[PATCH v2 2/7] gstreamer: Factor out video pool creation

[Laurent Pinchart]

On Wed, Jun 04, 2025 at 01:08:16PM -0400, Nicolas Dufresne wrote:
> Le mercredi 04 juin 2025 à 16:07 +0300, Laurent Pinchart a écrit :
> > The gst_libcamera_src_negotiate() function uses 5 identation levels,
> > causing long lines. Move video pool creation to a separate function to
> > increase readability.
> > 
> > Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> > ---
> > Changes since v1:
> > 
> > - Document the gst_libcamera_create_video_pool() function
> > - Keep the gst_libcamera_extrapolate_info() call out of the new function
> > - Reorder function arguments
> > ---
> >  src/gstreamer/gstlibcamerasrc.cpp | 114 +++++++++++++++++++-----------
> >  1 file changed, 72 insertions(+), 42 deletions(-)
> > 
> > diff --git a/src/gstreamer/gstlibcamerasrc.cpp b/src/gstreamer/gstlibcamerasrc.cpp
> > index 6ede43b06a8a..79b94c7ee7c2 100644
> > --- a/src/gstreamer/gstlibcamerasrc.cpp
> > +++ b/src/gstreamer/gstlibcamerasrc.cpp
> > @@ -29,6 +29,7 @@
> > 
> >  #include <atomic>
> >  #include <queue>
> > +#include <tuple>
> >  #include <vector>
> > 
> >  #include <libcamera/camera.h>
> > @@ -521,6 +522,72 @@ gst_libcamera_src_open(GstLibcameraSrc *self)
> >  	return true;
> >  }
> > 
> > +/**
> > + * \brief Create a video pool for a pad
> > + * \param[in] self The libcamerasrc instance
> > + * \param[in] srcpad The pad
> > + * \param[in] caps The pad caps
> > + * \param[in] info The video info for the pad
> > + *
> > + * This function creates and returns a video buffers pool for the given pad if
> 
> Usually no s to buffer when saying "buffer pool". Its like "a noodle soup" versus
> "a bowl of noodles".
> 
> > + * needed to accommodate stride mismatch. If the peer element supports the meta
> > + * API, the stride will be negotiated, and no pool if needed.
> 
> if needed -> is needed ? 

Oops. I've updated the comment to

 * This function creates and returns a video buffer pool for the given pad if
 * needed to accommodate stride mismatch. If the peer element supports stride
 * negotiation through the meta API, no pool is needed and the function will
 * return a null pool.
 *
 * \return A tuple containing the video buffers pool pointer and an error code

