前面已经实现了一个球在一个窗口中随机运动,下面将在前面的基础上实现两个球的随机运动及碰撞,此次的代码中用到的算法参考了Twinsen写的<向量几何在游戏编程中的使用>一文中关于两球碰撞时的算法.程序仍旧有两个类,一个Ball类,一个BallCanvas类,Ball类与前面相同,而BallCanvas类作了修改,修改后的代码如下:
import java.awt.Canvas;
import java.awt.Color;
import java.awt.Graphics;
import java.util.Random;
public class BallCanvas extends Canvas implements Runnable {
private int ballRadius = 40; //球的半径
private int ballAX,ballAY; //当前A,B球的位置
private int ballBX,ballBY;
private double ballAXMoveLength= 7; //A,B球当前速度在X,Y轴上的分速度
private double ballAYMoveLength = 9; //为了减少计算中数据丢失,用double型而不用int型
private double ballBXMoveLength = 6; //
private double ballBYMoveLength = 5; //如果用int型两球最终将停止运动
private Random r;
private boolean move = true; //标志球是否移动
private int screenWidth, screenHeight; //屏幕宽及高
private int ballARX, ballARY; //A球圆心位置
private int ballBRX, ballBRY; //B球圆心位置
public BallCanvas(int screenWidth, int screenHeight){
r = new Random();
ballAX = r.nextInt(screenWidth – 2*ballRadius); //随机初始化A球的初始位置
ballAY = r.nextInt(screenHeight – 2*ballRadius);
do{ //随机初始化B球的初始位置,且确定A球跟B球不发生碰撞
ballBX = r.nextInt(screenWidth – 2*ballRadius);
ballBY = r.nextInt(screenHeight – 2*ballRadius);
}while((int)Math.sqrt((ballAX-ballBX)*(ballAX-ballBX) +
(ballAY-ballBY)*(ballAY-ballBY)) < 2*ballRadius);
this.screenHeight = screenHeight;
this.screenWidth = screenWidth;
}
public void paint(Graphics g){
//g.setColor(Color.WHITE); //此处使用背景色而不用白色,如果要自己清空屏幕,则需加上缓存,不然会产生画面抖动
//g.fillRect(0, 0, screenWidth, screenHeight);
g.setColor(Color.RED);
g.fillArc((int)ballAX, (int)ballAY, (int)ballRadius*2, (int)ballRadius*2, 0, 360);
g.fillArc((int)ballBX, (int)ballBY,(int) ballRadius*2, (int)ballRadius*2, 0, 360);
}
/**
* 退出
*/
public void exit(){
move = false;
}
public void run(){
while(move){
//处理A球
if(ballAX + ballAXMoveLength + 2*ballRadius > screenWidth ||
ballAX + ballAXMoveLength < 0){ //当在X轴上碰到墙时,X轴行进方向改变
ballAXMoveLength*=-1;
}else{
ballAX += ballAXMoveLength; //没碰壁时继续前进
}
if(ballAY + ballAYMoveLength + 2*ballRadius > screenHeight ||
ballAY + ballAYMoveLength < 0){ //当在Y轴上碰到墙时,Y轴行进方向改变
ballAYMoveLength*=-1;
}else{
ballAY += ballAYMoveLength;
}
//处理B球
if(ballBX + ballBXMoveLength + 2*ballRadius > screenWidth ||
ballBX + ballBXMoveLength < 0){ //当在X轴上碰到墙时,X轴行进方向改变
ballBXMoveLength*=-1;
}else{
ballBX += ballBXMoveLength; //没碰壁时继续前进
}
if(ballBY + ballBYMoveLength + 2*ballRadius > screenHeight ||
ballBY + ballBYMoveLength < 0){ //当在Y轴上碰到墙时,Y轴行进方向改变
ballBYMoveLength*=-1;
}else{
ballBY += ballBYMoveLength;
}
ballsCollide(); //检查两球是否碰撞
repaint(); //更新画面
try{
Thread.sleep(10);
}catch(InterruptedException e){
}
