inline float calcR(float x,float y) {
	VECTOR3D a,b,c;
	a.x=x-pX;
	a.y=y-pY;
	a.z=0;
	b.x=0;
	b.y=0;
	b.z=0;
	c.x=c.z=0;
	c.y=1;
	VECTOR3D ac,bc,cb;
	ac=a-c;
	bc=b-c;
	cb=c-b;
	float ans;
	/*
	* cos＜A,B＞=(ac+bd)/(根号a*a+b*b)(根号c*c+d*d)
	* 两向量夹角余弦等于向量数量积除以两向量模的乘积
	*/
	if(a.x>b.x) {
		ans=acos((ac.x * cb.x + ac.y * cb.y) / (sqrt(ac.x * ac.x + ac.y * ac.y) * sqrt(cb.x * cb.x + cb.y * cb.y)));
	} else {
		ans=acos((ac.x * cb.x + ac.y * cb.y) / (sqrt(ac.x * ac.x + ac.y * ac.y) * sqrt(cb.x * cb.x + cb.y * cb.y)))*-1;
	}

	return ans;
}