## A Basic Introduction to Depth

I end up writing a lot about depth. It’s the only universal constant for games far as I can tell. Everything always comes back to depth, so here’s one such writing on what depth is.

Depth is in some ways the raison d’etre of games. Many people have varying definitions of it, but my personal one is the number of non-redundant game states possible within a game. Non-redundant being used as my catch-all to eliminate game states that are essentially the same for all practical purposes.

A game in which jumps are only possible at specific contextual points and always cross the gap perfectly without allowing player input in the process has less depth than a game which allows a player to jump in a perfectly fixed arc when they press the button, which has less depth than a game that allows the player to control the character while that character is in the air, which has less depth than a game which allows you to also vary the jump height by the length of time the button is held, which has less depth than also inheriting your ground velocity in the transition to the air, which has less depth than allowing another jump in midair.

To resimplify the example, imagine you have fixed jump arcs and you can press jump again to jump in midair at a specific point in the jump, this creates 3 possibilities, jump in the normal arc, jump in the normal arc with another jump at the point specified, or don’t jump at all. Lets allow you to press jump at any arbitrary point in the first jump, this creates additional possibilities based on the number of points that actually exist in that jump arc. Allowing the player to modulate the height of each jump by the amount of time they hold the button down creates a number of possibilities relative to the amount of points at which holding or not holding the button down creates divergent game states, and this is then multiplied by the number of points at which they are allowed to double jump. In an exponential fashion, each of these factors creates between them an even larger number of potential game states.

The tricky part is with obsoletion or dominant game states/strategies. Some techniques, such as correcting for bullet spray in counter strike, obsolete some game states. If you know how to correct for bullet spray, you always will. Is this depth? Are those obsoleted states redundant? I would personally answer no, they are not redundant, and yes, this technique is something that contributes to depth, but in relation to it is dominant play styles. In some games, particular options or play styles obsolete others, such as Yun and Chun being the best characters in SF3, and completely destroying the rest of the cast so badly that in the current metagame many characters simply aren’t played. A similar situation exists in smash bros, where lower tier characters get snubbed by balance issues. In some games there are simply strategies so good that everyone does them and it prevents a much wider range of strategies from playing out, such as planking in Brawl, which eliminated a ton of the on-stage game. Do these things result in a loss in depth? Compare to a game where the characters were balanced and all of them could be seen playing at a high tournament level? I’d say yes, the dominance in these play styles results in a loss in depth for the game, though it is hard to say where exactly those extra game states that are lost to this dominance go. I have no term for precisely describing it and my definition of depth is thereby insufficient.

Super Monkey Ball is a simple game to understand and to play. It has relatively few complexities in its operational methods, one of which being that special diagonal movement can result in faster acceleration, yet the particular physics system and composition of the levels creates a large number of ways the goal can be attained, representing a type of depth.

On the other hand, some games have elements that I completely feel are redundant, not just accomplishing the same goals, but doing them by methods that are close to identical. Deus Ex featured lock picking and multi-tool use, but both of these functioned identically, allowing the player to wave a lockpick or multi-tool at a given node, having a bar move and after waiting a bit, the object would activate, opening a lock or otherwise. Hacking was similar, pressing a button then waiting for a bar to finish. The sequel by comparison had all locks be little minigames with a variety of scenarios possible within that mini-game. They lost some elements of level progression related to resource management, but also eliminated looking at bars move across the screen while doing nothing or holding a button down, which represents a net gain in depth, as an additive to the depth in the rest of the system. More depth could be gained if these elements were somehow integrated with the rest of the system, becoming a multiplicative depth gain instead of an additive depth gain. I have no proposal for how this is possible in this particular example, it’s just how depth works.

Many turn based RPG games feature a number of abilities that overlap each other with only slight differences, differences in elemental type, effect, attack power, and generally function is rather common, but does little to make the game a more complex thought process as many of the results of each action are just damage and modifications to damage rates. In order to have depth, a game needs more variables in flux than just HP, such as positional values on characters, acceleration, velocity, states, and occupation of those states. A common and easy means to achieve that is through physical information, information related to the spatial positioning and dimensions of the object. Thus turn based RPGs may be complex or have many game states, but few truly have depth (and I’d like to call out SMT Nocturne as being an exception and competitive pokemon, even if the latter is a silly clusterfuck).

