黑洞漩涡的实现

实现目标：用粒子产生一个圆形黑洞漩涡，如果敌人是在圆形内则暂停移动和射击，并作往圆心移动的圆周运动，旋转方向指向圆心，并逐步变小，并产生伤害，如果漩涡结束，敌人还没有被摧毁，则还原移动和射击动作。

接来下就来实现上面的过程：

首先要先实现一个圆周运动（由于cocos2d-x的自带例子中没有此类动作，就自己封装了一个）

其次要设置缩放，直接调用setScale即可

然后设置旋转，也是直接调用setRotation

实现都比较简单，直接上代码

class BlackHoleAction : public CCActionInterval
{
public:
	static BlackHoleAction* create(float dt, CCPoint circleCenter, float radius);
	bool init(float dt, CCPoint circleCenter, float radius);
	virtual void update(float dt);
protected:
	CCPoint _circleCenter;//圆心
	float _radius;//半径
	float _radius_var;//半径的变化变量
	float _radian;//每帧做圆周运动时旋转的弧度
	float _moveTimes;//移到圆心所用的时间
	float _scale;//缩放大小
	float _min_scale;//最小缩放到几倍
	float _scale_var;//缩放的变化变量
};

BlackHoleAction* BlackHoleAction::create(float dt, CCPoint circleCenter, float radius) {
	BlackHoleAction* blackHoleAction = new BlackHoleAction();
	blackHoleAction->init(dt, circleCenter, radius);
	blackHoleAction->autorelease();
	return blackHoleAction;
}
bool BlackHoleAction::init(float dt, CCPoint circleCenter, float radius) {
	bool result = false;
	if(CCActionInterval::initWithDuration(dt)) {
		_circleCenter = circleCenter;
		_radius = radius;
		_radius_var = CCDirector::sharedDirector()->getAnimationInterval() / dt * _radius;
		_moveTimes = 1;
		_radian = M_PI_2 / (dt / CCDirector::sharedDirector()->getAnimationInterval());
		_scale = 1;
		_scale_var = CCDirector::sharedDirector()->getAnimationInterval() / dt;
		_min_scale = 0.2f;
		result = true;
	}
	return result;
}
void BlackHoleAction::update(float dt) {
	if(this->m_pTarget) {
		Enemy* enemy = (Enemy*)this->m_pTarget;
		if(enemy->getIsInBlackHole()) {
			float radian = _radian * _moveTimes * 5;

			this->m_pTarget->setRotation(CC_RADIANS_TO_DEGREES(radian));

			float x = _radius * sin(radian);
			float y = _radius * cos(radian);

			CCPoint newPos = ccp(x + _circleCenter.x, y + _circleCenter.y);
			this->m_pTarget->setPosition(newPos);
			_moveTimes += 4;

			_scale = _scale - _scale_var;
			if(_scale > _min_scale) {
				this->m_pTarget->setScale(_scale);
			}
			if(_radius <= 0) {
				_radius = 0;
			}else {
				_radius = _radius - _radius_var;
			}
		}else {
			this->stop();
		}
	}
}