Keywords

1 Introduction

Over the last 30 years, videogames have evolved from toys aimed at children and young adults to complex entertainment platforms that impact the lives of millions of people from different backgrounds throughout the world; they are responsible for major financial results, runner-up only to the military and automotive industries (Santaella and Feitoza 2009). The ascension of videogames as a relevant medium has brought more than just many new players and products: the increase in competition, studio budgets and marketing stunts has turned the market into an intense, performance-driven race to win consumers’ attention among a long list of options that are chosen and consumed fiercely. Making a good game is not only a matter of good game design, but also a demonstration of whether the said game’s quality stands up to its competitors.

While this is true of many entertainment products and media such as movies and music, videogames rely heavily on technological advances to be able to provide new experiences once thought unimaginable. High-quality virtual reality (VR) experiences, for example, are only now becoming more popular thanks to large investments by relevant players in the market. Even more, internet and connectivity options have blurred the line between multiplayer gaming and social media, creating new challenges for experienced game makers.

Among the challenges presented to game developers, one in particular deserves attention as it impacts not only the way games are developed, but also what is at their core: game length and content. As game studios became larger, games became more complex and long, with single-player gameplay times going from a few minutes (as seen in games such as “Pitfall”) to hundreds of hours (such as “The Witcher 3: Wild Hunt” and “The Elder Scrolls V: Skyrim”). This increase in game time is a reflex of increased content generation. In a role-playing game such as those mentioned above, developers have to create a large, believable fictional world with characters, interactive assets and stories, and that is highly demanding in resources and development times. Unsurprisingly, game development teams have grown from small teams of up to five people to a staff of hundreds of developers; Ubisoft Montreal, the studio behind recent games such as “Watch Dogs 2”, has a workforce of more than 2,500 people.

In this race for increased content quantity, a particular technique is used and has been enhanced over the years: “procedural-content generation” (PCG). PCG consists of algorithms used by a software, in conjunction with several pre-made assets, to generate game content without direct intervention from a developer (Hendrickx et al. 2011). By using PCG, developers can program pre-made behaviours and assets for a game (such as different character traits and landscape features like forests and caves), and the algorithms will generate combinations of these assets to create infinite, endless maps or characters to interact with. In game development lingo, one can refer to content created by PCG as “procedural content”.

Procedural content can be seen at different levels in many games throughout the years. In “Grand Theft Auto: San Andreas”Footnote 1, for example, the game map is predefined and modelled by developers, but the inhabitants of the fictional city in which the game takes place are procedurally generated – save for those more closely connected to the game story. Other games, such as “The Elder Scrolls V: Skyrim”Footnote 2, use algorithms to generate “quests” - adventures in which the player fights against foes and explores caves and mysterious places. By this means, there are literally an infinite number of adventures the player can enjoy while playing the game, each time in a different place and with different foes.

While this may seem like an attractive option for developers for saving time and budget in development, there are risks in the use of PCG, most notably the quality of the content and the replayabilityFootnote 3 of the game relying on its game mechanics within a procedural world.

In this paper, some of these challenges will be addressed, with the goal of helping developers in adopting PCG according to their real needs, avoiding the risks of bad use of this technique. To do so, a case study with the recent game “No Man’s Sky”Footnote 4 is presented, highlighting the use of PCG and the positive and negative aspects of its use. Furthermore, a study in state-of-the-art procedural generation is presented, in order to help developers have a better understanding of its use and possibilities.

2 Uses of PCG in Games

Procedural content general can be implemented in several different ways, according to the nature of the project and the hardware and software capabilities available. Some of the possible combinations of PCG in games include (but are not limited to):

  • Map and level designs

  • ‘Quests’ or challenges

  • Character traits, appearance or names

Each of these categories contains several challenges and possibilities that can be highlighted, notably for their relevance in the game as a whole. Adopting each of these tools gives developers the possibility of extending plots, maps or world assets in a way that the core mechanics can be enjoyed over a long span of time by gamers.

2.1 Procedurally-Generated Map and Level Designs

The use of procedural map designs gives developers two main possibilities to work with: extending replayability value within a closed game, or allowing players to enjoy an “endless” game. To better illustrate both cases, known games are presented next.

