[libcamera-devel] [PATCH v2 10/11] Documentation: guides: pipeline-handler: Migrate to Camera::Private

[Laurent Pinchart]

Hi Jacopo,

On Tue, Aug 10, 2021 at 03:59:31PM +0200, Jacopo Mondi wrote:
> On Thu, Aug 05, 2021 at 08:58:47PM +0300, Laurent Pinchart wrote:
> > Update the pipeline handler guide following the migration from the
> > CameraData class to the Camera::Private class.
> >
> > Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> > Reviewed-by: Niklas Söderlund <niklas.soderlund at ragnatech.se>
> > ---
> >  Documentation/guides/pipeline-handler.rst | 67 ++++++++++++-----------
> >  1 file changed, 34 insertions(+), 33 deletions(-)
> >
> > diff --git a/Documentation/guides/pipeline-handler.rst b/Documentation/guides/pipeline-handler.rst
> > index 152776935a33..7e9ff824dd50 100644
> > --- a/Documentation/guides/pipeline-handler.rst
> > +++ b/Documentation/guides/pipeline-handler.rst
> > @@ -106,7 +106,7 @@ functionalities descibed above. Below is a brief overview of each of those:
> >     Abstracts camera sensor handling by hiding the details of the V4L2 subdevice
> >     kernel API and caching sensor information.
> >
> > --  `CameraData <http://libcamera.org/api-html/classlibcamera_1_1CameraData.html>`_:
> > +-  `Camera::Private <http://libcamera.org/api-html/classlibcamera_1_1Camera_1_1Private.html>`_:
> >     Represents device-specific data a pipeline handler associates to each Camera
> >     instance.
> >
> > @@ -416,26 +416,26 @@ receivers port output.
> >  The Pipeline Handler is responsible for defining the set of Streams associated
> >  with the Camera.
> >
> > -Each Camera has instance-specific data represented using the `CameraData`_
> > +Each Camera has instance-specific data represented using the `Camera::Private`_
> >  class, which can be extended for the specific needs of the pipeline handler.
> >
> > -.. _CameraData: http://libcamera.org/api-html/classlibcamera_1_1CameraData.html
> > +.. _Camera::Private: http://libcamera.org/api-html/classlibcamera_1_1Camera_1_1Private.html
> >
> >
> > -To support the Camera we will later register, we need to create a CameraData
> > +To support the Camera we will later register, we need to create a Camera::Private
> >  class that we can implement for our specific Pipeline Handler.
> >
> > -Define a new ``VividCameraData()`` class derived from ``CameraData`` by adding
> > -the following code before the PipelineHandlerVivid class definition where it
> > -will be used:
> > +Define a new ``VividCameraPrivate()`` class derived from ``Camera::Private`` by
> > +adding the following code before the PipelineHandlerVivid class definition where
> > +it will be used:
> >
> >  .. code-block:: cpp
> >
> > -   class VividCameraData : public CameraData
> > +   class VividCameraData : public Camera::Private
> >     {
> >     public:
> >            VividCameraData(PipelineHandler *pipe, MediaDevice *media)
> > -                : CameraData(pipe), media_(media), video_(nullptr)
> > +                : Camera::Private(pipe), media_(media), video_(nullptr)
> >            {
> >            }
> >
> > @@ -457,17 +457,17 @@ single stream, represented by the ``VividCameraData`` class members. More
> >  complex pipeline handlers might register cameras composed of several video
> >  devices and sub-devices, or multiple streams per camera that represent the
> >  several components of the image capture pipeline. You should represent all these
> > -components in the ``CameraData`` derived class when developing a custom
> > +components in the ``Camera::Private`` derived class when developing a custom
> >  PipelineHandler.
> >
> >  In our example VividCameraData we implement an ``init()`` function to prepare
> > -the object from our PipelineHandler, however the CameraData class does not
> > +the object from our PipelineHandler, however the Camera::Private class does not
> >  specify the interface for initialisation and PipelineHandlers can manage this
> > -based on their own needs. Derived CameraData classes are used only by their
> > +based on their own needs. Derived Camera::Private classes are used only by their
> >  respective pipeline handlers.
> >
> > -The CameraData class stores the context required for each camera instance and
> > -is usually responsible for opening all Devices used in the capture pipeline.
> > +The Camera::Private class stores the context required for each camera instance
> > +and is usually responsible for opening all Devices used in the capture pipeline.
> >
> >  We can now implement the ``init`` method for our example Pipeline Handler to
> >  create a new V4L2 video device from the media entity, which we can specify using
> > @@ -488,11 +488,11 @@ capture device named 'vivid-000-vid-cap' by the device.
> >            return 0;
> >     }
> >
> > -The CameraData should be created and initialised before we move on to register a
> > -new Camera device so we need to construct and initialise our
> > +The VividCameraData should be created and initialised before we move on to
> > +register a new Camera device so we need to construct and initialise our
> >  VividCameraData after we have identified our device within
> >  PipelineHandlerVivid::match(). The VividCameraData is wrapped by a
> > -std::unique_ptr to help manage the lifetime of our CameraData instance.
> > +std::unique_ptr to help manage the lifetime of the instance.
> 
> If the ownership is not transfered, this is really an implementation
> detail of each pipeline's match() implementation

Indeed, but even then, I think it's nice to show best practices in the
documentation. In any case I've modified Camera::create() to take a
unique_ptr, so it's now part of the API.

