Soldier of Fortune 2: Double Helix Paris York CIS 588

Jumping, Climbing, and Tactical Reasoning: How to Get More Out of a Navigation System Christopher Reed and Benjamin Geisler Raven Software/Activision “using navigation to give AI more than just routes from one place to another.” Image Sources:

Navigation system is graph-based –Points - represent locations –Edges - represent safe routes

Enhanced Navigation Data Points and edges have static attributes attached to them, these are available to the AI in a look up table The data allows the appearance of more intelligent NPCs, and allows the system to be less resource intensive The path is selected by at a higher level, traversing points and edges is handled separately

Example: Bounding Overwatch –NPCs act in tandem, one covers while the other advances; roles then switch until the goal is reached –Points are marked as safe cover, the path selection is then biased towards these safe points.

Example: Throwing Grenades –Problem -- How do we get the AI to know the best place to throw a grenade? –Answer -- Compute all possible grenade throws in advance and encode results in navigation system Obstacle Closest Point to Player Closest Point to Agent Standard Edge Throw Edge over Obstacle Agent Player

Biasing Edge Cost –Bias edge cost to prevent NPCs from taking undesirable routes simply by increasing edge cost. –Edges can also be biased for unique behaviour, such as flying ParentPoint = OpenList.GetFromOpenList() For each edge from ParentPoint Switch Edge.type() Case FLY_EDGE: If (actor.CanFly() ) Edge.cost = actor.FlyBiasCost() OpenList.AddToOpenList(Edge)

Dynamic Movement: Opening a Door –The path is already generated, so encountering a door is a simple matter. –The edge has the door attribute, the AI automatically selects the appropriate animation, then continues on the path –This also applies to using ladders, special doors, etc.

The Navigation Point Points provide discrete locations in space where agents can move to and from Can be any shape, sphere is easier to store -- point, radius Shape covers navigable area around point -- no obstacles, holes, etc

Obstacle Visibility -- Side to Side and Vertical –If an obstacle is detected close to a navigation point, information about this obstacle, such as height and width, can be pre-computed and stored in the nav system A low wall is good cover, so is the side of a building

The Navigation Edge Edges connect points to tell the nav system how to safely move between points Certain characters may not be able to traverse an edge, or may require a special action to do so

Examples of Edge Data Size –Sometimes characters are big, really big and can’t fit down some paths. –Using collision detection, the maximum size of a character that could travel a path can be determined and encoded in the nav system

Jumping or Flying –If points in the air and the ground are connected, they need to be encoded so that only flying characters attempt to follow –If points connect over a hole, the edge can be encoded as a jump edge, restricted by game animation and physics

Through Moveable Obstacles –Actions necessary to remove the obstacle are encoded into the edge Opening a door Destroying a crate