[libcamera-devel] [PATCH v2 5/8] libcamera: stream: Add basic stream usages

[Niklas Söderlund]

Hi Jacopo,

Thanks for your feedback.

On 2019-04-05 10:26:48 +0200, Jacopo Mondi wrote:
> Hi Niklas,
>    thank you for the patch
> 
> On Fri, Apr 05, 2019 at 04:02:53AM +0200, Niklas Söderlund wrote:
> > In preparation of reworking how a default configuration is retrieved
> > from a camera add stream usages. The usages will be used by applications
> > to describe how they intend to use a camera and replace the Stream IDs
> > when retrieving default configuration from the camera using
> > streamConfiguration().
> >
> > Signed-off-by: Niklas Söderlund <niklas.soderlund at ragnatech.se>
> > ---
> >  include/libcamera/stream.h | 40 +++++++++++++++++
> >  src/libcamera/stream.cpp   | 92 ++++++++++++++++++++++++++++++++++++++
> >  2 files changed, 132 insertions(+)
> >
> > diff --git a/include/libcamera/stream.h b/include/libcamera/stream.h
> > index 970c479627fab064..1dea696f2e5ca95d 100644
> > --- a/include/libcamera/stream.h
> > +++ b/include/libcamera/stream.h
> > @@ -8,6 +8,7 @@
> >  #define __LIBCAMERA_STREAM_H__
> >
> >  #include <libcamera/buffer.h>
> > +#include <libcamera/geometry.h>
> >
> >  namespace libcamera {
> >
> > @@ -21,9 +22,48 @@ struct StreamConfiguration {
> >  	unsigned int bufferCount;
> >  };
> >
> > +class StreamUsage
> > +{
> > +public:
> > +	enum Role {
> > +		StillCapture,
> > +		VideoRecording,
> > +		Viewfinder,
> > +	};
> > +
> > +	Role role() const { return role_; }
> > +	Size size() const { return size_; }
> 
> Maybe not that relevant as Size is just two integers, but
>         Size &size() const
> or maybe even
>         const Size &size() const

I have no strong opinion, I will make it so in next version.

> 
> Also
>         const Role role() const

As this returns a value and not a reference this can not be const :-)

> > +
> > +protected:
> > +	StreamUsage(Role role);
> 
> explicit
> 
> > +	StreamUsage(Role role, int width, int height);
> > +
> > +private:
> > +	Role role_;
> > +	Size size_;
> > +};
> > +
> >  class Stream final
> >  {
> >  public:
> > +	class StillCapture : public StreamUsage
> > +	{
> > +	public:
> > +		StillCapture();
> > +	};
> > +
> > +	class VideoRecording : public StreamUsage
> > +	{
> > +	public:
> > +		VideoRecording();
> > +	};
> > +
> > +	class Viewfinder : public StreamUsage
> > +	{
> > +	public:
> > +		explicit Viewfinder(int width, int height);
> 
> No need for explicit, it takes two arguments.

Wops, my intention was for this to be on StreamRole, somthing went very 
wrong :-) Thanks for spotting it!

