Gym-MiniGrid/minigrid/envs/blockedunlockpickup.py

from __future__ import annotations

from minigrid.core.constants import COLOR_NAMES
from minigrid.core.mission import MissionSpace
from minigrid.core.roomgrid import RoomGrid
from minigrid.core.world_object import Ball


class BlockedUnlockPickupEnv(RoomGrid):
    """

    ## Description

    The agent has to pick up a box which is placed in another room, behind a
    locked door. The door is also blocked by a ball which the agent has to move
    before it can unlock the door. Hence, the agent has to learn to move the
    ball, pick up the key, open the door and pick up the object in the other
    room. This environment can be solved without relying on language.

    ## Mission Space

    "pick up the {color} {type}"

    {color} is the color of the box. Can be "red", "green", "blue", "purple",
    "yellow" or "grey".

    {type} is the type of the object. Can be "box" or "key".

    ## Action Space

    | Num | Name         | Action            |
    |-----|--------------|-------------------|
    | 0   | left         | Turn left         |
    | 1   | right        | Turn right        |
    | 2   | forward      | Move forward      |
    | 3   | pickup       | Pick up an object |
    | 4   | drop         | Unused            |
    | 5   | toggle       | Unused            |
    | 6   | done         | Unused            |

    ## 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/core/constants.py](minigrid/core/constants.py)
    - `STATE` refers to the door state with 0=open, 1=closed and 2=locked

    ## Rewards

    A reward of '1 - 0.9 * (step_count / max_steps)' is given for success, and '0' for failure.

    ## Termination

    The episode ends if any one of the following conditions is met:

    1. The agent picks up the correct box.
    2. Timeout (see `max_steps`).

    ## Registered Configurations

    - `MiniGrid-BlockedUnlockPickup-v0`

    """

    def __init__(self, max_steps: int | None = None, **kwargs):
        mission_space = MissionSpace(
            mission_func=self._gen_mission,
            ordered_placeholders=[COLOR_NAMES, ["box", "key"]],
        )

        room_size = 6
        if max_steps is None:
            max_steps = 16 * room_size**2

        super().__init__(
            mission_space=mission_space,
            num_rows=1,
            num_cols=2,
            room_size=room_size,
            max_steps=max_steps,
            **kwargs,
        )

    @staticmethod
    def _gen_mission(color: str, obj_type: str):
        return f"pick up the {color} {obj_type}"

    def _gen_grid(self, width, height):
        super()._gen_grid(width, height)

        # Add a box to the room on the right
        obj, _ = self.add_object(1, 0, kind="box")
        # Make sure the two rooms are directly connected by a locked door
        door, pos = self.add_door(0, 0, 0, locked=True)
        # Block the door with a ball
        color = self._rand_color()
        self.grid.set(pos[0] - 1, pos[1], Ball(color))
        # Add a key to unlock the door
        self.add_object(0, 0, "key", door.color)

        self.place_agent(0, 0)

        self.obj = obj
        self.mission = f"pick up the {obj.color} {obj.type}"

    def step(self, action):
        obs, reward, terminated, truncated, info = super().step(action)

        if action == self.actions.pickup:
            if self.carrying and self.carrying == self.obj:
                reward = self._reward()
                terminated = True

        return obs, reward, terminated, truncated, info