Monday 24 November 2008

Left4Dead Week: Failing is Fun

Left4Dead week will feature one short piece on Left4Dead each day this week to celebrate the full release of the game.

No other game celebrates the fun of failure like Left4Dead. (Except roguelikes. And Dwarf Fortress. Screw you Jonathan Blow for making failure impossible...) So it's time to second guess the designers and come up with some game 'improvements' to see if our hypothetical Left4Dead design can improve on the high standards set by the original.

And nothing says improving game play by adding stuff randomly without testing. So I'm going to suggest the addition of three more weapon types, and one more playable zombie. Ah... variety. The spice of life to cover up the stench of death.

Three additional weapons

These weapons are placed by the AI director - but instead of having a table from which you can pick 3 from, there's only a maximum of one per level, which comes with a fixed amount of ammunition which you can't refill. Think of these as a short term power up that one player gets to steal from everyone else. And fails with it.

The Chainsaw: How Valve released a zombie game without a featuring a chain saw beggars belief. Of course, they should really have included a lawnmower. But a chainsaw is close enough.

Primary fire: You saw through zombie flesh. It doesn't so much do damage, as carve up any regular zombie as soon as you hit it. Against special zombies, the shower of blood blocks your vision much as a Boomer's vomit does, but in a different colour.

Secondary fire: Melee attack like every other weapon which pushes zombies away. Occasionally your chainsaw will get stuck in a zombie while using primary fire and you'll have to clear it with the secondary fire.

How failing with it is fun: You'll notice that the primary fire doesn't push zombies away... so getting surrounded is just as bad as before. Plus: play a coop game, and take away someone's ability to use their primary weapon at range. Then see how everyone else feels.

Wait. Valve did that in Left4Dead with the Akimbo Assassin achievement. Nothing to see here then. Move along.

The Flamethrower: Lots of burning stuff. Check. Zombies on fire. Check. Ability to set zombies on fire using a flamethrower... didn't Valve watch the Thing?

Primary fire: Flame. Glorious flame. Watch how it burns. I'm waiting right now for a barbecue to get delivered. True story. I wonder what zombie flesh tastes like. I'm guess a chicken version of Spekekjøtt... mmm...

Secondary fire: Melee attack. Like everything else. Of course bashing the flaming end of a petrol tank against something hard is a low risk proposition. I wonder how often it'll blow up.

How failing with it is fun: Aside from the random petrol tank explosions - and how often have you accidentally shot a fuel canister in Left4Dead already without strapping one to your back and standing in front of your companions - the flamethrower doesn't have any stopping power. So instead of being rushed by zombies, you'll be rushed by zombies. On fire.

The RPG: Midtown USA features lots of military grade equipment. Like Russian made Rocket Propelled Grendade launchers. And General Purpose Machine Guns. I actually thought long and hard about suggesting a GPMG. Until I realised that you'd have to go prone to set it up. And as Counterstrike has shown, going prone just encourages tea bagging... can I point out that tea bagging an AI tank you've just taken down doesn't have quite the same emotional force as someone who is forced to watch you sit over them with the in-game camera? It's funny when someone tries it on a downed comrade in Left4Dead. Because your dual pistols beats their dual... no wait. Lets not go there with this analogy.

Primary fire: Great for busting tanks. And fixed emplacements. Except most tanks move reasonably slowly and you can get at the weak armour from behind. Not charge at you throwing chunks of concrete while on fire (if you're lucky).

Secondary fire: Me... I think you can guess by now.

How failure is fun: Slow loading weapon. Fast moving zombies. Hmmm...

One additional playable special zombie

I didn't quite intend this article to end up as a humour piece. How the best laid plans go awry. But that's what we're talking about here.

One of the best laid plans in Left4Dead is to hole up somewhere while you're getting rushed. If you've got good line of fire and disciplined players you can hold off the regular zombies, push Boomers and melee release your colleagues who get caught by Smokers. Ideally your position shouldn't even be accessible to the special zombies because you've closed the doors leading to it.

So that's what this zombie type does. Force you to move...

The Swarmer

Picture the Candyman. But with flies crawling out his eyeless sockets instead of bees. And pale, decayed flesh, with red raw scars. And no hook. Maybe just the stump of a hand. But you get the idea.

