Getting the Behavior Index

Sometimes behaviors may need to know which behaviors executed before it, and which behaviors will execute after it, in the agent's behavior chain. For this, the agent's state has a special method — state.behaviorIndex() in Javascript and state.behavior_index() in Python — which returns the index of the currently executing behavior in the agent's behavior chain.

const behavior = (state, context) => {
  const index = state.behaviorIndex();
  console.log("behavior index =", index);
  console.log("behavior name =", state.behaviors[index]);
};

You can see an example use of this method in the Wildfires simulation. When a tree burns down, or begins to regrow, it cycles through three behaviors: tree.js, fire.js and ember.js.

The switching is accomplished by indexing into the agent's behavior array using state.behaviorIndex() and assigning the next behavior.

// fire.js

function behavior(state, context) {
  // Replace the fire behavior with the ember behavior
  state.behaviors[state.behaviorIndex()] = "ember.js";

  state.color = context.globals().fireColor;
  state.shape = "fire";
  state.height = 3;
}