Непонятность в одной граф либе

#include <Simple_window.h>
#include <Graph.h>
#include <GUI.h>
 
int main()
{
    Simple_window win(Point(0, 0), 800, 600, "My");
    Lines ln;
    ln.add(Point(100, 300), Point(300, 100));
    ln.add(Point(320, 110), Point(300, 100));
    ln.add(Point(300, 100), Point(280, 110));
    win.attach(ln);
    win.wait_for_button();
}

    ln.add(Point(100, 300), Point(300, 100));
    ln.add(Point(290, 120), Point(300, 100));
    ln.add(Point(300, 100), Point(280, 110));

#include <cmath>
#include <cstdlib>
#include <iostream>
 
struct Point
{
  size_t x,y;
};
 
std::ostream& operator<<(std::ostream& os, const Point& p)
{
   return os << "Point(" << p.x << "," << p.y << ") ";
}
 
int main()
{
   Point v[] = { {300,100}, {300,300}, {290,290}, {290,310} };
   size_t length = sizeof(v)/sizeof(v[0]);
   for( int i=0;i<length;++i )
   {
     v[i].x = v[i].x * cos( M_PI / 4 );
     v[i].y = v[i].y * sin( M_PI / 4 );
   }    
   std::cout << v[0] << v[1] << std::endl;
   std::cout << v[1] << v[2] << std::endl;   
   std::cout << v[1] << v[3] << std::endl;    
}

#include <cmath>
#include <cstdlib>
#include <iostream>
 
struct Point
{
  double x,y;
};
 
std::ostream& operator<<(std::ostream& os, const Point& p)
{
   return os << "Point(" << p.x << "," << p.y << ") ";
}
 
int main()
{
   Point v[] = { {100,300}, {300,300}, {290,290}, {290,310} };
   size_t length = sizeof(v)/sizeof(v[0]);
   double angle = - M_PI / 4; 
   for( int i=0;i<length;++i ) 
   {
     v[i].x = v[0].x + (v[i].x-v[0].x) * cos( angle )
                     - (v[i].y-v[0].y) * sin( angle );
     v[i].y = v[0].y + (v[i].x-v[0].x) * sin( angle )
                     + (v[i].y-v[0].y) * cos( angle ); 
   }    
   std::cout << v[0] << v[1] << std::endl;
   std::cout << v[1] << v[2] << std::endl;   
   std::cout << v[1] << v[3] << std::endl;    
}