Cooperative Path Finding

Big Bucket's game Space Age can be described as a mashup of an Real-time strategy and an adventure game. Space Age has units and missions, but also inventory and dialogue. When a unit needs to navigate between map locations, it uses the A* pathfinding algorithm. As well as A*, Space Age employs some novel techniques to ensure that units don't bump each other while also ensuring that their navigation appear natural and ad-hoc, not coordinated or precognitive. I will be discussing some of these techniques.

Transcript

1. Cooperative Path Finding Matt Comi
2. bigbucketgames.com
3. Matt Comi CODE Neven Mrgan ART Cabel Sasser MUSIC
9. Unit
11. Heuristic Manhattan Distance
13. A* Algorithm
14. Open Set Closed Set G Score F Score
15. Tiles that are on the fringe of the explored path. Open Set Closed Set G Score F Score
16. Tiles that have been explored. Open Set Closed Set G Score F Score
17. Cost of getting from the origin to this tile. Open Set Closed Set G Score F Score
18. Cost of getting from the origin to the destination, via this tile. (G Score + Heuristic) Open Set Closed Set G Score F Score
19. Data Structures
20. Tile Map PointI Node Set
21. struct Tile { var obstructed: Bool } Tile Map PointI Node Set
22. struct Map { var tiles: [[Tile]]() } Tile Map PointI Node Set
23. struct PointI { var x: Int var y: Int // use your imagination for these static func ==(lhs: PointI, rhs: PointI) -> Bool { } var neighbors : [PointI] { get } } Tile Map PointI Node Set
24. class Node { var position: PointI var fScore: Float var gScore: Float var parent: Node? = nil init(position: PointI, fScore: Float, gScore: Float, parent: Node?) { self.position = position self.fScore = fScore self.gScore = gScore self.parent = parent } } Tile Map PointI Node Set
25. Tile Map PointI Node Set protocol Set { func insert(node: Node) func remove(node: Node) func find(position: PointI) -> Node? var nodeWithLowestFScore : Node? { get } var isEmpty: Bool { get } }
26. protocol PathFinderDelegate { func isValidPosition(position: PointI) -> Bool func isDestination(position: PointI) -> Bool func movementCost(from: PointI, to: PointI) -> Float func heuristicCost(from: PointI) -> Float }
27. class MoveToPathFinderDelegate : PathFinderDelegate { let map: Map let destination: PointI init(map: Map, destination: PointI) // within the bounds of the map and unobstructed. func isValidPosition(position: PointI) -> Bool // position == destination. func isDestination(position: PointI) -> Bool // 1 if horizontal or vertical, 1.5 if diagonal. func movementCost(from: PointI, to: PointI) -> Float // manhattan distance between from and destination. func heuristicCost(from: PointI) -> Float }
28. class MoveToPathFinderDelegate : PathFinderDelegate { let map: Map let destination: PointI init(map: Map, destination: PointI) // within the bounds of the map and unobstructed. func isValidPosition(position: PointI) -> Bool // position == destination. func isDestination(position: PointI) -> Bool // 1 if horizontal or vertical, 1.5 if diagonal. func movementCost(from: PointI, to: PointI) -> Float // manhattan distance between from and destination. func heuristicCost(from: PointI) -> Float }
29. class MoveToPathFinderDelegate : PathFinderDelegate { let map: Map let destination: PointI init(map: Map, destination: PointI) // within the bounds of the map and unobstructed. func isValidPosition(position: PointI) -> Bool // position == destination. func isDestination(position: PointI) -> Bool // 1 if horizontal or vertical, 1.5 if diagonal. func movementCost(from: PointI, to: PointI) -> Float // manhattan distance between from and destination. func heuristicCost(from: PointI) -> Float }
30. class MoveToPathFinderDelegate : PathFinderDelegate { let map: Map let destination: PointI init(map: Map, destination: PointI) // within the bounds of the map and unobstructed. func isValidPosition(position: PointI) -> Bool // position == destination. func isDestination(position: PointI) -> Bool // 1 if horizontal or vertical, 1.5 if diagonal. func movementCost(from: PointI, to: PointI) -> Float // manhattan distance between from and destination. func heuristicCost(from: PointI) -> Float }
31. class MoveToPathFinderDelegate : PathFinderDelegate { let map: Map let destination: PointI init(map: Map, destination: PointI) // within the bounds of the map and unobstructed. func isValidPosition(position: PointI) -> Bool // position == destination. func isDestination(position: PointI) -> Bool // 1 if horizontal or vertical, 1.5 if diagonal. func movementCost(from: PointI, to: PointI) -> Float // manhattan distance between from and destination. func heuristicCost(from: PointI) -> Float }