“Diablo”Footnote 5 is a classic game known for the use of procedurally-generated maps. While the game offers a closed plot and gameplay length (divided into several acts with a unique foe to be defeated at the end of each act), the challenges and adventures lived through in each act happen in maps formed by combinations of map tiles that are randomized during each gameplay.

These random maps always offer similar experiences, such as special rooms with rewards for players, areas with stronger enemies and a way in and out of each “dungeon”. However, since their layout is procedural, players have to discover their way out of the mazes and caves every time they play, thus reducing some common practices in metagames that change the way experienced players enjoy the game. Figure 1 shows a scene from “Diablo 2”.

Fig. 1.
figure 1

(Source: Destructoid)

“Diablo 2”

Full size image

The use of randomly generated maps in “Diablo” comes with two notable characteristics. First of all, the increase in replayability is noticeable as it adds more variety during each playthrough. Seasoned players, familiar with the items and enemies in the game, will still have to face new challenges and discoveries even after several experiences with the game.

On the other hand, since the map works with predefined assets and structures, there is a lack of landmark spots or points of interest. Because of that, “Diablo” relies on preset special areas (such as boss stages or other fixed structures to support the plot) that do not follow the algorithms used to generate the maps. This is an interesting design decision, since it allows developers to work on a complex plot with characters that interact with pieces of the scenery without compromising the PCG and the story presented to the player.

The second game example refers to the use of PCG to create a seemingly endless game that can be explored and enjoyed infinitely. “Minecraft”Footnote 6 (Fig. 2) - a game that focuses on gathering resources and surviving in a lush green world - uses one of these algorithms to create a world so large it is, in fact, endless (save for occasional glitches and software limitations on console ports). Players can enjoy the game and its adventures – including one of the possible endings – just by staying in a relatively small area. Other players can explore, build and travel as far as their time and dedication allows, increasing the replayability of the game.

Fig. 2.
figure 2

(Source: Digital Foundry)

Minecraft

Full size image

Again, there are considerations to be made on this game design decision. “Minecraft” is a game in which players are not given a strict goal; there is no complex plot or deeply-engineered characters to interact with. Because of that, the idea of an endlessly large world with mineral resources, animals and plants fits in to the game’s enjoyment without harsh consequences.

The same formula could not be applied in other games where core mechanics rely on more complex interactions, or more diversity in terms of scenery and landscapes. In that case, the PCG used in “Diablo” might be a more appropriate choice, giving developers more flexibility when needed.

2.2 Quests’ and Challenges

Several games within many of the more popular genres (such as action and RPG games) have their core gameplay rely on a “quest” system. That is, while the player has the freedom to play the game, develop a character and visit different parts of a game world, it is only by partaking in given challenges or ‘quests’ that he can be rewarded for his efforts. In other words, ‘quests’ are the missions given to the player within a game world.

A recent example of procedural ‘quests’ or missions within a complex world is presented in “The Elder Scrolls V: Skyrim”. In “Skyrim”, the player enters a fictional world of adventures where a main storyline is supported by the possibility of having the player also enjoy “sidequests” or additional missions that will allow them to explore the world of Skyrim further.

Bethesda developed an algorithm called “Radiant Quest System” (Maciak 2011) to generate endless adventures in the world of Skyrim (Fig. 3). By combining several of the game assets – including a large number of voice acting lines – the characters are able to give the player entirely new missions that extend the gameplay time for as long as desired. As an example, a character that becomes a ‘Dark Brotherhood’ member (a guild that takes on assassination contracts in different parts of the fictional world) may talk to his contractors to receive missions such as “eliminate character X in part of the world Y”.

Fig. 3.
figure 3

(Source: Game Pressure)

The Elder Scrolls V: Skyrim

Full size image

In “Skyrim”, this quest system is used in complement to the main game plot – in which characters have unique names and interactions – allowing players to become stronger, collect more items and explore the large world of Skyrim.

On the other hand, a quest system that provides an endless number of quests also falls short in giving them a deeper significance. Players know how far these quests go, to the point of knowing that they will not affect the status quo of the world significantly – in a similar fashion to what happens in Massively Multiplayer RPG games (in which the “persistent” game world must not change much in order to give new player a similar first-time experience).

