[PATCH 2/4] gstreamer: Factor out video pool creation

[Laurent Pinchart]

On Thu, May 22, 2025 at 01:34:57PM -0400, Nicolas Dufresne wrote:
> 
> Hi,
> 
> Le jeudi 22 mai 2025 à 14:55 +0200, 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>
> > ---
> >  src/gstreamer/gstlibcamerasrc.cpp | 105 +++++++++++++++++-------------
> >  1 file changed, 61 insertions(+), 44 deletions(-)
> > 
> > diff --git a/src/gstreamer/gstlibcamerasrc.cpp b/src/gstreamer/gstlibcamerasrc.cpp
> > index 70bb0606c72c..71f5700d9de7 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>
> > @@ -519,6 +520,61 @@ gst_libcamera_src_open(GstLibcameraSrc *self)
> >  	return true;
> >  }
> >  
> > +static std::tuple<GstBufferPool *, int>
> 
> Either document the return values, or drop the tuple. Note that I prefer the
> second since there is no value added in the usage of tuple, since it has only
> one error code which always imply a nullptr pool pointer. Being a private
> helper, it can be extended later.

As discussed in patch 4/4, the error code is needed. I will document the
function, but you'll see from the documentation in v2 that I don't fully
understand what it does :-)

> > +gst_libcamera_create_video_pool(GstLibcameraSrc *self,
> > +				const StreamConfiguration &stream_cfg,
> > +				GstVideoInfo *info, GstPad *srcpad,
> > +				GstCaps *caps)
> > +{
> > +	GstQuery *query = NULL;
> > +	const gboolean need_pool = true;
> > +	gboolean has_video_meta = false;
> > +	GstBufferPool *video_pool = NULL;
> 
> Oops, NULL started to re-appear, when I wrote the initial version I was asked to
> turn them all into nullptr instead. It might be a good moment to fix it, of course
> separate from the refactoring.

OK, I'll do so.

> > +
> > +	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);

I think this is a but. I'll add a new patch in v2 to fix it.

> > +			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)
> > @@ -601,50 +657,11 @@ 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, stream_cfg,
> > +								&info, srcpad, caps);
> > +			if (ret)
> > +				return false;
> 
> This is good improvement otherwise.
> 
> Reviewed-by: Nicolas Dufresne <nicolas.dufresne at collabora.com>
> 
> >  		}
> >  
> >  		GstLibcameraPool *pool = gst_libcamera_pool_new(self->allocator,

-- 
Regards,

Laurent Pinchart