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

["Tomas Härdin" <git@haerdin.se>]

ons 2023-08-16 klockan 23:44 +0800 skrev Zhao Zhili:
> 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 }
>  
>  /**
>   * @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 }

For C++ compat you could use some constructor magic instead, and turn
these into proper constants. Hidden behind #ifdef __cplusplus of
course.

IMO having untyped #defines like this is mega ugly. At the very least
it should be (AVChannelLayout){...}. It's likely cargo culted from when
channel layouts were bitmasks.

/Tomas
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