2.3 Character Traits, Appearance or Names

Developing characters for a new game is often a complex part of game development, requiring a large effort by the writing and design team. Complex characters feel life-like, and players can relate to them on an emotional level and thus obtain good enjoyment from the game (Brown and Cairns 2004).

By using PCG, developers can combine several different personality traits in order to create an infinite number of game characters, be it to provide a large world that feels lively or to work within a limited world, increasing the replayability factor by generating random scenarios in which the player will have different interactions and challenges each time they play the game.

The most notable example for this use of PCG is the strategy game “Crusader Kings”. In this game, the player assumes the role of a ruler in medieval Europe and must develop their own nation, interact with other rulers and, if necessary, wage war with them. These interactions with other rulers (Fig. 4) is complex and takes into account several character traits – such as age, behavior, health, family lineage and even private life (to the point of including love interests as part of character descriptions), which the player can use to their advantage when necessary.

Fig. 4.
figure 4

(Source: Game Pressure)

Character description in “Crusader Kings”

Full size image

In “Crusader Kings”, these interactions with other characters, despite their complexity, do not get to the point of direct interaction (such as voiced dialogue or real-time combat). Because of that, characters are described by players as lively and believable, since they stray from typical formulae of character creation by mixing different characteristics that result in “human” characters with flaws and peculiarities. Other players point out that the algorithm used in the game allows for so much randomness in character generation that uncanny scenes and stories may take place within the game. There are forums on the internet dedicated to describing some of the tales of the game characters.

By analysing the games presented and the different uses of PCG, it may be clear that the use of this technique allows for an increase in game content quantity, and if correctly applied it can support a well-written plot and game world. Relying on it, though, might prove to be a disadvantage if it is used as main storytelling tool, as seen in the next topic.

3 Challenges of PCG and the “No Man’s Sky” Case

Procedural content generation is a powerful tool to enhance the game time and the possibilities provided by a solid game world. By using algorithms, developers can extend the life cycle of a game, allowing players to enjoy a well-developed game mechanic infinitely, without relying on expansion packs or online-dependent content (which may run offline sometime in the future or when a new game comes out).

On the other hand, relying on said content as a main feature might also prove to be a disadvantage in two specific situations: flawed implementation and lack of quality in the core mechanics. To better illustrate these flaws, here we present a recent game that was taken for a “promising” new title, but which received harsh critiques from the media and gamers, including a notable amount of refund requests throughout the world, pointing out that the game was not “up to the promises” it made during development stages.

“No Man’s Sky” is a game developed by Hello Games and released in 2016 for the PC and the Playstation 4. In this game, the player controls a space explorer that must repair his ship and visit many different worlds in search of unique new specimens, as well as logging the many different planets they land on. There is an optional plot that players can take part in, travelling ever further towards the centre of the galaxy to uncover a mystery.

The main selling point in “No Man’s Sky”, though, is the creation of procedurally generated planets. By using an algorithm to generate planets, the game offers the notable figure of 18,446,744,073,709,551,616 planets to be explored (Murray 2014). Naturally, these planets were not crafted individually by the developers, but rather generated by the computer. The catch behind this particular use of PCG is that all the players in the world play the game with the same PCG “seed” (a number that triggers the different combinations generated by the algorithm). Also, each player starts a new game in a different part of the virtual galaxy, in a unique, unclaimed planet.

Because of that, and in addition to the game’s internet connectivity features, “No Man’s Sky” allows players to name each planet they land on and explore, sharing the data obtained with the game server. In other words, the game community can help in “charting” the unique and huge universe created.

The downside of the system created as the core mechanic of the game, though, received a backlash from the media and gamers for being overly simple and not allowing for much variety – as one would expect from a game based on space exploration (Kollar 2016). The planets created by the game vary in their weathers (some colder, some hotter), their unique creatures and landscapes, but they do not have enough diversity to truly represent the plethora of possibilities gamers expected from a giant uncharted universe (Fig. 5).

Fig. 5.
figure 5

(Source: Playstation Lifestyle)

A planet in No Man’s Sky

Full size image

According to game reviewer Kollar (2016), all planets look and feel similar, with just different colour schemes and weather figures as the only differences between them. There is no mention of extreme landscapes, more complex life forms, or even planets with more unexpected compositions or characters with different behaviours.

