在平面旋转一个点

|
    |       .P
    |      /| 
    |     / |     
    |    /  |    
    |  r/   | y
    |  /    |  
    | /     |
    |/ @    |
    ------------------------------------------>
    |--x----|

    x = r * cos@;
    y = r * sin@;
    
    p点旋转 Z 角度以后 得到p1(x1,y1)点
    
    x1 = r * cos(@+Z);
    y1 = r * sin(@+Z);
    
    //两角正弦和差公式
    //http://zhidao.baidu.com/question/49451901.html
    //cos(a+b)=cosa*cos(-b)+sina*sin(-b)=cosa*cosb-sina*sinb
    //sin(a+b)=cos(a-pai/2)cosb-sin(a-pai/2)sinb=sina*cosb+cosa*sinb
    
    x1 = r * (cos@*cosZ-sin@*sinZ);
       = r*cos@*cosZ - r*sin@*sinZ // x = r * cos@; y = r * sin@;
       = x*cosZ - y*sinZ;
       
    y1 = r * (sin@*cosZ+cos@*sinZ);
       = r*sin@*cosZ + r*cos@*sinZ // x = r * cos@; y = r * sin@;
       = y*cosZ + x*sinZ
         
    p1(x1, y1); 

备忘！