protected void rewriteLetters(Word word) {
		int dx=0, dy=0;
		// ̎擾
		switch ( word.getOrient() ) {
		case RIGHT: dx = 1; break;
		case DOWN: dy = 1; break;
		}
		// ̏
		int x = word.getX();
		int y = word.getY();
		for ( char c : word.getString().toCharArray() ) {
			letters[x+y*columns] = c;
			x += dx; y += dy;
		}
	}