Gym-MiniGrid/gym_minigrid/envs/putnear.py

from gym_minigrid.minigrid import (
    COLOR_NAMES,
    Ball,
    Box,
    Grid,
    Key,
    MiniGridEnv,
    MissionSpace,
)


class PutNearEnv(MiniGridEnv):

    """
    ### Description

    The agent is instructed through a textual string to pick up an object and
    place it next to another object. This environment is easy to solve with two
    objects, but difficult to solve with more, as it involves both textual
    understanding and spatial reasoning involving multiple objects.

    ### Mission Space

    "put the {move_color} {move_type} near the {target_color} {target_type}"

    {move_color} and {target_color} can be "red", "green", "blue", "purple",
    "yellow" or "grey".

    {move_type} and {target_type} Can be "box", "ball" 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         | Drop an object    |
    | 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
        [gym_minigrid/minigrid.py](gym_minigrid/minigrid.py)
    - `STATE` refers to the door state with 0=open, 1=closed and 2=locked

    ### Rewards

    A reward of '1' 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 wrong object.
    2. The agent drop the correct object near the target.
    3. Timeout (see `max_steps`).

    ### Registered Configurations

    N: number of objects.

    - `MiniGrid-PutNear-6x6-N2-v0`
    - `MiniGrid-PutNear-8x8-N3-v0`

    """

    def __init__(self, size=6, numObjs=2, **kwargs):
        self.size = size
        self.numObjs = numObjs
        self.obj_types = ["key", "ball", "box"]
        mission_space = MissionSpace(
            mission_func=lambda move_color, move_type, target_color, target_type: f"put the {move_color} {move_type} near the {target_color} {target_type}",
            ordered_placeholders=[
                COLOR_NAMES,
                self.obj_types,
                COLOR_NAMES,
                self.obj_types,
            ],
        )
        super().__init__(
            mission_space=mission_space,
            width=size,
            height=size,
            max_steps=5 * size,
            # Set this to True for maximum speed
            see_through_walls=True,
            **kwargs,
        )

    def _gen_grid(self, width, height):
        self.grid = Grid(width, height)

        # Generate the surrounding walls
        self.grid.horz_wall(0, 0)
        self.grid.horz_wall(0, height - 1)
        self.grid.vert_wall(0, 0)
        self.grid.vert_wall(width - 1, 0)

        # Types and colors of objects we can generate
        types = ["key", "ball", "box"]

        objs = []
        objPos = []

        def near_obj(env, p1):
            for p2 in objPos:
                dx = p1[0] - p2[0]
                dy = p1[1] - p2[1]
                if abs(dx) <= 1 and abs(dy) <= 1:
                    return True
            return False

        # Until we have generated all the objects
        while len(objs) < self.numObjs:
            objType = self._rand_elem(types)
            objColor = self._rand_elem(COLOR_NAMES)

            # If this object already exists, try again
            if (objType, objColor) in objs:
                continue

            if objType == "key":
                obj = Key(objColor)
            elif objType == "ball":
                obj = Ball(objColor)
            elif objType == "box":
                obj = Box(objColor)
            else:
                raise ValueError(
                    "{} object type given. Object type can only be of values key, ball and box.".format(
                        objType
                    )
                )

            pos = self.place_obj(obj, reject_fn=near_obj)

            objs.append((objType, objColor))
            objPos.append(pos)

        # Randomize the agent start position and orientation
        self.place_agent()

        # Choose a random object to be moved
        objIdx = self._rand_int(0, len(objs))
        self.move_type, self.moveColor = objs[objIdx]
        self.move_pos = objPos[objIdx]

        # Choose a target object (to put the first object next to)
        while True:
            targetIdx = self._rand_int(0, len(objs))
            if targetIdx != objIdx:
                break
        self.target_type, self.target_color = objs[targetIdx]
        self.target_pos = objPos[targetIdx]

        self.mission = "put the {} {} near the {} {}".format(
            self.moveColor,
            self.move_type,
            self.target_color,
            self.target_type,
        )

    def step(self, action):
        preCarrying = self.carrying

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

        u, v = self.dir_vec
        ox, oy = (self.agent_pos[0] + u, self.agent_pos[1] + v)
        tx, ty = self.target_pos

        # If we picked up the wrong object, terminate the episode
        if action == self.actions.pickup and self.carrying:
            if (
                self.carrying.type != self.move_type
                or self.carrying.color != self.moveColor
            ):
                terminated = True

        # If successfully dropping an object near the target
        if action == self.actions.drop and preCarrying:
            if self.grid.get(ox, oy) is preCarrying:
                if abs(ox - tx) <= 1 and abs(oy - ty) <= 1:
                    reward = self._reward()
            terminated = True

        return obs, reward, terminated, truncated, info