如何用cocos2d-x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。

本文转自Walzer博客园博客，原文链接：http://www.cnblogs.com/walzer/archive/2010/10/11/1848106.html，如需转载请自行联系原作者

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