[libcamera-devel] [PATCH v4 1/6] libcamera: stream: add initial Stream class

[Kieran Bingham]

Hi Niklas,

On 29/01/2019 02:00, Niklas Söderlund wrote:
> Add an initial Stream implementation. The idea is that once capability
> support is added to the library each stream will describe its
> capabilities using this class. An application will then select one or
> more streams based on these capabilities and use them to configure the
> camera and capture.
> 
> At this stage the Stream class is empty as capabilities are yet to be
> added. The class is still useful as it will be used to communicate how
> many streams a Camera object provides.
> 
> Signed-off-by: Niklas Söderlund <niklas.soderlund at ragnatech.se>

Reviewed-by: Kieran Bingham <kieran.bingham at ideasonboard.com>

Some queries about capitalisation in the Doxygen - but I'm you can
handle that however you see fit.

--
Kieran


> ---
>  include/libcamera/libcamera.h |  1 +
>  include/libcamera/meson.build |  1 +
>  include/libcamera/stream.h    | 18 +++++++++++++
>  src/libcamera/meson.build     |  1 +
>  src/libcamera/stream.cpp      | 51 +++++++++++++++++++++++++++++++++++
>  5 files changed, 72 insertions(+)
>  create mode 100644 include/libcamera/stream.h
>  create mode 100644 src/libcamera/stream.cpp
> 
> diff --git a/include/libcamera/libcamera.h b/include/libcamera/libcamera.h
> index c0511cf6d662b63f..272dfd5e4a67d5de 100644
> --- a/include/libcamera/libcamera.h
> +++ b/include/libcamera/libcamera.h
> @@ -12,6 +12,7 @@
>  #include <libcamera/event_dispatcher.h>
>  #include <libcamera/event_notifier.h>
>  #include <libcamera/signal.h>
> +#include <libcamera/stream.h>
>  #include <libcamera/timer.h>
>  
>  #endif /* __LIBCAMERA_LIBCAMERA_H__ */
> diff --git a/include/libcamera/meson.build b/include/libcamera/meson.build
> index d7cb55ba4a49e1e8..54a680787e5c17aa 100644
> --- a/include/libcamera/meson.build
> +++ b/include/libcamera/meson.build
> @@ -5,6 +5,7 @@ libcamera_api = files([
>      'event_notifier.h',
>      'libcamera.h',
>      'signal.h',
> +    'stream.h',
>      'timer.h',
>  ])
>  
> diff --git a/include/libcamera/stream.h b/include/libcamera/stream.h
> new file mode 100644
> index 0000000000000000..4f47d85ed6382b36
> --- /dev/null
> +++ b/include/libcamera/stream.h
> @@ -0,0 +1,18 @@
> +/* SPDX-License-Identifier: LGPL-2.1-or-later */
> +/*
> + * Copyright (C) 2019, Google Inc.
> + *
> + * stream.h - Video stream for a Camera
> + */
> +#ifndef __LIBCAMERA_STREAM_H__
> +#define __LIBCAMERA_STREAM_H__
> +
> +namespace libcamera {
> +
> +class Stream final
> +{
> +};
> +
> +} /* namespace libcamera */
> +
> +#endif /* __LIBCAMERA_STREAM_H__ */
> diff --git a/src/libcamera/meson.build b/src/libcamera/meson.build
> index f9f25c0ecf1564cc..9f6ff99eebe2f5bc 100644
> --- a/src/libcamera/meson.build
> +++ b/src/libcamera/meson.build
> @@ -10,6 +10,7 @@ libcamera_sources = files([
>      'media_object.cpp',
>      'pipeline_handler.cpp',
>      'signal.cpp',
> +    'stream.cpp',
>      'timer.cpp',
>      'v4l2_device.cpp',
>  ])
> diff --git a/src/libcamera/stream.cpp b/src/libcamera/stream.cpp
> new file mode 100644
> index 0000000000000000..01f4e5008af8ac46
> --- /dev/null
> +++ b/src/libcamera/stream.cpp
> @@ -0,0 +1,51 @@
> +/* SPDX-License-Identifier: LGPL-2.1-or-later */
> +/*
> + * Copyright (C) 2019, Google Inc.
> + *
> + * stream.cpp - Video stream for a Camera
> + */
> +
> +#include <libcamera/stream.h>
> +
> +/**
> + * \file stream.h
> + * \brief Video stream for a Camera
> + *
> + * A camera device can provide frames in different resolutions and formats

Should we capitalise 'camera' as it's the name of one of our classes?



> + * concurrently from a single image source. The Stream class represents
> + * one of the multiple concurrent streams.
> + *
> + * All streams exposed by a camera device share the same image source and are

Same here ? 'Camera'?

> + * thus not fully independent. Parameters related to the image source, such as
> + * the exposure time or flash control, are common to all streams. Other
> + * parameters, such as format or resolution, may be specified per-stream,
> + * depending on the capabilities of the camera device.
> + *
> + * Camera devices expose at least one stream, and may expose additional streams

Stream? on the same basis?

> + * based on the device capabilities. This can be used, for instance, to
> + * implement concurrent viewfinder and video capture, or concurrent viewfinder,
> + * video capture and still image capture.
> + */
> +
> +namespace libcamera {
> +
> +/**
> + * \class Stream
> + * \brief Video stream for a camera
> + *
> + * The Stream class models of all static information which are associated
> + * with a single video stream. Stream are exposed by the Camera object they

s/video stream/video Stream/ ?

s/Stream are exposed by/Streams are exposed by/

> + * belong to.
> + *
> + * Some cameras are capable of supplying more then one stream from the same

Some Cameras, ... one Stream ?

> + * video source. In such cases an application can inspect all available streams
> + * and select the ones that best fit its use case.
> + *
> + * \todo Add capabilities to the stream API. Without this the Stream class only
> + * serves to reveal how many streams of unknown capabilities a camera supports.
> + * This in itself is productive as it allows applications to configure and
> + * capture from one or more streams even if they won't be able to select the
> + * optimal stream for the task.

I agree - even just for abstraction - it's better to get this in soon to
model the layouts.


> + */
> +
> +} /* namespace libcamera */
> 

-- 
Regards
--
Kieran