Primary Attack: Melee attacks. Roughly boomer strength. This guy wants to get reasonably close to the enemies. Not boomer close. But faster moving.

Secondary Attack: Fly strike.

The fly strike spits a decayed lump of flesh surrounded by a swarm of flies at slightly further a distance than Boomer vomit. The location the fly strike hits is immediately filled with a cloud of flies which lasts, say, 15 seconds. This has no initial impact, but if any survivor stays within the cloud of flies for more, say, than 5 seconds, they are affected by a denser swarm of flies.

The swarm of flies effect causes the survivor to continuously lose health until either they become incapacitated, or have another survivor remove the swarm of flies effect, using the E key for a short duration.

Fatality: Killing the Swarmer releases a cloud of flies, with the same impact as their secondary attack. (Maybe this guy plays too much like a Boomer).

Sounds: The Swarmer is identified by the sound of the buzzing of flies around it. A intense, angry buzzing as if drawn to a putrid corpse...


Sunday 23 November 2008

Left4Dead Week: The Befriendening

Left4Dead week will feature one short piece on Left4Dead each day this week to celebrate the full release of the game.

Several other bloggers, who shall remain nameless, are delaying playing Left4Dead until they can find some friends to play through with. The call for friends is pretty wide: if you've read any of these blogs, you'll see that they're asking for game tags in the comments post so that they can add their readers to their Steam or Xbox accounts.

I'd suggest that Left4Dead is best played with anonymous strangers. Not because griefing is fun, but because the game's cooperative mechanics brings out the best in people. You must keep everyone alive or you die. Horribly. And I've never had so many Steam friend requests as I have had with people I've played Left4Dead with.

(That's not to say I don't seem to end up taking the brunt of zombie abuse. I've yet to finish a 'movie' - a map sequence in Left4Dead parlance - without being killed between 6-10 seconds before rescue turns up. And everyone else getting away... for the greater good. If not achievements).

Saturday 22 November 2008

Left4Dead Week: The AI Director – Part Three – The Rise and Fall

Left4Dead week will feature one short piece on Left4Dead each day this week to celebrate the full release of the game.

A number of reviews have highlighted the sophistication of the spawn system, so that you never see the director spawning zombies directly - they always appear off screen and then rush you.

What reviewers don't seem to have mentioned as frequently is the way the level design aids and abets this. If you're in a wide open area, you can be sure the zombies will be clambering over a nearby fence, crashing through windows or running over a rooftop. And in enclosed areas, you'll find holes in the ceiling from which they'll pour. The most elegantly designed area for this is the start of the first map for No Mercy, which features in the demo.

An in a post 9/11 world, Valve can't be ignorant of the significance of watching bodies falling through space.

(No Mercy has the best opening area of any of the first maps. For the best opening sequence of a final map, you'll need to play through Dead Air. At which point one of my fellow players yelled Game Over man, Game Over! the second time we watched it through.)

Friday 21 November 2008

Left4Dead Week: An Open Question for the former Turtle Rock Studios

Left4Dead week will feature one short piece on Left4Dead each day this week to celebrate the full release of the game.

I see Left4Dead has inherited what I like to think of as the ‘grenade problem’. What I mean by this is that the investment required to get the AI to use grenades correctly is too high to justify; and unlike many other AI problems, an intermediate implementation (that is getting the AI to pickup and throw grenades badly) is worse than no implementation at all.

Ironically, the friendly AI bots in Counter Strike seem to use grenades reasonably well, and Turtle Rock Studios implemented this as well. So I was wondering what the issue behind not doing the same in Left4Dead was? And I suspect it is a simple return on investment problem. Left4Dead is intended as a coop game and friendly AI using grenades was well down the list.

(Other than that, great job guys).

[Edit: Robin has suggested an interesting alternative in the comments].

Thursday 20 November 2008

Left4Dead Week: The AI Director – Part Two – The Zombies

Left4Dead week will feature one short piece on Left4Dead each day this week to celebrate the full release of the game.

The problem with the AI director is that I think the implementation works too well for zombies, and won’t be adaptable enough for anything else. The quiet, eerie moments of being unsure whether an area will be filled with mindless undead, crouched shivering in a corner, leaning helplessly against a wall or vomiting up raw chunks of flesh, or completely empty; the variation in threats from rushing hordes, against the lesser special zombies (boomer, smoker or hunter), the adrenal rush of fighting a tank or trying to creep past a witch.

