int dy = (dir == GD_MV_UP ? +1 : dir == GD_MV_DOWN ? -1 : 0);
int old_x = cave->getx(cave, x + dx, y + dy);
int old_y = cave->gety(cave, x + dx, y + dy);
int dy = (dir == GD_MV_UP ? +1 : dir == GD_MV_DOWN ? -1 : 0);
int old_x = cave->getx(cave, x + dx, y + dy);
int old_y = cave->gety(cave, x + dx, y + dy);