Asteroids

../../_images/asteroids.gif

This environment is part of the Atari environments. Please read that page first for general information.

Action Space

Discrete(14)

Observation Space

Box(0, 255, (210, 160, 3), uint8)

Import

gymnasium.make("ALE/Asteroids-v5")

For more Asteroids variants with different observation and action spaces, see the variants section.

Description

This is a well-known arcade game: You control a spaceship in an asteroid field and must break up asteroids by shooting them. Once all asteroids are destroyed, you enter a new level and new asteroids will appear. You will occasionally be attacked by a flying saucer.

For a more detailed documentation, see the AtariAge page

Actions

Asteroids has the action space of Discrete(14) with the table below listing the meaning of each action’s meanings. To enable all 18 possible actions that can be performed on an Atari 2600, specify full_action_space=True during initialization or by passing full_action_space=True to gymnasium.make.

Value

Meaning

Value

Meaning

Value

Meaning

0

NOOP

1

FIRE

2

UP

3

RIGHT

4

LEFT

5

DOWN

6

UPRIGHT

7

UPLEFT

8

UPFIRE

9

RIGHTFIRE

10

LEFTFIRE

11

DOWNFIRE

12

UPRIGHTFIRE

13

UPLEFTFIRE

See environment specification to see more information on the action meaning.

Observations

Atari environments have three possible observation types: "rgb", "grayscale" and "ram".

  • obs_type="rgb" -> observation_space=Box(0, 255, (210, 160, 3), np.uint8)

  • obs_type="ram" -> observation_space=Box(0, 255, (128,), np.uint8)

  • obs_type="grayscale" -> Box(0, 255, (210, 160), np.uint8), a grayscale version of the “rgb” type

See variants section for the type of observation used by each environment id by default.

Rewards

You score points for destroying asteroids, satellites and UFOs. The smaller the asteroid, the more points you score for destroying it. For a more detailed documentation, see the AtariAge page.

Variants

Asteroids has the following variants of the environment id which have the following differences in observation, the number of frame-skips and the repeat action probability.

Env-id

obs_type=

frameskip=

repeat_action_probability=

Asteroids-v0

"rgb"

(2, 5)

0.25

Asteroids-ram-v0

"ram"

(2, 5)

0.25

Asteroids-ramDeterministic-v0

"ram"

4

0.25

Asteroids-ramNoFrameskip-v0

"ram"

1

0.25

AsteroidsDeterministic-v0

"rgb"

4

0.25

AsteroidsNoFrameskip-v0

"rgb"

1

0.25

Asteroids-v4

"rgb"

(2, 5)

0.0

Asteroids-ram-v4

"ram"

(2, 5)

0.0

Asteroids-ramDeterministic-v4

"ram"

4

0.0

Asteroids-ramNoFrameskip-v4

"ram"

1

0.0

AsteroidsDeterministic-v4

"rgb"

4

0.0

AsteroidsNoFrameskip-v4

"rgb"

1

0.0

ALE/Asteroids-v5

"rgb"

4

0.25

ALE/Asteroids-ram-v5

"ram"

4

0.25

Difficulty and modes

It is possible to specify various flavors of the environment via the keyword arguments difficulty and mode. A flavor is a combination of a game mode and a difficulty setting. The table below lists the possible difficulty and mode values along with the default values.

Available Modes

Default Mode

Available Difficulties

Default Difficulty

[0, ..., 31, 128]

0

[0, 3]

0

Version History

A thorough discussion of the intricate differences between the versions and configurations can be found in the general article on Atari environments.

  • v5: Stickiness was added back and stochastic frame-skipping was removed. The environments are now in the “ALE” namespace.

  • v4: Stickiness of actions was removed

  • v0: Initial versions release