Contrast this with Half-Life 2, where there is a similar variety in enemies, but all of which are pre-figured by the environment you are moving through: no mix of head crabs, combine and Ant Lions together would make as much sense. And the simplicity of the zombie AI will make it hard to have a similar flood, of say, Nazis en mass. Any more intelligence in the enemies than that which the zombies display would dilute the flood to a surge or trickle, as they found alternate routes, held back or hid within the level to wait for you. The techniques used by the ALife in S.T.A.L.K.E.R. makes more sense for the most games: where each enemy has a distinct personality and set of goals to move through large free roaming levels.

Wednesday 19 November 2008

Left4Dead Week: The AI Director – Part One – The Musical

Left4Dead week will feature one short piece on Left4Dead each day this week to celebrate the full release of the game.

The AI director works well, especially in conjunction with the musical cues which are used to tell you when you are about to be swarmed with undead en mass. I suspect some of these cues will become repetitive over time – it would be good to mix them up a little with sound cues for the same effect (such as the sound of zombies crashing through a wall, or baying for blood in the distance). I also missed the sound of other people fighting the zombie apocalypse: surely the four survivors can’t be the only people trying to escape the city. The Miles Sound system API in Source works well for this as demonstrated by the sound of gunfire in the distance in Day of Defeat or Half-Life 2.

Tuesday 18 November 2008

Left4Dead Week: Destructible Scenery

Left4Dead week will feature one short piece on Left4Dead each day this week to celebrate the full release of the game.

Left4Dead has a reasonably robust implementation of destructible scenery, without reaching the flexibility of Fracture or Red Faction. Elements of the level, notably windows, doors and some walls can be destroyed; mostly by the marauding undead who feature in the game. There’s several nice features of the way Valve has implemented this:

1. There’s no obvious seaming of destructible elements, or any other indicator to differentiate destructible or non-destructible. This means you can never be sure if a wall will be torn asunder as a zombie crashes through it. Some walls do get destroyed too frequently to be a surprise: such as the wall below the collapsed room in the apartments; but I bet you didn’t know that one of the upstairs room walls can similarly be blown apart by a Hunter coming down from the roof.

2. Closed doors block the undead from moving through them - instead they start to bash chunks out of the door in horror movie cliché style. This can be used tactically, such as to hold up a flood of zombies while you shoot them apart.

3. The tank can tear up chunks of concrete and throw them at you. These chunks don’t have any long term effects, but it sure looks good.

4. The fragments of the destroyed scenery end up as physics elements which can be pushed around further, such as when a boomer or pipe bomb explodes.

5. You’re not forced to progress through any destructible scenery yourself: there’s always a route around. This means you don’t have to figure out which part of the map the level designer was hinting you should blow up.

Sunday 16 November 2008

Results for 'What is your favourite element;'; new poll

I guess this new fangled electricity thing is more popular than old reliable fire; kids these days have it lucky. Why in my day I had to cast spells of gravel element, while walking backwards through snow element twenty mile elements to school elements...

26 (15%)
24 (14%)
10 (6%)
18 (10%)
21 (12%)
9 (5%)
33 (19%)
13 (7%)
11 (6%)
15 (9%)
10 (6%)
11 (6%)
19 (11%)
17 (10%)
13 (7%)
10 (6%)
11 (6%)

New poll: having read the description of Unangband schools, which Unangband school of magic would you choose?

The Saga of Bondas the Ironman

There is not enough roguelike poetry in this world.

(For those unfamiliar with the term, Ironman implies that you don't shop, and only ever descend in the dungeon. Extreme Ironman involves taking the first downwards stair you find at every opportunity.)

Saturday 15 November 2008

Designing a Magic System - Part Fourteen (Classes)

(You'll probably want to read parts one, two, three, four, five, six, seven, eight, nine, ten, eleven, twelve and thirteen).

In part eleven, I suggested that a class-based system was the most appropriate mechanism for provide alternative spell types. In Unangband I cheat this slightly, and term the choices between different spellbooks schools. When you choose a school, you are actually choosing which spell book you start with, and which spell books are stocked in the shops. Each school has 4 spell books in increasing order of difficulty, which you can learn spells from, and these shape the starting experience as a player.

