Add sticky actions for Atari games (#1286)

* repeat_action_probability

* Add test

* Undo atari wrapper doc change since CI fails

* remove action_repeat_probability from make_atari_env

* Add sticky action wrapper and improve documentation

* Update changelog

* handle the case noop_max=0

* Update tests

* Comply to ALE implementation

* Reorder doc

* Add doc warning and don't wrap with sticky action when not needed

* fix docstring and reorder

* Move `action_repeat_probability` args at the last position

* Add ref

* Update doc and wrap with frameskip only if needed

* Update changelog

Co-authored-by: Antonin RAFFIN <antonin.raffin@ensta.org>

docs/misc/changelog.rst

@@ -4,7 +4,7 @@ Changelog
 ==========
 
 
-Release 1.8.0a2 (WIP)
+Release 1.8.0a3 (WIP)
 --------------------------
 
 
@@ -14,6 +14,8 @@ Breaking Changes:
 
 New Features:
 ^^^^^^^^^^^^^
+- Added ``repeat_action_probability`` argument in ``AtariWrapper``.
+- Only use ``NoopResetEnv`` and ``MaxAndSkipEnv`` when needed in ``AtariWrapper``
 
 `SB3-Contrib`_
 ^^^^^^^^^^^^^^

stable_baselines3/common/atari_wrappers.py

@@ -12,13 +12,39 @@ except ImportError:
 from stable_baselines3.common.type_aliases import GymObs, GymStepReturn
 
 
+class StickyActionEnv(gym.Wrapper):
+    """
+    Sticky action.
+
+    Paper: https://arxiv.org/abs/1709.06009
+    Official implementation: https://github.com/mgbellemare/Arcade-Learning-Environment
+
+    :param env: Environment to wrap
+    :param action_repeat_probability: Probability of repeating the last action
+    """
+
+    def __init__(self, env: gym.Env, action_repeat_probability: float) -> None:
+        super().__init__(env)
+        self.action_repeat_probability = action_repeat_probability
+        assert env.unwrapped.get_action_meanings()[0] == "NOOP"
+
+    def reset(self, **kwargs) -> GymObs:
+        self._sticky_action = 0  # NOOP
+        return self.env.reset(**kwargs)
+
+    def step(self, action: int) -> GymStepReturn:
+        if self.np_random.random() >= self.action_repeat_probability:
+            self._sticky_action = action
+        return self.env.step(self._sticky_action)
+
+
 class NoopResetEnv(gym.Wrapper):
     """
     Sample initial states by taking random number of no-ops on reset.
     No-op is assumed to be action 0.
 
-    :param env: the environment to wrap
-    :param noop_max: the maximum value of no-ops to run
+    :param env: Environment to wrap
+    :param noop_max: Maximum value of no-ops to run
     """
 
     def __init__(self, env: gym.Env, noop_max: int = 30) -> None:
@@ -47,7 +73,7 @@ class FireResetEnv(gym.Wrapper):
     """
     Take action on reset for environments that are fixed until firing.
 
-    :param env: the environment to wrap
+    :param env: Environment to wrap
     """
 
     def __init__(self, env: gym.Env) -> None:
@@ -71,7 +97,7 @@ class EpisodicLifeEnv(gym.Wrapper):
     Make end-of-life == end-of-episode, but only reset on true game over.
     Done by DeepMind for the DQN and co. since it helps value estimation.
 
-    :param env: the environment to wrap
+    :param env: Environment to wrap
     """
 
     def __init__(self, env: gym.Env) -> None:
@@ -120,9 +146,11 @@ class EpisodicLifeEnv(gym.Wrapper):
 class MaxAndSkipEnv(gym.Wrapper):
     """
     Return only every ``skip``-th frame (frameskipping)
+    and return the max between the two last frames.
 
