android开源项目DivideAndConquer中的小球碰撞问题

1.

 /*看小球是否重叠*/
    public boolean isCircleOverlapping(Ball otherBall) {
        final float dy = otherBall.mY - mY;
        final float dx = otherBall.mX - mX;

        final float distance = dy * dy + dx * dx;//两小球间的距离

        return (distance < ((2 * mRadiusPixels) * (2 *mRadiusPixels)))//如果距离小于半径的两倍并且不是碰撞后离开的状态，即重叠
                // avoid jittery collisions
                && !movingAwayFromEachother(this, otherBall);
    }

2.

    /*如何判定连个球朝相反方向运动??*/
    private boolean movingAwayFromEachother(Ball ballA, Ball ballB) {
        double collA = Math.atan2(ballB.mY - ballA.mY, ballB.mX - ballA.mX);
        double collB = Math.atan2(ballA.mY - ballB.mY, ballA.mX - ballB.mX);

        double ax = Math.cos(ballA.mAngle - collA);
        double bx = Math.cos(ballB.mAngle - collB);

        return ax + bx < 0;        
    }

3.

/**
     * Given that ball a and b have collided, adjust their angles to reflect their state
     * after the collision.
     * 弹性碰撞中的能量守恒和动量守恒定律
     * This method works based on the conservation of energy and momentum in an elastic
     * collision.  Because the balls have equal mass and speed, it ends up being that they
     * simply swap velocities along the axis of the collision, keeping the velocities tangent
     * to the collision constant.
     *
     * @param ballA The first ball in a collision
     * @param ballB The second ball in a collision
     */
    /*碰撞后两个小球的方向??*/
    public static void adjustForCollision(Ball ballA, Ball ballB) {

        final double collA = Math.atan2(ballB.mY - ballA.mY, ballB.mX - ballA.mX);
        final double collB = Math.atan2(ballA.mY - ballB.mY, ballA.mX - ballB.mX);

        final double ax = Math.cos(ballA.mAngle - collA);
        final double ay = Math.sin(ballA.mAngle - collA);

        final double bx = Math.cos(ballB.mAngle - collB);
        final double by = Math.cos(ballB.mAngle - collB);

        final double diffA = Math.atan2(ay, -bx);
        final double diffB = Math.atan2(by, -ax);

        ballA.mAngle = collA + diffA;
        ballB.mAngle = collB + diffB;
    }

对于以上问题，尤其是后两个，不是很明白，有明白的客官，路过后可以留言，灰常感谢！