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);
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// objc with cocos2d-iphone
self.isTouchEnabled = YES;
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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) );
}
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// 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]];
}
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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;
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// objc with cocos2d-iphone
NSMutableArray *_targets;
NSMutableArray *_projectiles;
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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*>;
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// objc with cocos2d-iphone
// Initialize arrays
_targets = [[NSMutableArray alloc] init];
_projectiles = [[NSMutableArray alloc] init];
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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)
{
}
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// objc with cocos2d-iphone
- (void) dealloc
{
[_targets release];
_targets = nil;
[_projectiles release];
_projectiles = nil;
// don't forget to call "super dealloc"
[super dealloc];
}
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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);
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// objc with cocos2d-iphone
// Add to targets array
target.tag = 1;
[_targets addObject:target];
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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);
}
}
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// 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];
}
}
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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();
}
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// 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];
}
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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) );
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// objc with cocos2d-iphone
[self schedule:@selector(update:)];
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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。
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