feat(2048): environment performance improvements (#172)

Co-authored-by: Clément Bonnet <56230714+clement-bonnet@users.noreply.github.com>

jumanji/environments/logic/game_2048/env.py

@@ -23,12 +23,7 @@
 from jumanji import specs
 from jumanji.env import Environment
 from jumanji.environments.logic.game_2048.types import Board, Observation, State
-from jumanji.environments.logic.game_2048.utils import (
-    move_down,
-    move_left,
-    move_right,
-    move_up,
-)
+from jumanji.environments.logic.game_2048.utils import can_move, move
 from jumanji.environments.logic.game_2048.viewer import Game2048Viewer
 from jumanji.types import TimeStep, restart, termination, transition
 from jumanji.viewer import Viewer
@@ -181,11 +176,7 @@ def step(
             timestep: the next timestep.
         """
         # Take the action in the environment: Up, Right, Down, Left.
-        updated_board, additional_reward = jax.lax.switch(
-            action,
-            [move_up, move_right, move_down, move_left],
-            state.board,
-        )
+        updated_board, reward = move(state.board, action)
 
         # Generate new key.
         random_cell_key, new_state_key = jax.random.split(state.key)
@@ -209,7 +200,7 @@ def step(
             action_mask=action_mask,
             step_count=state.step_count + 1,
             key=new_state_key,
-            score=state.score + additional_reward.astype(float),
+            score=state.score + reward,
         )
 
         # Generate the observation from the environment state.
@@ -227,12 +218,12 @@ def step(
         timestep = jax.lax.cond(
             done,
             lambda: termination(
-                reward=additional_reward,
+                reward=reward,
                 observation=observation,
                 extras=extras,
             ),
             lambda: transition(
-                reward=additional_reward,
+                reward=reward,
                 observation=observation,
                 extras=extras,
             ),
@@ -303,15 +294,7 @@ def _get_action_mask(self, board: Board) -> chex.Array:
         Returns:
             action_mask: action mask for the current state of the environment.
         """
-        action_mask = jnp.array(
-            [
-                jnp.any(move_up(board, final_shift=False)[0] != board),
-                jnp.any(move_right(board, final_shift=False)[0] != board),
-                jnp.any(move_down(board, final_shift=False)[0] != board),
-                jnp.any(move_left(board, final_shift=False)[0] != board),
-            ],
-        )
-        return action_mask
+        return jax.vmap(can_move, (None, 0))(board, jnp.arange(4))
 
     def render(self, state: State) -> Optional[NDArray]:
         """Renders the current state of the game board.