lerobot/src/lerobot/cameras/camera.py

#!/usr/bin/env python

# Copyright 2024 The HuggingFace Inc. team. All rights reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

import abc
import warnings
from typing import Any

from numpy.typing import NDArray  # type: ignore  # TODO: add type stubs for numpy.typing

from .configs import CameraConfig


class Camera(abc.ABC):
    """Base class for camera implementations.

    Defines a standard interface for camera operations across different backends.
    Subclasses must implement all abstract methods.

    Manages basic camera properties (FPS, resolution) and core operations:
    - Connection/disconnection
    - Frame capture (sync/async/latest)

    **Attributes**:
        - **fps** (`int | None`) -- Configured frames per second.
        - **width** (`int | None`) -- Frame width in pixels.
        - **height** (`int | None`) -- Frame height in pixels.
    """

    def __init__(self, config: CameraConfig):
        """Initialize the camera with the given configuration.

        Args:
            config: Camera configuration containing FPS and resolution.
        """
        self.fps: int | None = config.fps
        self.width: int | None = config.width
        self.height: int | None = config.height

    def __enter__(self):
        """
        Context manager entry.
        Automatically connects to the camera.
        """
        self.connect()
        return self

    def __exit__(self, exc_type, exc_value, traceback) -> None:
        """
        Context manager exit.
        Automatically disconnects, ensuring resources are released even on error.
        """
        self.disconnect()

    def __del__(self) -> None:
        """
        Destructor safety net.
        Attempts to disconnect if the object is garbage collected without cleanup.
        """
        try:
            if self.is_connected:
                self.disconnect()
        except Exception:  # nosec B110
            pass

    @property
    @abc.abstractmethod
    def is_connected(self) -> bool:
        """Check if the camera is currently connected.

        Returns:
            bool: True if the camera is connected and ready to capture frames,
                  False otherwise.
        """
        pass

    @staticmethod
    @abc.abstractmethod
    def find_cameras() -> list[dict[str, Any]]:
        """Detects available cameras connected to the system.
        Returns:
            List[Dict[str, Any]]: A list of dictionaries,
            where each dictionary contains information about a detected camera.
        """
        pass

    @abc.abstractmethod
    def connect(self, warmup: bool = True) -> None:
        """Establish connection to the camera.

        Args:
            warmup: If True (default), captures a warmup frame before returning. Useful
                   for cameras that require time to adjust capture settings.
                   If False, skips the warmup frame.
        """
        pass

    @abc.abstractmethod
    def read(self) -> NDArray[Any]:
        """Capture and return a single frame from the camera synchronously.

        This is a blocking call that will wait for the hardware and its SDK.

        Returns:
            np.ndarray: Captured frame as a numpy array.
        """
        pass

    @abc.abstractmethod
    def async_read(self, timeout_ms: float = ...) -> NDArray[Any]:
        """Return the most recent new frame.

        This method retrieves the latest frame captured by the background thread.
        If a new frame is already available in the buffer (captured since the last call),
        it returns it immediately.

        It blocks up to `timeout_ms` only if the buffer is empty or if the latest frame
        was already consumed by a previous `async_read` call.

        Essentially, this method return the latest unconsumed frame, waiting if necessary
        for a new one to arrive within the specified timeout.

        Usage:
            - Ideal for control loops where you want to ensure every processed frame
            is fresh, effectively synchronizing your loop to the camera's FPS.
            - Causes of a timeout usually include: very low camera FPS, heavy processing load,
            or if the camera is disconnected.

        Args:
            timeout_ms: Maximum time to wait for a new frame in milliseconds.
                        Defaults to 200ms (0.2s).

        Returns:
            np.ndarray: Captured frame as a numpy array.

        Raises:
            TimeoutError: If no new frame arrives within `timeout_ms`.
        """
        pass

    def read_latest(self, max_age_ms: int = 500) -> NDArray[Any]:
        """Return the most recent frame captured immediately (Peeking).

        This method is non-blocking and returns whatever is currently in the
        memory buffer. The frame may be stale,
        meaning it could have been captured a while ago (hanging camera scenario e.g.).

        Usage:
            Ideal for scenarios requiring zero latency or decoupled frequencies & when
            we want a guaranteed frame, such as UI visualization, logging, or
            non-critical monitoring.

        Returns:
            NDArray[Any]: The frame image (numpy array).

        Raises:
            TimeoutError: If the latest frame is older than `max_age_ms`.
            NotConnectedError: If the camera is not connected.
            RuntimeError: If the camera is connected but has not captured any frames yet.
        """
        warnings.warn(
            f"{self.__class__.__name__}.read_latest() is not implemented. "
            "Please override read_latest(); it will be required in future releases.",
            FutureWarning,
            stacklevel=2,
        )
        return self.async_read()

    @abc.abstractmethod
    def disconnect(self) -> None:
        """Disconnect from the camera and release resources."""
        pass