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Definition of Goals and definitions of actions to execute those Goals.
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Each possible action has a weight and conditionals to be executed, generating a "pseudo-score" for each possible action to fulfill the Goal, choosing the best action at the end.
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Goals must be ordered so you need to execute the first Goal in the list before moving to the next.
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Has an initially complex and confusing implementation for sure.
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Can have some performance issues since each entity must consider every possible plan of actions to fulfill the Goal before taking any action.
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In the worst case, one has $O((nm)^d)$, where $n$ is the number of possible actions, $m$ is the number of goals and $d$ is the depth of the path.
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Because of this, "design short plans" is repeated billions of times due to performance concerns.
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For this reason, A* is also normally used to do the "pathfinding" to choose the best action within the Tree, to optimize the speed of this decision-making in the Tree.
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Has some visualization and debugging difficulties.
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Supposedly allows "emergent behavior", but that is quite obtuse; this kind of thing is not obvious due to implementation complexity. Very likely Utility AI can achieve more emergence more easily.
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*Impressions:
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I found the definition of a 'goal' very abstract, sometimes giving the impression that something could be defined both as an action and as a goal.
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Seems very oriented to stealth games or games with autonomous NPCs, but it is somewhat irrelevant for combat moments.
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I did not like it very much overall, as decision-making and goal definition are somewhat abstract.
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I have the impression that the strategy seems very "literal", but its implementation is somewhat confusing because of that.
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Considering the target cases for this strategy, using Utility AI sounds better because it is more organic and allows emergence in NPC behavior.
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Games that use it
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F.E.A.R. .
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Meh, basically a documentary, not very technical.
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Shadow of Mordor.
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Same company as F.E.A.R.
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Condemned 1 and 2.
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Same company as F.E.A.R.
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Tomb Raider.
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Rise of Tomb Raider.
Explanations
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Good explanation and comparisons between FSM and Behavior Trees .
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GDC on using GOAP in Shadow of Mordor and Tomb Raider .
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The first and second presentations are kind of bad, while the third presentation (about analytics) is okay.
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The first two presentations seem like the speakers did not rehearse well or simply assume everyone knows what they are talking about.
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Much is said about performance optimization when using GOAP, which is not so relevant for indie devs normally.
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In the last part of the video analytics are shown about the number of plans per NPC and the number of NPCs that can be active at the same time; that may be interesting.
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