Zero-K units are generally quite simple, with many of them designed around a single weapon or ability. The idea is that the complexity of an army should come from how it combines unit types, rather than having any individual unit be particularly complicated. I call this the principle of atomic unit design, because it characterises units as the building blocks of armies, and simple units are, in a sense, indivisible. Simplicity is a good enough goal on its own, but atomic unit design also has an important role in fighting monospam.

Monospam, i.e. spamming a single unit type, can be a contentious issue in RTS. Many players consider such a strategy "unfair" or "cheap", and games are often designed to discourage it, including Zero-K. This makes Zero-K a bit unusual within the Total Annihilation lineage, since TA had a bit of a reputation for monospam, and many successors dealt with it by culling the "excess" units. Zero-K went the other way, and found ways to balance a large unit roster without the resulting monospam. But before we get to that, we need to pin down what makes monospam powerful in the first place.

Monospam derives a lot of its power from being easy to manage. The logistics are simple. Just set your factory to repeat-build Scorchers, spam Ctrl+Z to keep them all selected, then repeatedly hit your opponent with them. The Scorchers move at the same speed and want to fight the same types of battles. But mix in more unit types, and it becomes much more complicated. Even maintaining the right mix is a challenge, since different units often die at different rates, and reinforcements take time to reach the fight. A mixed army that loses most of one type has to wait for the build ratios to be adjusted, while monospam can rely on a constant stream of appropriate reinforcements.

To skew things further, mixed armies are as bad as their weakest unit across many attributes. For example, mixed armies move at the speed of their slowest unit, and are as vulnerable to attrition as their most fragile. Consider an army of tanky Minotaurs and glass cannon Ogres. Such an army is either going to lose a lot of Ogres, or it is going to avoid taking fights that Minotaurs would weather without hesitation. In many situations, half an army wants to fight while the other half wants to run away. None of this is an issue for an army of a single unit type, with uniform strengths and weaknesses. Essentially, most units synergise best with themselves.

So, why do we want to discourage monospam? In short, because there is no crunch in easy decisions, and Zero-K is largely about deciding what to build and how to use it. This is much more involved when dealing with multiple unit types, both on your side and in the enemy army. And, as mentioned previously, the goal is mixed armies of combat units. Mixing battle tanks and anti-air is fine, but the tactical goals for such an army are often quite simple, depending on the type of enemy that is coming at you.

Now that we know what makes monospam powerful, how can we avoid it? The first principle is that mixed armies are 'allowed' to be much more powerful than monospam. My gut says 1.5-2x as powerful, but there is no definite value. The principle is great for guiding balance discussion though. For example, say we are thinking about how Rover might counter Fencer. Scorcher is a decent suggestion, but then some theorycrafter objects that Scorcher is solved by mixing in a few Rippers. At this point, we can invoke the principle, and say that Scorcher losing to a mix of units is fine. Forcing your opponent into a mixed army is half the battle, with the other half being to wait for them to succumb to the extra complexity. So we are free to focus on whether pure Scorcher beats pure Fencer.

Likewise, the second principle for avoiding monospam is that everything needs a hardcounter. It is not enough for a unit to have bad matchups, it needs some absolutely terrible ones. This because straight-up cost-for-cost fights fail to take logistic and self-synergistic advantages into account, and such fights in a vacuum are an important part of judging counter relationships. So any unit that manages to not lose too badly against anything is a prime candidate for monospam. This is not to say that hardcounters have to feature prominently in how the game plays, they just have to be lurking in the background, threatening players with annihilation if they invest too much into one unit type.

This is where atomic unit design comes into play. A unit that does one thing well tends to have weaknesses everywhere else, so must rely on other units to cover those weaknesses. Atomic unit design is not a strict rule though, as it often fights the Rule of Cool. This is a hard fight, especially when big units are concerned, but we still try to keep the abilities of complicated units pointed towards the same purpose. Sea has struggled the most with the Rule of Cool, since ships want to have multiple weapons, and the disparate weapons of Siren are a remaining nod in that direction. The worst offender was Envoy, which used to have a depth charge that acted as inbuilt riot support against anything on or below the water.

