The AI is what you'll be playing against in the single player campaign and the skirmish mode.
In this first post, I'll give you a quick overview, and then wander off (if you'll pardon the pun) into pathfinding.
The basic behaviours are pretty simple:
- defend your own power plants
- advance towards the opponent
- attack whatever is in your way
- finally, blow up their power plants
Unfortunately, a computer is basically looking at the board through a tube that's one tile across. Suddenly, just figuring out where to go is hard - try it!
The granddaddy of pathfinding is an algorithm called A* (A-star). It's one of my favourite algorithms! I'll try (and fail) to be brief, since there's loads of good reading already available online. Amit Patel of Red Blob Games has an awesome series on pathfinding in general and A* in particular. It's a must read for anyone in game dev, and there's much more great stuff there!
I'll try to sum up A* in a few sentences, though, and how it applies to Powargrid.
A* works on any grid - it just needs to be told which points are connected to which others. In Powargrid, that's just the tiles of the playfield and their neighbours.
To find a path, you give it a list of tiles you want to go, and which tiles to start from. If we're trying to attack another player, we can start from any tile we already built on, and we're looking to reach any tile from which we can shoot at their power plants.
Then, for every tile it currently knows, A* looks at its neighbours and estimates how far each might be from the goal. In our case, that estimate is easy! It's just how many tiles the target is away, horizontally and vertically (this is called the Manhattan distance because it's like measuring distance in city blocks). It then continues finding a path by looking at the best estimates first, which makes it much faster than just looking at everything. And it still guarantees you it'll find the shortest possible path!
In Powargrid, we tell A* your own tiles are cheap - you already own them! Empty tiles are a little more expensive, since you'll have to spend power to actually build something on them. Tiles occupied by an opponent are much more expensive, because you'll have to build and charge weapons to blast through them. The costs are 1 point for your own tiles, 3 for empty tiles, and 20 for enemy tiles. That means the AI will make a 7 tile detour if it can avoid going through one of your buildings.
These simple rules will make the AI build around your buildings, unless the path gets too long. Then it'll just plop down a tower and shoot you inna face.
Defending also uses pathfinding, but the other way around: the AI knows how much power you'll have next turn, and figures out where you'll be able to go. If that includes places where it would like you not to be, it'll claim those tiles itself.