[libcamera-devel] [PATCH v3 7/8] libcamera: camera: Add CameraConfiguration

[Laurent Pinchart]

Hi Niklas,

Another comment.

On Sat, Apr 06, 2019 at 08:01:00PM +0300, Laurent Pinchart wrote:
> On Sat, Apr 06, 2019 at 01:58:41AM +0200, Niklas Söderlund wrote:
> > To properly support both multiple streams and stream usages the library
> > must provide a method to map the stream usages to the returned streams
> > configurations. Add a camera configuration object to handle this
> > mapping.
> > 
> > Applications can iterate over the returned camera configuration to
> > retrieve the streams selected by the library in the same order as the
> > usages it provided to the library.
> > 
> > Application can use the operator[] to retrieve the stream pointer and
> > the stream configuration. Using a numerical index retrieves the stream
> > pointer, the numerical indexes corresponds to the insertion order of
> > usages by the application, using the stream pointer retrieves the
> > stream's configuration.
> > 
> > Signed-off-by: Niklas Söderlund <niklas.soderlund at ragnatech.se>
> > ---
> >  include/libcamera/camera.h |  28 ++++++
> >  src/libcamera/camera.cpp   | 173 +++++++++++++++++++++++++++++++++++++
> >  2 files changed, 201 insertions(+)
> > 
> > diff --git a/include/libcamera/camera.h b/include/libcamera/camera.h
> > index 0386671c902e55e8..8455049151d5c5a2 100644
> > --- a/include/libcamera/camera.h
> > +++ b/include/libcamera/camera.h
> > @@ -24,6 +24,34 @@ class Stream;
> >  class StreamConfiguration;
> >  class StreamUsage;
> >  
> > +class CameraConfiguration
> > +{
> > +public:
> > +	using iterator = std::vector<Stream *>::iterator;
> > +	using const_iterator = std::vector<Stream *>::const_iterator;
> > +
> > +	CameraConfiguration();
> > +
> > +	iterator begin();
> > +	iterator end();
> > +	const_iterator begin() const;
> > +	const_iterator end() const;
> > +
> > +	bool valid() const;
> > +	bool empty() const;

valid() and empty() vs. isValid() and isEmpty() ? I have a preference
for the latter due to my Qt bias, but I'm open to discuss this.

