BlendTreeRandomizer.cs

using UnityEngine;
using System.Collections;

public class BlendTreeRandomizer : MonoBehaviour {

	public Animator animator; //animator on which to act upon
	public string key; //what is the key in the blend tree
	public int numStates = 2; //how many states are there
	public float minTime = 1.0f; //minimum time spent in a state
	public float maxTime = 5.0f; //maximum time spent in a state
	public float transitionTime = 0.5f; //time to transition from one state to the other

	private float elapsedTime = 0.0f;
	private float stateStep = 1.0f;
	private float nextRandomTime = 0.0f;
	private int lastState = 0;
	private int currentState = 0;
	private float currentStateValue = 0.0f;

	private float transitionValue;

	void Start () {
		Debug.Assert(transitionTime <= minTime);
		Debug.Assert(numStates > 1);
		stateStep = 1.0f / (numStates - 1);
	}
	
	void Update () {
		elapsedTime += Time.deltaTime;

		if (elapsedTime >= nextRandomTime) {
			ResetTime();
			UpdateState();
		}

		if (lastState != currentState) {
			float lastStateValue = lastState * stateStep;
			float t = (Mathf.Abs(currentStateValue - lastStateValue) * elapsedTime) / transitionTime;
			transitionValue = Mathf.Lerp(lastStateValue, currentStateValue, t);

			//Finish the transition when the desired value is almost there
			if (Mathf.Abs(transitionValue - currentStateValue) < 0.01) {
				lastState = currentState;
				transitionValue = currentStateValue;
			}

			UpdateAnimator(transitionValue);
		}
	}

	void ResetTime () {
		elapsedTime = 0.0f;
		nextRandomTime = Random.Range(minTime, maxTime);
	}

	void UpdateState () {
		currentState = GetNextState();
		currentStateValue = currentState * stateStep;
	}

	void UpdateAnimator (float value) {
		animator.SetFloat(key, value);
	}

	int GetNextState () {
		return Random.Range(0, numStates); 
	}
}