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设计师应合理设置游戏中的机率因素

发布时间:2011-08-18 10:22:25 Tags:,,

作者:Soren Johnson

设计师开发游戏的一个强有力工具是机率,通过随机机会决定玩家行为结果或创建游戏环境。但借助运气元素也存在缺陷,设计师需把握其中取舍——什么机会元素能够植入游戏中,什么时候会产生反效果。

游戏回馈机率

借助随机元素的一大挑战是人类通常无法准确评估机率。一个典型例子是赌徒谬论,认为机率会逐步均等。若轮盘连续5次出现黑色,玩家会认为其再次出现黑色的机率非常小,虽然其机率都一样。相反,人类总是认为存在某些根本不存在的相关联系——例如,认为篮球场上带有“热手效应”的射手还会屡屡得手,这是个误区。调查显示,若二者存在某种联系,那就是成功射击通常预示着随后的失误。

老虎机 from pcpop.com

老虎机 from pcpop.com

同时,就像老虎机和MMO游戏设计师了然于心的那样,不均衡设置奖励关卡机率通常会令玩家觉得奖励频繁(游戏邦注:胜过其实际情况)。某商业老虎机公司曾于2008年公布其回馈比例:

* 每8回合的回报率是1:1

* 每600回合的回报率是2:1

* 每33回合的回报率是5:1

* 每2320回合的回报率是20:1

* 每219回合的回报率是80:1

* 每6241回合的回报率是150:1

80:1回报率能够带给玩家挑战困难,大获全胜的快感,但这个概率实际上仍然极小,根本不会让赌场陷入赔钱的风险。此外,人类通常无法准确评估极限可能——人们太常预测1%机率,而且通常认为99%机率同100%一样保险。

公平竞争

人们无法准确评估机率这点令游戏设计师处在有利位置。简单游戏机制,例如《Settlers of Catan》中基于骰子的资源生成系统,令人难以把握。

其实,运气促使游戏变得更通俗易懂,因为它缩小熟练玩家同新手之间的差距(游戏邦注:不论是从理论上,还是从实际情况来看)。在融入强大运气元素的游戏中,初学者会认为无论如何他们都有获胜机会。很少人愿意竞争国际象棋大师位置,而西洋双陆棋戏老手更具吸引力——融入少量运气令所有玩家都有获胜机会。

在设计师Dani Bunten看来,“虽然多数玩家都讨厌会破坏其精密预期策略的随机事件,但没有什么能够像作品中的曲折因素那样令内容栩栩如生。不要让玩家决定内容。他们无法把握结果,但若他们失败,游戏要给予适当理由,同时在其获胜时享有‘挑战困难’的机会。”

因此,运气就像个社交润滑剂,能够提高多人游戏的吸引力,这通常不适合残酷的肉搏竞争内容。

运气元素失效的情况

然而,随机性并不适合所有情形或游戏。“糟糕惊喜”绝非好主意。若木箱在打开时会出现弹药和其他奖励,但在其中1%的时间里会爆炸,玩家就无法以安全方式把握机率。若爆炸提早发生,玩家就会立即停止打开木箱。若稍后才发生,玩家就会措手不及,感觉上当受骗。

同时,当随机性变成干扰性元素,运气就会降低玩家对游戏的理解。若《星际争霸》的机械兵以摇骰子的机率进行射击,其发射速率就会变得不均衡。运气带给游戏结果的影响就会逐渐变得微不足道,由于出现这些额外随机因素的干扰性,玩家越发无法把握机械兵攻击的强度。

history of the world from pairodicegames.com

history of the world from pairodicegames.com

此外,运气会不必要地放缓游戏进程。棋盘游戏《History of the World》和《Small World》就有非常类似的征服机制(游戏邦注:除前者使用骰子,后者未采用该元素)。每次攻击都旋转骰子促使《History of the World》的持续时间比《Small World》长3-4倍。原因不单是转动如此多骰子所存在的逻辑问题——获悉决策结果具有可预测性促使玩家提前策划所有步骤,而无需担心意外事件。通常来说,应对意外事件是游戏设计的核心内容,但游戏速度也是个重要元素,所以设计师需确保取舍具有价值。

最后,运气不适合计算胜算。在游戏结束之前,玩家经历越长时间才遇到不幸的摇骰结果,游戏就越能呈现一种公平感。因此,运气越早发生作用,游戏给人的平衡感就越好。很多经典纸牌游戏——《皮纳克尔》、《桥牌》和《红心大战》,都遵循最初随机分配的标准模式,这促使这类游戏逐步建立起自己的市场,该领域随后开始出现运气之外决定输赢的游戏诀窍。

机率就是内容

的确,随机性带来最初挑战观念在传统游戏中扮演重要角色,从《踩地雷》之类的简单游戏到《NetHack》和《 帝国时代》之类的深层游戏。就其核心来看,《单人纸牌》和《暗黑破坏神》差别不大——二者都呈现玩家需巧妙进展方能获胜的随机环境。

