Minimising AI usage in a gme

Question

I have been working on a 2D top down shooter game for a while, I've implemented most of the game and wrote the engine from scratch in JOGL but i ran into a small problem and would like to get other peoples view on how to best approach the problem. So I have creeps spawning at random locations in the map, and each of these creeps use A* path finding, it has been optimized to minimize unnecessary checks, but the maps are massive can be anything from 10x10 to 200x200 tiles and the only thing slowing down the game significantly is the AI, I've also tried to implement a distance based solution where the creeps Idle until i am in a certain range but that still slows down the game a lot because a lot of creeps are spawned. Any advice would be appreciated.

Answer 1

There are numbers of ways of speeding up your code.

First - there are many modifications of the A* algorithm, which may be used, like:

• Hierarchical A*, which is often used method in games, where the map is analyzed on many resolution levels, from "general planning" to the "local path search" http://aigamedev.com/open/review/near-optimal-hierarchical-pathfinding/
• Jump Point Search A*, which dramaticaly speeds up A* for maps with lots of open spaces (like RPG games) http://gamedev.tutsplus.com/tutorials/implementation/speed-up-a-star-pathfinding-with-the-jump-point-search-algorithm/

Other modifications can be more application specific, if your creeps are searching a path to the player (there is one goal for all creeps), then you can change your search to one of following algorithms:

• calculate distance from player to each point in the map using Dijkstra algorithm, for 200x200 it will be very quick (40,000 vertices with O(nlgn) algorithm), and simply move your creep to any adjacent point with less distance to player then current one
• run A* search from the player to any creep (with lowest id for example), once the path is found - change aim to the next creep but do not reset the algorithm itself, let if use already computed paths and distances (as they are already optimal paths from player), obviously - if during execution you encounter another creep then your goal - you simply record it (found path is optimal).

Another possible modification, which can be applied if your map is somehow specific (contains doors/entrances to some parts of it) is to place triggers, which "enable" creeps AI. This is O(1) solution, but requires a specific type of map.

And one final idea would be to implement some suboptimal solutions, by for example:

• First, calculate A* for each creep
• If the distance to the player is smaller then some threshold value T , then in next iteration - recalculate your path, so there is no lag
• otherwise - follow your path for at least 10-50 iterations before another path search

There are countless more optimizations, but we would need more details regarding your game as well as time you wish to spend on those optimizations.