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Designing Usable and Accessible Games with Interaction Design Patterns
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Designing Usable and Accessible Games with Interaction Design Patterns


May 17, 2007 Article Start Previous Page 4 of 6 Next
 

4. Interaction design Patterns

Patterns and pattern languages for describing patterns are ways to describe best practices, good designs, and capture experience in a way that it is possible for others to reuse this experience. Each pattern is a three-part rule, which expresses a relation between a certain context, a problem, and a solution. Usually a rationale is also provided. Patterns originated as an architectural concept by Christopher Alexander , but patterns in software became popular with the “Gang of four” design patterns book. Since then a pattern community has emerged that has specified patterns for all sorts of domains including interaction design.

Patterns have been used to describe knowledge about game design yet these have focused on describing game play and not on usability/accessibility solutions. In this article we propose to use interaction design patterns. An interaction design pattern describes a repeatable solution to a commonly occurring usability problem. The quintessential example used to illustrate an interaction design pattern is undo.

Name: undo

Problem: User made a mistake and cannot revert this.

Context: Any application where a user can manage information or create new artifacts such as word processors or graphical applications.

Solution: Maintain a list of user actions and allow users to reverse selected actions.

Why: users will explore more since they know mistakes can beundone, facilitating learning the application.

Patterns and guidelines do not exclude each other; patterns describe one or more rules in a very specific situation (depth) making them more useful as design tools, whereas guidelines are more high level (breadth) and are useful as requirements.

Several pattern collections can be found online of which the Yahoo UI pattern collection is probably the most well known. Existing pattern collections focus on problems in web and user interfaces (UI) for general-purpose software, which makes them hard to use as tools for game design. Although certain patterns such as a wizard are applicable to games (e.g. an installation wizard), many others such as container navigation, calendar picker or form validation are typically not applicable to game design.

 

We identified that games exhibit some unique usability/accessibility problems, e.g. lack of closed captions or not being able to skip a cut scene is usually not a problem for web applications. As a result we decided to develop our own interaction design pattern collection that specifically addresses accessibility and usability problems in games. The next section gives three examples of patterns we identified in existing games.

5. Example patterns

Another benefit of using patterns to describe design knowledge is their consistent format. To increase the readability of our collection we use the following format:

  • Problem: problems are related to playing the game, which is either a usability and/or an accessibility problem.

  • Context: the context extends the plain problem-solutions dichotomy by describing specific situations or types of games in which the problems may occur.

  • Forces: within the context, a number of forces act, which need to be resolved.

  • Solution: a proven solution to the problem, which resolves the forces.

  • Why: the rationale provides a reasonable argumentation for the specified impact on aspects of usability when the pattern is applied.

  • Examples: Examples of how this pattern has successfully been implemented in a game.

We have currently identified 23 interaction design patterns, all of them may improve the usability of a game and 8 may improve accessibility. We give three example patterns: adaptive difficulty level, seamless gameworld and slow. Only three patterns are included but the reader of his paper is encouraged to visit the rest of our pattern collection on our website http://www.helpyouplay.com.

Adaptive difficulty level

 


Figure 1: adaptive difficulty level in God of War

Problem

Problem - Player gets killed/injured repeatedly because –

Accessibility- the game is too hard to play on the current difficulty setting for someone with a disability e.g. cannot respond quickly or precisely position a pointer/crosshair (physical) or unable to deal with many events at the same time (physical /cognitive)

Usability - the game is too hard to play for the player on the current difficulty setting.

Use when

Games that offer different difficulty levels to cater for different types of players. The most common terms for levels of difficulty are easy, normal and hard. Depending on the difficulty level:

  • The enemies are stronger or weaker.

  • Puzzles are harder or easier to solve.

  • More or less guidance is provided.

  • More or less control assistance is provided (e.g. auto aim or auto steering).

The player has to choose a difficulty level when starting the game, and usually it is not possible to switch to a different difficulty level halfway without starting over.

Forces

  • Players want the game to be challenging yet forgiving. For example, it should be challenging to play the game, but players do not want to have to try getting past a point in the game over and over again.

  • Some players may have experience playing similar games. Others have little experience

  • Some players are better or worse than others at certain game aspects such as shooting or puzzle solving.

  • The game's difficulty level with regard to a certain aspect may vary during the game e.g. one part of the game may focus more on shooting and another part of the game on solving puzzles.

Solution

Adjust the difficulty level to the player.

The game should adapt to different players during different parts of the game. There are two options for implementing this pattern:

  • Suggest a different difficulty level according to the player’s performance. E.g. the game could suggest an easier difficulty setting after the player has failed/been killed a number of times to pass a point in the game.

  • Automatically adjust the difficulty level based on the player's performance. Every time the player dies or fails, there is a chance that the player will switch to the next easiest difficulty setting. If playing well for a while there is a chance the player will go up a difficulty level. This solution is better as you can create a large amount of difficulty levels (more than the traditional easy / medium / hard). You can either notify the player or just make it transparent to the player. The player does not have to choose a difficulty level when it starts playing the game.

Why

Accessibility - Adjusting the difficulty level to the disabled player may make it easier to play the game and the player may make less errors. The game will automatically determine the difficulty level the disabled player is comfortable with.

Usability - Adjusting the difficulty level to the player may increase satisfaction and efficiency. Players will not become frustrated.

Examples

God of War - This 3rd person action game suggests adjusting the difficulty level, if the player dies frequently in a short period of time e.g. 7 times in a row, a screen is presented which offers the option to switch to an easier difficulty level.

Resident Evil 4 - This 3rd person shooter has 5 levels of difficulty. It automatically adjusts the difficulty level based on the player's performance.

