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