最近融入随机元素的典型例子是《洞穴探险》,在这款游戏中,独立开发者Derek Yu既融入《NetHack》中的随机生成关卡,也借鉴《Lode Runner》当中的2D装置。游戏沉浸性来自于其蕴含的无数有待探索的新关卡,但游戏融入某些意外怪兽和隧道,其难度颇令人沮丧。

其实,纯粹随机性就像头难以控制的野兽,其创造令原本稳固设计失去平衡的游戏机制。例如,《文明 3》引入战略资源理念,这是建设特定单元的必需品——战车需要马匹,坦克需要石油。这些资源随机分配于世界各角落,这当然会把玩家带入一个广阔大陆,这其中只有一簇由某AI敌人控制的铁矿。我们常常会看到社区中有人抱怨由于缺乏资源无法组建军队。

至于《文明 4》,游戏通过在某些重要资源中隔开一些空间以解决原有问题,这样两个烙铁资源就不会同时出现在7块砖的距离之内。游戏资源仍旧出乎意料地分布于世界各个角落,但若资源不是成簇存在,就会出现不幸玩家。此外,游戏鼓励集聚不那么重要的奢侈资源(游戏邦注:包括香、宝石和香料),以推动有趣交易机制。

呈现机率

最终,当谈到机率元素时,设计师需扪心自问:“运气的促进或阻碍度如何?”随机性是否巧妙地令玩家失去平衡,这样他们就无法轻易解决问题?或者它只是在体验中融入令人沮丧的意外因素,这样玩家就不会寄希望于他们的决定?

一个确保游戏采用前种模式的因素是清楚呈现机率。策略游戏《Armageddon Empires》的战斗基于少数简单的掷骰子活动,然后在屏幕上直接显示骰子结果。让玩家接触游戏算法能够提高机制的方便度,将机会变得一个工具,而不是一个谜团。

同样地,在《文明 4》中,我们引入帮助模式,这准确呈现战斗成功的机率,能够大大提高玩家对于潜在机制的满意度。由于人类无法准确评估可能性,帮助他们做出明智决定能够有效提高游戏体验。

Magic The Gathering from gamespy.com

Magic The Gathering from gamespy.com

有些纸牌游戏,例如《Magic: The Gathering》或者《Dominion》,通过将游戏体验集中于是否能够在玩家构建平面中绘制纸牌,把可能性元素放在显著位置。把握稀有和普遍元素比例,知晓纸牌每次只能通过平面绘制一次的玩家在能够在这些游戏中取得胜利。这个理念可以通过提供虚拟“平面骰子”(游戏邦注:以确保骰子旋转能够保持平衡)延伸到其他机会游戏中。

另一源自古老游戏历史的有趣理念是回合策略游戏《Lords of Conquest》中“机会元素”游戏选项。3个选项(低、中和高)决定运气是仅用于打破僵局,还是决定战斗方面扮演重要角色。决定机会在游戏中的最合理角色非常主观,给予玩家调整旋钮的权利能够促使游戏吸引更广泛口味不同的用户。(本文为游戏邦/gamerboom.com编译,如需转载请联系:游戏邦

Game Developer Column 9: Playing the Odds

By Soren Johnson

One of the most powerful tools a designer can use when developing games is probability, using random chance to determine the outcome of player actions or to build the environment in which play occurs. The use of luck, however, is not without its pitfalls, and designers should be aware of the trade-offs involved – what chance can add to the experience and when it can be counterproductive.

Failing at Probability

One challenge with using randomness is that humans are notoriously poor at accurately evaluating probability. A common example is the Gambler’s Fallacy, which is the belief that odds will even out over time. If the Roulette wheel comes up black five times in a row, players often believe that the odds of coming up black again are quite small, even though clearly the streak makes no difference whatsoever. Conversely, people also see streaks where none actually exist – the shooter with a ‘hot hand’ in basketball, for example, is a myth. Studies show that, if anything, a successful shot actually predicts a subsequent miss.

Also, as designers of slot machines and MMO’s are quite aware, setting odds unevenly between each progressive reward level makes players think that the game is more generous than it really is. One commercial slot machine had its payout odds published by wizardofodds.com in 2008:

* 1:1 per 8 plays

* 2:1 per 600 plays

* 5:1 per 33 plays

* 20:1 per 2,320 plays

* 80:1 per 219 plays

* 150:1 per 6,241 plays

The 80:1 payoff is common enough to give players the thrill of beating the odds for a a big win but stillrare enough that the casino is in no risk of losing money. Furthermore, humans have a hard time estimating extreme odds – a 1% chance is anticipated too often and 99% odds are considered to be as safe as 100%.

Leveling the Field

These difficulties in accurately estimating odds actually work in the favor of the game designer. Simple game design systems, such as the dice-based resource generation system in Settlers of Catan, can be tantalizingly difficult to master with a dash of probability.

In fact, luck makes a game more accessible because it shrinks the gap – whether in perception or in reality – between experts and novices. In a game with a strong luck element, beginners believe that, no matter what, they have a chance to win. Few people would be willing to play a chess Grandmaster, but playing a backgammon expert is much more appealing – a few lucky throws can give anyone a chance.

