cocos3 抛物线运动

#pragma once
#include "cocos2d.h"

USING_NS_CC;

class Parabola:public ActionInterval
{
public:
    static Parabola* create(const CCPoint& startPosition, const CCPoint& endPosition,
        float angle, float g,float &return_duration);

     //override
    virtual Parabola* clone() const override;
    virtual Parabola* reverse() const override;

    virtual void update(float time) override;

protected:
    bool initWithDuration(float duration, const CCPoint& startPosition,
        const CCPoint& endPosition, float angle, float g, float vx0, float vy0);

protected:
    float    m_vx0;
    float    m_vy0;
    Point    m_startPosition;
    Point    m_endPosition;
    float    m_angle;
    float    m_dur ;
    float    m_tan_a;
    float    m_g;
};

#include "Parabola.h"

#define PIXELS_PER_METER 100

Parabola* Parabola::create(const CCPoint& startPosition, const CCPoint& endPosition,
                           float angle, float g,float &return_duration)
{
    Parabola *pRet = new Parabola();
    float vx0,vy0, x1, y1,  duration;

    x1 = endPosition.x - startPosition.x;
    y1 = endPosition.y - startPosition.y;
    x1 /= PIXELS_PER_METER; //像素到米的转换，PIXELS_PER_METER为转换系数，这里设置为100
    y1 /= PIXELS_PER_METER;
    angle = angle*3.14 / 180;//convert t to radian

    if (x1<0)
    {
        angle *= -1;
    }

    vx0 = x1*sqrt(g / 2 / (x1*tan(angle) - y1)); //求出初速度
    vy0 = vx0 * tan(angle);

    duration = x1 / vx0; //求出整个运动的时间
    return_duration = duration; //将duration通过参数返回
    pRet->initWithDuration(duration,startPosition, endPosition, angle,g, vx0, vy0);
    pRet->autorelease();

    return pRet;
}

bool Parabola::initWithDuration(float duration, const Point& startPosition, const Point& endPosition, float angle, float g, float vx0, float vy0)
{
    if (CCActionInterval::initWithDuration(duration))
    {
        m_vx0 = vx0;
        m_vy0 = vy0;
        m_startPosition = startPosition;
        m_endPosition = endPosition;
        angle = angle*3.14 / 180;//convert t to radian
        m_angle = angle;
        m_dur = duration;
        m_tan_a = tan(angle);
        m_g = g;
        return true;
    }

    return false;
}

Parabola* Parabola::clone() const
{
    CC_ASSERT(0);
    return nullptr;
}

Parabola* Parabola::reverse() const
{
    CC_ASSERT(0);
    return nullptr;
}

void Parabola::update(float time)
{
    if (_target)
    {
        float elapsed = _elapsed; //获得当前的运动时间
        float diff_x = m_vx0 * elapsed;
        float diff_y = m_vy0 * elapsed - 0.5 * m_g * elapsed * elapsed; 

        CCPoint newPos = ccpAdd(m_startPosition, ccp(diff_x * PIXELS_PER_METER, diff_y * PIXELS_PER_METER)); //单位由米转换为像素
        _target->setPosition(newPos);

    }
}