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Support specifying fill behavior in frame_stacking #287

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Support specifying fill behavior in frame_stacking #287

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29 changes: 24 additions & 5 deletions acme/wrappers/frame_stacking.py
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Original file line number Diff line number Diff line change
Expand Up @@ -18,17 +18,25 @@

from acme import types
from acme.wrappers import base
import enum
import dm_env
from dm_env import specs as dm_env_specs
import numpy as np
import tree


class FillBehavior(enum.Enum):
"""Class to enumerate available options for frame-stacking behavior at episode starts."""
ZEROS = 'zeros'
FIRST = 'first'


class FrameStackingWrapper(base.EnvironmentWrapper):
"""Wrapper that stacks observations along a new final axis."""

def __init__(self, environment: dm_env.Environment, num_frames: int = 4,
flatten: bool = False):
flatten: bool = False,
fill_behavior: FillBehavior = FillBehavior.ZEROS):
"""Initializes a new FrameStackingWrapper.

Args:
Expand All @@ -39,7 +47,8 @@ def __init__(self, environment: dm_env.Environment, num_frames: int = 4,
self._environment = environment
original_spec = self._environment.observation_spec()
self._stackers = tree.map_structure(
lambda _: FrameStacker(num_frames=num_frames, flatten=flatten),
lambda _: FrameStacker(
num_frames=num_frames, flatten=flatten, fill_behavior=fill_behavior),
self._environment.observation_spec())
self._observation_spec = tree.map_structure(
lambda stacker, spec: stacker.update_spec(spec),
Expand All @@ -65,9 +74,16 @@ def observation_spec(self) -> types.NestedSpec:
class FrameStacker:
"""Simple class for frame-stacking observations."""

def __init__(self, num_frames: int, flatten: bool = False):
def __init__(self,
num_frames: int,
flatten: bool = False,
fill_behavior: FillBehavior = FillBehavior.ZEROS
):
self._num_frames = num_frames
self._flatten = flatten
if not isinstance(fill_behavior, FillBehavior):
raise TypeError("Expect fill_behavior to be an FillBehavior enum")
self._fill_behavior = fill_behavior
self.reset()

@property
Expand All @@ -80,8 +96,11 @@ def reset(self):
def step(self, frame: np.ndarray) -> np.ndarray:
"""Append frame to stack and return the stack."""
if not self._stack:
# Fill stack with blank frames if empty.
self._stack.extend([np.zeros_like(frame)] * (self._num_frames - 1))
if self._fill_behavior == FillBehavior.ZEROS:
# Fill stack with blank frames if empty.
self._stack.extend([np.zeros_like(frame)] * (self._num_frames - 1))
elif self._fill_behavior == FillBehavior.FIRST:
self._stack.extend([frame] * (self._num_frames - 1))
self._stack.append(frame)
stacked_frames = np.stack(self._stack, axis=-1)

Expand Down
14 changes: 14 additions & 0 deletions acme/wrappers/frame_stacking_test.py
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Original file line number Diff line number Diff line change
Expand Up @@ -21,6 +21,7 @@

from absl.testing import absltest

from acme.wrappers import frame_stacking

class FakeNonZeroObservationEnvironment(fakes.ContinuousEnvironment):
"""Fake environment with non-zero observations."""
Expand Down Expand Up @@ -76,6 +77,19 @@ def test_second_reset(self):
timestep = env.reset()
self.assertTrue(np.all(timestep.observation[..., 0] == 0))

def test_fill_behavior(self):
original_env = FakeNonZeroObservationEnvironment()
env = wrappers.FrameStackingWrapper(
original_env, 2,
fill_behavior=frame_stacking.FillBehavior.FIRST,
)
action_spec = env.action_spec()

env.reset()
env.step(action_spec.generate_value())
timestep = env.reset()
self.assertTrue(np.all(timestep.observation == 1))


if __name__ == '__main__':
absltest.main()