Game Interaction Design Pattern Library: Accessibility

Slow

admin — Fri, 22 Apr 2011 14:31:19 +0000

Slow Eelke Folmer The player needs to successfully perform a series of actions in a short period of time, which is difficult 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. Players have to wait for something to complete in the game. Match between system and the real world 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. Use when – 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). 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. Implementing a speedup should be fairly simple if the game uses a tick based system to schedule the simulation (there may be constraints however). Increasing the number of ticks may affect rendering: it may not be possible to still smoothly visualize the game and one may decide to revert to showing only intermediate states.

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.

Auto Save

admin — Fri, 22 Apr 2011 14:30:07 +0000

Auto Save Eelke Folmer The player wants to restart the game from a certain point in the game but there is no save game at or close to that point. Avoid Errors Games that allow storing game progress, such as role playing games, first person shooters, adventure games etc. The player wants to replay the game from a certain point because:

The player died
The player may want to go back to an earlier stage in the game to get particular information or to make a different decision.
The player is unhappy with a certain outcome or results that have been achieved at this stage of the game.

The player wants to restart from a certain point, but there is no save game at or close to that point because:

The player may have forgotten to make a save game at that point.
The player may have overwritten an existing save game at that point with a new save game at a different point.

The player is left with only two choices:

Load a save game before the desired point (if one exists) and play from there which may take some time.
If the amount of time it takes to catch up to the desired savepoint is very long, the player is forced to stick to the existing game, which may leave the player frustrated

Automatically save the game Depending on how saving has been implemented, there are different strategies on how it can be implemented:

Autosave after regular time intervals e.g. every five or ten minutes, this is possible when you can save anytime.
Autosave at certain predefined spots in the game e.g. after defeating an end level boss or after completing a level or reaching a specific location. This scenario is possible when using savepoints but also when you can save anytime.

One can offer the player the option to set the autosave time interval in the game options. Always make sure the player gets some nonobtrusive feedback when autosave is being executed. Without this feedback the player may not notice this pattern at all and not use it. Care must be taken that autosaving can result in a large number of save games, which can potentially waste disk space if the savegames are large, which may be a concern for game devices with limited storage capabilities. A large number of savegames may also make it hard for the player to locate a particular savegame. Proper naming of savegames or visual cues should be considered. Players don’t want to have to play part of the game over and over again when they die. Having to save manually continously may make the player feel anxious. Autosaving during game play may briefly interrupt the game -depending on how it has been implemented- which may be perceived as annoying. A non obtrusive saving mechanism such as saving in the background wihtout interuting gameplay should be considered. The player does not have to replay the game all the way from a save point before the desired point. Not having autosave makes the player very aware of the need to save manually. Player does not have to save manually. Both increase efficiency. Automatically saving also affects reliability. Command and Conquer: Generals – This realtime strategy automatically saves progress.

Pause

admin — Fri, 22 Apr 2011 14:29:18 +0000

Pause Eelke Folmer The player needs to interrupt the game quickly because of an external event and wants to continue it later. Avoid Errors Players don’t want to have to play part of the game over and over again when they die. Players do not want their game to be interrupted. Players may want to change settings during the game Real time action games. Games being played on devices which can be interrupted by external events, such as mobile phones or PDA’s. Something may happen in the player’s surroundings that requires interrupting the game such as in incoming phone call. The player may also want to pause as he wants to do something such as change settings, make a save game or screenshot. Allow the player to pause the game When the pause button is pressed all:

sounds

music

vibrations/output devices

other animations

Should be stopped at any stage during the game (even cutscenes). The game should minimize the the amount of resources being used while it is open in the background as it may negatively affect the performance of other multitasking applications that are open (not valid for consoles). There are several ways to present the pause feature:

Have a separate pause menu. This is recommended for more complex games, e.g. also changing settings etc should be.

Combine the main game menu and pause menu into a single menu, recommended for simple games.

Have a time control widget with a pause button (||) in the main screen. This is common in simulation games, which also allow you to fast forward the gameplay.