Despite the commercial result of the game and the fact that the development team was small, this case indicates that the reliance on PCG as a core mechanic must necessarily be combined with gameplay mechanics that are complex enough to support the relatively bland set of combinations that come with the procedurally generated universe of “No Man’s Sky”.

In order to help developers in evaluating their reliance on PCG for their games, Table 1 provides recommendations and points out important aspects of implementation of PCG within games. It is divided into three PCG usages (basic, intense, core) and it shows the desired effects. The table is based on the analysis of the games previously mentioned and on the description of uses of PCG by Karonen (2013) and Hendrickx (2011), and takes into account a similar size of development team, budget and time.

Table 1. Reliance on PCG and basic effects
Full size table

These three PCG usages are explained below.

Base usage of PCG

When using little or no PCG in creating game elements, most game assets, stories, characters and maps must be crafted individually, generating unique pieces. By doing so, developers can fine-tune combinations, relationships and game balance. While this option seems optional in terms of quality, it must be noted that “handcrafted” assets demand more production time and budget (Hendrickx 2011). For a smaller studio, this may mean that a game with little or no reliance on PCG should be shorter and more focused on the positive aspects of the game core design – be it an interesting plot or game mechanics that thrive with fine adjustments for a nearly-perfect experience within the limits of the game. Larger studios with heftier budgets may be able to handcraft content to create games large enough to be considered long, expansive experiences by players and media. One notable example from 2015 is “The Witcher 3: Wild Hunt”, by Projekt CD Red, which offers completely unique content – including voice acting and animations – clocking over 200 h of game time (Tach 2015). As a suggestion for smaller developers, this option is the most recommended one if the studio aims to deliver unique, enthralling experiences.

Another reasonable base usage of PCG is in generating content during development stage. Instead of using predetermined “seeds” to generate content on-the-go according to players’ actions, PCG can be used to create a large game area or non-playable characters. By doing so, developers can work with a predetermined template and build up on it, instead of creating every asset from scratch. That is an adequate solution in many cases, for it reduces time spent during initial stages of design.

Intense use of PCG

Just as seen in “Skyrim” and its “Radiant Quest System”, PCG can be a powerful asset to extend game time and enjoyment beyond the base experience. Also, just as seen on “Diablo”, an intense use of PCG is desirable when it does not detract from the possibilities provided by the game. Keeping core points from plot and game universe separate can help in obtaining the best of both worlds, giving room to writers working on a plot or a more complex game element, while still allowing players to have an “endless” area or experience in which they can hone their skills or just enjoy the gameplay further when not focusing on the main plot – be it for greater enjoyment or for “late-game” performance.

Core use of PCG

When procedurally generated content is at the core of a game, it is essential that the core gameplay mechanics must be strong enough to support worlds and assets that are clearly detracted from a dedicated writing. This level of reliance on PCG requires a larger amount of fine-tuning and game balance to keep the player’s interest in the game stable over the expected course of gameplay. Csikszentmihalyi’s (1990) description of the state of Flow points out that, to achieve such a state of immersion and engagement, the user must be faced with a balanced level of difficulty and stimuli, so their mind is always on a comfortable “edge”. Using PCG as a core element requires, above all, solid gameplay that can overcome the test of time and be enjoyable over long game times, not only a game which “feels good for a few hours”.

It should be noted that the recommendations provided are not the only aspects that must be taken into account when making design choices during the development of a game.

Each game is unique in its own design, and therefore aspects that range from budget to marketing plan must be taken into account, so players will be familiar with what to expect from the game, avoiding unpleasant experiences like the public backlash “No Man’s Sky” suffered. The game, designed with several design choices in mind, was marketed under the banner of a large company, raising expectations far beyond the capabilities of a smaller studio (Kollar 2016). In the end, “No Man’s Sky” was perceived by the general public to be a game with little content and gameplay possibilities, but it was extended immensely thanks to procedurally-generated worlds that allow gamers to play it infinitely without ever experimenting all that the game has to offer.

This leads to a relevant discussion of the role of procedurally generated assets in a game, and how they affect not only how it is played but also the very essence of some particular experiences.

4 Discussion

When working with procedurally generated content for a game, one of the most relevant concerns is the impact of the use of algorithms and predefined assets in the creative process of a game.