}
}
/**
* 检查并处理两球碰撞
* 此处用向量来计算两球碰撞后的速度,具体算法分析请参见”向量几何在游戏编程中的使用”
*/
public void ballsCollide(){
if(Math.sqrt((ballAX-ballBX)*(ballAX-ballBX) + //并没有产生碰撞
(ballAY-ballBY)*(ballAY-ballBY)) > 2*ballRadius){
return;
}else{ //碰撞了
ballARX = ballAX + ballRadius; //A球圆心位置
ballARY = ballAY + ballRadius;
ballBRX = ballBX + ballRadius; //B球圆心位置
ballBRY = ballBY + ballRadius;
// 求出s'(球心连线上的向量)
double sx = ballARX – ballBRX ;
double sy = ballARY – ballBRY ;
// 求出s1(球心连线上的单位向量)
double s1x = sx / Math.sqrt(sx*sx + sy*sy) ;
double s1y = sy / Math.sqrt(sx*sx + sy*sy) ;
// 求出t'(与球心连线垂直的向量)
double tx = -sy ;
double ty = sx ;
// 求出t1(与球心连线垂直的单位向量)
double t1x = tx / Math.sqrt(tx*tx + ty*ty) ;
double t1y = ty / Math.sqrt(tx*tx + ty*ty) ;
// 求v1a在s1上的投影v1s
double v1s = ballAXMoveLength * s1x + ballAYMoveLength * s1y ;
// 求v1a在t1上的投影v1t
double v1t = ballAXMoveLength * t1x + ballAYMoveLength * t1y ;
// 求v2a在s1上的投影v2s
double v2s = ballBXMoveLength * s1x + ballBYMoveLength * s1y ;
// 求v2a在t1上的投影v2t
double v2t = ballBXMoveLength * t1x + ballBYMoveLength * t1y ;
// 用公式求出v1sf和v2sf
double v1sf = v2s ;
double v2sf = v1s ;
// 最后一步,注意这里我们简化一下,直接将v1sf,v1t和v2sf,v2t投影到x,y轴上,也就是v1’和v2’在x,y轴上的分量
// 先将v1sf和v1t转化为向量
double nsx = v1sf * s1x ;
double nsy = v1sf * s1y ;
double ntx = v1t * t1x ;
double nty = v1t * t1y ;
ballAXMoveLength =(nsx + ntx) ;
ballAYMoveLength =(nsy + nty) ;
// 然后将v2sf和v2t转化为向量
nsx = v2sf * s1x ;
nsy = v2sf * s1y ;
ntx = v2t * t1x ;
nty = v2t * t1y ;
ballBXMoveLength = (nsx + ntx );
ballBYMoveLength =(nsy + nty );
//碰撞之后两球速度变化了,可是两球的位置仍处于碰撞时的位置,此时可能导致程序误以后两球再次发生碰撞
//于是再次处理碰撞,造成程序的死循环,故碰撞后,两球应该以碰撞后的速度迅速产生一段距离避免碰撞的状态
while(Math.sqrt((ballAX-ballBX)*(ballAX-ballBX) + //仍旧处于碰撞时的位置
(ballAY-ballBY)*(ballAY-ballBY)) < 2*ballRadius){
if(ballAX + ballAXMoveLength + 2*ballRadius > screenWidth ||
ballAX + ballAXMoveLength < 0){ //当在X轴上碰到墙时,X轴行进方向改变
ballAXMoveLength*=-1;
}else{
ballAX += ballAXMoveLength; //没碰壁时继续前进
}
if(ballAY + ballAYMoveLength + 2*ballRadius > screenHeight ||
ballAY + ballAYMoveLength < 0){ //当在Y轴上碰到墙时,Y轴行进方向改变
ballAYMoveLength*=-1;
}else{
ballAY += ballAYMoveLength;
}
if(ballBX + ballBXMoveLength + 2*ballRadius > screenWidth ||
ballBX + ballBXMoveLength < 0){ //当在X轴上碰到墙时,X轴行进方向改变
ballBXMoveLength*=-1;
}else{
ballBX += ballBXMoveLength; //没碰壁时继续前进
}
if(ballBY + ballBYMoveLength + 2*ballRadius > screenHeight ||
ballBY + ballBYMoveLength < 0){ //当在Y轴上碰到墙时,Y轴行进方向改变
ballBYMoveLength*=-1;
}else{
ballBY += ballBYMoveLength;
}
}
}
}
/**
* 重新调整屏幕大小
*/
public void canvasResize(){
screenWidth = this.getWidth();
screenHeight = this.getHeight();
}
}