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  1. At game start or load a bot is thrown into cold water. He might discover a very hostile environment in terms of resources, units, buildings and enemies. Interestingly game start and end can be very similar, meaning eveything is low, if the human opponnent has victory within his grasp. But a bot doesn't give up, as long there is a small chance of success - he takes it, right? What is the worst case? Let's say no civic centers. That's close to ground zero in 0 A.D., because without CC you lack the territory to build any other structure. So, naturally the very first questions in this case are: Can I build a CC? And if not, what can I do at all? It turns out, these are very complex questions. Let's start with some simple conditions: has only resources -> whiteflag has only buildings -> whiteflag has only units -> whiteflag or fight like hellOk, that's not so difficult. And it looks translatable into straight forward JavaScript, too. Here comes the next level: has buildings, units, no resources has no CC has no CC builder can not train CC builder -> whiteflag or fight like hell can train CC builder -> gather resources -> train CC builder -> construct CC has CC builder -> gather resources -> construct CCActually that's only the surface. It assumes the units are not champions and the needed resources are available. Here are a few more: and finally: has units, resources, buildings has no CC has CC builder -> construct CC has no CC builder can train CC builder -> train builder -> construct CC can not train CC builder -> whiteflag or fight like hellCan you imagine how many conditions the bot has to check just to find out he has definetly lost? Now add more edge cases, mixin technologies, multiply with all buildings and all factions and you'll end up with tens of thousands lines of code, hard to read, difficult to maintain and taking months to write. That's where planners jump in. They know which conditions to check and how to answer them. Ontop they come up with a list of actions leading to your goal or none if your goal is unreachable. HTN (hierarchical task network) planners are conceptually fairly simple, but extremely powerful. They define a state, that's the starting point, a goal and operators and methods, the latter are just functions. Operators can change the state and methods result in more methods or operators. So, you initialize a planner with a state, your goal and then call the first method. From there it tries to decompose the problem until only an ordered list of operators is left - that's your plan. 0 A.D example: state = { resources: {food: 300, wood: 300}, entities: { structures.athen.civil.centre: 1 }, technologies: [phase.village]};goal = { resources: {}, entities: { structures.athen.field: 1}, technologies: [gather.wicker.baskets]}The goal basically says: I don't care about resources and the civic centre, but in any case I want a field and foragers better equipped. Do you see the two traps? Here's the plan: HTN: SUCCESS, actions: 8, 1 msecs op: 1, train_units ( units.athen.support.female.citizen, 1 ) op: 2, wait_secs ( 10 ) op: 3, build_structures ( structures.athen.farmstead, 1 ) op: 4, wait_secs ( 45 ) op: 5, build_structures ( structures.athen.field, 1 ) op: 6, wait_secs ( 100 ) op: 7, research_tech ( gather.wicker.baskets, 1 ) op: 8, wait_secs ( 40 )See how the planner automatically found out he needs a builder for the field and the farmstead for the technology. And the final state: resources: { food: 250, wood: 150, time: 195, metal: 0, stone: 0, pop: 1, popmax: 300, popcap: 20 }entities: { structures.athen.civil.centre: 1 units.athen.support.female.citizen: 1 structures.athen.farmstead: 1 structures.athen.field: 1}technologies: [phase.village, gather.wicker.baskets]... which can be used for your next goal. HTN Planners are well used in RTS games. The link finds a a few interesting presentations. Some games have highly optimized ones, checking hundreds of plans each tick, looking for the optimal strategy to keep the human opponent entertained. So far Hannibal's planner lacks a few features, he needs a better awareness of time e.g. calculate how long it takes to get a given amount of resources and more challenging learns the concept of parallel tasks. I'll continue when it produces heros. PS: Did I mention that's probably the first JS planner ever written for an RTS?
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