手把手教你制作一款Box2D小游戏（三）



接着我们先来重写ContactListener：

类声明：

#import "Box2D.h"

 

class ContactListener : public b2ContactListener

{

public:

      voidBeginContact(b2Contact* contact);

      voidPreSolve(b2Contact* contact, const b2Manifold* oldManifold);

      voidPostSolve(b2Contact* contact, const b2ContactImpulse* impulse);

      voidEndContact(b2Contact* contact);

};

类定义：

#import "ContactListener.h"

#import "cocos2d.h"

#import "GameLayer.h"

 

void ContactListener::BeginContact(b2Contact*contact)

{

    b2Body* body =contact->GetFixtureA()->GetBody();

    NSNumber* userData =(NSNumber*)(body->GetUserData());

    if (userData == nil) {

        return;

    }

    int tag = [userDataintValue];

    if (tag == -1) {

        body= contact->GetFixtureB()->GetBody();

        userData= (NSNumber*)(body->GetUserData());

        if(userData == nil) {

            return;

        }

        tag= [userData intValue];

        if(tag == -2) {

            return;

        }

    }

   

    int lastScoredStep =[[GameLayer gameLayer] lastScoredStep];

    if (lastScoredStep == -1){

        [GameLayergameLayer].lastScoredStep = tag;

        return;

    } else if (lastScoredStep!= tag) {

        [GameLayergameLayer].lastScoredStep = tag;

        [[GameLayergameLayer] addScore];

    }

}

void ContactListener::PreSolve(b2Contact* contact,const b2Manifold* oldManifold){}

void ContactListener::PostSolve(b2Contact*contact, const b2ContactImpulse* impulse){}

void ContactListener::EndContact(b2Contact*contact){}

这里我们重写了BeginContact方法，当有刚体之间的碰撞发生时，我们通过判断两个刚体的类型来判断是否得分，刚体类型的判断就用的是我们前面的tag，注意这里我们做了判断，由于我们没有为墙体指定tag，所以当墙体的userData转换为NSNumber指针时为nil，这时候就没有必要再做判断了，并且我们为了防止重复记分，例如小球连续两次碰到当前Block（例如小球碰撞之后弹起又碰撞，或者遇到高矮台阶的那种Block），这时候就通过lastScoredStep来比较，lastScoredStep始终记录前一次得分的StepBlock。

最后我们来定义Ball类：

声明如下：

#import "CCNode.h"

#import "cocos2d.h"

#import "Box2D.h"

 

@interface Ball : CCNode{

    float screenWidth;

    float screenHeight;

    b2Body* body;

    CCSprite* shape;

}

 

+ (Ball*)ball;

 

- (void)reset;

- (void)pushLeft;

- (void)pushRight;

 

@end

定义：

#import "Ball.h"

#import "cocos2d.h"

#import "GB2ShapeCache.h"

#import "TagDefinitions.h"

#import "GameLayer.h"

 

@implementation Ball

 

+ (Ball*)ball{

    return [[[Ball alloc]init] autorelease];

}

 

- (id)init{

    if (self = [super init]) {

        //screendimensions

        CGSizescreenSize = [[CCDirector sharedDirector] winSize];

        screenHeight= screenSize.height;

        screenWidth= screenSize.width;

       

        shape= [CCPhysicsSprite spriteWithFile:@"ball.png"];

        shape.anchorPoint= ccp(0.5f, 0.5f);

        CGPointposition = ccp(screenWidth*0.5f, screenHeight*0.5f+50);

        b2BodyDefbodyDef;

        bodyDef.type= b2_dynamicBody;

        bodyDef.userData= [NSNumber numberWithInteger:-1];

        bodyDef.position.Set(position.x/PTM_RATIO,position.y/PTM_RATIO);

        body= [[GameLayer gameLayer] sharedWorld]->CreateBody(&bodyDef);

        [[GB2ShapeCachesharedShapeCache] addFixturesToBody:body forShapeName:@"ball"];

        [shapesetPTMRatio:PTM_RATIO];

        [shapesetB2Body:body];

        [shapesetPosition:position];

       

        [selfaddChild:shape];

    }

   

    return self;

}

 

- (void)pushLeft{

    b2Vec2 force;

    force.Set(-4.0f, 0);

    body->ApplyForceToCenter(force);

}

 

- (void)pushRight{

    b2Vec2 force;

    force.Set(4.0f, 0);

    body->ApplyForceToCenter(force);

}

 

- (void)reset{

    CGPoint position =ccp(screenWidth*0.5f, screenHeight*0.5f+50);

    b2Vec2 pos;

    pos.Set(position.x/PTM_RATIO,position.y/PTM_RATIO);

    body->SetTransform(pos,0);

    [shapesetPosition:position];

}

 

- (CGPoint)position{

    return shape.position;

}

 

@end

小球的图片素材：



小球类比较简单，通过ApplyForceToCenter来对小球施力即可。

这样我们的游戏就基本制作完成了，限于篇幅，我们没有列出各个类的dealloc方法，请读者补充完成，释放资源。此外，还可以添加一些音效，添加开始界面和GameOver界面等等。

 

教程就到这里，如果有问题，欢迎留言~