anchor.diff:    CollisionField(this.x,this.y,this.w,this.h);
   
     set x2(int value) => w = value-x;
  -  int get x2() => x+w;
  +  int get x2 => x+w;
     set y2(int value) => h = value-y;
  -  int get y2() => y+h;
  +  int get y2 => y+h;
   
     set midpointy(int value) => _midpointy = value;
  -  int get midpointy()
  +  int get midpointy
     {
       if(_midpointy == -1)
         return (y + h/2).toInt();
  
positive.code: @author Danny Hendrix
  **/
  
  #library('PlatformGame');
  
  
  /**
  
negative.code:   }
  
    set midpointx(int value) => _midpointx = value;
    int get midpointx
    {
      if(_midpointx == -1)
        return (x + w/2).toInt();
  