Dialogue is also usually a poor representation of depth or challenge, as it lacks physical information, such as spatial positioning, time sensitivity, velocity acceleration, temperature or other possible analog varaibles. By contrast, most dialogue is just a set of choices leading to other sets of choices with variables occasionally remembering prior choices, altering the outcome of future ones. In comparison to something like mario or civilization, this usually represents a low level of depth, and probably always will until better conversational AI is feasible on a commercial level (or at all).

Difficulty is important in relation to depth, as a system may have a lot of depth, but without difficulty it won’t be brought out. There will be no reason to explore it and learn what’s possible. Games are the art of challenge, and depth is a means to a more varied as well as intellectual challenge. However without difficulty, suboptimal strategies may be good enough for many players and hard counters or ideal options for specific situations may become soft or nonexistent ones. Normal pokemon may have a lot of depth, but only competitive pokemon really brings it out by forcing players to develop and learn strategies in order to overcome others who may use those strategies against them. A similar example would be many speedrun games like mirror’s edge, where many of the advanced techniques have incredible depth in of themselves, but without the pressure of going fast, are never necessary or even practical in the normal game. One example from Mirror’s Edge is the kick glitch, which has variance based on the angle relative to the wall, the time running on the wall, the angle facing away from the wall, and is completely impractical for anything but getting through levels more quickly, despite being one of the deepest and most interesting things in the game. Speedruns give many of these techniques a reason to exist, and a pressure to use them competently in order to perform well. Difficulty is related to the prior issue of dominant strategies, and again I have an issue with whether it is redundancy going on here or not, and I think there is a more precise term. It is the dominant strategy problem in reverse, where instead of having a strategy that obsoletes or represses others, many strategies are possible, but pointless.

Here’s my big 4 criteria for whether a game, or a specific mechanic in a game has depth:

1. Does the game feature a variety of options all with their own niche? Alternately does this specific option occupy its own niche?
2. Does this/these option(s) have a variety of applications in the game?
3. Does this/these option(s) allow the player to leverage it to get more or less out of it, or different results that may have value relative to the situation?
4. Can this/these option(s) combine with other options to either create new states entirely, or to generally form a type of synergy?

Not all options in a game need to have all 4 of these traits. Not all games have this type of structure where this criteria is even applicable. You will have to judge a bit for yourself, but this is a good starting point for analysis or design, meaning they’re important for game reviewers, game critics, and game designers. I write more about these traits here.

Mirror’s Edge’s kick glitch fits the bill perfectly. It can only be used when wallrunning on a wall that goes off a ledge. Some traversals are only possible with the kick glitch, and others are just more efficient with it, thus it has a niche. It can be used to cross gaps, move more quickly, fall further distances, and chain together other wallruns, thus it has a multitude of applications. Players can use it more well or poorly, getting more or less speed out of it, controlling the angle differently, and coming out of the wallrun at different points, thus it has variance in its application relative to the situation and to more effective use. Double jumping or variable height jumping are other perfect examples that I will leave you to deconstruct.

I think having an understanding of what depth is and what elements in a game add to it or harm it is an important thing for absolutely anyone talking about games critically.

## Different Types of Depth

I think a good semantic here is, “Potential Depth” or “Absolute Depth”, referring to the possibilities inherent in the system regardless of who is looking at the system or not, and “Relevant Depth” or “Accessible Depth” to refer to depth as it applies to the playerbase. Both can be referred to more simply as depth, and both are consistent with how most people use the word depth in a broad sense.

Another dichotomy that can be drawn is between depth and breadth. This is another component of how a system can be complex, but not deep. Dynasty Warriors has a lot of different characters, but all of these characters only have a few attacks, so there is a limited range of expression with each individual character. There is a little depth added by having so many characters, the characters are like options unto themselves, but if each one is shallow or occupies an overlapping design space, then the depth gain is small.