What experience should different classes provide? This is as much about the significance of the choice of class in the game. In a multi-player game choosing a class is as much about complementing the choices of the team you are on (or all choosing Pyro and spamming the opposition with flamethrowers in Team Fortress 2); in a single player game with multiple avatars, it is about wish fulfillment - what kind of person are you to lead others; in a single player game, each class must be capable of surviving the game on their own. It is a delicate balancing act to ensure that class is not necessarily a proxy choice for difficulty level - although many standard class choices end up having different difficulty curves throughout the game. I believe classes should instead be a choice about playing style.

Roguelikes are uniquely replayable, and class choice can be as much about playing particularly challenging games. On one hand, harder class choices should not be made available to starting players; on the other hand, harder class choices are required to learn and understand various advanced strategies of play. In Angband and variants, mages typically have a hard start and mid game, warriors have a harder mid game, and priests have an easy mid game and potentially hard end game due to their lack of damage output. As further anecdotal evidence, you may want to refer to analysis of the character dumps on the landder.

But I don't want to link spell choices to this implicit difficulty curve - and I have worked to ensure that the start game for mages is easier through increasing mana availability (although at the same time harder, because I have removed the link between mana gained and spells learned - these are now controlled by separate attributes, rather than Intelligence being a catch all for mages and Wisdom being the equivalent for priests). So to me, the playing style argument is the most compelling.

But what do I mean by playing style? Well in Angband, consider the difference in play mechanics between a mage, a warrior and a priest. The warrior is best bumping into monsters one at a time at melee distance, and built to endure frequent mistakes (the worst of which is holding down a direction key and filling the keyboard buffer); the priest is a weak warrior mage, with a ready supply of resets which makes their gameplay style very forgiving; the mage is a glass battleship, and plays more like a game of chess, where each choice has much greater impact and many more choices are available.

The function of schools in Unangband is primarily to facilitate spell choices, and secondarily to encourage different playing styles for mage-like classes. The schools I ended up creating are:

The school of Wizardry contains the most flexible spell selection for defense and a broad and powerful range of direct offensive spells. Wizardry has few weaknesses: no reliable method of
satisfying a wizard's hunger and few spells that can be used to attack an enemy without putting the wizard in harm's way. Wizards should be thoughtful in offense and quick to escape or evade an enemy that exhausts the resources at their disposal.

Aspiring Wizards start with the book of Cantrips.

The school of Druidry contains a wide variety of different spells, include a good low level offense, but is hampered by difficult to use defensive spells and offensive magic that takes a while to get
going and may leave the Druid in close proximity to harm should they fail to work. A Druid operates best when he is able to prepare the ground upon which he fights, and works best in open spaces: conjuring trees, calling forth lightning and fire and so on. This is also the Druid's weakness: he must operate in the open, and takes a while to prepare his magic, which means he can be overwhelmed before his magic can be used.

Novice Druids start with the book of Hedges.

The school of Mastery contains some useful low-level magics, but at higher levels is heavily reliant on the ability to summon and control minions for the great part of both offense and defense. This is a double-edged sword: while the minions are more than capable of providing the Master protection and dealing out damage, he has a heavy investment in them, and will have to pay a 'mana debt' or 'blood debt' should they be destroyed. This reliance on minions means that the tables can turn very quickly on the Master and get out of control.

Wouldbe Masters start with the book of Curses.

The school of Sorcery is both deceptively weak and strong. A Sorcerer lacks the immediate damage dealing capacity of the Wizard and the long term damage capability of the Druid, and does not have the same range of minions as the Master. The Sorcerer's spells and minions are useful in preparing the ground like the Druid, in particular with a range of traps and mimics, and enraging and drawing in the enemy. But his abilities to ensorcle perhaps any enemy, will give him opportunities and gambits far greater than the Master is capable of.

Neophyte Sorcerers start with the book of Glamours.

The school of Thaumaturgy contains the widest range of direct offensive spells, to allow a thaumaturgist to find and exploit the weakness of any opposition. The Thaumaturgical energies at his disposal randomly vary from individual to individual, and as a result, the exact spell selection will vary. The weakness of the Thaumaturgist is a distinct lack of flexibility in defense: with limited and hard to use escapes and utility magics.

