[libcamera-devel] [RFC PATCH 1/2] android: Document the structures and functions for post-processing

[Laurent Pinchart]

Hi Umang,

Thank you for the patch, it's really useful.

On Fri, Nov 19, 2021 at 06:45:05PM +0530, Umang Jain wrote:
> Specifically document:
>  - CameraDevice::sendCaptureResults()
>  - CameraDevice::completeDescriptor()
>  - CameraDevice::streamProcessingComplete()
> 
>  - CameraStream::PostProcessorWorker class
>  - Camera3RequestDescriptor::StreamBuffer structure
> 
> Signed-off-by: Umang Jain <umang.jain at ideasonboard.com>
> ---
>  src/android/camera_device.cpp  | 35 +++++++++++++++++++++++++++++++
>  src/android/camera_request.cpp | 38 ++++++++++++++++++++++++++++++++++
>  src/android/camera_stream.cpp  | 12 +++++++++++
>  3 files changed, 85 insertions(+)
> 
> diff --git a/src/android/camera_device.cpp b/src/android/camera_device.cpp
> index f2e0bdbd..fb46be4d 100644
> --- a/src/android/camera_device.cpp
> +++ b/src/android/camera_device.cpp
> @@ -1147,6 +1147,16 @@ void CameraDevice::requestComplete(Request *request)
>  	}
>  }
>  
> +/**
> + * \brief Complete the Camera3RequestDescriptor
> + * \param[in] descriptor The Camera3RequestDescriptor deemed to be complete

s/deemed to be complete/that has completed/

> + *
> + * Marks the Camera3RequestDescriptor as 'complete'. This means all the streams

s/Marks/This function marks/
s/This means/It shall be called when/

> + * in the Camera3RequestDescriptor have completed capture (or generated via

s/generated/have been generated/

> + * post-processing) and is ready be sent back to the framework.

s/is ready/the request is ready/

> + *
> + * \context This function is \threadsafe.
> + */
>  void CameraDevice::completeDescriptor(Camera3RequestDescriptor *descriptor)
>  {
>  	MutexLocker lock(descriptorsMutex_);
> @@ -1155,6 +1165,17 @@ void CameraDevice::completeDescriptor(Camera3RequestDescriptor *descriptor)
>  	sendCaptureResults();
>  }
>  
> +/**
> + * \brief Sequentially send capture results to the framework
> + *
> + * Inspect the head of the descriptors' queue and see if it is ready to be sent
> + * back to the framework. Populate a locally-scoped camera3_capture_result_t
> + * using the fields of the descriptor and send the capture result back by
> + * calling the process_capture_result() callback.

I'd be more explicit about the fact that the function loops over the
queue:

 * Iterate over the descriptors queue to send completed descriptors back to the
 * framework, in the same order as they have been queued. For each complete
 * descriptor, populate a locally-scoped camera3_capture_result_t from the
 * descriptor, send the capture result back by calling the
 * process_capture_result() callback, and remove the descriptor from the queue.
 * Stop iterating if the descriptor at the front of the queue is not complete.

> + *
> + * This function should never be called directly in the codebase. Use
> + * completeDescriptor() instead.
> + */
>  void CameraDevice::sendCaptureResults()
>  {
>  	while (!descriptors_.empty() && !descriptors_.front()->isPending()) {
> @@ -1214,6 +1235,20 @@ void CameraDevice::setBufferStatus(Camera3RequestDescriptor::StreamBuffer &strea
>  	}
>  }
>  
> +/**
> + * \brief Handle post-processing completion of a stream in a capture request
> + * \param[in] streamBuffer The StreamBuffer for which processing is complete
> + * \param[in] status Stream post-processing status
> + *
> + * This is invoked in the post-processor's thread whenever a camera stream has

s/This/This function/

s/invoked in/called from/ ?

