unsigned short int Cline::intersectionsWithCircle(Cpoint c, double r, vector<Cpoint> &intersections)
{
intersections.clear();
// move circle to (0,0)
//Cpoint p1 = aa - c; cout << "DEBUG: p1 is " << p1 << endl;
//Cpoint p2 = bb - c; cout << "DEBUG: p2 is " << p2 << endl;
Cpoint p1(aa.get_xx() - c.get_xx(), aa.get_yy() - c.get_yy()); //cout << "DEBUG: p1 is " << p1 << endl;
Cpoint p2(bb.get_xx() - c.get_xx(), bb.get_yy() - c.get_yy()); //cout << "DEBUG: p1 is " << p1 << endl;
// discriminant
double dx = p2.get_xx() - p1.get_xx();
double dy = p2.get_yy() - p1.get_yy();
double dr_sq = dx*dx + dy*dy;
double D = p1.get_xx() * p2.get_yy() - p2.get_xx() * p1.get_yy();
double disc = r*r * dr_sq - D*D;
if(disc < 0)
return 0;
else if(disc == 0)
{
double x = D * dy / dr_sq;
double y = -D * dx / dr_sq;
// check if point belongs to segment
Cpoint i = Cpoint(x + c.get_xx(), y + c.get_yy());
if( i.d2point2(&aa) <= aa.d2point2(&bb) && i.d2point2(&bb) <= aa.d2point2(&bb))
intersections.push_back( i );
return intersections.size();
}
else
{
int sign_dy = (dy >= 0) ? 1 : -1;
double x1 = ( D * dy + sign_dy * dx * sqrt(disc) ) / dr_sq;
double x2 = ( D * dy - sign_dy * dx * sqrt(disc) ) / dr_sq;
double abs_dy = ( dy >= 0 ) ? dy : -dy;
double y1 = ( -D * dx + abs_dy * sqrt(disc) ) / dr_sq;
double y2 = ( -D * dx - abs_dy * sqrt(disc) ) / dr_sq;
Cpoint i1 = Cpoint(x1 + c.get_xx(), y1 + c.get_yy());
Cpoint i2 = Cpoint(x2 + c.get_xx(), y2 + c.get_yy());
if( i1.d2point2(&aa) <= aa.d2point2(&bb) && i1.d2point2(&bb) <= aa.d2point2(&bb))
intersections.push_back( i1 );
if( i2.d2point2(&aa) <= aa.d2point2(&bb) && i2.d2point2(&bb) <= aa.d2point2(&bb))
intersections.push_back( i2 );
return intersections.size();
}
}
