Assuming a game with square tiles and vector movement:
All shortest paths are either a straight line, or consist of the straight line from the original location to an outside corner, a series of straight lines between outside corners, and a straight line from an outside corner to the destination. (An outside corner is any 2x2 square with three walkable and one wall tile.)
You can easily find all the outside corners. You can find which pairs of outside corners can be walked between using N^2 ray casts. Once you've done that, you can detect when an outside corner has been removed and drop it from the map, or detect when one has been created and perform N ray casts to add it to your pathing list.
Running A* on the resulting structure is really fast, because it's smaller and more connected than a tile list. The slowest remaining part is finding the corners immediately reachable from your start/end points, which I think could also be sped up but I'd benchmark it before worrying about that.
All shortest paths are either a straight line, or consist of the straight line from the original location to an outside corner, a series of straight lines between outside corners, and a straight line from an outside corner to the destination. (An outside corner is any 2x2 square with three walkable and one wall tile.)
You can easily find all the outside corners. You can find which pairs of outside corners can be walked between using N^2 ray casts. Once you've done that, you can detect when an outside corner has been removed and drop it from the map, or detect when one has been created and perform N ray casts to add it to your pathing list.
Running A* on the resulting structure is really fast, because it's smaller and more connected than a tile list. The slowest remaining part is finding the corners immediately reachable from your start/end points, which I think could also be sped up but I'd benchmark it before worrying about that.