如何用cocos2dx来开发简单的Uphone游戏：(三) 射击子弹 & 碰撞检测

五、射击子弹

首先，我们先让这游戏里唯一的图层可以支持触摸。添加下面一行到init方法： 

// cpp with cocos2d-x this->setIsTouchEnabled(true);

// objc with cocos2d-iphone self.isTouchEnabled = YES;

因为图层已经支持触摸，所以我们可以收到触摸事件的回调。现在我们实现ccTouchesEnded方法，只要用户完成触摸，该方法就会被调用。

先在HelloWorldScene.h里增加函数声明 void ccTouchesEnded(cocos2d::NSSet* touches, cocos2d::UIEvent* event); 

然后到HelloWorldScene.cpp里增加函数实现

// cpp with cocos2d-x void HelloWorld::ccTouchesEnded(NSSet* touches, UIEvent* event) { // Choose one of the touches to work with CCTouch* touch = (CCTouch*)( touches->anyObject() ); CGPoint location = touch->locationInView(touch->view()); location = CCDirector::getSharedDirector()->convertToGL(location); // Set up initial location of projectile CGSize winSize = CCDirector::getSharedDirector()->getWinSize(); CCSprite *projectile = CCSprite::spriteWithFile("Projectile.png", CGRectMake(0, 0, 20, 20)); projectile->setPosition( ccp(20, winSize.height/2) ); // Determinie offset of location to projectile int offX = location.x - projectile->getPosition().x; int offY = location.y - projectile->getPosition().y; // Bail out if we are shooting down or backwards if (offX <= 0) return; // Ok to add now - we've double checked position this->addChild(projectile); // Determine where we wish to shoot the projectile to int realX = winSize.width + (projectile->getContentSize().width/2); float ratio = (float)offY / (float)offX; int realY = (realX * ratio) + projectile->getPosition().y; CGPoint realDest = ccp(realX, realY); // Determine the length of how far we're shooting int offRealX = realX - projectile->getPosition().x; int offRealY = realY - projectile->getPosition().y; float length = sqrtf((offRealX * offRealX) + (offRealY*offRealY)); float velocity = 480/1; // 480pixels/1sec float realMoveDuration = length/velocity; // Move projectile to actual endpoint projectile->runAction( CCSequence::actions( CCMoveTo::actionWithDuration(realMoveDuration, realDest), CCCallFuncN::actionWithTarget(this,                  callfuncN_selector(HelloWorld::spriteMoveFinished)),        NULL) ); }

// objc with cocos2d-iphone - (void)ccTouchesEnded:(NSSet *)touches withEvent:(UIEvent *)event { // Choose one of the touches to work with UITouch *touch = [touches anyObject]; CGPoint location = [touch locationInView:[touch view]]; location = [[CCDirector sharedDirector] convertToGL:location]; // Set up initial location of projectile CGSize winSize = [[CCDirector sharedDirector] winSize]; CCSprite *projectile = [CCSprite spriteWithFile:@"Projectile.png" rect:CGRectMake(0, 0, 20, 20)]; projectile.position = ccp(20, winSize.height/2); // Determine offset of location to projectile int offX = location.x - projectile.position.x; int offY = location.y - projectile.position.y; // Bail out if we are shooting down or backwards if (offX <= 0) return; // Ok to add now - we've double checked position [self addChild:projectile]; // Determine where we wish to shoot the projectile to int realX = winSize.width + (projectile.contentSize.width/2); float ratio = (float) offY / (float) offX; int realY = (realX * ratio) + projectile.position.y; CGPoint realDest = ccp(realX, realY); // Determine the length of how far we're shooting int offRealX = realX - projectile.position.x; int offRealY = realY - projectile.position.y; float length = sqrtf((offRealX*offRealX)+(offRealY*offRealY)); float velocity = 480/1; // 480pixels/1sec float realMoveDuration = length/velocity; // Move projectile to actual endpoint [projectile runAction:[CCSequence actions: [CCMoveTo actionWithDuration:realMoveDuration position:realDest], [CCCallFuncN actionWithTarget:self                          selector:@selector(spriteMoveFinished:)],     nil]];     }

