Monday, November 03, 2008

XNA Series - AI - Better Steering - Part 1

I have been reading Steering Behaviors For Autonomous Characters by Craig Reynolds and after several reads I have decided to try to implement it in my own code and I think I am ready to explain it to you my loyal reader.

In his paper Mr Reynolds take a different approach that we have been taking thus far. Rather than having our steering be a simple rotation and moving forward at a set speed. He takes several other aspects into consideration, making a much more detailed simulation. To start we think about it in these terms: First we decide what direction and "magnitude" we need to move in that direction to steer us toward our goal. This is called our "Steering Vector". If we applied the steering vector all at once, we would immediately be put on the right path, but that would make for a very non-realistic simulation. Instead, rather, in the application of the steering vector, we take into consideration our current velocity, direction, mass and maximum force we can exert. We then factor these items against our steering vector to get an acceleration in a new direction to be added to our current velocity, we truncate this new velocity to our maximum speed and in that timestep we take a step towards steering to our goal.

The benefit of this method really lies in the Steering Vector. Since vectors can be scaled, added, subtracted, etc. We could apply several steering vectors. Say an object was following waypoints, we could say if an enemy is within a given distance, add the Flee steering vector times 50% and the Waypoint vector times 50%. We would then apply this new steering vector rather than just Waypoint or Flee, so that the object is still trying to do the waypoints, while evading.

In my next post, I will start looking at how we can adapt this method into our GameObject class.

The paper to which I am referring.
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