Re: [FFmpeg-devel] [PATCH] avutil/channel_layout: make pre-defined channel layouts C++ friendly

["Zhao Zhili" <quinkblack@foxmail.com>]

> From: ffmpeg-devel <ffmpeg-devel-bounces@ffmpeg.org> On Behalf Of James Almer
> Sent: 2023年8月17日 0:22
> To: ffmpeg-devel@ffmpeg.org
> Subject: Re: [FFmpeg-devel] [PATCH] avutil/channel_layout: make pre-defined channel layouts C++ friendly
> 
> On 8/16/2023 12:44 PM, Zhao Zhili wrote:
> > From: Zhao Zhili <zhilizhao@tencent.com>
> >
> > C++ doesn't support designated initializers until C++20. We have
> > a bunch of pre-defined channel layouts, the gains to make them
> > usable in C++ exceed the losses.
> >
> > Signed-off-by: Zhao Zhili <zhilizhao@tencent.com>
> > ---
> >   libavutil/channel_layout.h | 4 ++--
> >   1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/libavutil/channel_layout.h b/libavutil/channel_layout.h
> > index f345415c55..817a5ad370 100644
> > --- a/libavutil/channel_layout.h
> > +++ b/libavutil/channel_layout.h
> > @@ -359,7 +359,7 @@ typedef struct AVChannelLayout {
> >   } AVChannelLayout;
> >
> >   #define AV_CHANNEL_LAYOUT_MASK(nb, m) \
> > -    { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = (nb), .u = { .mask = (m) }}
> > +    { AV_CHANNEL_ORDER_NATIVE, (nb), { m }, NULL }
> 
> Comment out the field names instead of removing them altogether, and add
> a comment about how this is done for the sake of c++ projects including
> this header.

OK. So it won't be reverted by accident.

> 
> >
> >   /**
> >    * @name Common pre-defined channel layouts
> > @@ -397,7 +397,7 @@ typedef struct AVChannelLayout {
> >   #define AV_CHANNEL_LAYOUT_STEREO_DOWNMIX    AV_CHANNEL_LAYOUT_MASK(2,  AV_CH_LAYOUT_STEREO_DOWNMIX)
> >   #define AV_CHANNEL_LAYOUT_22POINT2          AV_CHANNEL_LAYOUT_MASK(24, AV_CH_LAYOUT_22POINT2)
> >   #define AV_CHANNEL_LAYOUT_AMBISONIC_FIRST_ORDER \
> > -    { .order = AV_CHANNEL_ORDER_AMBISONIC, .nb_channels = 4, .u = { .mask = 0 }}
> > +    { AV_CHANNEL_ORDER_AMBISONIC, 4, { 0 }, NULL }
> >   /** @} */
> >
> >   struct AVBPrint;
> 
> This needs a minor bump IMO. Something said c++ projects can look for
> before using these defines.

Good idea.

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