Yacht AI

One of the lessons that we learned from PAX is that it is very nice to be able to switch between a human and AI player while playing the game. The only game that had this feature at PAX was Parcheesi. It made people more likely to start a game since they knew that they could be replaced by a computer player if they got bored or had to leave.

So one of our goals is to update the existing games so that you can switch back and forth between a human and computer player during the game instead of just at startup. Most of the games will be fairly easy to adapt to this system. We generally write the computer players in C++ while the rest of the game logic is in torquescript. This separation has meant that we generally pass everything the AI needs to make a decision each time the AI has to play.

Yacht didn’t have an AI at all, so to adapt it to the new system required me to write a computer player for it.

Yacht is a moderately complex game for a computer to play. The decision of which dice to keep depends not just on what you have rolled, but also on which categories are left to score. To play well, the AI needs to take into account the relative value and difficulty of each category and the chances of getting the bonus.

Fortunately, Yacht has been solved(pdf). Unfortunately, it is still too computationally expensive to use this method while playing a game. I implemented a simpler system. It is fairly simple to find the “best” way to play each round if you ignore future rounds. This is similar to solving for one “widget” as described in the paper linked above. Then, instead of trying to solve for all possible futures, I simply use a set of rules to describe the value of each category. I can also tweak the constants used when applying these rules to make different two computer players play slightly differently.

The computer player plays a pretty good game and is fast enough to not be noticeable. If I wanted the AI to be more sophisticated, I would add more logic for determining the probability of getting the bonus based on the current scores. Then I would try to improve the value that I assign to each category by having AIs play against each other with different settings to see what works best.

Here is what the new GUI looks like:

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