[PATCH 1/4] gstreamer: Document improvements when updating minimum GStreamer version

[Laurent Pinchart]

On Thu, May 22, 2025 at 01:25:24PM -0400, Nicolas Dufresne wrote:
> Le jeudi 22 mai 2025 à 14:55 +0200, Laurent Pinchart a écrit :
> > A const_cast<> was recently added to fix a compilation issue with older
> > GStreamer versions. Add a comment to indicate it can be removed when
> > bumping the minimum GStreamer version requirement. While at it, also
> > document a possible future improvement in the same function, and wrap
> > long lines.
> > 
> > Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> > ---
> >  src/gstreamer/gstlibcamerasrc.cpp | 18 +++++++++++++++---
> >  1 file changed, 15 insertions(+), 3 deletions(-)
> > 
> > diff --git a/src/gstreamer/gstlibcamerasrc.cpp b/src/gstreamer/gstlibcamerasrc.cpp
> > index b34f089778ec..70bb0606c72c 100644
> > --- a/src/gstreamer/gstlibcamerasrc.cpp
> > +++ b/src/gstreamer/gstlibcamerasrc.cpp
> > @@ -285,10 +285,17 @@ gst_libcamera_extrapolate_info(GstVideoInfo *info, guint32 stride)
> >  }
> >  
> >  static GstFlowReturn
> > -gst_libcamera_video_frame_copy(GstBuffer *src, GstBuffer *dest, const GstVideoInfo *dest_info, guint32 stride)
> > +gst_libcamera_video_frame_copy(GstBuffer *src, GstBuffer *dest,
> > +			       const GstVideoInfo *dest_info, guint32 stride)
> >  {
> > -	GstVideoInfo src_info = *dest_info;
> > +	/*
> > +	 * When dropping support for versions earlier than v1.22.0, use
> > +	 *
> > +	 * g_auto (GstVideoFrame) src_frame = GST_VIDEO_FRAME_INIT;
> > +	 * g_auto (GstVideoFrame) dest_frame = GST_VIDEO_FRAME_INIT;
> 
> Do you think your readers will understand that g_auto() allows the removal of all
> the unmap() calls ? Otherwise I'd add this to the comment too.

That's a good idea. I'll expand the comment to

	/*
	 * When dropping support for versions earlier than v1.22.0, use
	 *
	 * g_auto (GstVideoFrame) src_frame = GST_VIDEO_FRAME_INIT;
	 * g_auto (GstVideoFrame) dest_frame = GST_VIDEO_FRAME_INIT;
	 *
	 * and drop the gst_video_frame_unmap() calls.
	 */

> > 
> > +	 */
> >  	GstVideoFrame src_frame, dest_frame;
> > +	GstVideoInfo src_info = *dest_info;
> >  
> >  	gst_libcamera_extrapolate_info(&src_info, stride);
> >  	src_info.size = gst_buffer_get_size(src);
> > @@ -298,7 +305,12 @@ gst_libcamera_video_frame_copy(GstBuffer *src, GstBuffer *dest, const GstVideoIn
> >  		return GST_FLOW_ERROR;
> >  	}
> >  
> > -	if (!gst_video_frame_map(&dest_frame, const_cast<GstVideoInfo *>(dest_info), dest, GST_MAP_WRITE)) {
> > +	/*
> > +	 * When dropping support for versions earlier than 1.20.0, drop the
> > +	 * const_cast<>().
> > +	 */
> > +	if (!gst_video_frame_map(&dest_frame, const_cast<GstVideoInfo *>(dest_info),
> > +				 dest, GST_MAP_WRITE)) {
> >  		GST_ERROR("Could not map dest buffer");
> >  		gst_video_frame_unmap(&src_frame);
> >  		return GST_FLOW_ERROR;
> 
> Nothing major otherwise, feel free to edit and add:
> 
> Reviewed-by: Nicolas Dufresne <nicolas.dufresne at collabora.com>

-- 
Regards,

Laurent Pinchart