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我正在用java制作一个简单的基于物理的游戏,并且我一直在实现碰撞检测方法。我有几个类继承自 comman 基类形状。我将所有可见对象存储在形状类的数组列表中。我为每个可能的对象碰撞创建了几种碰撞检测方法。当我开始实现这些方法时,我最终得到了这样的代码:

private void collision_detector(Shape s1,Shape s2){

    if(s1.getClass()==Ball.class)
        if(s2.getClass() == Block.class) collision_detector((Ball)s1,(Block)s2);
        else collision_detector((Ball)s1,(Ball)s2);
    else if(s1.getClass()==Block.class)
        if(s2.getClass()==Block.class) collision_detector((Block)s1,(Block)s2);
        else collision_detector((Ball)s2,(Block)s1);        
}

感觉这不是实现碰撞检测的正确方法,因为每次添加三角形或六边形等新形状时,我都必须更新此方法以检查每个可能的组合。我对访客模式有所了解。但是有没有更好的方法来做到这一点?

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1 回答 1

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如果您不介意将碰撞检测代码放在对象本身中,您可以通过执行以下操作来消除检查的一侧:

public abstract class Shape {
    public abstract boolean collidesWith (Shape s);
}

public class Ball extends Shape {
    @Override public boolean collidesWith (Shape s) {
        if (s instanceof Block)
            return Collision.blockBall((Block)s, this);
        else if (s instanceof Ball)
            return Collision.ballBall(this, (Ball)s);
        else
            return false;
    }
}

public class Block extends Shape {
    @Override public boolean collidesWith (Shape s) {
        if (s instanceof Block)
            return Collision.blockBlock(this, (Block)s);
        else if (s instanceof Ball)
            return Collision.blockBall(this, (Ball)s);
        else
            return false;
    }
}

public class Collision {
    public static boolean blockBlock (Block a, Block b) { ... }
    public static boolean blockBall (Block a, Ball b) { ... }
    public static boolean ballBall (Ball a, Ball b) { ... }
}

如果需要,这也使您可以自由地为形状本身中的某些形状组合实现碰撞算法——您甚至可以摆脱碰撞并只制作例如 Block.collideWithBall、Block.collideWithBlock 和 Ball.collideWithBlock,将它们称为适当的,例如:

public abstract class Shape {
    public abstract boolean collidesWith (Shape s);
}

public class Ball extends Shape {
    @Override public boolean collidesWith (Shape s) {
        if (s instanceof Block)
            return collidesWithBlock((Block)s);
        else if (s instanceof Ball)
            return collidesWithBall((Ball)s);
        else
            return false;
    }
    public boolean collidesWithBall (Ball b) {
        ... 
    }
    public boolean collidesWithBlock (Block b) {
        ...
    }
}

public class Block extends Shape {
    @Override public boolean collidesWith (Shape s) {
        if (s instanceof Block)
            return collidesWithBlock((Block)s);
        else if (s instanceof Ball)
            return ((Ball)s).collidesWithBlock(this);
        else
            return false;
    }
    public boolean collidesWithBlock (Block b) { 
        ...
    }
}

就个人而言,我更喜欢后者,因为它保留了相关类中包含的碰撞代码。请注意,不需要 Block.collidesWithBall,因为可以使用 Ball.collidesWithBlock。

每次添加新形状时,您仍然需要更新上述代码。如果性能不是问题,您也可以执行以下操作:

public abstract class CollisionAlgorithm {
    public abstract boolean canCollide (Class<? extends Shape> a, Class<? extends Shape> b);
    public abstract boolean collide (Shape a, Shape b);
}

public class Collider {

    private static final List<CollisionAlgorithm> algorithms;

    public static void registerAlgorithm (CollisionAlgorithm a) { 
        algorithms.append(a); 
    }

    public static CollisionAlgorithm findAlgorithm (Class<? extends Shape> a, Class<? extends Shape> b) {
        for (CollisionAlgorithm algo : algorithms)
            if (algo.canCollide(a, b))
                return algo; 
        return null;
    }

    public static boolean collide (Shape a, Shape b) {
        if (a == null || b == null) 
            return false;
        CollisionAlgorithm algo = findAlgorithm(a.getClass(), b.getClass());
        if (algo != null)
            return algo.collide(a, b);
        algo = findAlgorithm(b.getClass(), a.getClass()); // try swapped order
        if (algo != null)
            return algo.collide(b, a);
        return false;
    }

}

// usage: first register algorithms
Collider.registerAlgorithm(new BallBallAlgorithm());
Collider.registerAlgorithm(new BallBlockAlgorithm());
Collider.registerAlgorithm(new BlockBlockAlgorithm());

// then 
Shape myShape1 = ...;
Shape myShape2 = ...;
boolean collide = Collider.collide(myShape1, myShape2);

请注意:我在这里快速输入了这个,它是为了说明一个概念——可以进行许多改进。例如,可以将地图与两个 Shape 类一起使用作为提高性能的关键,或者可以为 CollisionAlgorithm 提供通用参数以消除铸造 Shapes 的需要。不过,请记住,每次您需要执行碰撞测试时,这种方法都需要在算法容器中进行查找。

于 2013-08-07T03:30:35.143 回答