前面已經(jīng)實現(xiàn)了一個球在一個窗口中隨機運動,下面將在前面的基礎(chǔ)上實現(xiàn)兩個球的隨機運動及碰撞,此次的代碼中用到的算法參考了Twinsen寫的一文中關(guān)于兩球碰撞時的算法.程序仍舊有兩個類,一個Ball類,一個BallCanvas類,Ball類與前面相同,而BallCanvas類作了修改,修改后的代碼如下:

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;?? //球的半徑

private int ballAX,ballAY;??????? //當(dāng)前A,B球的位置

private int ballBX,ballBY;

private double ballAXMoveLength= 7;???? //A,B球當(dāng)前速度在X,Y軸上的分速度

private double ballAYMoveLength = 9;??? //為了減少計算中數(shù)據(jù)丟失,用double型而不用int型

private double ballBXMoveLength = 6;??? //

private double ballBYMoveLength = 5;???? //如果用int型兩球最終將停止運動

private Random r;

private boolean move = true;?????? //標(biāo)志球是否移動

private int screenWidth, screenHeight;??????? //屏幕寬及高

private int ballARX, ballARY;? //A球圓心位置

private int ballBRX, ballBRY;?? //B球圓心位置

public BallCanvas(int screenWidth, int screenHeight){

r = new Random();

ballAX = r.nextInt(screenWidth – 2*ballRadius);???? //隨機初始化A球的初始位置

ballAY = r.nextInt(screenHeight – 2*ballRadius);

do{??????? //隨機初始化B球的初始位置,且確定A球跟B球不發(fā)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);??????????? //此處使用背景色而不用白色,如果要自己清空屏幕,則需加上緩存,不然會產(chǎn)生畫面抖動

//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){

//處理A球

if(ballAX + ballAXMoveLength + 2*ballRadius > screenWidth ||

ballAX + ballAXMoveLength < 0){???????? //當(dāng)在X軸上碰到墻時,X軸行進(jìn)方向改變

ballAXMoveLength*=-1;

}else{

ballAX += ballAXMoveLength;???????????????? //沒碰壁時繼續(xù)前進(jìn)

}

if(ballAY + ballAYMoveLength + 2*ballRadius > screenHeight ||

ballAY + ballAYMoveLength < 0){???????? //當(dāng)在Y軸上碰到墻時,Y軸行進(jìn)方向改變

ballAYMoveLength*=-1;

}else{

ballAY += ballAYMoveLength;

}

//處理B球

if(ballBX + ballBXMoveLength + 2*ballRadius > screenWidth ||

ballBX + ballBXMoveLength < 0){???????? //當(dāng)在X軸上碰到墻時,X軸行進(jìn)方向改變

ballBXMoveLength*=-1;

}else{

ballBX += ballBXMoveLength;???????????????? //沒碰壁時繼續(xù)前進(jìn)

}

if(ballBY + ballBYMoveLength + 2*ballRadius > screenHeight ||

ballBY + ballBYMoveLength < 0){???????? //當(dāng)在Y軸上碰到墻時,Y軸行進(jìn)方向改變

ballBYMoveLength*=-1;

}else{

ballBY += ballBYMoveLength;

}

ballsCollide();?? //檢查兩球是否碰撞

repaint();??? //更新畫面

try{

Thread.sleep(10);

}catch(InterruptedException e){

}

}

}

/**

* 檢查并處理兩球碰撞

* 此處用向量來計算兩球碰撞后的速度,具體算法分析請參見”向量幾何在游戲編程中的使用”

*/

public void ballsCollide(){

if(Math.sqrt((ballAX-ballBX)*(ballAX-ballBX) +????????????? //并沒有產(chǎn)生碰撞

(ballAY-ballBY)*(ballAY-ballBY)) > 2*ballRadius){

return;

}else{?????????? //碰撞了

ballARX = ballAX + ballRadius;? //A球圓心位置

ballARY = ballAY + ballRadius;

ballBRX = ballBX + ballRadius;?? //B球圓心位置

ballBRY = ballBY + ballRadius;

// 求出s'(球心連線上的向量)

double sx = ballARX – ballBRX ;

double sy = ballARY – ballBRY ;

// 求出s1(球心連線上的單位向量)

double s1x = sx / Math.sqrt(sx*sx + sy*sy) ;

double s1y = sy / Math.sqrt(sx*sx + sy*sy) ;

// 求出t'(與球心連線垂直的向量)

double tx = -sy ;

double ty = sx ;

// 求出t1(與球心連線垂直的單位向量)

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，注意這里我們簡化一下，直接將v1sf,v1t和v2sf,v2t投影到x，y軸上，也就是v1’和v2’在x,y軸上的分量

// 先將v1sf和v1t轉(zhuǎn)化為向量

double nsx = v1sf * s1x ;

double nsy = v1sf * s1y ;

double ntx = v1t * t1x ;

double nty = v1t * t1y ;

ballAXMoveLength =(nsx + ntx) ;

ballAYMoveLength =(nsy + nty) ;

// 然后將v2sf和v2t轉(zhuǎn)化為向量

nsx = v2sf * s1x ;

nsy = v2sf * s1y ;

ntx = v2t * t1x ;

nty = v2t * t1y ;

ballBXMoveLength = (nsx + ntx );

ballBYMoveLength =(nsy + nty );

//碰撞之后兩球速度變化了,可是兩球的位置仍處于碰撞時的位置,此時可能導(dǎo)致程序誤以后兩球再次發(fā)生碰撞

//于是再次處理碰撞,造成程序的死循環(huán),故碰撞后,兩球應(yīng)該以碰撞后的速度迅速產(chǎn)生一段距離避免碰撞的狀態(tài)

while(Math.sqrt((ballAX-ballBX)*(ballAX-ballBX) +????????????? //仍舊處于碰撞時的位置

(ballAY-ballBY)*(ballAY-ballBY)) < 2*ballRadius){

if(ballAX + ballAXMoveLength + 2*ballRadius > screenWidth ||

ballAX + ballAXMoveLength < 0){???????? //當(dāng)在X軸上碰到墻時,X軸行進(jìn)方向改變

ballAXMoveLength*=-1;

}else{

ballAX += ballAXMoveLength;???????????????? //沒碰壁時繼續(xù)前進(jìn)

}

if(ballAY + ballAYMoveLength + 2*ballRadius > screenHeight ||

ballAY + ballAYMoveLength < 0){???????? //當(dāng)在Y軸上碰到墻時,Y軸行進(jìn)方向改變

ballAYMoveLength*=-1;

}else{

ballAY += ballAYMoveLength;

}

if(ballBX + ballBXMoveLength + 2*ballRadius > screenWidth ||

ballBX + ballBXMoveLength < 0){???????? //當(dāng)在X軸上碰到墻時,X軸行進(jìn)方向改變

ballBXMoveLength*=-1;

}else{

ballBX += ballBXMoveLength;???????????????? //沒碰壁時繼續(xù)前進(jìn)

}

if(ballBY + ballBYMoveLength + 2*ballRadius > screenHeight ||

ballBY + ballBYMoveLength < 0){???????? //當(dāng)在Y軸上碰到墻時,Y軸行進(jìn)方向改變

ballBYMoveLength*=-1;

}else{

ballBY += ballBYMoveLength;

}

}

}

}

/**

* 重新調(diào)整屏幕大小

*/

public void canvasResize(){

screenWidth = this.getWidth();

screenHeight = this.getHeight();

}

}

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