-    :param env: the environment
-    :param skip: number of ``skip``-th frame
+    :param env: Environment to wrap
+    :param skip: Number of ``skip``-th frame
+        The same action will be taken ``skip`` times.
     """
 
     def __init__(self, env: gym.Env, skip: int = 4) -> None:
@@ -159,9 +187,9 @@ class MaxAndSkipEnv(gym.Wrapper):
 
 class ClipRewardEnv(gym.RewardWrapper):
     """
-    Clips the reward to {+1, 0, -1} by its sign.
+    Clip the reward to {+1, 0, -1} by its sign.
 
-    :param env: the environment
+    :param env: Environment to wrap
     """
 
     def __init__(self, env: gym.Env) -> None:
@@ -182,9 +210,9 @@ class WarpFrame(gym.ObservationWrapper):
     Convert to grayscale and warp frames to 84x84 (default)
     as done in the Nature paper and later work.
 
-    :param env: the environment
-    :param width:
-    :param height:
+    :param env: Environment to wrap
+    :param width: New frame width
+    :param height: New frame height
     """
 
     def __init__(self, env: gym.Env, width: int = 84, height: int = 84) -> None:
@@ -213,20 +241,29 @@ class AtariWrapper(gym.Wrapper):
 
     Specifically:
 
-    * NoopReset: obtain initial state by taking random number of no-ops on reset.
+    * Noop reset: obtain initial state by taking random number of no-ops on reset.
     * Frame skipping: 4 by default
     * Max-pooling: most recent two observations
     * Termination signal when a life is lost.
     * Resize to a square image: 84x84 by default
     * Grayscale observation
     * Clip reward to {-1, 0, 1}
+    * Sticky actions: disabled by default
 
-    :param env: gym environment
-    :param noop_max: max number of no-ops
-    :param frame_skip: the frequency at which the agent experiences the game.
-    :param screen_size: resize Atari frame
-    :param terminal_on_life_loss: if True, then step() returns done=True whenever a life is lost.
+    See https://danieltakeshi.github.io/2016/11/25/frame-skipping-and-preprocessing-for-deep-q-networks-on-atari-2600-games/
+    for a visual explanation.
+
+    .. warning::
+        Use this wrapper only with Atari v4 without frame skip: ``env_id = "*NoFrameskip-v4"``.
+
+    :param env: Environment to wrap
+    :param noop_max: Max number of no-ops
+    :param frame_skip: Frequency at which the agent experiences the game.
+        This correspond to repeating the action ``frame_skip`` times.
+    :param screen_size: Resize Atari frame
+    :param terminal_on_life_loss: If True, then step() returns done=True whenever a life is lost.
     :param clip_reward: If True (default), the reward is clip to {-1, 0, 1} depending on its sign.
+    :param action_repeat_probability: Probability of repeating the last action
     """
 
     def __init__(
@@ -237,9 +274,15 @@ class AtariWrapper(gym.Wrapper):
         screen_size: int = 84,
         terminal_on_life_loss: bool = True,
         clip_reward: bool = True,
+        action_repeat_probability: float = 0.0,
     ) -> None:
-        env = NoopResetEnv(env, noop_max=noop_max)
-        env = MaxAndSkipEnv(env, skip=frame_skip)
+        if action_repeat_probability > 0.0:
+            env = StickyActionEnv(env, action_repeat_probability)
+        if noop_max > 0:
+            env = NoopResetEnv(env, noop_max=noop_max)
+        # frame_skip=1 is the same as no frame-skip (action repeat)
+        if frame_skip > 1:
+            env = MaxAndSkipEnv(env, skip=frame_skip)
         if terminal_on_life_loss:
             env = EpisodicLifeEnv(env)
         if "FIRE" in env.unwrapped.get_action_meanings():

stable_baselines3/version.txt

@@ -1 +1 @@
-1.8.0a2
+1.8.0a3

tests/test_utils.py

@@ -9,7 +9,7 @@ from gym import spaces
 
 import stable_baselines3 as sb3
 from stable_baselines3 import A2C
-from stable_baselines3.common.atari_wrappers import ClipRewardEnv, MaxAndSkipEnv
+from stable_baselines3.common.atari_wrappers import MaxAndSkipEnv
 from stable_baselines3.common.env_util import is_wrapped, make_atari_env, make_vec_env, unwrap_wrapper
 from stable_baselines3.common.evaluation import evaluate_policy
 from stable_baselines3.common.monitor import Monitor
@@ -55,30 +55,54 @@ def test_make_vec_env_func_checker():
     env.close()
 