32. func findPath(origin: PointI) -> [PointI] { let open = SimpleSet() let closed = SimpleSet() open.insert(node: Node(position: origin, fScore: delegate.heuristicCost(from: origin), gScore: 0, parent: nil)) while open.count != 0 { guard let node = open.nodeWithLowestFScore else { return [] } if delegate.isDestination(position: node.position) { return makePath(node) } open.remove(node: node) closed.insert(node: node) for neighborPosition in node.position.neighbors { if !delegate.isValidPosition(position: neighborPosition) { continue } if closed.find(position: neighborPosition) != nil { continue } let g = node.gScore + delegate.movementCost(from: node.position, to: neighborPosition) if let existingNode = open.find(position: neighborPosition) { if g >= existingNode.gScore { continue } open.remove(node: existingNode) } let f = g + delegate.heuristicCost(from: neighborPosition) open.insert(node: Node(position: neighborPosition, fScore: f, gScore: g, parent: node)) } } return [] }
47. Coordination & Cooperation
48. Avoidance Stalling Groups Deadlocks
49. Avoidance Stalling Groups Deadlocks
50. // True if the tile is: // - Within the bounds of map // - Unobstructed // - Unoccupied or occupied by a unit that is *not* attacking. func isValidPosition(position: PointI) -> Bool
51. // Normally 1 if horizontal or vertical, 1.5 if diagonal. // If the destination is occupied, add 6. func movementCost(from: PointI, to: PointI) -> Float
52. enum UnitState { case Idle case Moving case Attacking } protocol Unit { var position: PointI { get } var path: [PointI] { get } var state: UnitState { get } }
53. struct Tile { var isObstructed: Bool }
55. Avoidance Stalling Groups Deadlocks
59. Avoidance Stalling Groups Deadlocks
67. Avoidance Stalling Groups Deadlocks
70. class MoveAwayPathFinderDelegate : PathFinderDelegate { let map: Map let otherUnits: [Unit] init(map: Map, otherUnits: [Unit]) // within the bounds of the map, unobstructed and not occupied by any // Unit in otherUnits. func isValidPosition(position: PointI) -> Bool // any position that isn’t along any of otherUnits’ paths. func isDestination(position: PointI) -> Bool // 1 if horizontal or vertical, 1.5 if diagonal. func movementCost(from: PointI, to: PointI) -> Float // always 0. func heuristicCost(from: PointI) -> Float }
71. class MoveAwayPathFinderDelegate : PathFinderDelegate { let map: Map let otherUnits: [Unit] init(map: Map, otherUnits: [Unit]) // within the bounds of the map, unobstructed and not occupied by any // Unit in otherUnits. func isValidPosition(position: PointI) -> Bool // any position that isn’t along any of otherUnits’ paths. func isDestination(position: PointI) -> Bool // 1 if horizontal or vertical, 1.5 if diagonal. func movementCost(from: PointI, to: PointI) -> Float // always 0. func heuristicCost(from: PointI) -> Float }
72. class MoveAwayPathFinderDelegate : PathFinderDelegate { let map: Map let otherUnits: [Unit] init(map: Map, otherUnits: [Unit]) // within the bounds of the map, unobstructed and not occupied by any // Unit in otherUnits. func isValidPosition(position: PointI) -> Bool // any position that isn’t along any of otherUnits’ paths. func isDestination(position: PointI) -> Bool // 1 if horizontal or vertical, 1.5 if diagonal. func movementCost(from: PointI, to: PointI) -> Float // always 0. func heuristicCost(from: PointI) -> Float }
73. class MoveAwayPathFinderDelegate : PathFinderDelegate { let map: Map let otherUnits: [Unit] init(map: Map, otherUnits: [Unit]) // within the bounds of the map, unobstructed and not occupied by any // Unit in otherUnits. func isValidPosition(position: PointI) -> Bool // any position that isn’t along any of otherUnits’ paths. func isDestination(position: PointI) -> Bool // 1 if horizontal or vertical, 1.5 if diagonal. func movementCost(from: PointI, to: PointI) -> Float // always 0. func heuristicCost(from: PointI) -> Float }
74. class MoveAwayPathFinderDelegate : PathFinderDelegate { let map: Map let otherUnits: [Unit] init(map: Map, otherUnits: [Unit]) // within the bounds of the map, unobstructed and not occupied by any // Unit in otherUnits. func isValidPosition(position: PointI) -> Bool // any position that isn’t along any of otherUnits’ paths. func isDestination(position: PointI) -> Bool // 1 if horizontal or vertical, 1.5 if diagonal. func movementCost(from: PointI, to: PointI) -> Float // always 0. func heuristicCost(from: PointI) -> Float }
76. @mattcomi http://bigbucketgames.com/playgroundscon