text: class GameScreen : public Screen2D {
  	public:
  
  	virtual void draw(){
  		glEnable (GL_LIGHTING);
  		glShadeModel(GL_FLAT);
  
  		for( int i=0; i<perFrame; i++ ){
  			yacht1.clean_temp( );
  			yacht1.applySailForces(  windSpeed,  watterSpeed );
  			yacht1.move( dt );
  		}
  
  		chain1->move( yacht1.pos );
  		glColor3f( 0.3f, 0.3f, 0.3f ); chain1->draw( yacht1.pos );
  
  		glColor3f( 0.8f, 0.8f, 0.8f ); 	yacht1.draw_shape( );  
  		glColor3f( 0.2f, 0.2f, 0.2f );  yacht1.draw( ); 
  
  		Vec2d compass_pos; compass_pos.set( 0.8*ASPECT_RATIO*zoom, 0.8*zoom );
  
  		glColor3f( 0.2f, 0.2f, 0.2f );  drawPointCross( compass_pos, zoom*0.1 );
  		glColor3f( 0.2f, 0.5f, 0.2f );  drawVecInPos( windSpeed*zoom*0.1,   compass_pos );
  		glColor3f( 0.2f, 0.2f, 0.8f );  drawVecInPos( watterSpeed*zoom*0.1, compass_pos );
  
  		glDisable  (GL_LIGHTING);
  		drawAxis( 10 );
  	}
  
  	GameScreen( int& id, int WIDTH_, int HEIGHT_ ) : Screen2D( id, WIDTH_, HEIGHT_ )  {	};
  
  };
  