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

[Nicolas Dufresne]

Hi,

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.

> 
> +	 */
>  	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>

Nicolas