> 
> > +	};
> > +
> >  	Stream();
> >  	BufferPool &bufferPool() { return bufferPool_; }
> >  	const StreamConfiguration &configuration() const { return configuration_; }
> > diff --git a/src/libcamera/stream.cpp b/src/libcamera/stream.cpp
> > index c4943c91b2e6ce13..816dff2d12acd923 100644
> > --- a/src/libcamera/stream.cpp
> > +++ b/src/libcamera/stream.cpp
> > @@ -60,6 +60,65 @@ namespace libcamera {
> >   * \brief Requested number of buffers to allocate for the stream
> >   */
> >
> > +/**
> > + * \class StreamUsage
> > + * \brief Stream usage information
> > + *
> > + * The StreamUsage class describes how an application intends to use a stream.
> > + * Usages are specified by applications and passed to cameras, that then select
> > + * the most appropriate streams and their default configurations.
> > + */
> > +
> > +/**
> > + * \enum StreamUsage::Role
> > + * \brief Identify the role a stream is intended to play
> > + * \var StreamUsage::StillCapture
> > + * The stream is intended to capture high-resolution, high-quality still images
> > + * with low frame rate. The captured frames may be exposed with flash.
> > + * \var StreamUsage::VideoRecording
> > + * The stream is intended to capture video for the purpose of recording or
> > + * streaming. The video stream may produce a high frame rate and may be
> > + * enhanced with video stabilization.
> > + * \var StreamUsage::Viewfinder
> > + * The stream is intended to capture video for the purpose of display on the
> > + * local screen. The StreamUsage includes the desired resolution. Trade-offs
> > + * between quality and usage of system resources are acceptable.
> > + */
> > +
> > +/**
> > + * \fn StreamUsage::role()
> > + * \brief Retrieve the stream role
> > + *
> > + * \return The stream role
> > + */
> > +
> > +/**
> > + * \fn StreamUsage::size()
> > + * \brief Retrieve desired size
> > + *
> > + * \return The desired size
> > + */
> > +
> > +/**
> > + * \brief Create a stream usage
> 
> should you somehow mention "a stream usage with sizes = 0" ?

No, this should IMHO be explained in the documentation for Size. As 
similar behavior would be true for all instances of Size.

> 
> > + * \param[in] role Stream role
> > + */
> > +StreamUsage::StreamUsage(Role role)
> > +	: role_(role), size_(Size(0, 0))
> 
> Size default contructor initialize both fields to 0, so you can drop
> the assignement.

Cool then I will drop it for v3.

> 
> > +{
> > +}
> > +
> > +/**
> > + * \brief Create a stream usage with size hint
> > + * \param[in] role Stream role
> > + * \param[in] width Desired width
> > + * \param[in] height Desired height
> 
> "The desired" ?

You are correct this seems to be the convention in other places, will do 
so for v3.

> 
> > + */
> > +StreamUsage::StreamUsage(Role role, int width, int height)
> > +	: role_(role), size_(Size(width, height))
> > +{
> > +}
> > +
> >  /**
> >   * \class Stream
> >   * \brief Video stream for a camera
> > @@ -78,6 +137,39 @@ namespace libcamera {
> >   * optimal stream for the task.
> >   */
> >
> > +/**
> > + * \class Stream::StillCapture
> > + * \brief Describe a still capture usage
> > + */
> > +Stream::StillCapture::StillCapture()
> > +	: StreamUsage(Role::StillCapture)
> > +{
> > +}
> > +
> > +/**
> > + * \class Stream::VideoRecording
> > + * \brief Describe a video recording usage
> > + */
> > +Stream::VideoRecording::VideoRecording()
> > +	: StreamUsage(Role::VideoRecording)
> > +{
> > +}
> > +
> > +/**
> > + * \class Stream::Viewfinder
> > + * \brief Describe a viewfinder usage
> > + */
> > +
> > +/**
> > + * \brief Create a viewfinder usage with dimension hints
> 
> Nit: you have used "size" everywhere in place of dimension if I'm not
> wrong. I like dimension too though.

I like dimension, no strong feeling will bend to popular opinion else 
keep it as is.

> 
> Thanks
>    j
> 
> > + * \param[in] width Desired viewfinder width
> > + * \param[in] height Desired viewfinder height
> > + */
> > +Stream::Viewfinder::Viewfinder(int width, int height)
> > +	: StreamUsage(Role::Viewfinder, width, height)
> > +{
> > +}
> > +
> >  /**
> >   * \brief Construct a stream with default parameters
> >   */
> > --
> > 2.21.0
> >
> > _______________________________________________
> > libcamera-devel mailing list
> > libcamera-devel at lists.libcamera.org
> > https://lists.libcamera.org/listinfo/libcamera-devel



-- 
Regards,
Niklas Söderlund