> >  If the camera data initialization fails, return ``false`` to indicate the
> >  failure to the ``match()`` method and prevent retrying of the pipeline handler.
> > @@ -508,9 +508,9 @@ failure to the ``match()`` method and prevent retrying of the pipeline handler.
> >  Once the camera data has been initialized, the Camera device instances and the
> >  associated streams have to be registered. Create a set of streams for the
> >  camera, which for this device is only one. You create a camera using the static
> > -`Camera::create`_ method, passing the pipeline handler, the id of the camera,
> > -and the streams available. Then register the camera and its data with the
> > -pipeline handler and camera manager using `registerCamera`_.
> > +`Camera::create`_ method, passing the Camera::Private instance, the id of the
> > +camera, and the streams available. Then register the camera with the pipeline
> > +handler and camera manager using `registerCamera`_.
> >
> >  Finally with a successful construction, we return 'true' indicating that the
> >  PipelineHandler successfully matched and constructed a device.
> > @@ -548,23 +548,24 @@ Our match function should now look like the following:
> >
> >     	/* Create and register the camera. */
> >     	std::set<Stream *> streams{ &data->stream_ };
> > -   	std::shared_ptr<Camera> camera = Camera::create(this, data->video_->deviceName(), streams);
> > -   	registerCamera(std::move(camera), std::move(data));
> > +        const std::string &id = data->video_->deviceName();
> 
>        ^ weird spacing

Oops. Will fix.

> > +   	std::shared_ptr<Camera> camera = Camera::create(data.release(), id, streams);
> > +   	registerCamera(std::move(camera));
> >
> >     	return true;
> >     }
> >
> > -We will need to use our custom CameraData class frequently throughout the
> > +We will need to use our custom VividCameraData class frequently throughout the
> >  pipeline handler, so we add a private convenience helper to our Pipeline handler
> > -to obtain and cast the custom CameraData instance from a Camera instance.
> > +to obtain and cast the custom VividCameraData instance from a Camera::Private
> > +instance.
> >
> >  .. code-block:: cpp
> >
> >     private:
> > -       VividCameraData *cameraData(const Camera *camera)
> > +       VividCameraData *cameraData(Camera *camera)
> >         {
> > -               return static_cast<VividCameraData *>(
> > -                        PipelineHandler::cameraData(camera));
> > +               return static_cast<VividCameraData *>(camera->_d());
> >         }
> >
> >  At this point, you need to add the following new includes to provide the Camera
> > @@ -594,12 +595,12 @@ are defined by src/libcamera/`properties_ids.yaml`_.
> >
> >  Pipeline handlers can optionally register the list of controls an application
> >  can set as well as a list of immutable camera properties. Being both
> > -Camera-specific values, they are represented in the ``CameraData`` base class,
> > -which provides two members for this purpose: the `CameraData::controlInfo_`_ and
> > -the `CameraData::properties_`_ fields.
> > +Camera-specific values, they are represented in the ``Camera::Private`` base
> > +class, which provides two members for this purpose: the
> > +`Camera::Private::controlInfo_`_ and the `Camera::Private::properties_`_ fields.
> >
> > -.. _CameraData::controlInfo_: http://libcamera.org/api-html/classlibcamera_1_1CameraData.html#ab9fecd05c655df6084a2233872144a52
> > -.. _CameraData::properties_: http://libcamera.org/api-html/classlibcamera_1_1CameraData.html#a84002c29f45bd35566c172bb65e7ec0b
> > +.. _Camera::Private::controlInfo_: http://libcamera.org/api-html/classlibcamera_1_1Camera_1_1Private.html#ab4e183eb4dabe929d1b2bbbb519b969f
> > +.. _Camera::Private::properties_: http://libcamera.org/api-html/classlibcamera_1_1Camera_1_1Private.html#ad31f12f5ed9c1fbe25750902f4791064
> >
> >  The ``controlInfo_`` field represents a map of ``ControlId`` instances
> >  associated with the limits of valid values supported for the control. More
> > @@ -617,7 +618,7 @@ Complete the initialization of the ``VividCameraData`` class by adding the
> >  following code to the ``VividCameraData::init()`` method to initialise the
> >  controls. For more complex control configurations, this could of course be
> >  broken out to a separate function, but for now we just initialise the small set
> > -inline in our CameraData init:
> > +inline in our VividCameraData init:
> 
> The rest looks ok
> Reviewed-by: Jacopo Mondi <jacopo at jmondi.org>
> 
> >
> >  .. code-block:: cpp
> >

-- 
Regards,

Laurent Pinchart