[FFmpeg-devel] [PATCHv2 3/4] avutil/pixdesc: add AV_PIX_FMT_FLAG_ALPHA to AV_PIX_FMT_PAL8

[wm4]

On Thu, 19 Apr 2018 23:25:03 +0200
Marton Balint <cus at passwd.hu> wrote:

> Signed-off-by: Marton Balint <cus at passwd.hu>
> ---
>  doc/APIchanges            | 3 +++
>  libavutil/pixdesc.c       | 3 +--
>  libavutil/pixdesc.h       | 8 ++------
>  libavutil/tests/pixdesc.c | 4 ----
>  libavutil/version.h       | 2 +-
>  5 files changed, 7 insertions(+), 13 deletions(-)
> 
> diff --git a/doc/APIchanges b/doc/APIchanges
> index 4f6ac2a031..d9b457e080 100644
> --- a/doc/APIchanges
> +++ b/doc/APIchanges
> @@ -15,6 +15,9 @@ libavutil:     2017-10-21
>  
>  API changes, most recent first:
>  
> +2018-04-xx - xxxxxxxxxx - lavu 56.16.100 - pixdesc.h
> +  Add AV_PIX_FMT_FLAG_ALPHA to AV_PIX_FMT_PAL8.
> +
>  -------- 8< --------- FFmpeg 4.0 was cut here -------- 8< ---------
>  
>  2018-04-03 - d6fc031caf - lavu 56.13.100 - pixdesc.h
> diff --git a/libavutil/pixdesc.c b/libavutil/pixdesc.c
> index 8ed52751c1..a8be7b66e6 100644
> --- a/libavutil/pixdesc.c
> +++ b/libavutil/pixdesc.c
> @@ -288,7 +288,7 @@ static const AVPixFmtDescriptor av_pix_fmt_descriptors[AV_PIX_FMT_NB] = {
>          .comp = {
>              { 0, 1, 0, 0, 8, 0, 7, 1 },
>          },
> -        .flags = AV_PIX_FMT_FLAG_PAL,
> +        .flags = AV_PIX_FMT_FLAG_PAL | AV_PIX_FMT_FLAG_ALPHA,
>      },
>      [AV_PIX_FMT_YUVJ420P] = {
>          .name = "yuvj420p",
> @@ -2432,7 +2432,6 @@ void ff_check_pixfmt_descriptors(void){
>          av_assert0(d->log2_chroma_h <= 3);
>          av_assert0(d->nb_components <= 4);
>          av_assert0(d->name && d->name[0]);
> -        av_assert0((d->nb_components==4 || d->nb_components==2) == !!(d->flags & AV_PIX_FMT_FLAG_ALPHA));
>          av_assert2(av_get_pix_fmt(d->name) == i);
>  
>          for (j=0; j<FF_ARRAY_ELEMS(d->comp); j++) {
> diff --git a/libavutil/pixdesc.h b/libavutil/pixdesc.h
> index 1ab372782a..4f9c5a271f 100644
> --- a/libavutil/pixdesc.h
> +++ b/libavutil/pixdesc.h
> @@ -167,12 +167,8 @@ typedef struct AVPixFmtDescriptor {
>  
>  /**
>   * The pixel format has an alpha channel. This is set on all formats that
> - * support alpha in some way. The exception is AV_PIX_FMT_PAL8, which can
> - * carry alpha as part of the palette. Details are explained in the
> - * AVPixelFormat enum, and are also encoded in the corresponding
> - * AVPixFmtDescriptor.
> - *
> - * The alpha is always straight, never pre-multiplied.
> + * support alpha in some way, including AV_PIX_FMT_PAL8. The alpha is always
> + * straight, never pre-multiplied.
>   *
>   * If a codec or a filter does not support alpha, it should set all alpha to
>   * opaque, or use the equivalent pixel formats without alpha component, e.g.
> diff --git a/libavutil/tests/pixdesc.c b/libavutil/tests/pixdesc.c
> index 7fbfeea96c..34e2bea932 100644
> --- a/libavutil/tests/pixdesc.c
> +++ b/libavutil/tests/pixdesc.c
> @@ -37,10 +37,6 @@ int main(void){
>              skip = 0;
>          }
>          av_log(NULL, AV_LOG_INFO, "pix fmt %s avg_bpp:%d colortype:%d\n", desc->name, av_get_padded_bits_per_pixel(desc), get_color_type(desc));
> -        if ((!(desc->flags & AV_PIX_FMT_FLAG_ALPHA)) != (desc->nb_components != 2 && desc->nb_components != 4)) {
> -            av_log(NULL, AV_LOG_ERROR, "Alpha flag mismatch\n");
> -            err = 1;
> -        }
>      }
>      return err;
>  }
> diff --git a/libavutil/version.h b/libavutil/version.h
> index 387421775f..23567000a3 100644
> --- a/libavutil/version.h
> +++ b/libavutil/version.h
> @@ -79,7 +79,7 @@
>   */
>  
>  #define LIBAVUTIL_VERSION_MAJOR  56
> -#define LIBAVUTIL_VERSION_MINOR  15
> +#define LIBAVUTIL_VERSION_MINOR  16
>  #define LIBAVUTIL_VERSION_MICRO 100
>  
>  #define LIBAVUTIL_VERSION_INT   AV_VERSION_INT(LIBAVUTIL_VERSION_MAJOR, \

Probably fine. While I like it, we also have to be careful about the
consequences. Does it change FATE or the results of that pixfmt choosing
function, avcodec_find_best_pix_fmt_of_list()? Are there any formats
that decode to PAL8, but write garbage to the alpha component of the
palette?