Sin Episodes - This first person shooter offers a very advanced dynamic difficulty system. It continuously monitors performance and will tailor enemies’ health ammo, armor and damage to a specific playing style.

 

Seamless Game world

 


Figure 2: seamless game world in Dungeon Siege

Problem

Usability - Players need to wait before entering a (new) part of the game.

Context

Typical to "free roaming" games e.g. 3rd person shooters, role-playing, action or simulation games with the ability to move around freely in a large world. These games usually have a nonlinear game plot (if any). Usually such a world is partitioned into zones as such a world cannot be loaded in whole in the memory. When a player moves from one zone to another (e.g. goes into a house) the player usually has to wait for the new zone to be loaded into the memory.

Forces

• Players are impatient and do not want to wait.

• Players do not want their game to be interrupted.

Solution

Provide a seamless game world.

Instead of letting the player wait before entering a new zone, pre-load the level before the player enters the zone. Rendering a huge seamless world may have a significant effect on the game engine design; an example implementation could be as follows:

• The entire world is broken up into chunks (chunk size depending on available memory).

• Only 9 chunks are loaded into memory at any given time, the chunk the player is currently in and the 8 surrounding chunks.

• As the player moves out of the central chunk into one of the bordering chunks, the 3 chunks farthest from the player are discarded and the chunk the player just entered then becomes the center chunk. Then the 3 new chunks make the 3x3 grid are loaded. Some more detailed implementation issues (such as loading parts of chunks and dealing with hardware constraints) can be found in Bilas

Why

Having a large, persistent world adds a level of constant immersion for the player, as the game never stops and never loads. This solution increases efficiency and satisfaction.

Example

Dungeon Siege - This role playing game provides "content streaming" which eliminates the need for "level loading".

World of Warcraft - This massive multiplayer online game provides a seamless world it connects a number of different places and makes them appear as if they all belong as parts of a whole. Loading times are as rare as they are brief. They only crop up when traveling across the game's enormous continents or entering some specific higher-level zones that are instanced for each player group.


Slow

 


Figure 3: Slow in Max Payne

Problem

The player needs to successfully perform a series of actions in a short period of time, which is difficult.

Accessibility problem - if the player suffers from a physical, cognitive or visual disability since they need more time to respond to multiple events at the same time.

Usability problem- if the player is not experienced.

Context

This is common to action games such as first person shooters or platform games. Achieving a certain goal (such as finishing a level) depends on successfully performing a series of actions. Sometimes this has to be done within a constrained period of time. For example, the player may push a button to open a door. The door closes in a certain amount of time. In order to go trough the door, the player may need to jump over a pit, defeat an enemy etc.

Game designers put such 'challenges' in the game to pace the game and make it more exciting. For advanced players such a challenge may not be an obstacle but (novice) players may find it very hard to accomplish and the player often has to try several times before the player succeeds (if the player succeeds at all).

Forces

  • Time manipulation cannot be implemented in multiplayer games.

  • Players don't want to have to play part of the game over and over again when they die.

  • Making the game too easy ruins gameplay.

Solution

Solution - Allow the player to slow down the time.

Throwing the world into slow motion while moving around in real-time gives several advantages.

  • Faster movement - being able to run, jump, dodge, fight and shoot gives unique advantages over enemies and obstacles, which is especially helpful when trying to achieve time related goals.

  • Increased damage - when fighting enemies one can do more damage as one can deal more blows/hits/kicks and the enemy has a harder time blocking the attacks.

Care must be taken that the world can only be slowed for a brief period of time as slowing it all the time can make the game too easy. In order to achieve this one can consider letting the player sacrifice something in order to activate slow. In the action game Prince of Persia slow is activated by means of tokens that can be collected during the game. At any given time there is only a limited amount of activation tokens available. This makes sure the player only uses slow sparsely.

For disabled gamers this might not be an issue and they should be able to use slow whenever they feel the need to, it can also be automatically triggered when multiple enemies attack. The player however needs to be notified when slow is about to be enabled to minimize confusion. This mechanism is also known as bullet-time in first person shooters.

Why

Accessibility - Throwing the world in slow motion will allow disabled players to make less errors because:

  • Players with a cognitive or physical disability have a hard time responding quickly and dealing with multiple events, slowing down the game will adjust the pace of the game to what they are capable of handling without overwhelming them.

  • Players with a cognitive or physical disability who find it difficult to position a pointer or cross-hair have more time to achieve this task when the game slows down.

Usability - Slowing down the game makes will improve reliability and satisfaction as the player has more time to respond and will make less errors.

Examples

Max Payne - One of the first game to introduce matrix style bullet-time (slow) in a first person shooter. The gameplay of Max Payne revolves heavily around bullet-time. When triggered, bullet-time slows down the passage of time to such an extent that the movements of bullets can be seen by the naked eye. The player, although his movement is also slowed, is still able to aim and react in real time, providing a unique advantage over enemies.

Prince of Persia: Warrior Within - This platform/action/puzzle game allows the main character to slow time through the use of a dagger. The dagger contains "charges" of the Sands of Time from the hourglass that allow the Prince to "slow" time for a while. The usages of the dagger are limited. However, defeated enemies leave behind piles of the Sands of Time, which can be absorbed by the dagger to replenish its stock. This encourages the player to confront and vanquish enemies (as opposed to avoiding them) in order to replenish the power to manipulate time during the more tricky acrobatic sections of the game.

Blinx: The Time Sweeper - This third person platform game offers time control which allows one to control the flow of time e.g. slowing, speeding up, reversing or stopping its flow entirely.


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