android - 球对球碰撞解决

Question

我正在创建一个弹跳球项目。

我的项目的唯一问题是当两个球彼此相交时的碰撞解决方案。碰撞检测很好，因为当两个球相交时它们反弹回来但随后它们一次又一次地碰撞。当球与墙壁碰撞时它们弹跳正确，但我不知道为什么当它们相互碰撞时会出现问题。

我已经尝试了各种代码，但仍然无法得到它。

我该怎么做？

您可以像我一样使用此链接..

Ball to Ball Collision - Detection and Handling

这是我的代码:

package com.example.bouncer;


import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.Point;
import android.provider.SyncStateContract.Constants;
public class Ball {

private Point p;   //Point p:Represents the x and y position of the Ball
private int c;     //Represents the color of the Ball
private int r;      //Represents the Radius of the Ball.
private int dx;             //Integer dx:Represents the change in x position of ball  
                            // Integer dy:Represents the change in y position of ball
private int dy;
private Paint paint;      //Android Object holding the color for drawing on the canvas
public Ball(int x,int y,int col,int radius)
{
    p=new Point(x,y);
    c=col;
    r=radius;
    paint=new Paint();
    dx=0;
    dy=0;
}
public int getX()
{return p.x;
}
public int getY()
{
    return p.y;
}
public int getRadius()
{return r;
}
public Paint getPaint()
{return paint;
}
public void setColor(int col)
{c=col;
}
public void goTo(int x,int y)
{p.x=x;
p.y=y;
}
public void setDX(int speed)
{dx=speed;
}
public void setDY(int speed)
{
    dy=speed;
}
public void move()
{
    p.x=p.x+dx;
    p.y=p.y+dy;
}
public void bounce(Canvas canvas)       //COLLISION DETECTION AND RESOLUTION WITH WALLS
{
    move();
    if(p.x>canvas.getWidth()|| p.x<0)
    {

        dx=dx * -1;
    }
    if(p.y>canvas.getWidth()|| p.y<0)
    {

        dy=dy * -1;
    }


    }


    public void bounceoff(Ball b)          //BALL TO BALL COLLSION DETECTION
    {
       float x = b.getX() - p.x;
       float y = b.getY() - p.y;
       float distanceSquared = x*x + y*y;
       float radius = b.getRadius()+r;
       float radiusSquared = radius*radius;
       if (distanceSquared <= radiusSquared)
       {
            dx=dx * -1;
            dy=dy * -1;

       }
    }
}

动画 View .java

package com.example.bouncer;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.os.Handler;
import android.util.AttributeSet;
import android.view.View;
public class AnimationView extends View{
  private final int FRAME_RATE=15;
  private Paint paint;
  private Handler h;
  Ball myball;
  Ball greenball;
  Ball redball;
    public AnimationView(Context context,AttributeSet attrs) {
        super(context,attrs);
        // TODO Auto-generated constructor stub
        h=new Handler();
        paint=new Paint();
        paint.setColor(Color.BLUE);
        myball=new Ball(100,100,Color.BLUE,50);
        greenball=new Ball(200,200,Color.GREEN,50);
        redball=new Ball(50,400,Color.RED,50);
        myball.setDX(10);
        myball.setDY(10);
        greenball.setDX(-20);
        greenball.setDY(-15);
        redball.setDX(5);
        redball.setDY(-5);

    }
    protected void onDraw(Canvas c)
    {
        myball.bounce(c);
        greenball.bounce(c);
        redball.bounce(c);
        myball.bounceoff(myball);
        greenball.bounceoff(greenball);
        redball.bounceoff(redball);
        c.drawCircle(myball.getX(), myball.getY(),myball.getRadius(), myball.getPaint());
        c.drawCircle(greenball.getX(), greenball.getY(),greenball.getRadius(), greenball.getPaint());
        c.drawCircle(redball.getX(), redball.getY(),redball.getRadius(), redball.getPaint());

        h.postDelayed(r, FRAME_RATE);

    }
    private Runnable r=new Runnable()
    { public void run()
    { invalidate();
    }
    };
    }

如果您想要我的完整项目代码，请查看链接.. https://stackoverflow.com/questions/22892736/balls-keep-colliding-again-and-again-android

Answer 1

我认为使用检测球与球碰撞的标准可能会导致错误碰撞。如果 AB 是球 A 和 B 的中心之间的向量，并且 rA 是 的半径A 和 rB B 的半径然后你可以使用这个标准来检查球是否碰撞

|AB| < rA + rB

其中|AB|表示向量AB的长度

计算这个的优化方法(避免昂贵的平方根计算)是

int xDiff = b.getX()-p.x;
int yDiff = b.getY()-p.y;
int radii = b.getRadius() + r;
if ( ( xDiff * xDiff + yDiff * yDiff ) < radii * radii ) {
    // Collision response. Change the balls velocity

此外，还有一些旁注。

1. 我认为最好将 move 从 bounce 中取出，这样您就可以先移动所有的球，然后检查它们是否与另一个球或墙。

2. 您的碰撞响应(当球碰撞时会发生什么)即仅当球速度除了符号相同(例如 vA = 1m/s，vB = -1 米/秒)。在其他情况下，球不会按预期反弹。