In the words of designer Dani Bunten, “Although most players hate the idea of random events that will destroy their nice safe predictable strategies, nothing keeps a game alive like a wrench in the works. Do not allow players to decide this issue. They don’t know it but we’re offering them an excuse for when they lose (‘It was that damn random event that did me in!’) and an opportunity to ‘beat the odds’ when they win.”

Thus, luck serves as a social lubricant – the alcohol of gaming, so to speak – that increases the appeal of multiplayer gaming to audiences which would not normally be suited for cutthroat head-to-head competition.

Where Luck Fails

Nonetheless, randomness is not appropriate for all situations or even all games. The ‘nasty surprise’ mechanic is never a good idea. If a crate provides ammo and other bonuses when opened but explodes 1% of the time, the player has no chance to learn the probabilities in a safe manner. If the explosion occurs early enough, the player will immediately stop opening crates. If it happens much later, the player will feel unprepared and cheated.

Also, when randomness becomes just noise, the luck simply detracts from the player’s understanding of the game. If a die roll is made every time a StarCraft Marine shoots at a target, the rate of fire will simply appear uneven. Over time, the effect of luck on the game’s outcome will be negligible, but the player will have a harder time grasping how strong a Marine’s attack actually is with all the extra random noise.

Further, luck can slow down a game unnecessarily. The board games History of the World and Small World have a very similar conquest mechanic, except that the former uses dice and the latter does not (until the final attack). Making a die roll with each attack causes a History of the World turn to last at least three or four times as long as a turn in Small World. The reason is not just the logistical issues of rolling so many dice – knowing that the results of one’s decisions are completely predictable allows one to plan out all the steps at once without worrying about contingencies. Often, handling contingencies are a core part of the game design, but game speed is an important factor too, so designers should be sure that the trade-off is worthwhile.

Finally, luck is very inappropriate for calculations to determine victory. Unlucky rolls feel the fairest the longer players are given to react to them before the game’s end. Thus, the earlier luck plays a role, the better for the perception of game balance. Many classic card games – pinochle, bridge, hearts – follow a standard model of an initial random distribution of cards that establishes the game’s ‘terrain’ followed by a luck-free series of tricks which determines the winners and losers.

Probability is Content

Indeed, the idea that randomness can provide an initial challenge to be overcome plays an important role in many classic games, from simple games like Minesweeper to deeper ones like NetHack and Age of Empires. At their core, solitaire and Diablo are not so different – both present a randomly-generated environment that the player needs to navigate intelligently for success.

An interesting recent use of randomness was Spelunky, which is indie developer Derek Yu’s combination of the random level generation of NetHack with the game mechanics of 2D platformers like Lode Runner. The addictiveness of the game comes from the unlimited number of new caverns to explore, but frustration can emerge from the wild difficulty of certain, unplanned combinations of monsters and tunnels.

In fact, pure randomness can be an untamed beast, creating game dynamics that throw an otherwise solid design out of balance. For example, Civilization 3 introduced the concept of strategic resources which were required to construct certain units – Chariots need Horses, Tanks need Oil, and so on. These resources were sprinkled randomly across the world, which inevitably led to large continents with only one cluster of Iron controlled by a single AI opponent. Complaints of being unable to field armies for lack of resources were common among the community.

For Civilization 4, the problem was solved by adding a minimum amount of space between certain important resources, so that two sources of Iron could never be within seven tiles of each other. The result was a still unpredictable arrangement of resources around the globe but without the clustering that could doom an unfortunate player. On the other hand, the game actively encouraged clustering for less important luxury resources – Incense, Gems, Spices – to promote interesting trade dynamics.

Showing the Odds

Ultimately, when considering the role of probability, designers need to ask themselves ‘how is luck helping or hurting the game?’ Is randomness keeping the players pleasantly off-balance so that they can’t solve the game trivially? Or is it making the experience frustratingly unpredictable so that players are not invested in their decisions?

One factor which helps ensure the former is making the probability as explicit as possible. The strategy game Armageddon Empires based combat on a few simple die rolls and then showed the dice directly on-screen. Allowing the players to peer into the game’s calculations increases their comfort level with the mechanics, which makes chance a tool for the player instead of a mystery.

Similarly, with Civilization 4, we introduced a help mode which showed the exact probability of success in combat, which drastically increased player satisfaction with the underlying mechanics. Because humans have such a hard time estimating probability accurately, helping them make a smart decision can improve the experience immensely.

Some deck-building card games, such as Magic: The Gathering or Dominion, put probability in the foreground by centering the game experience on the likelihood of drawing cards in the player’s carefully constructed deck. These games are won by players who understand the proper ratio of rares to commons, knowing that each card will be drawn exactly once each time through the deck. This concept can be extended to other games of chance by providing, for example, a virtual “deck of dice” that ensures the distribution of die rolls is exactly even.

Another interesting – and perhaps underused – idea from the distant past of gaming history is the “Element of Chance” game option from the turn-based strategy game Lords of Conquest. The three options available – Low, Medium, and High – determined whether luck was only used to break ties or to play a larger role in resolving combat. The appropriate role of chance in a game is ultimately a subjective question, and giving players the ability to adjust the knobs themselves can open up the game to a larger audience with a greater variety of tastes.(Source:designer-notes


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