Latent Thaumaturges start with the book of Fireworks.

In addition, there is a school for each semi-spell class, that is the Ranger, Artisan and Rogue classes who don't have access to attack magic, but do use a variety of utility spells. The Rangers prefer the Statecraft school, starting with the book of Trailcraft, Artisans prefer the Science school, starting with the book of Trades and Rogues prefer the Spellstealing school, starting with the book of Tricks.

The emphasis for Wizards and Thaumaturges is on spells that deliver damage to line of sight targets only, with the Wizard having the capability of evading or redirecting opponents that get too close, while the Thaumaturge tries to overwhelm them with greater variety of attacks. For Druids, Masters and Sorcers, the emphasis is on indirect damage, through devastating attack spells which take a while to take full effect for the Druid, through pets for the Master and through a combination of traps and usurping enemy assets for the Sorcerer. Indirect damage is lower risk and to compensate, these classes should require more complex set ups to get this damage delivered.

With these thematic ideas in place, and the base framework of spell choices to build it on, it becomes a matter of building the individual spell books for each class to implement these ideas. The spell books as they currently are designed are shown below:






Detect Monsters

Wizard Lock

Light Area

Magic Missile

Phase Door


Cure Light Wounds

Find Hidden Traps/Doors

Stinking Cloud

Confuse Monster

Detect Life

Dryad's Embrace

Lightning Spark



Find Water

Purify Self

Warp Wood




Detect Evil



Blood Binding


Detect Traps

Stinking Cloud

Find Familiar

Detect Minds

Wizard Lock


Mind Thrust

Temporary Displacement

Ignore Pain


Detect Doors/Stairs

Ego Whip

Force Bolt

Wizard Lock

Acid Splash




Ignore Pain


Thaumaturgic Missile

Find Flame

Fire Blast

Teleport Self

Spear of Light

Polymorph Other

Trap/Door Dest-ruction

Detect Power

Fire Bolt

Frost Bolt

Gauge Magic

Lightning Beam

Minor Acid Ball

Slow Poison

Wizard Light


Sleep Monster



Dryad's Tryst

Ent's Song

Satisfy Hunger

Sleep Monsters

Turn Stone to Mud


Minor Frost Ball


Snuff Small Life

Poison Missile

Curse Monster

Animate Dead

Sticks to Snakes

Change into Bat

Slip into Shadows

Sense Magic

Air Spirit

Curse Monsters

Fire Spirit

Darkness Bolt


Turn Undead

Summon Lemure

Create Golem





Animate Object

Change into Mouse


Enrage Monster

Probability Travel

Value Magic

Rune of Escape

Slow Metabolism

Gust of Wind


Spider's Web

Thaumaturgic Minor Bolt

Blind Monster




Minor Acid Ball

Smoke and Mirrors

Thaumaturgic Minor Beam


Minor Fire Ball

Thaumaturgic Bolt

Minor Lightning Ball

Dispel Magic

Acid Bolt

Lightning Beam II

Slow Monster

Frost Bolt II


Cone of Cold

Frost Ball

Recharge Item I


Ent's Seeds

Runic Magic


Ent's Draught

Change into Goat

Earth Spirit

Water Spirit

Wizard Eye

Sense Invisible

Unseen Servant

Dark Rituals

Animate Elements

Summon Insects

Vampiric Drain

Charm Bird or Mammal

Change into Cat

Charm Person


Charm Insect

Charm Reptile


Mind over Body

Mind's Eye

Psychic Blast


Alt Thaumaturgic Beam

Thaumaturgic Beam

Acid Ball

Alt Thaumaturgic Minor Ball


Thaumaturgic Ball

Thaumaturgic Minor Ball

Mass Sleep

Teleport Other

Haste Self


Wonder II


Fire Ball

Fire Swarm

Melting Ray

Dryad's Kiss



Mana Pool


Tree of Life




Swallowed by Shadow

Bind Demon

Mass Curse

Darkness Ball

Summon Spirit

Phantasmal Force

Banish Evil

Release Curse

Path of Blood


Thrust Away

Psychic Crown

Change into Serpent

Change into Wolf

Charm Monster

Flame's Reach

Test Magic

Wonder II

Arc of Thaumaturgy

Fire Ball

Thaumaturgic Ball II

Thaumaturgic Bolt II

Thaumaturgic Bolt III

Thaumaturgic Major Ball

Thaumaturgic Major Ball II

Key: Spell choices, where an equivalent spell exists for each class in italic

Summoning spells underlined

Direct damage spells in bold


What is obvious from the above chart, is that the desire to use classes to keep equivalent spell choices separate is in conflict with trying to use classes to keep a consistent playing style. For instance, the thematic linking between Druids and frost spells, and Thuamaturgist and fire and acid spells encouraged me initially to spread the summon elemental spirit spells out to these classes. This of course runs counter to the reasoning that Masters should be the summoning class. But if all elementals are summoned by Masters, then I end up in the same design problem that I highlighted by making all elemental bolts available to the same spell caster.

