Cold Takes/9 - Energy as Supply

Cold Take #9 - Energy as Supply

Posted March 23, 2024

Why does Zero-K have energy? The previous article stopped just short of asking this question, but it is well worth asking. Continuing on, everything costs equal amounts of metal and energy, so it would seem simple enough to drop energy from the equation. Doing so would certainly make the economy smoother. Look at the Command and Conquer franchise, it seems to do just fine with one resource. But hold on, that is not quite right, since C&C has another resource, power, which plays much the same role as energy in Zero-K. Both resources are used to control the pace of escalation in their respective games.

Energy in Zero-K is like houses in Age of Empires, or Supply Depots in Starcraft. Fundamentally, these resources act as an expandable limit on some other aspect of the game, while being fairly unlimited themselves. The big difference is that houses limit the size of your army, while energy limits your rate of production. But we can call them both supply resources, as the effect these resources is to make it more expensive to build something for the first time around. Or to give it a more positive spin, supply provides a discount for rebuilding back up to your previous capacity, be it army, rate of production, or something else. Many resources fit the supply mould once you see the pattern.

Consuming supply is generally a good thing, as units would prefer to do so than cost an equivalent amount of resources. Consider the Supply Depots in Starcraft, which cost 100 minerals and produce 8 supply. Now consider two variations on the Marine, if we ignore things like build times and hard supply caps, which is more powerful?

• The original Marine that costs 50 minerals and 1 supply.
• A modified Marine that costs 25 minerals and 3 supply.

A point of supply costs 12.5 minerals, so the converted cost of each Marine is 62.5 minerals. Notably, the full price only has to be paid to expand your army beyond its previous size. If your army dies, then you only need to pay the base minerals cost to rebuild. The modified Marine much cheaper in this case, so it would usually be considered more powerful. Of course, factors such as the army cap and the build time of Supply Depots would make the original Marine better in some cases, but the general point holds. This is what it means for supply to act as a discount on rebuilding.

The same supply dynamic happens Zero-K, just with production and energy, rather than armies and houses. Consider a bare bones economy, with just solar collectors and metal extractors (mexes). A mex makes +2 metal while a solar makes +2 energy. All construction costs the same amount of metal as energy, so every single bit of metal has to eventually be paired with the same amount of energy, if it is to be spent. This makes solar collectors act as a supply structure for mexes. Increasing your total metal income, for the first time, is more expensive than rebuilding after a raid.

Supply, in any game, exists to slow players down as they try to blast through the early stages of the game. It stops aggressive Starcraft players executing unbeatable all-in rushes with unreasonably large armies, and it stops Zero-K players greedily grabbing every single metal spot in an expanding cloud of constructors. This is vital for a game with income so strongly tied to territory, since the openings of such games can devolve into an all-out land grab. Overly explosive expansion runs the risk of determining the winner via early economic superiority, which feels bad and makes it hard to reach the midgame. Mexes have had their cost adjusted over the years with this balance in mind.

Metal extractors were quite cheap in Complete Annihilation, costing as little as 50 metal, but their cost rose to 75 fairly early on. Mex cost peaked at 90 metal in Zero-K and it has since dropped to 85. It takes approximately one solar, costing 70, to support a mex, so taking a new metal spot costs 155 in total, and 85 to rebuild, provided the solar is sitting safe in your base. It can be even cheaper though, as dead mexes leave 40% of their cost in wreckage, so rebuilding can only cost 51 metal. This might not seem like much, but a 100 metal discount on rebuilding adds up and stabilises the early game. Recovering from a raid would be much harder without this discount, however, reducing the cost of mexes to compensate would lead to explosive expansion. The game could probably be rebalanced with the discount removed, probably involving weaker raiders, but it would be a game of less back and forth, since losing a mex would be inherently more impactful.

There are many ways to make a supply system. The most common implementation has you try to build a unit, hear a voice yell "Construct additional Pylons", and then has you sit on your hands until a pylon is built. Many people find this frustrating, and it looks a lot like fighting the UI, so Zero-K opts for a more forgiving approach. The main differences are:

• Energy and metal can be stockpiled.
• Energy is supply for the rate of production, not for the total amount you can produce.

