docs: add notes on JPS, landmarks

glitchassassin · Dec 17, 2024 · 1cb326a · 1cb326a
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diff --git a/docs/primitives/astar.md b/docs/primitives/astar.md
@@ -2,9 +2,29 @@
 
 The [venerable A\* algorithm](https://www.redblobgames.com/pathfinding/a-star/introduction.html) provides the baseline for pathfinding in Screeps.
 
-Red Blob Games has some [WIP articles on heuristics](https://www.redblobgames.com/blog/2024-05-05-wip-heuristics/).
+Within a single room, the Clockwork implementation of the A\* algorithm alone is competitive with PathFinder. However, across longer distances (greater than a single room), PathFinder's JPS optimizations make a significant difference.
+
+We'll experiment with a few different options.
+
+## Optimizations
+
+- [Jump-Point Search](https://zerowidth.com/2013/a-visual-explanation-of-jump-point-search/) is also used under the hood by PathFinder
+- [Pre-computed landmarks](https://www.redblobgames.com/blog/2024-05-05-wip-heuristics/) for more accurate A\* heuristics
+
+### Landmarks
+
+The theory:
+
+1. Pick a non-wall spot near the middle of the room and Dijkstra-map out from there.
+2. Cache the center spot, one exit on each of the (1-4) sides, and cost for each.
+3. Use these points as landmarks for the A\* heuristic.
+
+Drawbacks:
+
+Cost matrix used for calculating landmarks needs to be the same as cost matrix for pathing
+
+## Other interesting variants
 
 - [Cooperative Pathfinding](https://theory.stanford.edu/~amitp/GameProgramming/MovingObstacles.html#predicting-obstacle-movement) (building a table of the paths of other units)
-- JPS (generating paths, ignoring terrain costs)
 - [Incremental heuristic search](https://en.wikipedia.org/wiki/Incremental_heuristic_search) (tracking moving targets)
 - [Parallel Breadth-First Search](https://arxiv.org/abs/2210.16351)
diff --git a/docs/wasm/index.md b/docs/wasm/index.md
@@ -3,3 +3,4 @@
 We are using wasm-bindgen to create the WASM and a JS shim (`packages/wasm`). There are a few things we tweak to improve performance (such as passing in the `__packedPos` instead of the whole RoomPosition), so this is further wrapped in a Typescript library (`packages/screeps-clockwork`) which wraps and re-exports the WASM functionality.
 
 - Copying data across the [WASM boundary](./boundary.md) adds up, so we must be thoughtful about when and how we copy data back and forth.
+- Javascript can't garbage-collect our Rust objects, so we need to [clean them up explicitly](./cleanup.md).
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		We are using wasm-bindgen to create the WASM and a JS shim (`packages/wasm`). There are a few things we tweak to improve performance (such as passing in the `__packedPos` instead of the whole RoomPosition), so this is further wrapped in a Typescript library (`packages/screeps-clockwork`) which wraps and re-exports the WASM functionality.

		- Copying data across the [WASM boundary](./boundary.md) adds up, so we must be thoughtful about when and how we copy data back and forth.
		- Javascript can't garbage-collect our Rust objects, so we need to [clean them up explicitly](./cleanup.md).