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

[Laurent Pinchart]

Hi Niklas,

Thank you for the patch.

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;
> +	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