Cohesion.java

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 * Copyright 2014 See AUTHORS file.
 * 
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 *   http://www.apache.org/licenses/LICENSE-2.0
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package com.badlogic.gdx.ai.steer.behaviors;

import com.badlogic.gdx.ai.steer.GroupBehavior;
import com.badlogic.gdx.ai.steer.Limiter;
import com.badlogic.gdx.ai.steer.Proximity;
import com.badlogic.gdx.ai.steer.Proximity.ProximityCallback;
import com.badlogic.gdx.ai.steer.Steerable;
import com.badlogic.gdx.ai.steer.SteeringAcceleration;
import com.badlogic.gdx.math.Vector;

/** {@code Cohesion} is a group behavior producing a linear acceleration that attempts to move the agent towards the center of mass
 * of the agents in its immediate area defined by the given {@link Proximity}. The acceleration is calculated by first iterating
 * through all the neighbors and averaging their position vectors. This gives us the center of mass of the neighbors, the place
 * the agents wants to get to, so it seeks to that position.
 * <p>
 * A sheep running after its flock is demonstrating cohesive behavior. Use this behavior to keep a group of agents together.
 * 
 * @param <T> Type of vector, either 2D or 3D, implementing the {@link Vector} interface
 * 
 * @author davebaol */
public class Cohesion<T extends Vector<T>> extends GroupBehavior<T> implements ProximityCallback<T> {

	private T centerOfMass;

	/** Creates a {@code Cohesion} for the specified owner and proximity.
	 * @param owner the owner of this behavior.
	 * @param proximity the proximity to detect the owner's neighbors */
	public Cohesion (Steerable<T> owner, Proximity<T> proximity) {
		super(owner, proximity);
	}

	@Override
	protected SteeringAcceleration<T> calculateRealSteering (SteeringAcceleration<T> steering) {

		steering.setZero();

		centerOfMass = steering.linear;

		int neighborCount = proximity.findNeighbors(this);

		if (neighborCount > 0) {

			// The center of mass is the average of the sum of positions
			centerOfMass.scl(1f / neighborCount);

			// Now seek towards that position.
			centerOfMass.sub(owner.getPosition()).nor().scl(getActualLimiter().getMaxLinearAcceleration());
		}

		return steering;
	}

	@Override
	public boolean reportNeighbor (Steerable<T> neighbor) {
		// Accumulate neighbor position
		centerOfMass.add(neighbor.getPosition());
		return true;
	}

	//
	// Setters overridden in order to fix the correct return type for chaining
	//

	@Override
	public Cohesion<T> setOwner (Steerable<T> owner) {
		this.owner = owner;
		return this;
	}

	@Override
	public Cohesion<T> setEnabled (boolean enabled) {
		this.enabled = enabled;
		return this;
	}

	/** Sets the limiter of this steering behavior. The given limiter must at least take care of the maximum linear acceleration.
	 * @return this behavior for chaining. */
	@Override
	public Cohesion<T> setLimiter (Limiter limiter) {
		this.limiter = limiter;
		return this;
	}
}