Cold Take #40 - The Retreat Range Bonus

Cold Takes usually cover a concept used in the design of Zero-K, but this one is about a term invented by players to describe an issue with the game. This issue involved the "retreat range bonus", but the term was initially perplexing because it describes something that is both emergent and ubiquitous. Nobody could tell me how other games dealt with it, and it seemed very hard to remove without breaking some of the basic rules of Zero-K.

The retreat range bonus is the apparent range gained by units as they retreat from a battle. Consider two identical units called Chaser and Runner, locked in a battle where Chaser follows Runner while Runner tries to retreat. The retreat range bonus is the observation that, at a certain distance, Runner will be able to fire, while Chaser cannot. In other words, it appears as if Runner gained bonus range on Chaser merely by retreating. Taken at face value, this looks like a weird arbitrary bonus, and the type of thing Zero-K would certainly not want.

The paradox of the retreat range bonus is that it was not added; it is just the inevitable result of the common type of game physics. If a game physically simulates its projectiles, then it probably has some form of retreat range bonus. Many, possibly all, first-person shooters have it, and there might even be a term for it in that space. Games like Supreme Commander and Planetary Annihilation should have it too, but to this day I have not found any discussion of retreat range in those games. I am often met with confusion when I ask people about it, even after explaining the generality of the mechanism.

The retreat range bonus is caused by units leading their shots. In other words, to hit a moving target, you need to shoot at where it is going to be, rather than where it is. In particular, for a unit to hit a fleeing target near the edge of its range, it would have to fire at a point beyond its range. Doing so would violate the No Void Ray rule, i.e. that the capabilities of weapons are independent of their target, so the unit cannot shoot at such a target. In the case of Chaser and Runner, both units are just within each other's range, but Chaser is moving towards Runner while Runner is moving away, so only Runner gets to shoot. The effect is compounded by the fact that units predict when an enemy will enter range, and fire towards the edge of their range in anticipation.

The retreat range bonus is fundamentally caused by a lack of Galilean relativity. Galilean relativity only really shows up in actual sports, and is responsible for mechanics such as taking a run-up to throw a ball faster. Simulated games tend to avoid it, and are right to do so. Humans are pretty good at accounting for relativity when doing human things, but not when shooting pretend rocket launchers. Imagine firing while strafing, only for the shot to go wide due to your own velocity. I would definitely play a Zero-K mod with Galilean relativity, just to experience the nonsense, but I expect it would make units quite stupid, as many of them would want to suddenly lurch towards their target for extra range as they fire.

So far so good. The retreat range bonus is baked into the game, and removing it would make less sense than leaving it in. The problems arise when we consider the tactical implications. The