编译后，带头大哥就可以BIU~BIU~地扔飞镖出去了。这里会产生一些float和int隐式转换导致的warning，我们为了和objc代码保持一致而在坐标计算里使用了不少int变量，实际上全部用float会更合适。

 

六、碰撞检测

光扔飞镖是杀不死人的，我们还需要加入碰撞检测。要做到这一点，首先得在场景中更好地跟踪目标和子弹。

在这个游戏中，我们得为小怪和飞镖两种sprite加入一个tag成员变量，以区分两种不同的游戏物体。tag=1的时候这个CCSprite对象为小怪，tag=2的时候则为飞镖。由于在CCNode里面有m_nTag这个成员变量，并且有setTag和getTag方法，因此CCSprite就继承了这些方法，我们可以利用之。

修改完毕，现在可以专心地跟踪小怪和飞镖了。把以下代码添加到class HelloWorld的声明中

// cpp with cocos2d-x protected: cocos2d::NSMutableArray<cocos2d::CCSprite*> *_targets; cocos2d::NSMutableArray<cocos2d::CCSprite*> *_projectiles;

// objc with cocos2d-iphone NSMutableArray *_targets; NSMutableArray *_projectiles;

在这里，cocos2d-x模拟iOS的SDK实现了NSMutableArray,里面只能放NSObject及其子类。但不同的是，你必须告诉他里面要放的是哪种具体类型。

然后在init方法中初始化这两个数组

// cpp with cocos2d-x // Initialize arrays _targets = new NSMutableArray<CCSprite*>; _projectiles = new NSMutableArray<CCSprite*>;

// objc with cocos2d-iphone // Initialize arrays _targets = [[NSMutableArray alloc] init]; _projectiles = [[NSMutableArray alloc] init];

同时在类的析构函数里释放之. 严谨地说，我们还应在class HelloWorld的构造函数里初始化_targets和_projectiles两个指针为NULL

// cpp with cocos2d-x HelloWorld::~HelloWorld() { if (_targets) { _targets->release(); _targets = NULL; } if (_projectiles) { _projectiles->release(); _projectiles = NULL; } // cpp don't need to call super dealloc // virtual destructor will do this } HelloWorld::HelloWorld() :_targets(NULL) ,_projectiles(NULL) { }

// objc with cocos2d-iphone - (void) dealloc { [_targets release]; _targets = nil; [_projectiles release]; _projectiles = nil; // don't forget to call "super dealloc" [super dealloc]; }

 现在修改addTarget方法，添加新目标到目标数组中，并给它设置Tag标记以和飞镖sprite区分开来

// cpp with cocos2d-x // Add to targets array taget->setTag(1); _targets->addObject(target);

// objc with cocos2d-iphone // Add to targets array target.tag = 1; [_targets addObject:target];

然后，修改spriteMoveFinished方法，根据标记的不同，在对应的数组中移除精灵

// cpp with cocos2d-x void HelloWorld::spriteMoveFinished(CCNode* sender) { CCSprite *sprite = (CCSprite *)sender; this->removeChild(sprite, true); if (sprite->getTag() == 1) // target { _targets->removeObject(sprite); } else if (sprite->getTag() == 2) // projectile { _projectiles->removeObject(sprite); } }

// objc with cocos2d-iphone -(void)spriteMoveFinished:(id)sender { CCSprite *sprite = (CCSprite *)sender; [self removeChild:sprite cleanup:YES]; if (sprite.tag == 1) // target { [_targets removeObject:sprite]; } else if (sprite.tag == 2) // projectile { [_projectiles removeObject:sprite]; } }

