int collision( void * sp1 ,  void * sp2 , int dx , int dy)
{
    SPR_PTR b1 = sp1 , b2 = sp2 ;
	if ((b1->x > b2->x + b2->w - 1) || // is b1 on the right side of b2?
		(b1->y > b2->y + b2->h - 1) || // is b1 under b2?
		(b2->x > b1->x + b1->w - 1) || // is b2 on the right side of b1?
		(b2->y > b1->y + b1->h - 1))   // is b2 under b1?
	{
		// no collision
		return 0;
	}

	// collision

   return 1 ;
}