鼠标操作图形旋转

算法思路：
寻找图形的中心点或者给定一个点，将影响图形形状的关键点绕着这个点旋转，然后根据旋转后的新值重绘图形。这里旋转的角度，即为鼠标移动开始点与定点的向量，和移动结束点与定点的向量之间的夹角。

用到的数学公式：

部分函数实现：

//////////////////////////////////////////////////////////////////////////struct POINTF {    float x;     float y;    POINTF::POINTF(){}    POINTF::POINTF(float a,float b):x(a),y(b){}};//判断向量顺时针旋转还是逆时针旋转（两向量起点相同）//向量a，旋转前的向量//向量b，旋转后的向量//返回值1-顺时针 0-平行 -1-逆时针int vecCross(const POINTF& a,const POINTF& b){    float fValue = a.x*b.y - b.x*a.y;    if (fValue > 1e-6)//正    {        return 1;    }    else if(fValue < -1e-6)//负    {        return -1;    }    else//零    {        return 0;    }}//点pta绕ptCenter点旋转int vecCross(const POINTF& ptCenter,const POINTF& pta,const POINTF& ptScreen){    POINTF a = POINTF(pta.x-ptCenter.x,pta.y-ptCenter.y);    POINTF b = POINTF(ptScreen.x-ptCenter.x,ptScreen.y-ptCenter.y);    int axb = vecCross(a,b);    return axb;}//计算向量旋转角度cos值//点pta绕ptCenter点旋转float rotCosAngle(const POINTF& ptCenter,const POINTF& pta,const POINTF& ptScreen){       POINTF a = POINTF(pta.x-ptCenter.x,pta.y-ptCenter.y);    POINTF b = POINTF(ptScreen.x-ptCenter.x,ptScreen.y-ptCenter.y);    POINTF c = POINTF(ptScreen.x-pta.x,ptScreen.y-pta.y);    float A = sqrtf(a.x*a.x+a.y*a.y);    float B = sqrtf(b.x*b.x+b.y*b.y);    float C = sqrtf(c.x*c.x+c.y*c.y);    float CosC = (A*A+B*B-C*C)/(2*A*B);//cosC = (a^2+b^2-c^2)/2ab  此处没有考虑除数为0的情况    return CosC;}//计算一个点绕另一个点旋转，得到的点POINTF getRotationPoint(const POINTF& ptCenter,const POINTF& pta,const int& axb,const float& costheta){    POINTF pt(0.0,0.0);    POINTF a = POINTF(pta.x-ptCenter.x,pta.y-ptCenter.y);    //POINTF b = POINTF(ptScreen.x-ptCenter.x,ptScreen.y-ptCenter.y);    //int axb = vecCross(a,b);    //float costheta = rotCosAngle(ptCenter,pta,ptScreen);    float sintheta = sqrtf(1-costheta*costheta);//计算sin值，sinA^2+cosA^2 = 1    POINTF ptTemp;    switch(axb)    {        case 0:            pt = pta;            break;        case -1://逆时针            ptTemp = POINTF(a.x*costheta+a.y*sintheta+ptCenter.x,-a.x*sintheta+a.y*costheta+ptCenter.y);            pt = ptTemp;            break;        case  1://顺时针            ptTemp = POINTF(a.x*costheta-a.y*sintheta+ptCenter.x,a.x*sintheta+a.y*costheta+ptCenter.y);            pt = ptTemp;            break;    }    return pt;}