The default action (possibly highlighted) in a pause menu should be resume. E.g. when the player presses a key the game should resume immediately. Provide feedback that the game is paused, so the player is aware of it. On non-multitasking game systems (such as some mobile phones) one could implement pause by autosaving the game and quitting the game. When the player decides to play the game one should offer the option to resume the last game. If the player would not be able to pause the game the player has to play on which it might not be able to resulting in errors, the player might have to start over. Pause hence increases efficiency and reliability. It also increases satisfaction. At The Core Of Mobile Game Usability: The Pause Menu, Nokia Research

Slow Mode

admin — Fri, 22 Apr 2011 14:23:16 +0000

Aliases

bullettime

Problem

The player needs to successfully perform a series of actions in a short period of time.

Use when

This is common to action games such as first person shooters or platform games. achieving a certain goal (such as finishing a level, going through a door) 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

Succesfully performing a series of actions in a short time is difficult for disabled players as they cannot:

Respond quickly with a controller (Physical/ cognitive disability)
Precisely position a pointer/crosshair (physical/ cognitive disability)
Deal with many events at the same time (physical/ cognitive disability)
The amount of trivial interaction needs to be minimal for disabled gamers.

In addition the following constraints apply:

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

Allow the player to slow down the time.

The implementation of slow is different from the traditional way of implementing Slow (see also Slow for a more generic description). Disabled gamers should be able to use slow whenever they feel the need to. Traditionally slow can only be activated for a brief period of time as slowing it down all the time may make the game too easy, but for disabled gamers this is not an issue. Slow mode can be triggered by the player but this would require an extra input trigger. It can also be automated but it needs to be scripted in. Also suddenly putting things in slow mode might be confusing to some extent so we may need to warn the player when it gets activated.

Principle

Error prevention

Why

Throwing the world into slow motion is a good mechanism for increasing game accessibility. Disabled gamers will make less errors because:

Disabled gamers have more time to respond to multiple events which otherwise might overwhelm them and possibly lead to a catastrophic outcome.
Disabled gamers have more time to position a pointer or crosshair allowing them to achieve their goals.
Disabled gamers will have more time to respond to timed events which will allow them to meet time related challenges.

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 – it is a form of slow motion. The player, although his movement is also slowed, is still able to aim and react in real time, providing a unique advantage over enemies. This makes avoiding being shot easier and enables Max to perform special moves, such as shootdodges where Max leaps sideways through the air while continuing to fire his weapon

Prince of Persia: warrior within – This platform/action/puzzle game allows the main character (a prince) 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. When slow is activated

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.

Skippable Cutscenes

admin — Fri, 22 Apr 2011 14:19:12 +0000

usability problem -

The player has to watch a cutscene or replay which –in the case of the cutscene– it has already seen or the player or is impatient and just doest not want to see the cutscene or replay.

use when – When playing a game players want as much control as possible. Putting them in a situation such as watching a cutscene where they have no control over the game (switch from an active to a passive mode) can make them feel uncomfortable. Players prefer interactivity over a passive experience. If they have seen the cutscene before (or not for impatient players), skipping the cutscene speeds up efficiency and improves satisfaction as they can quickly continue with the playing the game rather than waiting for the cutscene to end.

solution – Offer the player the option to skip the cutscene.
Skipping the cutscene can be activated by either by a key-press or by clicking on a visual cue such as a link which states “skip this cutscene”. This pattern can also be applied to splash-screens e.g. the first screen the player sees when loading the games sometimes featuring the logo of the company that made the game.

forces:

Players are impatient and do not want to wait.

Players usually want to watch a cutscene only the first time they see it.

Cut scenes are essential in advancing the plot, portray character, and provide background information, atmosphere, dialogue and clues.

why – Players are much more likely to remember the correct save game when visual feedback is provided. The search time for a particular save game is decreased because of these visual clues. Otherwise, first a particular save game has to be loaded before a player would know if it is the right one which takes time. This solution improves performance and satisfaction.

examples

Halo – This first person shooter lets you skip cutscenes.

Resident Evil 4 – This action game allows you to skip cutscenes.

Dynamic Difficulty Adjustment

admin — Fri, 22 Apr 2011 14:12:58 +0000

usability problem -

Player gets killed or injured repeatedly because the game is too hard to play for the player on the current difficulty setting.