Even with these constraints in place, I keep redesigning the spell layout for each school. Since designing the first version of chart, I've changed my mind again and moved all the summon elemental spells back to the Master class. I worry that I'll be perpetually rearranging the chairs on this game design Titanic, unable to get off and actually release a final version of the game.

In part fifteen, I'll discuss more design decisions that I made to come up with this list and try to point to a better solution.

Saturday 8 November 2008

Laptop gaming

I've cracked and bought Left4Dead, earlier than I had planned, just to get access to the demo. As a laptop gamer, I thought I'd share a screen shot from the opening of the game with you (Click to enlarge).I'm downloading new drivers at the moment, but I'm not holding out much hope of resolving these graphic glitches.

In unrelated news, a regular reader of this blog, VRBones, was fortunate enough to be part of an interesting dialog with Clint Hocking, Creative Director at Ubisoft Montreal, about the ethics of Far Cry 2. It's thought provoking reading.

Friday 7 November 2008

Designing a Magic System - Part Thirteen (Digression)

(You'll probably want to read parts one, two, three, four, five, six, seven, eight, nine, ten, eleven and twelve).

So what is the appropriate mechanism for character progression? While I've argued previously that magic systems should use a class based progression system, this doesn't necessarily imply that only a single choice at the start of play should define what abilities the player has, and what order additional abilities are acquired in.

I'm going to develop here a terminology similar to the game design patterns I've already described to explore the progression options open to a game designer. Although I'm defining the patterns by name (highlighted in bold), I'm skipping the detailed methodology here for brevity. I've also not considered the 'Problem' part of the game design patterns in any detail. This is because it's not clear necessarily what the problem each progression type addresses, and, as I've discussed in part twelve, character progress is sometimes a solution in search of a problem.

There are two parts to character progression, that are interrelated but which can be considered separately.

The first is ability choice: that is what restrictions are placed on the choices the player makes to acquiring the possible abilities during the game. At one extreme is linear progression, where the player gains abilities in a fixed order throughout the game. The other extreme is no progression, where the player starts with all abilities that they can possibly have, and does not progress further. Careful consideration highlights a third extreme: where the player can acquire abilities in any order without restriction - I'll refer to this as open progression. Open progression sounds like skills, but is subtly different; with skills, there is still the potential for scalar progression for each skill, and some abilities may be unlocked with sufficiently high skill levels.

Skills are closer to open progression than talent trees (also called technology trees): with skills, the player may invest points in any skill at any time, but with a talent tree, some abilities are only accessible after investment has been made in other abilities. Abilities in talent trees can be restricted in a variety of different ways: such as through having one or more prerequisites that the player must have one, some or all of; having exclusions which prevent other skills from being learned; or requiring a minimum number of points from a pooled list, where existing abilities contribute one or more points towards the total required (this is one possible generalisation of prerequisites). Skills may be arranged in a talent tree like structure: the key differentiator is the frequency of choice, where talents indicate less frequent decisions be made as to which ability to acquire or progress, and skills indicate more frequent decisions (to the point of choosing where each skill point is invested). Talent trees are from a design point strongly related to technology trees, but technology trees require further investment to 'express' the ability - by developing an item, a unit or otherwise investing resource in an in-game element of play. And a variety of matrix development models, seen frequently in Japanese RPGs, represent the character progression in a two or three dimensional board, or a mini-game environment.

