ballwar.model
Class AElasticMassCollisionCmd

java.lang.Object
  ballwar.model.AElasticMassCollisionCmd

All Implemented Interfaces:

IBallCmd

public abstract class AElasticMassCollisionCmd
extends Object
implements IBallCmd

Superclass for commands involving elastic collisions of round balls with individual masses. This superclass provides protected utility methods for the calculations. Sub-classes must implement the "public void apply(Ball target)" method of IBallCmd. The apply method must determine if the source and target balls are within collision distance and then calculate the impulse of the collision. The collisionUpdate method can be used to change the velocity of the source and target balls by calling it with appropriate source and target balls and with the appropriate sign on the impulse. Copyright (c) 2010 by Stephen Wong

Author:

Stephen Wong

Field Summary

private double

Nudge The amount to add to the separation distance to insure that the two balls are beyond collision distance

Constructor Summary

AElasticMassCollisionCmd()

Method Summary

protected Point2D.Double	impulse(Point lSource, Point vSource, Point lTarget, Point vTarget, double reducedMass, double distance, double deltaR) Calculates the impulse (change in momentum) of the collision in the direction from the source to the target This method calculates the impulse on the source ball.
protected double	reducedMass(double mSource, double mTarget) Returns the reduced mass of the two balls (m1*m2)/(m1+m2) Gives correct result if one of the balls has infinite mass.
protected void	updateCollision(Ball source, Ball target, double impX, double impY) Updates the velocity of the source ball, given an impulse, then calls the source's update strategy's updateCollision method.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface ballwar.model.IBallCmd

apply

Field Detail

Nudge

private double Nudge

The amount to add to the separation distance to insure that the two balls are beyond collision distance

Constructor Detail

AElasticMassCollisionCmd

public AElasticMassCollisionCmd()

Method Detail

reducedMass

protected double reducedMass(double mSource,
                             double mTarget)

Returns the reduced mass of the two balls (m1*m2)/(m1+m2) Gives correct result if one of the balls has infinite mass.

Parameters:

mSource - Mass of the source ball

mTarget - Mass of the target ball

impulse

protected Point2D.Double impulse(Point lSource,
                                 Point vSource,
                                 Point lTarget,
                                 Point vTarget,
                                 double reducedMass,
                                 double distance,
                                 double deltaR)

Calculates the impulse (change in momentum) of the collision in the direction from the source to the target This method calculates the impulse on the source ball. The impulse on the target ball is the negative of the result. Also moves source ball out of collision range along normal direction. The change in velocity of the source ball is the impulse divided by the source's mass The change in velocity of the target ball is the negative of the impulse divided by the target's mass Operational note: Even though theoretically, the difference in velocities of two balls should be co-linear with the normal line between them, the discrete nature of animations means that the point where collision is detected may not be at the same point as the theoretical contact point. This method calculates the rebound directions as if the two balls were the appropriate radii such that they had just contacted _at_the_point_of_collision_detection_. This may give slightly different rebound direction than one would calculate if they contacted at the theoretical point given by their actual radii.

Parameters:

lSource - Location of the source ball

vSource - Velocity of the source ball

lTarget - Location of the target ball

vTarget - Velocity of the target ball

reducedMass - Reduced mass of the two balls

distance - Distance between the two balls.

deltaR - The difference in minimum minus actual separation. Should be a pos. value.

Returns:

updateCollision

protected void updateCollision(Ball source,
                               Ball target,
                               double impX,
                               double impY)

Updates the velocity of the source ball, given an impulse, then calls the source's update strategy's updateCollision method. The change in velocity is the impulse divided by the (source) ball's mass. To change the velocity of the target ball, switch the source and target input parameters and negate the impulse values.

Parameters:

source - The ball to update

target - The ball being collided with

impX - x-coordinate of the impulse

impY - y-coordinate of the impulse