> + * finished post processing. The corresponding entry is dropped from the
> + * descriptor's pendingStreamsToProcess_ map.
> + *
> + * If the pendingStreamsToProcess_ map is found to be empty, it is perceived

s/is found to be empty/is then/
s/it is perceived that //

> + * that all the streams requiring to be generated from post-processing have been
> + * completed. Mark the descriptor as complete using completeDescriptor() in that
> + * case.
> + */
>  void CameraDevice::streamProcessingComplete(Camera3RequestDescriptor::StreamBuffer *streamBuffer,
>  					    Camera3RequestDescriptor::Status status)
>  {
> diff --git a/src/android/camera_request.cpp b/src/android/camera_request.cpp
> index 8162aa78..4e017792 100644
> --- a/src/android/camera_request.cpp
> +++ b/src/android/camera_request.cpp
> @@ -53,6 +53,44 @@ Camera3RequestDescriptor::Camera3RequestDescriptor(
>  
>  Camera3RequestDescriptor::~Camera3RequestDescriptor() = default;
>  
> +/**
> + * \struct Camera3RequestDescriptor::StreamBuffer
> + * \brief Groups information for per-stream buffer of Camera3RequestDescriptor

s/Groups/Group/

> + *
> + * A capture request placed to the libcamera HAL can contain multiple streams.
> + * Each stream will have an associated buffer to be filled. StreamBuffer struct

s/StreamBuffer struct/The StreamBuffer structure/

or

s/StreamBuffer struct/StreamBuffer/

> + * tracks this buffer with contextual information which aids in the stream's
> + * generation. The generation of stream will depend on its type (refer

s/of stream/of the stream/
s/refer/refer to the/

> + * CameraStream::Type documentation).
> + *
> + * \var Camera3RequestDescriptor::StreamBuffer::stream
> + * \brief Corresponding pointer to CameraStream

 * \brief Pointer to the corresponding CameraStream

> + *
> + * \var Camera3RequestDescriptor::StreamBuffer::camera3Buffer
> + * \brief Native handle to the buffer
> + *
> + * \var Camera3RequestDescriptor::StreamBuffer::frameBuffer
> + * \brief Encapsulate the dmabuf handle inside a libcamera::FrameBuffer for
> + * direct streams
> + *
> + * \var Camera3RequestDescriptor::StreamBuffer::fence
> + * \brief Acquire fence of the buffer
> + *
> + * \var Camera3RequestDescriptor::StreamBuffer::status
> + * \brief Track the status of the buffer
> + *
> + * \var Camera3RequestDescriptor::StreamBuffer::internalBuffer
> + * \brief Pointer to a buffer internally handled by CameraStream (if any)
> + *
> + * \var Camera3RequestDescriptor::StreamBuffer::srcBuffer
> + * \brief Pointer to source frame buffer required for post-processing

s/source/the source/
s/required for/used for/

> + *
> + * \var Camera3RequestDescriptor::StreamBuffer::dstBuffer
> + * \brief Pointer to destination frame buffer required for post-processing

s/destination/the destination/
s/required for/used for/

> + *
> + * \var Camera3RequestDescriptor::StreamBuffer::request
> + * \brief Back pointer to Camera3RequestDescriptor to which StreamBuffer belongs
> + */
>  Camera3RequestDescriptor::StreamBuffer::StreamBuffer(
>  	CameraStream *cameraStream, const camera3_stream_buffer_t &buffer,
>  	Camera3RequestDescriptor *requestDescriptor)
> diff --git a/src/android/camera_stream.cpp b/src/android/camera_stream.cpp
> index 9023c13c..3cda58c9 100644
> --- a/src/android/camera_stream.cpp
> +++ b/src/android/camera_stream.cpp
> @@ -231,6 +231,18 @@ void CameraStream::putBuffer(FrameBuffer *buffer)
>  	buffers_.push_back(buffer);
>  }
>  
> +/**
> + * \class CameraStream::PostProcessorWorker
> + * \brief Post process a CameraStream on an internal thread

s/Post process/Post-process/
s/on an/in an/

> + *
> + * If the association between CameraStream and camera3_stream_t dictated by
> + * CameraStream::Type is internal or mapped, the stream is generated by post
> + * processing of a libcamera stream. Such a request is queued to

s/queued to/queued to a/

Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>

> + * PostProcessorWorker in CameraStream::process(). A queue of post-processing
> + * requests is maintained by the PostProcessorWorker and it will run the
> + * post-processing on an internal thread as soon as any request is available on
> + * its queue.
> + */
>  CameraStream::PostProcessorWorker::PostProcessorWorker(PostProcessor *postProcessor)
>  	: postProcessor_(postProcessor)
>  {

-- 
Regards,

Laurent Pinchart