Slots are a mechanism for restricting open progression: the player may freely fill slots with abilities without regard for other abilities they have acquired. Sockets are like slots, except that the each item fits in a particular socket type, of which the player has one or more of (think of the restriction of the number of rings, amulets, armour etc. that can be worn). Slots and sockets can be restricted by encumbrance, which places further restrictions on the total number of abilities that can be carried by imposing some kind of numeric limit, and containers, which restrict equipment based on the equipment shape, requiring that the player fit together different shaped items in a number of virtual two-dimensional grids. Containers and sockets are usually represented by a paper doll system, which is a two or three dimensional model representing where slots or sockets can be filled. More complex three dimensional models allow abilities to be selected using a more complex design and modelling software.

Class progression limits the character progression by forcing the player to make a (potentially uninformed) decision at the start of play, which impacts on the overall abilities available. It is also possible to mix and match these progression types. For instance, class progression may then determine that the player gains some abilities through linear progression, and others through one or more talent trees or skills. And the majority of RPGs have a slot/socket/encumberance system for individuals.

The emphasis so far has been on single avatar games, but many games feature multiple avatars per player, each of which has it's individual character progression system. Multiple avatars may be controlled directly, or through a party system, where the player is forced to recruit additional avatars without necessarily having direct control of their starting abilities (or even advancement choices). Finally indirect control is typical for units, which are separate avatars which typically have fixed abilities, but require the character progress, typically through a technology tree type, in order to be able to recruit and control more powerful units.

The second mechanism is ability acquirement: that is how does the player acquire abilities as they progress.

The three axis of acquirement are currency, which supports complete interchangeability of accrued acquisition between abilities, various item systems, where abilities are acquired separately and not interchangeable, and achievement systems, which track acquisition of each ability separately. I'm not going to exhaustively list game design patterns of acquisition here, but note that the concept of drawing cards from a deck into a hand falls within this scope.

There are a number of important design issues around the ability acquirement mechanics. I've already highlighted that problem with acquirement grind, caused by allowing small improvements at low difficulty levels accumulate to large improvements. This is a big problem with currency systems, but can also affect some achievement systems where an achievement is gained through the result of accumulating a large number of individual actions. This can even occur with items, when the ability choice system does not sufficiently restrict the number of a particular item that can be acquired. Even ammunition can be unbalancing in this regard.

Another issue is the fallacy of point equivalence. This is the incorrect assumption that two abilities are equally useful (or the scalar improvement of two abilities are equally useful). In reality, a well-designed game will almost always have one ability to be more useful than another at any point in time (otherwise, why are the abilities any different at all). Allowing the points, or currency, accumulated towards acquiring or improving one ability to be transferred across to another ability will mean that the player will almost always favour one ability and disregard the other.

This suggests that a currency system will encourage grinding and discourage acquiring unusual abilities. A currency system is still important for developing an in-game economy, making them suited more to multiplayer games where a real economy can develop, as opposed to single player games which can only support the simulation of an economy and not the real thing. If you do intend to have currency in a single player game, you are strongly urged to read 'Designing a Single Player Economy', and play Freshly Picked: Tingle's Rosy Rupeeland for further inspiration.

Defining types of character progression in games seems an academic exercise, and one I'll probably pursue further in a different format. For the moment, this is intended as a checklist and inspiration for the various ways you can design character progression in a game.

But it is important to define the language of games further, and game design patterns offer a systematic method of doing so. We are still in the infancy of game design: although the forms are becoming more regular, we still don't have a common vocabulary to define game design the way we talk about the technical language of film. We need the game design equivalent for the terms long shot, pan and zoom. But more than that: game design is at its heart mathematical and logical, and so we can attempt to take this vocabulary and define it more formally using symbolic logic.

With a formal model for game design, we can potentially prove that a game can be completed (unless we fall within the bounds of the Halting Problem), and vary the rules to explore the game space. We could design games algorithmically, or the spaces within games using procedural generation based on the formal rules of the game expressed as an expert system. If this concept intrigues you, I recommend reading Mark J Nelson's work on automated support for game design. I can only sketch the briefest of concepts here, but a fuller treatment would be the subject of more post-graduate work.

Back on track in part fourteen.