Factory abilities further dilute the idea of atomic unit design. If you count things like personal shields, jumpjets, and spider legs as abilities, then a lot of units have two abilities; one weapon and one utility ability appropriate to their factory. However, this extra complexity is well worth it, as having an ability in common strengthens the feel of factories as cohesive factions. The same could be said of, say, Zerg Burrow. Besides, a "faction ability", one shared by many units, has a much lower complexity penalty than an ability that arbitrarily exists for a single unit.

Atomic unit design also applies to structures. For example, Complete Annihilation had a few types of metal extractor, including an armed metal extractor. This structure was not atomic since it had two distinct abilities, metal extraction and a laser turret, so it was removed in favour of the more interesting method of defending a metal extractor: just make a Lotus. This confers all the subtlety inherent in atomic units, A turret might be built forwards to better protect the mex, or in a more defensive position and use the mex as cover. A weak raiding party might have to choose between killing the turret or the extractor. Armed metal extractors provide none of these decisions, approaching one is the same every time, and a fight with one only has two possible outcomes.

Commanders, being the opposite of simple, are a constant thorn in the side of atomic unit design. They are upgraded a bit like a composition of units, with each module adding a single weapon or ability, but fight like a single unit. A high level commander is akin to a one-unit monospam, with all the logistic simplicity and self-synergy, so it needs strong counters. This is hard to square with the feel of commanders, but that deserves its own whole article.

By now you might be wondering, is this all just Quant's Rule? Yes and no, I would say that the ideas are complementary. Atomic unit design is more of a goal than a method, while Quant's Rule is not so strict about how many strengths a unit can have. Quant's Rule guides us through day-to-day balance changes, while atomic unit design is more holistic. Waffling aside, it is mostly just useful to look at things from multiple directions, and it should not be surprising that many of the principles behind Zero-K lead to the same place. So stay tuned for the third I can't believe it's not Quant's Rule article, where I expect to cover Moonwells and the nature of greed.

Index of Cold Takes[zero-k.info]

Most player actions in real time strategy boil down to giving commands. After all, these are games about telling units what to do. But there is a subtle difference between RTS and most other genres, in that players tend to act indirectly, by assigning goals to units. The game world itself is only ever affected by units as they try to achieve their goals. This takes a certain level of unit intelligence, and the stakes are high. The fantasy of commanding an army can be shattered by a single unit wandering off in a weird direction.

Issuing commands also has to feel good, since it is your primary way of interacting with the game. This implies that common commands should be small and simple, like short words. In fact, commands can be thought of as the language used by players to tell their units what to do. This analogy turns unit control into a communication problem; how can the player communicate their grand plans to the fragile bundles of code that stand-in for the brains of their units?

The units of Zero-K are relatively smart. Here are some examples.

• Units in almost all games know how to close range with the enemy, but Zero-K units also know how to step backwards when the enemy gets uncomfortably close.
  
• They can be told to hold their fire against cheap targets, and know how to stop short of firing enough missiles to kill something twice over.
  
• They can be told to repair or reclaim everything in an area, rather than requiring that the player point out each target individually.
  
• Some can be told to avoid wasting their precious reload time on wobbly radar dots, while others can be told to fire in the general direction of distant targets.
  
• Units even know how to spread themselves out along a line.

The examples above hardly seem earth-shattering, but that is by design. Zero-K units are only much smarter than average because they understand a wider range of commands. The more complicated behaviours, such as the ability to move away from enemies, are optional. Set a unit to hold position and avoid telling it to Attack Move, and it will stay put. This is vital because the principle fight your opponent, not over-automated ingrained unit behaviours is just as important as fight your opponent, not the UI.

In short, Zero-K units are smart by virtue of their expanded command vocabulary, rather than by making decisions themselves. Units should not be making significant decisions, those are for the player to make, because otherwise we start diluting the "Strategy" in RTS. To this end, the complexity of each command has to be quite limited. Notice how the examples above were explained in about half a sentence? You have to be able to to describe your intention when giving commands, otherwise unit control becomes a process of clicking random buttons while hoping for a good result. So unit behaviours need to be predictable. For example, the "keep enemies at a distance" aspect of Attack Move only considers the closest enemy, since a whole-battle view would be too chaotic.

