bool add(SpriteObject *object, int main)
{
  if(object == NULL)
    return false;

  if(entryNum[main]+1 == listSize[main])
  {
    SpriteObject **list = realloc(spriteList[main], listSize[main]*2);
    if(list != NULL)
    {
      spriteList[main] = list;
      listSize[main] *= 2;
    }
    else
      return false;
  }

  entryNum[main]++;
  spriteList[main][entryNum[main]] = object;

  return true;
}

delete(SpriteObject *object, int main)
{
  if(object == NULL)
    return;

  for(int i = 0; i < entryNum[main]; i++)
  {
    if(spriteList[main][i] == object)
    {
      spriteList[main][i] = spriteList[main][entryNum[main]-1]; //swap last entry with this one
      spriteList[main][entryNum[main]--] = NULL; //set last entry to NULL and decrement
    }
  }
}

int compareSpriteObject(const void * p1, const void * p2)
{
  SpriteObject *o1 = (SpriteObject*)p1;
  SpriteObject *o2 = (SpriteObject*)p2;

  //push NULLs to end
  if(o1 == o2)
    return 0;    //same pointer
  if(o1 == NULL)
    return 1;    //o2 is 'greater than' null
  if(o2 == NULL)
    return -1;   //o1 is 'less than' null

  return (((int)(o1->priority)) - ((int)(o2->priority)));
}