rl_algo_impls/shared/encoder/impala_cnn.py

from typing import Optional, Sequence, Type

import gym
import torch
import torch.nn as nn

from rl_algo_impls.shared.encoder.cnn import FlattenedCnnEncoder
from rl_algo_impls.shared.module.utils import layer_init


class ResidualBlock(nn.Module):
    def __init__(
        self,
        channels: int,
        activation: Type[nn.Module] = nn.ReLU,
        init_layers_orthogonal: bool = False,
    ) -> None:
        super().__init__()
        self.residual = nn.Sequential(
            activation(),
            layer_init(
                nn.Conv2d(channels, channels, 3, padding=1), init_layers_orthogonal
            ),
            activation(),
            layer_init(
                nn.Conv2d(channels, channels, 3, padding=1), init_layers_orthogonal
            ),
        )

    def forward(self, x: torch.Tensor) -> torch.Tensor:
        return x + self.residual(x)


class ConvSequence(nn.Module):
    def __init__(
        self,
        in_channels: int,
        out_channels: int,
        activation: Type[nn.Module] = nn.ReLU,
        init_layers_orthogonal: bool = False,
    ) -> None:
        super().__init__()
        self.seq = nn.Sequential(
            layer_init(
                nn.Conv2d(in_channels, out_channels, 3, padding=1),
                init_layers_orthogonal,
            ),
            nn.MaxPool2d(3, stride=2, padding=1),
            ResidualBlock(out_channels, activation, init_layers_orthogonal),
            ResidualBlock(out_channels, activation, init_layers_orthogonal),
        )

    def forward(self, x: torch.Tensor) -> torch.Tensor:
        return self.seq(x)


class ImpalaCnn(FlattenedCnnEncoder):
    """
    IMPALA-style CNN architecture
    """

    def __init__(
        self,
        obs_space: gym.Space,
        activation: Type[nn.Module],
        cnn_init_layers_orthogonal: Optional[bool],
        linear_init_layers_orthogonal: bool,
        cnn_flatten_dim: int,
        impala_channels: Sequence[int] = (16, 32, 32),
        **kwargs,
    ) -> None:
        if cnn_init_layers_orthogonal is None:
            cnn_init_layers_orthogonal = False
        in_channels = obs_space.shape[0]  # type: ignore
        sequences = []
        for out_channels in impala_channels:
            sequences.append(
                ConvSequence(
                    in_channels, out_channels, activation, cnn_init_layers_orthogonal
                )
            )
            in_channels = out_channels
        sequences.append(activation())
        cnn = nn.Sequential(*sequences)
        super().__init__(
            obs_space,
            activation,
            linear_init_layers_orthogonal,
            cnn_flatten_dim,
            cnn,
            **kwargs,
        )