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Today I'm going to talk to you about the mechanics and social interactions in a little-known Mac tank game. Those of you who understood the title already know which one. For those of you who don't, the game is Bolo. For people suddenly hit with nostalgia, there's a Carbon port now available which is amazingly authentic.

Bolo is a unique game in many respects. It was one of the first multiplayer games to be playable over the internet. It's also a tank game in which an event where tanks shoot at other tanks almost never happens. Bolo is one of those "a minute to learn, a lifetime to master" games where the mechanics are simple, but the emergent properties from those mechanics are wonderfully complex. Those emergent properties are what I'm going to concentrate on today.

Besides tanks, the Bolo world consists of resupply bases, automatic pillboxes, and a wide variety of changeable terrain. The bases take care of repairing tanks and resupplying them with ammunition. Pillboxes automatically shoot at enemies. Both are loyal only to a certain player or team, and hostile to everyone else. Shooting a base or pillbox enough will take it out of action, at which point it can be captured and put into the service of the side that captured it.

The terrain includes impassible walls, water, swamps, grass, roads, etc. And lest I forget, trees. The terrain influences gameplay enormously. Bad terrain makes tank movement slow, walls and trees will block bullets, and more. There's a little more to the game, but this is enough to illustrate the point.

Pillboxes are fixed emplacements, but when they're captured they can be moved around before being rebuilt. Aside from pillboxes, players can also build roads, walls, and boats. I specifically mentioned trees above, and for a very good reason. All of this construction activity is critical to the game, and it's not free. It takes trees to build all of these things. Each player has to harvest trees, which he can then use to build pillboxes, roads, and the rest.

As you might expect, games typically center around bases and pillboxes. Pillboxes have unlimited ammunition, never get tired, and will fire far more rapidly than a tank when provoked, so they are extremely valuable for defense. With care a good player can use them for offense as well. Bolo games typically center around "pill wars", in which clusters of pills are set up to create zones of control, killing fields, and barriers with which to conduct the war. Bases are all-important, being the only source of ammunition and repairs. While a team can survive without pillboxes, it can't survive without bases. Which is more important usually depends on the game, the players, and even whatever's happening at any particular moment.

Trees are important too, as I mentioned, but maps usually have plenty of trees....

The mutable terrain comes into play as the game goes on. Players often build walls as barriers, which leave rubble behind when destroyed, impeding movement. When a tank or a mine explodes, it leaves a crater behind which also impedes movement. After a while, players have to be careful about where they move to avoid getting stuck on bad terrain, where they become sitting ducks for enemy pillboxes and tanks. War zones gradually collect this bad terrain, making movement more and more difficult. They can be repaired by building roads, but this takes time which is often in short supply. It also takes trees....

Alright, so what about the trees? There's usually plenty of them, right? Well, there are at first. But a typical Bolo war has a voracious appetite for trees. Also, trees are very easy to destroy. Whenever a protracted fight breaks out, if there were any forests nearby at the start, they're usually gone at the end, either from stray bullets or players harvesting so they can build what they need to keep up the fight.

Trees grow back. Interestingly, Bolo preferentially places newly-grown trees next to existing trees. This makes trees grow in clusters, and also tends to encourage good harvesting practices. Stripping trees from the edge of a forest is a good way to destroy the forest over time. Harvesting the trees in a careful checkerboard pattern, or other patterns which leave treas around the newly-harvested areas, help ensure that the trees grow back quickly.

Deforestation is a devastatingly-effective tactic in Bolo, which is almost universally frowned-upon. It's very easy to carry out: load your tank up with bullets, drive into the enemy's forests, and fire away. If he wants to stop you, he has to shoot you, which will probably end up destroying even more trees. It's so easy and so effective that it's basically Bolo's equivalent of nuclear weapons. As soon as one side starts doing it, the other side has to retaliate to maintain parity. It short order, the trees are gone, and both sides are worse off than before. The trees grow back, but it takes a long time. Without trees, pillboxes can't be rebuilt or repaired, bad terrain can't be fixed, and the game quickly turns into a slugfest. Just like nuclear war, both sides usually try to avoid starting a round of deforestation.

The trees have another interesting twist. The rate at which they grow back never changes! But wait, you say, I just said that checkerboard harvesting makes them grow back faster. This is true, locally. Checkerboard harvesting makes trees grow back faster in the area where they were harvested, at the expense of other areas. But globally, trees are added to the map at a constant rate. (Technically, the rate depends on the number of players in the game, but that's about it.)

One more twist: typical Bolo games use trees faster than the global rate at which they grow.

This has interesting consequences. Even in a normal game without any nuclear wars of deforestation, the trees will eventually be depleted. For example, here are some screenshots from a game.

Above: the beginning of the game. The trees are in light green. They are everywhere.

Above: near the end. Note the lack of trees.

I stated above that games typically concentrate on pillboxes and bases. But really, games concentrate on whatever resource is most important to the players. Usually this resource is pillboxes and bases. But once the trees get scarce enough, the critical resource becomes trees. In a normal game, you can stock up on trees on a whim, and go riding into battle with plenty of building material. When you start to have to hunt for them, and possibly go behind enemy lines to find some, it can put a real crimp in your style. Since trees tend to grow near other trees, the remaining trees end up in clumps like the one in the screenshot above. As the number of clumps drops, the game shifts from pillboxes and bases to fighting over control of the remaining clumps.

As you can expect, by the time the game reached the state in the second screenshot, the fight was all about trees. You can see the ownership of the objects (pillboxes are round, bases are diamond-like) by their color. Blue owns little territory but controls all of the trees, which is a huge advantage. At this point in the game, most of the action centered around red's attempts to destroy the trees, and blue's attempts to defend them, with bursts of "normal" activity concentrating on other things. Since trees are hard to defend, it didn't work very well.

I hear people in the audience asking me to get to the point. The point is this: in a Bolo game, while the game starts out as a fight over military resources, if it goes on long enough then it will do sufficient damage to the game's ecology that the fight will shift to disputes over control and preservation of the remains of that ecology. Even when there is a conscious effort to preserve the ecology, it will eventually be destroyed because the fight is just too resource-hungry. But the two sides are rarely quite that careful about it. Military expediency in the moment usually trumps long-term concerns about the health of your forests. Would you avoid trying to kill the enemy tank that's getting away with your hard-earned pillbox just because your stray bullets could destroy some trees? They'll grow back, who cares!

There are probably lots of real-world situations where this exact kind of thinking applies, but I'm not going to make the comparison, I'm just going to very strongly imply it.

That wraps it up for today's military/emergent behavior/gaming/ecology post. Next time we'll hopefully get back to some code. Until then, stay warm and keep your trees safe.

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