> > +	std::size_t size() const;
> > +
> > +	Stream *front();
> 
> For completeness, should you have a const Stream *front() const ?
> 
> > +
> > +	Stream *operator[](unsigned int index) const;
> > +	StreamConfiguration &operator[](Stream *stream);
> > +	const StreamConfiguration &operator[](Stream *stream) const;
> > +
> > +private:
> > +	std::vector<Stream *> order_;
> > +	std::map<Stream *, StreamConfiguration> config_;
> > +};
> > +
> >  class Camera final
> >  {
> >  public:
> > diff --git a/src/libcamera/camera.cpp b/src/libcamera/camera.cpp
> > index 63fde0ffc3d02d6c..98145edea1ac9c91 100644
> > --- a/src/libcamera/camera.cpp
> > +++ b/src/libcamera/camera.cpp
> > @@ -39,6 +39,179 @@ namespace libcamera {
> >  
> >  LOG_DECLARE_CATEGORY(Camera)
> >  
> > +/**
> > + * \class CameraConfiguration
> > + * \brief Hold configuration for streams of the camera
> > + *
> > + * The CameraConfiguration is filled with information by the application either
> > + * manually or with the streamConfiguration() helper. The helper takes a list
> 
> s/streamConfiguration()/Camera::streamConfigure()/ (to get doxygen to
> generate a link)
> 
> > + * of usages describing how the application intends to use streams of the
> > + * camera, the application in return are provided with a default camera
> 
> s/are provided/is provided/
> 
> > + * configuration it can tune.
> 
> Maybe s/tune/fine-tune/ ?
> 
> > + *
> > + * Applications iterate over the CameraConfiguration to discover which streams
> > + * the camera has associated to the usages, and can inspect the configuration
> > + * of individual streams using the operator[].
> 
> This all explains how to use CameraConfiguration with the
> streamConfiguration() helper, which I think belongs more to the helper's
> documentation. Here I would explain what the CameraConfiguration is and
> how it is used. How about the following ?
> 
>  * The CameraConfiguration holds an ordered list of streams and their associated
>  * StreamConfiguration. From a data storage point of view, the class operates as
>  * a map of Stream pointers to StreamConfiguration, with entries accessed with
>  * operator[](Stream *). Accessing an entry for a Stream pointer not yet stored
>  * in the configuration inserts a new empty entry.
>  *
>  * The class also suppors iterators, and from that point of view operates as a
>  * vector of Stream pointers. The streams are iterated in insertion order, and
>  * the operator[](int) returns the Stream pointer based on its insertion index.
>  * Accessing a stream with an invalid index returns a null pointer.
> 
> The text you wrote should be reused to document Camera::streamConfiguration().
> 
> > + */
> > +
> > +/**
> > + * \typedef CameraConfiguration::iterator
> > + * \brief Iterator for the streams in the configuration
> > + */
> > +
> > +/**
> > + * \typedef CameraConfiguration::const_iterator
> > + * \brief Const iterator for the streams in the configuration
> > + */
> > +
> > +/**
> > + * \brief Create an empty camera configuration
> > + */
> > +CameraConfiguration::CameraConfiguration()
> > +	: order_({}), config_({})
> > +{
> > +}
> > +
> > +/**
> > + * \brief Retrieve an iterator to the first stream in the sequence
> > + *
> > + * \return An iterator to the first stream
> > + */
> > +std::vector<Stream *>::iterator CameraConfiguration::begin()
> > +{
> > +	return order_.begin();
> > +}
> > +
> > +/**
> > + * \brief Retrieve an iterator pointing to the past-the-end stream in the
> > + * sequence
> > + *
> > + * \return An iterator to the element following the last stream
> > + */
> > +std::vector<Stream *>::iterator CameraConfiguration::end()
> > +{
> > +	return order_.end();
> > +}
> > +
> > +/**
> > + * \brief Retrieve an iterator to the first element of the streams
> 
> Maybe "a const iterator" ?
> 
> > + *
> > + * \return An iterator to the first stream
> 
> And here too, and for the const version of end() as well.
> 
> > + */
> > +std::vector<Stream *>::const_iterator CameraConfiguration::begin() const
> > +{
> > +	return order_.begin();
> > +}
> > +
> > +/**
> > + * \brief Retrieve an iterator to the end of the streams
> 
> The non-const version mentions past-the-end.
> 
> > + *
> > + * \return An iterator to the element following the last stream
> > + */
> > +std::vector<Stream *>::const_iterator CameraConfiguration::end() const
> > +{
> > +	return order_.end();
> > +}
> > +
> > +/**
> > + * \brief Check if the camera configuration is valid
> 
> I think you should explain what an invalid configuration is.
> 
> > + *
> > + * \return True if the configuration is valid
> > + */
> > +bool CameraConfiguration::valid() const
> > +{
> > +	if (empty())
> > +		return false;
> > +
> > +	for (auto const &it : config_) {
> > +		const StreamConfiguration &conf = it.second;
> > +
> > +		if (conf.width == 0 || conf.height == 0 ||
> > +		    conf.pixelFormat == 0 || conf.bufferCount == 0)
> > +			return false;
> 
> Do we have use cases for a non-empty CameraConfiguration with invalid
> StreamConfiguration ? Or is it just for completeness ?
> 
> > +	}
> > +
> > +	return true;
> > +}
> > +
> > +/**
> > + * \brief Check if the camera configuration is empty
> > + *
> > + * \return True if the configuration is empty
> > + */
> > +bool CameraConfiguration::empty() const
> > +{
> > +	return order_.empty();
> > +}
> > +
> > +/**
> > + * \brief Retrieve the number of stream configurations
> > + *
> > + * \return Number of stream configurations
> > + */
> > +std::size_t CameraConfiguration::size() const
> > +{
> > +	return order_.size();
> > +}
> > +
> > +/**
> > + * \brief Access the first stream in the configuration
> > + *
> > + * \return The first stream in the configuration
> > + */
> > +Stream *CameraConfiguration::front()
> > +{
> > +	return order_.front();
> > +}
> > +/**
> > + * \brief Retrieve a stream pointer from index
> > + * \param[in] index Numerical index
> > + *
> > + * The \a index represents the zero bases insertion order of stream and stream
> 
> s/bases/based/
> 
> > + * configuration into the camera configuration.
> > + *
> > + * \return The stream pointer at index, or a nullptr if the index is out of
> > + * bounds
> > + */
> > +Stream *CameraConfiguration::operator[](unsigned int index) const
> > +{
> > +	if (index >= order_.size())
> > +		return nullptr;
> > +
> > +	return order_.at(index);
> > +}
> > +
> > +/**
> > + * \brief Retrieve a reference to a stream configuration
> > + * \param[in] stream Stream to retrieve configuration for
> > + *
> > + * If the camera configuration does not yet contain a configuration for
> > + * the requested stream, create and return an empty stream configuration.
> > + *
> > + * \return The configuration for the stream
> > + */
> > +StreamConfiguration &CameraConfiguration::operator[](Stream *stream)
> > +{
> > +	if (config_.find(stream) == config_.end())
> > +		order_.push_back(stream);
> > +
> > +	return config_[stream];
> > +}
> > +
> > +/**
> > + * \brief Retrieve a const reference to a stream configuration
> > + * \param[in] stream Stream to retrieve configuration for
> > + *
> > + * No new stream configuration is created if called with \a stream that is not
> > + * already part of the camera configuration, doing so is an illegal operation.
> 
> s/illegal/invalid/ ?
> 
> I would also say "and results in undefined behaviour" as the std::map
> will throw an exception.
> 
> > + *
> > + * \return The configuration for the stream
> > + */
> > +const StreamConfiguration &CameraConfiguration::operator[](Stream *stream) const
> > +{
> > +	return config_.at(stream);
> > +}
> > +
> >  /**
> >   * \class Camera
> >   * \brief Camera device

-- 
Regards,

Laurent Pinchart