Terrestrial Invaders is a descendent of the Access Invaders game that also follows the principles of UA-Games. Some indicative screenshot are illustrated in Figure 1. Just like its predecessor, the game is packed with several accessibility features that can be switched on and off, both off-line and on-the-fly. These features include:

1. Adjustable overall game speed.
2. Adjustable emenies speed (you can even stop them from moving).
3. Adjustable size of all game graphics.
4. Adjustable size of player's bombs.
5. Separately adjustable FX, music and speech volume.
6. Optional specification of the exact number of enemy bullets that can be concurrently active on the screen.
7. 2D sound for localizing objects on a 2D plane.
8. Presentation of spatially localised captions using text and / or graphics for visualizing all game sounds.
9. Reading aloud (for the visually impaired) and automatic scanning(for the motor-impaired) of the game menus.
10. Two high contrast modes (bright graphics on dark background and the inverse).
11. Two novel alternative types of audio descriptions (a summarizing and a more detailed one) that verbalise the relative position of attacking spaceships in relation to the player and warn for incoming fire.
12. The option of using simple shapes (e.g., rectangles, ellipses) to render all graphic elements. This option can be useful to people with severe visual impairments, by allowing them to replace detailed graphics with big blobs with high-contrast colors solid in combination with 2D sound and audio descriptions. Additionally, it can also be handy to people with some types of cognitive impairments.
13. Game difficulty adjustment cheats: get an extra life, destroy a random enemy, activate the shield.
14. Controls can also be redefined, but currently this can only be done by editing the respective XML level description files

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(b)

 

 

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Figure 4: Terrestrial Invaders screenshots:
a. Graphical sound captions; b. Large size graphics; c. High inverse contrast; d. Simple graphics

The game can be played using diverse alternative controls and interaction techniques, such as:

1. Multiple keyboard keys (or switches).
2. A single key (i.e., one-switch game).
3. The mouse.
4. By typing keywords consisting of any number of letters or symbols (e.g., "left" to go left, "right" to go right, etc.).
5. By blowing into a standard microphone. In this case, the game includes an auto-gain capability that automatically adjusts the microphone input level so that the game can still be played irrespectively of the microphone's volume and the environmental noise.

As was the case with Access Invaders, multiple concurrent players are supported, as well as multiple enemy groups. Each player can play against all or specific enemy groups, the characteristics of which (e.g., size, speed, firepower, etc.) can be adjusted to fit that player, so that players with diverse abilities can co-operatively play the same game, following the concept of Parallel Game Universes.

The game was developed in a preview version of Actionscript 3.0 using Adobe Flash® Professional 9 Public Alpha. The entire game and all its individual parameters (lives, speed, difficulty, controls, sounds, captions, colors, graphics, firepower, etc.) are loaded from a standard XML file. Thus, using any text editor it is quite simple and straightforward to create new versions of the game or extend the current one with new levels. Furthermore, it is possible to add new graphics and sounds through external Flash libraries.

Terrestrial Invaders is actually a byproduct of the development process of Game Over!, the world's first universally inaccessible game. Terrestrial Invaders, through its various accessibility features, is able to address most of the accessibility guidelines that Game Over! violates.