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1 Designing with the Player Experience in Mind: Dynamic Difficulty Adjustment Christian E. Erali and Professor Michael McCoy Jr. potential for such a system and how a simple DDA system Executive Summary: One of the hardest aspects of game design can be implemented and used in most first-person shooters. is balancing the flow, challenge, and skill of a player throughout The final, polished system adjusts the difficulty across the game’s experience. As such, it is relatively easy for games multiple levels of challenge by assessing time per encounter and even encounters within these games to shift between either and damage to the player and adjusts difficulty through being too easy for the player, making them bored; or becoming altering enemy placement and enemy type. too challenging, frustrating the player. Both boredom and frustration can be the death of a game offering the players little reason to continue, especially if all the game can offer is death or boredom. However, using dynamic difficulty adjustment, games can regulate certain variables to fit the player’s current skill level and make the experience more enjoyable. Most dynamic difficulty systems work behind the scenes, adjusting unseen aspects of the game so the player never feels like the game is cheating them. This study investigates the positives and negatives of using dynamic difficulty and documents the creation of a simple system in CryEngine 3. Index Terms: Dynamic Difficulty Adjustment, Design Optimization, Game Flow, Software Design I. INTRODUCTION NE of the more interesting problems that video game O developers face during the game creation process is the issue of balance. Developers want to ensure that their Figure 1: Image showing the intended flow zone result of Dynamic product is consumable by as many people as possible. Difficulty Adjustment [2] Trying to create a game that challenges a long-time gaming veteran can push less experienced gamers away. Vice II. RESEARCH REVIEW versa, developing only for the less skilled repels the veteran Overview: and hardcore gamers. While there are several systems that allow players to choose a level of difficulty or augment the The potential for DDA systems has often been explored game’s challenge, these options can sometimes be lacking and researched by both academics and professional game and force the player to set a level of challenge with little if designers. While the academic papers focus on the any context. potential of DDA systems, their ideal applications, or outline some of the basic needs and calculations for such a However, one idea that has been around for some time is system to function. Meanwhile the blogs and articles of the a collection of systems referred to as Dynamic Difficulty game designers focus on certain examples and what caused Adjustment (DDA). DDA systems adjust various factors the system to succeed or fail. The next section discusses the and variables in video games to augment a player’s game engine, CryEngine 3, and discusses some of the experience based on the player’s actions. These systems reasons why the engine was chosen as well as some of its allow developers to balance and build games that can limitations. Lastly, several games already use DDA change to fit a player’s playstyle and level of skill as the systems. For example, the Left 4 Dead Series with its well- gamer plays. known A.I. Director is a great example of a popular series using DDA. It the basic DDA systems turning an otherwise This thesis investigates many aspects of DDA systems simple game into a harrowing, new experience each time and explores their value through the development of such a the player played. system using CryEngine 3, the game engine used to create Crysis 2 [1]. Through dissecting and understanding the various iterations of the system, this thesis shows the 2 player’s action data and augmented a series of adjustable data points known as particle filters. These filters take the player’s data, in this case reaction time, and build a basic Texts: understanding of the player which it compares to the already existing player data. These systems then augments Due to the potential of such a system, there is a the experience and gives the player encounters based on the substantial amount of research about DDA systems. In her expected reaction, playstyle, and data of similar players. paper The Case for Dynamic Difficulty Adjustment in The system even changed the reward the player received, Games, Robin Hunicke of Northwestern University giving risky players more rewards such as more health and describes a DDA System in their game Hamlet that ammunition. measured various aspects of the player’s performance and then intervened appropriately [3]. According to Hunicke, One article that speaks about how exactly to apply and when it comes to First-Person-Shooters, players generally use DDA is Asher Einhorn’s article “Reducing Difficulty moved through four different states as part of the gameplay Dynamically and Invisibly” [6]. In the first part of his loop: three-part articles series, Einhorn discussed the need for • Search DDA to focus on more subtle ways to adjust difficulty and • Retrieve offered examples for both good and bad adjustments. To • Solving illustrate, a player in the heat of combat may not know • Fight exactly how much damage they take per-bullet from an Throughout a player’s experience, the systems behind enemy. This increase in damage, however slight, can help Hamlet endeavored to keep the players engaged by keeping to curtail a player’s more aggressive or reckless tactics and players in certain states and avoiding others. After the lead to a more challenging and rewarding fight. However, a system developed a database of information about the player does notice when the enemies’ health bar increases player, the Hamlet system checked if the player was or decreases due to the change in weapon effectiveness. “flailing” or having repeated difficulty with an encounter. Likewise, the player may not notice how quickly the If the system detected it, and to some extent predicted it, the enemies turn to fire upon them, as long as a hail of bullets system could then run a series of assessments and choose to eventually comes, but are more likely to notice when the either place extra health somewhere in the encounter, A.I. suddenly stops performing a certain power move or disrupt the enemy’s accuracy, or switch enemies for those action. Essentially, different aspects of a combat the player had already mastered. After some time, the encounters have their own level of readability and players system would check again to see if the change was are more likely to notice these aspects when they change. successful enough and assess its own alteration. Through At the same time, Einhorn also admits that in some cases this continual cycle of assessing, altering, and assessing, certain things can change, such as enemy number, as it Hamlet can mold itself to the current player. ultimately comes down to a designer’s judgement call. While most designers tend to be positive about DDA systems, one designer named Ernest Adams and his article, “The Designer’s Notebook: Difficulty Modes and Dynamic Difficulty,” speaks out against DDA [7]. Adams advocated static difficulty in levels in response to a previous article written by Andrew Glassner. While Adams does not discount DDA systems as an idea, he did list off several potential problems they face such as, players feeling patronized, the potential exploitability, and how DDA systems do not work for all types of challenges. According to Adams, if a player notices that a DDA system is in play, the player may become frustrated as they feel the game is pulling punches and not giving them the challenge they wanted. A player may also decide to exploit a system if they realize one is in play. This is seen multiple times in massive-multiplayer-games where players who find a Figure 2: Example of a flow curve and how well a player plays based loophole tend to milk it for resources and loot until the on their stress level [4] developers finally correct the problem. Lastly, DDA Another interesting paper offers insight into designing systems cannot be applied to all games, such as puzzle DDA systems is Dynamic Difficulty Balancing for Cautious games, and may in fact lead to massive upsets in game flow, Players and Risk Takers by Guy Hawkins, Keith Nesbitt, leading to awkward encounters or broken levels where and Scott Brown [5]. This paper brings up the idea of players just flounder not knowing what to do. finding ways to reward “risky” playstyles. Through this study, the authors used a unique DDA system that took the Adams is not alone in his thoughts as there are plenty of games who do not have DDA systems and many are very 3 successful. Some of these games draw in players based on One last article, “Game Changers: Dynamic Difficulty” a strong gameplay experience, using an in-built difficulty by Adam Saltsman, briefly described three major types of curve to create interest and flow. Other games provide DDA that are used in three different games [11]. The first players with compelling stories and roleplaying Saltsman discussed was rubberbanding, which is most opportunities to draw in customers and keep them playing. prevalently seen in Mario Kart and other racing games. Ultimately it comes down to the game project and whether a Rubberbanding is a system or series of mechanics that game even needs or could benefit from a DDA system. restricts the maximum distance between the racers in first and last place. Mario Kart achieved this by adjusting the Similar to what Adams spoke about in terms of combat A.I.

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