两圆 相交面积

double calArea(Circle c1, Circle c2){    double d;    double s,s1,s2,s3,angle1,angle2,temp;    d=sqrt((c1.x-c2.x)*(c1.x-c2.x)+(c1.y-c2.y)*(c1.y-c2.y));    if(d>=(c1.r+c2.r))//两圆相离        return 0;    if((c1.r-c2.r)>=d)//两圆内含,c1大        return acos(-1.0)*c2.r*c2.r;    if((c2.r-c1.r)>=d)//两圆内含,c2大        return acos(-1.0)*c1.r*c1.r;    angle1=acos((c1.r*c1.r+d*d-c2.r*c2.r)/(2*c1.r*d));    angle2=acos((c2.r*c2.r+d*d-c1.r*c1.r)/(2*c2.r*d));    s1=angle1*c1.r*c1.r;s2=angle2*c2.r*c2.r;    s3=c1.r*d*sin(angle1);    s=s1+s2-s3;    return s;}