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Extra Mechanisms used in Pure
As mentioned previously, we developed a few extra mechanisms to have the AI perform as expected:
The algorithm presented here offers a solution to "configure" or "script" your race in a fixed, predefined way, but allows a dynamic evolution of the race that tries to match the human player's performance -- but in a subtle way, and with bounds, so that it doesn't break the sensation of fairness.
We hope that the system explained here, which is the underlying AI behaviour in Pure, was never obvious to the player and kept the rewarding sensation from working their way through the race positions.
We think this method fits pretty well for our game since the genre is arcade racing. We wanted to present the player with exciting races where they are almost always surrounded by other guys and where they could easily progress, gaining positions, and overtaking opponents.
We wanted the top positions accessible but they had to fight for those positions at the end of the race, so that it's as thrilling and as exciting as possible. So we found this method fits our Hollywood-like goals very well.
We also think the algorithms described here may be used in any other kind of race game (simulators) and should be easy to implement.
We also think it could be used for other kind of games like FPS, RTSs, RPGs, etc. For instance, in a shooter you may want to have the player reaching certain strategic points with a certain amount of energy (assuming you don't have auto-regeneration).
If the player is over that energy, then you know your AI guys must press harder, but if the player is below that zone your guys should leave him some room to recover.
Then you can put some bounds to that, so that your guys never stop fighting and never have a lucky 100% headshot rate, and you set these bounds based on the difficulty level.
On easy levels they shouldn't press very hard, no matter what the human player's energy and the strategic points should have a higher reference energy values. It should be the opposite on the hardest difficulty level.
In short, this methodology presents a set of tools or values (the skills) that determine the way the AI characters behave. Then it uses those tools to try to match the player's experience to a predefined script, dynamically modifying the values of the skills based on the player's performance.
I would like to credit the people that worked shoulder by shoulder with me developing the Pure AI and whose ideas you may find in this article. It was thanks to working together and a lot of iteration and sharing our ideas that we ended up with the successful AI system we finally had.
The article presented here is the result of one year of hard work iterating over the initial ideas and doing lots of tests to improve and evolve the existing systems. The focus tests that we had were especially important, and helped us realize what the problems behind the AI were.
I would like to thank, in no particular order, Jason Avent, Michael Benfield, Jim Callin, Iain Gilfeather, and Tom Williams for their input as well as all of the people who helped us blind-test the product throughout development, without whom we couldn't have achieved the quality level we have.