First and foremost, it must be taken into account that using these assets could ultimately mean a more repetitive – and less creative – approach to the establishment of fictional worlds. Since games have become longer and more complex over the years, there is an increased need to explore game mechanics, plots and game worlds.

As happens in literature, music and other media, game content should not be measured by sheer quantity, but rather evaluated for the quality and content of a given piece. By using procedurally-generated assets, there is an intrinsic risk of creating uninteresting and unoriginal content. While this may seem obvious when discussing the creation of core assets (like the main characters in a story-driven game), it is not as obvious when dealing with second-class assets such as the population of a fictional world.

“The Elder Scrolls V: Skyrim”, while using PCG to create missions and adventures, does not use procedural generation for most of the world content. Each city has lively inhabitants with names and personalities. Gamers throughout the world discuss stories involving these characters, and they are distinct from one another during gameplay (despite the use of PCG for some traveller characters that appear in a few places). This allows for a deeper interaction with the world, a world in which every piece of knowledge adds to the narrative.

PCG can be positively used for an improved experience in several other ways. The previously mentioned examples of games like “Minecraft” and “Diablo 2” show that games with a heavy focus on gameplay or on building a narrative out of the player experience can benefit from the endless possibilities of a world created from scratch every time.

Thus, it can be pointed out that the biggest hurdle in creating an interesting world when using PCG is the balance between the need for a long game experience and the idea of creative, authorial writing to fill in the game world with interesting stories and elements.

With the ascension of independent game studios, which benefit from the increase in digital distribution options and social media to reach out to more gamers, it is important for small and new developers to find a position in the market where they can actively engage with their games by providing pleasant, memorable experiences. This paper intends to point out that procedural generation, while alluring for developers because it may create seemingly endless content, might make it impossible for them to work on authorial content or finely crafted experiences.

Several recent independent games have received critical acclaim and player fidelity for delivering short, yet meaningful, experiences to gamers. One of the reasons that “indie” games have reached this status relates to the lack of corporate demands that generally affect large “triple-A” titles. With a reduced need to appeal to corporate goals and more creative freedom, developers can focus on core aspects of gameplay, experiment with unique game mechanics and focus on writing and world-creating in shorter experiences.

It is notable that games that rely heavily on procedural generation might fall into the trap of creating a huge amount of content that may eventually not be backed by compelling gameplay or an audiovisual experience that provides the player with enough enjoyment to keep playing. The previously mentioned case of “No Man’s Sky” fits in that example, with the additional fact that the developers of the game were backed by a larger studio, which helped boost the game’s publicity prior to its release by announcing features and possibilities that would not be available in the final game.

The discussion also occupies a different level when it comes to the debate on how authorial and unique a videogame should be. As a powerful medium, it allows content creators to think of many different ways of presenting content to players, but it could be argued that any automatic or artificial content would lack the artistic value of an original creation.

Videogames have evolved from experiences created solely by programmers to multi-disciplinary pieces that can provide gamers with joyful moments, convey emotions and even spark debates on heated topics. Focusing on these experiences and emotions allows developers to make much more meaningful games – and that has been proved a positive outcome of development effort in many recent independent games.

5 Final Remarks

This paper has as its main goal the discussion of the effect of procedural generation in creating original content for games. While this may seem relatively trivial, it is important to spark the discussion on the nature of content created by developers – especially the ones in the independent games scene – who come from different backgrounds and whose work reflects on the very essence of games.

By taking into account the table presented and the case studies of recent games, this paper provides developers with insight into the effects of PCG and offers recommendations based on what developers want for their games. PCG can affect the general perception of the world by gamers, who will explore and be inspired by the content created and aimed at them. More importantly, it is vital to take into account that games offer developers a huge array of possibilities, experiences to be created and shared with the world, and that unique, creative content has proved to be a desirable feature of modern games, despite some recent cases of games considered unoriginal and uninspired.

Future work based on this paper can be developed, given time and resources, especially in analysing the direct effect of PCG in numbers, evaluating the increase in development time and using player reception metrics to evaluate their enjoyment throughout gameplay. Another relevant topic for further discussion is the market effect of game length – or whether long games fare better in sales compared to regular-sized or short games, naturally within similar core mechanics or themes.