Stockpiling lets you build up an energy buffer, and even if you run out, excess metal will be stored until the lack of energy is resolved. This would be like stunning units in Starcraft that exceed your current housing capacity, but still allowing them to be built. The basic properties of supply are still present, but overextending is not an immediate concern, which gives players more leeway. This is a bit of a double-edged sword though, since a blunt system is much easier to teach. Players are highly motivated to make a house when their entire production is being held for ransom. Storage makes it harder to correlate problems with their solutions, and people might even use their metal storage for long term storage, rather than as a temporary buffer. So there are legibility downsides to flexibility. C&C games may have found a good middle ground, since a lack of power shuts down your entire base, but it does not block structure production and can be mitigated immediately by selling a structure.

But wait, there's more! Energy powers cloak, charges shields, and lets constructors repair, just to name a few uses. This makes things a bit more complicated as, for example, cloaked units drain more energy while moving. But it still all adds up to some fuzzy concept of supply. A cloaked unit still has two costs; the price of the unit and the energy generators to cloak it. When it dies, you can rebuild it at a discount, or even use the freed up energy for something else.

It is easy to get caught up in the theme, in how much sense it makes for cloaking and shields to require energy. But forget the theme for a moment and just consider how arbitrary this is. Costing supply is a good thing, it makes rebuilding the unit cheaper, and it seems weird to bestow this benefit on only a handful of units. To understand this, I must now reveal the full power of energy, the thing that supercharges its control of pacing and escalation; energy is expensive at the start of the game and becomes progressively cheaper.

Do not be alarmed, the price of energy structures do not arbitrarily tick down over time. That sort of thing is so inelegant as to be near-nonexistent in RTS. Instead, energy becomes cheaper simply because more efficient structures are available later in the game. Players progress from solar panels to fusion generators, and sometimes even singularity reactors. Many games do this kind of thing; Total Annihilation did it with tech levels, but even that is insufficiently elegant. Zero-K just lets players build anything they want, and lets maths do the rest.

The trick is as follows: a 91% built fusion reactor produces zero energy, while the same value in solar collectors produces 26 energy, so the efficiency of fusion is balanced out by the time it takes to start generating energy. Solar production can outperform fusions for quite a while, with the duration depending on how rapidly they are built. This creates a breakpoint where you switch from solars to fusions based on how much income you can dedicate to energy production, and how much time you have for the efficiency to pay off. It is a fuzzier system than tech levels, which is how we like it, since it leaves more room for strategic judgement.

Energy becoming cheaper flows onto everything that drains energy, effectively making them cheaper too. We use this deliberately to push units and mechanics away from the early game. Mostly this means allowing something to be so powerful that it would warp the early game, then adding energy drain to balance things out. Here are some examples:

• Cloak is best early on, when there is space to move around.
• Tough expensive units rely on repair, but can be hard to answer without a large enough force.
• Personal shields do not drain energy because Shieldbots do not need to be worse early.

Reclaim sort of fits the pattern since energy is required to spend the windfall, but this is forced by the rest of the economy rather than being a deliberate decision. Overdrive does not really fit, since it lets energy structures general metal, rather than using their energy as supply. In fact, the diminishing returns of overdrive counteract the cheapening of energy.

I want to avoid the impression that energy is complicated. Many mechanics look complicated when analysed in detail, and while a lot of thought has gone into it, the goal is something that is intuitive and easy to use. Energy is basically supply, primarily for spending metal. Adding one solar per mex works quite well, and another good rule of thumb is to make 20% more energy than metal. Later on it is worth ramping up production to run overdrive, reclaim, and repair. Fusions are good at around 30 income, and singularity reactors are for when you feel extravagant. Energy can be managed quite easily.

Except...

Recall how construction costs three resources, with the third resource being buildpower. It might warrant its own article, but in brief, buildpower is another form of supply. It just happens to be generated locally, rather than globally, and it cannot be stored. So it can be more complicated, but luckily it is also dead cheap. Increasing your metal income costs about 40 metal/income, and energy starts at 35 and can drop all the way to 18 with singularity reactors. Buildpower starts at 18 metal/buildpower, in the form of the static Caretaker, and mobile constructors cost around 24 metal/BP. This is on top of the fact that your commander and factory provide about 3× more buildpower than your base metal and energy income. So play loose with it, having far more buildpower than your income is fine. Just err on the side of mobile buildpower, so it can be sent out to expand, repair, and reclaim.

The idea of supply can be taken even further. What is metal, if not a supply resource for the ability to construct in the first place? Every RTS can be boiled down a single "resource", time, however I am not going to go down that particular path to madness today. For those interested in doing so, ponder this: since constructors cannot build and move at the same time, does moving cost buildpower? If you would rather just spam singularity reactors, here is a bonus graph.