Commands are great, but how do they relate to the smartest unit in Zero-K? Well, players assign goals to units, which the units then try to execute. Achieving goals seems like a good measure of intelligence, so we can think of the smartest unit as the one that is the best at using its abilities to achieve goals. This includes goals that the player has trouble communicating due to a limited command vocabulary, so as to not give a free pass to abilities that are trapped behind poor UI. Also, since we are talking about game AI, it is more useful to think in terms of "least stupid", where stupidity is the misuse of an ability in pursuit of some goal.

The stupidity formulation of smartness turns abilities into liabilities. For example, if you tell a unit to move East and it ends up walking West, then we would say it uses its movement stupidly. But if the unit has no legs, so fails to move at all, we can hardly blame its failure to achieve the goal on its inbuilt AI. Thus, the only units with "perfect" pathfinding are those with the inability to move. And being incapable of failing is almost like intelligence.

So there you have it. The smartest unit in Zero-K is the humble Storage. It has a single ability - to blow itself up - and it is very rarely a good idea. Consider some alternative candidates. Most energy structures have impressive explosions, so it is more conceivable that a player would want to give them some sort of Fire At Will stance. Solar Collectors are out due to the wealth of agency bestowed upon them by the ability to armour up. But perhaps you have a more normal, less technical, definition of unit. One that involves the ability to move. In that case, I might have to argue for Aspis, the mobile shield generator, for the title of smartest unit. But if you have alternative candidates, be sure to post them.

So let's take stock of Aspis's abilities. Being unarmed is a good start, since deciding where and when to fire is a whole can of worms. Then there is the issue of pathfinding, which I could have avoided by nominating a plane or gunship. However, with great mobility comes great responsibility, so even Owls need to be pretty smart to not fly into an untimely end. No, a slow ground unit is safer, as its low speed makes it less responsible for its fate. And besides, the pathfinding in Zero-K is pretty good.

Aspis can also charge its shield, float, morph, and self-destruct. Floating and morphing are niche options for Aspis, and self-destructing is very rarely good. That leaves charging, which can be toggled on or off, and is integrated into the priority system. So Aspis has a pretty good command vocabulary in this area. Remember, it is not on Aspis to optimise its energy drain for the overall economy, it just needs to have a rich set of ways for the player to tell it what to do. So Aspis is very good at using its abilities. Now, those of you with some shield experience might be wondering, what about shield link? Aspis can share its shield charge with nearby shields, and there are some well known ways to exploit this ability.

Aspis' bid for the title of smartest unit hinges on the fact that shield link is a passive ability. Think back to Storage, is it "smart" or "stupid" for blocking projectiles? No, being hit by projectiles is part of being a Storage, it is a passive rather than an active ability. So too with shield link. If two allied shields touch, they share charge. Nobody can control it, and this sort of thing is a powerful technique for making units seem smart. Simply avoid giving units opportunities to be stupid.

Imagine if Aspis could control when to link, it would be an absolute AI nightmare. Linking is great when you need to pump charge into a Felon, but it can send a shield cluster below the threshold required to block tacnukes. The decision to link or not would take global information into account, and the best course of action would change too fast for players to manually control. A configurable linking stance would be unwieldy and riddled with edge cases, making it unpredictable. So it is better to keep linking innate, and let both sides of a battle work its straightforward behaviour into their plans.

Shield link is the highest-profile case of making an ability passive to avoid tricky optimisations, but we have many other more subtle ones. For example, Snitch and Imp have the ability to hide themselves by burrowing when stationary. If they took a significant amount of time to unburrow, then whether to burrow would be a decision with many strategic factors. Rather than make this decision, or make players manually press the burrow button, we made unburrowing near-instantaneous. Here are a few more examples.

• Bulkhead and Fencer pack up quickly for similar reasons.
  
• Units cannot hurt themselves with area of effect damage, as firing safely has tradeoffs.
  
• Vehicles are very bad at moving in reverse, so that they do not seriously consider doing it.

To sum up, unit intelligence has three parts; vocabulary, competence, and not expecting too much. Think about what is going on next time you encounter a stupid unit. Does it lack the command language to understand what you are trying to tell it, does it lack the competence to achieve the goal, or do its abilities mean it has to solve complex optimisation problems which lack a satisfactory answer?

Index of Cold Takes[zero-k.info]