[game] Reimplement pathfinding - #310
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BWM format stores vertices, faces, edges as separare arrays, effectively a structure of arrays. Before this patch we used to transform this into an array of structures (struct Face) and keep only one array in the Walkmesh. This approach had several problems: 1. Vertices are duplicated. Each vertex is a vec3, and there are 1.5x more faces than vertices, because most faces have adjecent faces. 2. It is more difficult to find adjecent faces, without keeping original vector indices. We have to check distance between vertices to find if it is the same vertex. With indices it is enough to check if indices are the same. The patch also updates return value of raycast function. They used to return a nullable pointer to the face and distance as an output parameter. Now they return a struct with an index of the face that the ray intersects, distance from the origin point to the intersection, and an error code if there is no intersection.
Pathfinding is implemented as a collection of algorithms: 1. Global pathfinding algorithm builds a coarse-grained path from A to B as a sequence of walkmesh faces. It ensures that a path exists, but makes no effort to make it "natural" from the player perspective. 2. Funnel algorithm takes a sequence of faces from the global pathfinding, and attempts to make a straight-line path through it. 3. Steering behaviour takes a direction from the funnel algorithm, and turns it into a "driving" force. It then calculates and combines other forces: - "keepout" force to steer away from borders and corners - "stuck" force to recover from pathfinding failures. The combined force is then integrated to smooth changes of direction and make the path more natural. Omissions: 1. Dynamic objects (creatures) are not handled. Each creature has a "personal space" radius that must be taken into account for pathfinding. 2. Static objects that do not have a carve-out for them in the room walkmesh are not reflected in the Uniwalk yet. Each object has it is own "non-walkable" mesh, which must be subtracted from the room mesh.
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Pathfinding is implemented as a collection of algorithms:
Global pathfinding algorithm builds a coarse-grained path from A to B as a
sequence of walkmesh faces. It ensures that a path exists, but makes no
effort to make it "natural" from the player perspective.
Funnel algorithm takes a sequence of faces from the global pathfinding,
and attempts to make a straight-line path through it.
Steering behaviour takes a direction from the funnel algorithm, and turns
it into a "driving" force. It then calculates and combines other forces:
The combined force is then integrated to smooth changes of direction and make
the path more natural.
Omissions:
Dynamic objects (creatures) are not handled. Each creature has a "personal
space" radius that must be taken into account for pathfinding.
Static objects that do not have a carve-out for them in the room walkmesh
are not reflected in the Uniwalk yet. Each object has it is own
"non-walkable" mesh, which must be subtracted from the room mesh.