Pathfinding Over Streaming Terrain

1
Pathfinding Over Streaming Terrain

• By
• James Stewart
• jmstewar_at_smu.edu

2
The Problem

• How do you find a path when the search
• space is too large to fit into memory?

3
Features of the Solution

• Use same data representation for both rendering
  and AI.
• Solution requires no explicit intervention by a
  designerterrain is by definition very large.
• Handles only static pathfinding. Dynamic
  obstacles such as deformable terrain or physics
  entities require a separate AI layer.

4
Terrain Preprocessing

• A simple tool packages a gigantic height map into
  leaf nodes of a Restricted Quadtree
  Triangulation.
• (Long story short, Wouters LOD method plus
  stripification and an error metric to collapse
  distant vertices.)

5
Terrain Preprocessing

• Lowest LOD used as a basis for a navmesh.
• Export neighbor accessibility summary (eight
  neighbors 3 bits / chunk)

6
Terrain Database

• 1. Dedicated thread asynchronously pages chunks
  from storage to be accessed as memory-mapped
  files.
• 2. Paging candidates and victims selected via
  motion prediction (prediction scheme very
  dependent on game design).

7
AI Solution

• Use neighbor accessibility classification to
  build a good enough path.
• Refine path over subsequent frames by paging in
  chunks along path.

8
Challenges

• Scalability How will database prioritize paging
  requests when many units each require different
  chunks, and memory is limited?
• Path Optimality Is the good enough path really
  good enough?
• Compression How can the size of the terrain and
  navmesh data be reduced?