编译并运行项目以确保一切正常。此时还看不出什么明显不同，但我们可以利用前面加的tag标记来实现碰撞检测

现在往class HelloWorld里添加一个update方法，计算碰撞，并让碰撞了的飞镖和小杂兵同时从屏幕消失

// cpp with cocos2d-x void HelloWorld::update(ccTime dt) { NSMutableArray<CCSprite*> *projectilesToDelete =                                 new NSMutableArray<CCSprite*>;   NSMutableArray<CCSprite*>::NSMutableArrayIterator it, jt;   for (it = _projectiles->begin(); it != _projectiles->end(); it++)   {     CCSprite *projectile =*it;     CGRect projectileRect = CGRectMake(     projectile->getPosition().x - (projectile->getContentSize().width/2),     projectile->getPosition().y - (projectile->getContentSize().height/2),     projectile->getContentSize().width,     projectile->getContentSize().height);     NSMutableArray<CCSprite*>*targetsToDelete =new NSMutableArray<CCSprite*>;                      for (jt = _targets->begin(); jt != _targets->end(); jt++)     {       CCSprite *target =*jt;       CGRect targetRect = CGRectMake(     target->getPosition().x - (target->getContentSize().width/2),     target->getPosition().y - (target->getContentSize().height/2),     target->getContentSize().width,     target->getContentSize().height);                                if (CGRect::CGRectIntersectsRect(projectileRect, targetRect))       {         targetsToDelete->addObject(target);       }     }     for (jt = targetsToDelete->begin(); jt != targetsToDelete->end(); jt++)     {       CCSprite *target =*jt;       _targets->removeObject(target);       this->removeChild(target, true);     }     if (targetsToDelete->count() >0)     {       projectilesToDelete->addObject(projectile);     }     targetsToDelete->release();   }   for (it = projectilesToDelete->begin(); it != projectilesToDelete->end(); it++)   {     CCSprite* projectile =*it;     _projectiles->removeObject(projectile);     this->removeChild(projectile, true);   }   projectilesToDelete->release(); }

// objc with cocos2d-iphone - (void)update:(ccTime)dt { NSMutableArray *projectilesToDelete =                             [[NSMutableArray alloc] init];   for (CCSprite *projectile in _projectiles)    {     CGRect projectileRect = CGRectMake(     projectile.position.x - (projectile.contentSize.width/2),      projectile.position.y - (projectile.contentSize.height/2),      projectile.contentSize.width,      projectile.contentSize.height);     NSMutableArray *targetsToDelete = [[NSMutableArray alloc] init];     for (CCSprite *target in _targets)      {              CGRect targetRect = CGRectMake(     target.position.x - (target.contentSize.width/2),      target.position.y - (target.contentSize.height/2),      target.contentSize.width,      target.contentSize.height);            if (CGRectIntersectsRect(projectileRect, targetRect))        {         [targetsToDelete addObject:target];                       }                             }              for (CCSprite *target in targetsToDelete)      {       [_targets removeObject:target];       [self removeChild:target cleanup:YES];                                         }              if (targetsToDelete.count >0)      {       [projectilesToDelete addObject:projectile];     }     [targetsToDelete release];   }        for (CCSprite *projectile in projectilesToDelete)    {     [_projectiles removeObject:projectile];     [self removeChild:projectile cleanup:YES];   }   [projectilesToDelete release]; }

上面有个注意点，我们用来检查矩形交叉的函数。实际上各平台都有用来检查矩形相交的函数，我们这里为了方便iphone开发者转换代码，实现了静态的CGRect::CGRectInterestcRect方法。上面的代码大致就是，遍历小怪和飞镖数组，一旦发现有矩形相交（碰撞），就把他们分别添加到targetsToDelete和projectileToDelete数组中，然后删除之

在运行之前，你还需要让这个update方法不断地被调用，可以在init方法中添加如下代码达成这个目的

// cpp with cocos2d-x this->schedule( schedule_selector(HelloWorld::update) );

// objc with cocos2d-iphone [self schedule:@selector(update:)];

编译运行，你就可以看到飞镖和小怪碰撞时，它们同时从屏幕消失了。

至此，一个简单cocos2d游戏的雏形就已经完成了。在下一篇里，我们会对这个游戏进行最后的润色，添加背景音乐和音效，已经过关和GAME OVER的提示界面。

系列教程

如何用cocos2d-x来开发简单的Uphone游戏：(一) 下载安装和HelloWorld

如何用cocos2d-x来开发简单的Uphone游戏：(二) 移动的精灵

如何用cocos2d-x来开发简单的Uphone游戏：(三) 射击子弹 & 碰撞检测

如何用cocos2d-x来开发简单的Uphone游戏：(四) 音乐音效 & 最后的润色

如何用cocos2d-x来开发简单的Uphone游戏：(五) 打包发布

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