Design space is also an important thing to have relative to this. There may be two options, but if both are the same option, they’re redundant, or overlapping as both game states and in design space. Design space is an abstract conception of a game as a collection of elements or niches. Different characters in fighting games typically occupy different design spaces, between rushdown, keepaway, grappler, shoto, or other archetypes. Different weapons in FPS games typically occupy different design spaces, between machine guns, rocket launchers, grenade launchers, snipers, shotguns, or other weapons. In games like Call of Duty or other realistic shooters, there is typically a big overlap in design space. Like in Vanquish, the Assault Rifle, Heavy Machine Gun, and Boost Machine Gun all have an overlapping design space, they’re all rapidfire machine gun type of weapons, and generally are good at the same things. This is a good general weapon type for many encounters, so having an overlap like that can work out rather well, because it means you’re able to carry multiple of a good general use type of weapon, making it just a bit harder to run out of ammo. The downside of overlapping design spaces is that as options are more similar in their function, the differences between the options tends towards creating a clear best between them. This is the Boost Machine Gun in Vanquish, and the SCAR in Crysis for example, or Toad/Peach/Yoshi in Mario Kart 64. Mario Kart 64 – Analyzing and Tiering Overlapping design space can serve a role in a game, but it doesn’t exactly lead to depth necessarily, unless the elements themselves have depth. It is possible to balance overlapping elements, and it is a lot easier usually than balancing elements that exist in disparate design spaces. A shortcut to balancing out a disparate design space is typically to homogenize the elements so they can be easily compared to one another, while also creating overlap and redundancy, reducing the potential depth of the system.

When it comes to design space, there is also the matter of something much like a nested tree, or a russian Matryoshka doll. Design spaces can be nested inside of design spaces. An example could be characters, each character represents an element in a total design space, having their own niche they play to (like peach, jigglypuff, marth, and fox in smash bros), but then within each character there is another design space, where the options they have all have their own niche (like Marth’s Fair, Fsmash, Dair, Dtilt, counter, and dancing blade), then there are submodalities of options which have their own design space, like how the dancing blade can vary the speed of its swings and also select between up, down, and forward attacks. And all of these design spaces and elements thereof nest inside each other, while also defining the niche of the design space above them. So collectively, all the small elements add up to all the larger elements, which each cement the position in design space of those elements.

To cover overlap a bit further, in order to prevent overlap, there must be room in the overall design space for more than one way of defining an elements characteristics. If the only property that a given element has is its damage, and absolutely nothing else, then every turn, you just deal damage and whoever exhausts the other entity’s damage pool first wins. If all the different options just deal different damage, then no option can occupy a non-overlapping design space with any other option. Most games create a varied design space through the inclusion of physical or temporal differences in the options, such as different periods of time over which an option is active, different movement through space, occupation of different physical dimensions. More abstract properties are also frequently assigned to avoid overlap, such as elemental typing, super armor, invincibility, buffs/debuffs, or other factors.

And returning back to depth versus breadth, the essential formula is based on interactions between the elements. If the elements are segregated then the depth gain is additive, if the elements are integrated, then the depth gain is multiplicative. A game may have many elements side by side, such as a large number of characters, or a combat mode next to an exploration mode, next to a race mode, next to a puzzle mode, but unless these each have depth unto themselves, or integrate with each other in some way to create a greater depth than any individually. Ideally you want a few nested design spaces that each contain a number of elements with unique characteristics. The other big deal is how much options are not just separated from one another but irrelevant to one another. In Quake, you have 8 weapons, in Call of Duty Ghosts, you have 52 (counting explosives and side arms). Many of these weapon options overlap each other, there are only 11 weapon categories in Call of Duty, and to further compress the range of expression available, only 3~ weapons can be equipped at once. This decision to only have a certain number of weapons equipped at one time creates two levels of design space, a broad high-level one with all 51 weapons (because these are selected typically before the match and are long term decisions), and a very narrow low-level one with only 3 or so (the weapons you actively can switch between, each with very short term consequences on individual shootouts). Specifics such as what weapon types can be simultaneously equipped can further compress what is possible in the low level design space, as does the huge overlap within weapon types. Meanwhile in Quake, all the weapons are available simultaneously, and there is a very short delay in weapon switching, allowing multi-weapon combos to be very viable. The higher level the choices, the less that the choices can hard counter other ones and remain fair (you don’t want to lose just because you picked the wrong character or weapon loadout), leading to differences between them becoming more arbitrary and more stylistic. Thereby, Quake has a huge Depth, and Call of Duty has a huge Breadth. Dark Souls has a large Depth, where Skyrim has a large Breadth. Breadth does contribute in part to depth, but doing a lot of things in a shallow way cannot compare to doing a few things in a deep way. It is like stacking a linear curve next to an exponential one.