Gym-MiniGrid/docs/environments/design.md

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layout: "contents" title: Design

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General Structure

Structure of the world:

• The world is an NxM grid of tiles
• Each tile in the grid world contains zero or one object
  • Cells that do not contain an object have the value None
• Each object has an associated discrete color (string)
• Each object has an associated type (string)
  • Provided object types are: wall, floor, lava, door, key, ball, box and goal
• The agent can pick up and carry exactly one object (eg: ball or key)
• To open a locked door, the agent has to be carrying a key matching the door's color

Actions in the basic environment:

• Turn left
• Turn right
• Move forward
• Pick up an object
• Drop the object being carried
• Toggle (open doors, interact with objects)
• Done (task completed, optional)

Default tile/observation encoding:

• Each tile is encoded as a 3 dimensional tuple: (OBJECT_IDX, COLOR_IDX, STATE)
• OBJECT_TO_IDX and COLOR_TO_IDX mapping can be found in minigrid/minigrid.py
• STATE refers to the door state with 0=open, 1=closed and 2=locked

By default, sparse rewards are given for reaching a green goal tile. A reward of 1 is given for success, and zero for failure. There is also an environment-specific time step limit for completing the task. You can define your own reward function by creating a class derived from MiniGridEnv. Extending the environment with new object types or new actions should be very easy. If you wish to do this, you should take a look at the minigrid/minigrid.py source file.