Player gets bored because the game is too easy to play for the player on the current difficulty setting.

accessibility problem -

A disability prevents a player to respond precisely or timely.

use when – To cater for different types of players, games usually offer a fixed number of difficulty levels. Common terms for difficulty levels are easy, normal and hard. Difficulty levels most commonly affect in game variables such as amount of health or damage that a particular weapon does. Depending on the difficulty level the game becomes harder or easier as:

The enemies are stronger or weaker
Weapons do more or less damage
The player is stronger or weaker

What exactly is modified when a particular difficulty level is chosen at the start of a new game very much depends on the type of game. E.g a first person shooter could have the enemies be weaker and the weapons do more damage for an easy level, but for a real time strategy game the player could start out with more units available on an easier level. The player has to choose a particular difficulty level when playing a new game and it is often impossible to switch to a different difficulty level without having to start over.

solution – Adjust the difficulty level to the player’s performance
Rather than have the player stick to a fixed level which may be too easy or too hard for the player, make the game automatically adapt the difficulty level to the player’s performance. There are two implementations for this pattern:

Suggest switching to a different difficulty level based on the player’s perfomance. If the player has failed or been killed a number of times, show a popup that suggests switching to an easier level. This could also be implemented the other way around. If the player has not died for a certain amount of time a popup can be shown suggesting to move to a harder level. This solution has to be carefully balanced as not to frustrate the player. When the player has a hard time beating an enemy a suggestion to move to an easier level could aggrevate the player. If the player refuses to move to an easier level for a few times this pattern should be disabled. Alternatively the player should be able to choose an easier or harder level through the options.
Automatically adjust the difficulty level based on the player’s performance. Every time the player dies or fails or plays well for a while, there is a chance that the player will switch to the next easiest/ harder difficulty level. This pattern should be completely transparant to the player hence there is no need to communicate a particular difficulty level. As a result a large number of difficulty levels can be implemented, which can cater to a larger number of players rather than having only 3 fixed levels (easy/medium/hard). No difficulty level has been chosen when starting playing the game. The first level needs to accurately determine the level of the player.

forces:

The game should be challenging but players do not want to try getting past a point in the game over and over again.

If players cannot go past a point in the game they may abandon playing the game.

Players have varying skill sets yet games usually only accomodate a limited number of difficulty levels.

Making the game harder or easier to play in an obtrusive way may put the player off.

why – Automatically adjusting the difficulty of the game may avoid the player getting stuck at difficult stages and ensure a players progress throughout the game which increases satisfaction and efficiency. Certain parts in the game may be too hard or too easy because of level design and this pattern may mitigate some of these differences in difficulty making the game more balanced. A disabled player may be unable to play the game on even the easiest level. A game using this pattern may have difficulty levels that go below the easy level and make the game playable to them.

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, a screen is presented which offers the option to switch to an easier difficulty level.

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.

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

Seamless GameWorld

admin — Thu, 22 Apr 2004 14:35:38 +0000

Seamless Gameworld Eelke Folmer The player has to wait before entering a (new) part of the game. Match between system and the real world Players are impatient and do not want to wait. Players do not want their game to be interrupted. Loading levels while playing may significantly burden the system. Typical to “open ended games” games e.g. 3rd person shooters, roleplaying, action or simulation games where players have the ability to move around freely in a large persistent world. These games usually have a nonlinear game plot (if any). Usually such a world is partitioned into separate zones as this world cannot be loaded in whole in the memory.

When a player moves from one zone to another the player usually has to wait for the new zone to be loaded into the memory. Provide a seamless gameworld. Instead of letting the player wait before entering a new zone, 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 3×3 grid are loaded

This algorithm can be fined tuned by having some adaptive caching algorithm that could check how close a player is getting to a certain border chunk. As the player gets closer more and more of it is paged in bits and pieces at a time, so that by the time the player gets to the chunk it is loaded and available for rendering/interaction. If the player gets a certain distance away from it, it can be completely trashed to free up resources.

The chunks can either be loaded in a separate thread or in the same as long as the player does not have to wait to load a chunk. This algorithm could potentially be extended to 3 dimensions where 27 chunks may need to be cached. 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.

The Continuous World of Dungeon Siege, Scott Bilas, Gas Powered Games, Game Developers Conference 2003