> > + *
> > + * \return A tuple containing the video buffers pool pointer and an error code.
> > + * When no error occurs, the pool can be null if the peer element supports
> > + * stride negotiation.
> 
> Sounds great.
> 
> Reviewed-by: Nicolas Dufresne <nicolas.dufresne at collabora.com>
> 
> > + */
> > +static std::tuple<GstBufferPool *, int>
> > +gst_libcamera_create_video_pool(GstLibcameraSrc *self, GstPad *srcpad,
> > +				GstCaps *caps, const GstVideoInfo *info)
> > +{
> > +	GstQuery *query = NULL;
> > +	const gboolean need_pool = true;
> > +	gboolean has_video_meta = false;
> > +	GstBufferPool *video_pool = NULL;
> > +
> > +	query = gst_query_new_allocation(caps, need_pool);
> > +	if (!gst_pad_peer_query(srcpad, query))
> > +		GST_DEBUG_OBJECT(self, "Didn't get downstream ALLOCATION hints");
> > +	else
> > +		has_video_meta = gst_query_find_allocation_meta(query, GST_VIDEO_META_API_TYPE, NULL);
> > +
> > +	if (!has_video_meta) {
> > +		GstBufferPool *pool = NULL;
> > +
> > +		if (gst_query_get_n_allocation_pools(query) > 0)
> > +			gst_query_parse_nth_allocation_pool(query, 0, &pool, NULL, NULL, NULL);
> > +
> > +		if (pool)
> > +			video_pool = pool;
> > +		else {
> > +			GstStructure *config;
> > +			guint min_buffers = 3;
> > +			video_pool = gst_video_buffer_pool_new();
> > +
> > +			config = gst_buffer_pool_get_config(video_pool);
> > +			gst_buffer_pool_config_set_params(config, caps, info->size, min_buffers, 0);
> > +
> > +			GST_DEBUG_OBJECT(self, "Own pool config is %" GST_PTR_FORMAT, config);
> > +
> > +			gst_buffer_pool_set_config(GST_BUFFER_POOL_CAST(video_pool), config);
> > +		}
> > +
> > +		GST_WARNING_OBJECT(self, "Downstream doesn't support video meta, need to copy frame.");
> > +
> > +		if (!gst_buffer_pool_set_active(video_pool, true)) {
> > +			gst_caps_unref(caps);
> > +			GST_ELEMENT_ERROR(self, RESOURCE, SETTINGS,
> > +					  ("Failed to active buffer pool"),
> > +					  ("gst_libcamera_src_negotiate() failed."));
> > +			return { NULL, -EINVAL };
> > +		}
> > +	}
> > +
> > +	gst_query_unref(query);
> > +	return { video_pool, 0 };
> > +}
> > +
> >  /* Must be called with stream_lock held. */
> >  static bool
> >  gst_libcamera_src_negotiate(GstLibcameraSrc *self)
> > @@ -603,50 +670,13 @@ gst_libcamera_src_negotiate(GstLibcameraSrc *self)
> >  		/* Stride mismatch between camera stride and that calculated by video-info. */
> >  		if (static_cast<unsigned int>(info.stride[0]) != stream_cfg.stride &&
> >  		    GST_VIDEO_INFO_FORMAT(&info) != GST_VIDEO_FORMAT_ENCODED) {
> > -			GstQuery *query = NULL;
> > -			const gboolean need_pool = true;
> > -			gboolean has_video_meta = false;
> > -
> >  			gst_libcamera_extrapolate_info(&info, stream_cfg.stride);
> > 
> > -			query = gst_query_new_allocation(caps, need_pool);
> > -			if (!gst_pad_peer_query(srcpad, query))
> > -				GST_DEBUG_OBJECT(self, "Didn't get downstream ALLOCATION hints");
> > -			else
> > -				has_video_meta = gst_query_find_allocation_meta(query, GST_VIDEO_META_API_TYPE, NULL);
> > -
> > -			if (!has_video_meta) {
> > -				GstBufferPool *pool = NULL;
> > -
> > -				if (gst_query_get_n_allocation_pools(query) > 0)
> > -					gst_query_parse_nth_allocation_pool(query, 0, &pool, NULL, NULL, NULL);
> > -
> > -				if (pool)
> > -					video_pool = pool;
> > -				else {
> > -					GstStructure *config;
> > -					guint min_buffers = 3;
> > -					video_pool = gst_video_buffer_pool_new();
> > -
> > -					config = gst_buffer_pool_get_config(video_pool);
> > -					gst_buffer_pool_config_set_params(config, caps, info.size, min_buffers, 0);
> > -
> > -					GST_DEBUG_OBJECT(self, "Own pool config is %" GST_PTR_FORMAT, config);
> > -
> > -					gst_buffer_pool_set_config(GST_BUFFER_POOL_CAST(video_pool), config);
> > -				}
> > -
> > -				GST_WARNING_OBJECT(self, "Downstream doesn't support video meta, need to copy frame.");
> > -
> > -				if (!gst_buffer_pool_set_active(video_pool, true)) {
> > -					gst_caps_unref(caps);
> > -					GST_ELEMENT_ERROR(self, RESOURCE, SETTINGS,
> > -							  ("Failed to active buffer pool"),
> > -							  ("gst_libcamera_src_negotiate() failed."));
> > -					return false;
> > -				}
> > -			}
> > -			gst_query_unref(query);
> > +			std::tie(video_pool, ret) =
> > +				gst_libcamera_create_video_pool(self, srcpad,
> > +								caps, &info);
> > +			if (ret)
> > +				return false;
> >  		}
> > 
> >  		GstLibcameraPool *pool = gst_libcamera_pool_new(self->allocator,

-- 
Regards,

Laurent Pinchart