double angle(point p) {
#ifdef DBGANGLE
printf("(%d, %d).(%d, %d) = ", x, y, p.x, p.y);
double dotmod = (*this ^ p) / mod() / p.mod();
printf(" %.3lf --> %.3lf\n", dotmod, acos(dotmod));
#endif
return acos((*this ^ p) / mod() / p.mod());
}
point reflect(point P,point direct,point A,point B,double mu)
{
double dot(point,point);
point rotate(point,double);
if (P==A || P==B)
return(direct);
if (dot(direct,A-B)<0)
swap(A,B);
point T=A-B;
double angle=pi/2-acos(dot(direct,T)/direct.mod()/T.mod());
double theta=asin(sin(angle)/mu);
if (direct*T>0)
return(rotate(direct,theta-angle));
else
return(rotate(direct,angle-theta));
}
