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Better pathfinding heuristic for A*.

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Seems to helps nicely in some cases (East-West path on flat, O(d)
instead of O(d^2)) but only few % better for more complex cases.
This commit is contained in:
Ali El Gariani 2009-09-02 17:03:02 +00:00
parent ea34bd1620
commit ba29ee85aa
1 changed files with 5 additions and 3 deletions
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8
src/astarsearch.cpp
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@ -34,7 +34,6 @@ double heuristic(const map_location& src, const map_location& dst)
// We will mainly use the distances in hexes
// but we substract a tiny bonus for shorter Euclidean distance
// based on how the path looks on the screen.
// We must substract (and not add) to keep the heuristic 'admissible'.
// 0.75 comes frome the horizontal hex imbrication
double xdiff = (src.x - dst.x) * 0.75;
@ -44,8 +43,11 @@ double heuristic(const map_location& src, const map_location& dst)
// we assume a map with a maximum diagonal of 300 (bigger than a 200x200)
// and we divide by 90000 * 10000 to avoid interfering with the defense subcost
// (see shortest_path_calculator::cost)
return distance_between(src, dst) -
(90000.0 - ( xdiff*xdiff + ydiff*ydiff)) / 900000000.0;
// NOTE: In theory, such heuristic is barely 'admissible' for A*,
// But not a problem for our current A* (we use heuristic only for speed)
// Plus, the euclidian fraction stay below the 1MP minumum and is also
// a good heuristic, so we still find the shortest path efficiently.
return distance_between(src, dst) + (xdiff*xdiff + ydiff*ydiff) / 900000000.0;
// TODO: move the heuristic function into the cost_calculator
// so we can use case-specific heuristic