package tesseract.forces;

import javax.vecmath.Vector3f;

import tesseract.objects.PhysicalObject;

/**
 * Generic downward force class (aka Gravity).
 * 
 * @author Jesse Morgan
 */
public class Gravity extends Force {
	/**
	 * Default gravity force.
	 */
	private static final float DEFAULT_GRAVITY = 1f;
	
	/**
	 * The force used here.
	 */
	private float myGravity;
	
	/**
	 * Create a default gravity.
	 */
	public Gravity() {
		myGravity = DEFAULT_GRAVITY;
	}
	
	/**
	 * Create gravity with a custom strength.
	 * 
	 * @param gravity The strength of gravity.
	 */
	public Gravity(final float gravity) {
		myGravity = gravity;
	}
	
	/**
	 * Calculate the force of gravity...
	 * 
	 * @param obj The object the force is calculated for.
	 * @return A vector describing the force
	 */
	protected Vector3f calculateForce(final PhysicalObject obj) {
		return new Vector3f(0, -myGravity, 0);
	}

}