodge them with less difficulties.

The effects in Darklaga were obvious, as different kinds of shots were used. In the high-difficulty modes, enemies used both a slow-moving shot type and a fast-moving one. The slow-moving type was initially used to spin a web, through which the player had to navigate. Because the fast-moving shots were almost the same color as the slow-moving ones, the player had many difficulties spotting them because he was concentrated on navigating through the web.

Delayed threats

The next step is the introduction of delayed threats. Indeed, right now all techniques only serve to increase the difficulty of dodging enemy fire, which is an immediate threat. Once an enemy shot is fired, the only solution is to dodge it. However, if a type of enemy is known for firing dangerous pellets, then that enemy is a delayed thread: if it is killed before it fires, then the game becomes easier. As such, destroying delayed threats is a top priority for the player (second only to the necessity to avoid immediate threats). Here are several pointers related to delayed threats:

  • Delayed threats fall into two categories: diversion and sneaking. The former must attract the concentration of the player onto itself to divert him from immediate threats. The latter will attempt to stay unseen in order to unleash an immediate threat of its own.
  • Diversion threats rely on attracting the player's attention, and to do this they use several properties of the human brain. They blink/are animated/have a distinct color, they appear in a clear area where nothing else can block the view, and are usually quite big. Average differences in movement speed are not noticed (but different movement directions are). The reverse is true for sneaking threats.
  • A delayed threat need not be an enemy. A wave of shots that moves towards the player is an immediate threat. Now, hide among these shots a similar-looking shot that moves in the same direction (so it will not stand out of the crowd), but at a smaller speed (so natural clustering will ignore it), and you have an unseen sneaking threat going straight for the player if he did not spot it fast enough to move away. This technique was used for the Blazing Star final boss, by the way.
  • A delayed threat need not even be hostile! By setting free a valuable power-up at the right time (and having that power-up 'leave' the screen after a short time), the player faces the 'danger' of not picking up that item. This is a very interesting diversion system, by the way.
  • Delayed threats that must be destroyed (essentially enemies) are stronger when the weapon of the player does not have a wide spray or auto-aiming. The harder it is to aim at a threat, the more difficult it will be to counter it.

What would be examples of this? Darklaga featured "warping" enemies which appeared somewhere on the screen, waited a short moment, and unleashed a vicious attack at the player. It was very important to destroy these enemies as soon as possible (and they were weak), or they would transform the playing field into hell in space. Another such "delayed" feature was the introduction of kamikaze enemies. These would slowly move down the screen vertically, stop, and suddenly move horizontally to ram the player's ship from its undefended sides. These enemies were mainly introduced to rebalance the otherwise unbalanced vertical laser (a very powerful weapon that ripped through enemies, but which required one to move fast enough to kill the kamikaze before it rushed in).

More diversions

There are even more ways to apply the constatation that the player can only concentrate on so many things at a given time:

  • Darklaga had a special class of enemy that rotated around the player. The enemy would usually do almost nothing (it did not shoot very often either), but it was safe from any attacks until its giratory movement placed it in front of the player's ship (at which point it died). However, a rotating enemy ship is enough to attract the player's attention, and divert it from more important concerns. Not having those enemies be completely inoffensive also helped keep a portion of the player's attention on them.
  • The player naturally concentrates on its target. This can be used to your advantage in several ways. The most obvious is to have the player keep its eyes on an enemy a few milliseconds after its death. Idea: a way to do this is to have a little slot machine appear where the enemy was (which can roll out an instant bonus for the player).
  • Another is to notice that players watch the enemy until it dies (and not until they fire the final shot that would kill it): if the lethal blow is not different from normal shots, the player will wait until it reaches the enemy. Idea: have the player weapon fire "targeted" missiles at the enemy, with missiles being slower and more powerful as time passes; the lethal missile will be very slow. It works even best with a flamethrower, since missiles can be counted.
  • Have threats appear as much more dangerous than they really are. Darklaga featured horizontal walls of enemies. If the player kept firing constantly, they would die whether or not the player was paying attention at them. However, even though it served no purpose, most testers kept their eyes on the enemy wall until it was destroyed, and were hit by enemy fire in the process.
  • Teleporting enemies can be made to teleport behind the player when he isn't looking (because his attention was diverted by something else). And the time spend on dispatching them can be put to use by other delayed threads coming from the other way.

That's all I could remember off the top of my head. But the basic idea is that psychology is the key.
Read January 21, 2006, 10:46:48 AM #2

Re: The Gaping Wolf Rules

original topic here Cached by Google for your pleasure Smiley

1. Each enemy type should have the same movement pattern. Never, ever re-use an enemy sprite with a different pattern as it will confuse the player. At least change the color.

Whoa, tell that to Shikigami no Shiro 2 developers. The same enemy has many different patterns, which saves on graphical assets Wink. The same goes to Ikaruga Tongue.
Read January 26, 2006, 12:54:21 AM #3

Re: The Gaping Wolf Rules


Some rules worked for some game
and some other don't work with other games.

Whoa, tell that to Shikigami no Shiro 2 developers. The same enemy has many different patterns, which saves on graphical assets . The same goes to Ikaruga .

I played Radiant Silvergun.
(Which ROCKED)
has also the same thing.


Be Attitude for Gains
Read January 26, 2006, 07:09:42 AM #4

Re: The Gaping Wolf Rules

I played Radiant Silvergun.
(Which ROCKED)
has also the same thing.

Not sure whether you already know this or not... RS and Ikaruga are both by the infamous developer of shmups, Treasure, which would explain the similarity of the patterns. Ikaruga is frequently seen as something of a (less brilliant) follow-up to Radiant Silvergun, which was the single game which compelled to get hold of a Saturn recently!

The reason Radiant Silvergun is quite unique for me, is that it gives the player a choice of six or so weapons to attack with - which frequently means the game actually requires you to learn which weapons are to be used in each area against each enemy / boss.
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