 
-@pytest.mark.parametrize("env_id", ["BreakoutNoFrameskip-v4"])
-@pytest.mark.parametrize("n_envs", [1, 2])
-@pytest.mark.parametrize("wrapper_kwargs", [None, dict(clip_reward=False, screen_size=60)])
-def test_make_atari_env(env_id, n_envs, wrapper_kwargs):
-    env = make_atari_env(env_id, n_envs, wrapper_kwargs=wrapper_kwargs, monitor_dir=None, seed=0)
+# Use Asterix as it does not requires fire reset
+@pytest.mark.parametrize("env_id", ["BreakoutNoFrameskip-v4", "AsterixNoFrameskip-v4"])
+@pytest.mark.parametrize("noop_max", [0, 10])
+@pytest.mark.parametrize("action_repeat_probability", [0.0, 0.25])
+@pytest.mark.parametrize("frame_skip", [1, 4])
+@pytest.mark.parametrize("screen_size", [60])
+@pytest.mark.parametrize("terminal_on_life_loss", [True, False])
+@pytest.mark.parametrize("clip_reward", [True])
+def test_make_atari_env(
+    env_id, noop_max, action_repeat_probability, frame_skip, screen_size, terminal_on_life_loss, clip_reward
+):
+    n_envs = 2
+    wrapper_kwargs = {
+        "noop_max": noop_max,
+        "action_repeat_probability": action_repeat_probability,
+        "frame_skip": frame_skip,
+        "screen_size": screen_size,
+        "terminal_on_life_loss": terminal_on_life_loss,
+        "clip_reward": clip_reward,
+    }
+    venv = make_atari_env(
+        env_id,
+        n_envs=2,
+        wrapper_kwargs=wrapper_kwargs,
+        monitor_dir=None,
+        seed=0,
+    )
 
-    assert env.num_envs == n_envs
+    assert venv.num_envs == n_envs
 
-    obs = env.reset()
+    needs_fire_reset = env_id == "BreakoutNoFrameskip-v4"
+    expected_frame_number_low = frame_skip * 2 if needs_fire_reset else 0  # FIRE - UP on reset
+    expected_frame_number_high = expected_frame_number_low + noop_max
+    expected_shape = (n_envs, screen_size, screen_size, 1)
 
-    new_obs, reward, _, _ = env.step([env.action_space.sample() for _ in range(n_envs)])
+    obs = venv.reset()
+    frame_numbers = [env.unwrapped.ale.getEpisodeFrameNumber() for env in venv.envs]
+    for frame_number in frame_numbers:
+        assert expected_frame_number_low <= frame_number <= expected_frame_number_high
+    assert obs.shape == expected_shape
 
-    assert obs.shape == new_obs.shape
+    new_obs, reward, _, _ = venv.step([venv.action_space.sample() for _ in range(n_envs)])
 
-    # Wrapped into DummyVecEnv
-    wrapped_atari_env = env.envs[0]
-    if wrapper_kwargs is not None:
-        assert obs.shape == (n_envs, 60, 60, 1)
-        assert wrapped_atari_env.observation_space.shape == (60, 60, 1)
-        assert not isinstance(wrapped_atari_env.env, ClipRewardEnv)
-    else:
-        assert obs.shape == (n_envs, 84, 84, 1)
-        assert wrapped_atari_env.observation_space.shape == (84, 84, 1)
-        assert isinstance(wrapped_atari_env.env, ClipRewardEnv)
+    new_frame_numbers = [env.unwrapped.ale.getEpisodeFrameNumber() for env in venv.envs]
+    for frame_number, new_frame_number in zip(frame_numbers, new_frame_numbers):
+        assert new_frame_number - frame_number == frame_skip
+    assert new_obs.shape == expected_shape
+    if clip_reward:
         assert np.max(np.abs(reward)) < 1.0