[FFmpeg-devel] [PATCH] avfilter/vf_chromakey: The chromakey filter preserves non-opaque alpha transparency.

[Gavin Smith]

On 10/06/2020 22:33, Gavin Smith wrote:
> From: Gavin Smith <gcs584 at yahoo.com>

Sorry, new to all this. A description would have been helpful. I'll work 
on getting it right.

So this patch is to address Trac ticket #8724:

https://trac.ffmpeg.org/ticket/8724

>
> ---
>   libavfilter/vf_chromakey.c | 43 ++++++++++++++++++++++----------------
>   1 file changed, 25 insertions(+), 18 deletions(-)
>
> diff --git a/libavfilter/vf_chromakey.c b/libavfilter/vf_chromakey.c
> index 4b1669d084..7206f44441 100644
> --- a/libavfilter/vf_chromakey.c
> +++ b/libavfilter/vf_chromakey.c
> @@ -47,7 +47,7 @@ typedef struct ChromakeyContext {
>                       int jobnr, int nb_jobs);
>   } ChromakeyContext;
>   
> -static uint8_t do_chromakey_pixel(ChromakeyContext *ctx, uint8_t u[9], uint8_t v[9])
> +static uint8_t do_chromakey_pixel(ChromakeyContext *ctx, uint8_t a, uint8_t u[9], uint8_t v[9])
>   {
>       double diff = 0.0;
>       int du, dv, i;
> @@ -62,13 +62,13 @@ static uint8_t do_chromakey_pixel(ChromakeyContext *ctx, uint8_t u[9], uint8_t v
>       diff /= 9.0;
>   
>       if (ctx->blend > 0.0001) {
> -        return av_clipd((diff - ctx->similarity) / ctx->blend, 0.0, 1.0) * 255.0;
> +        return av_clipd((diff - ctx->similarity) / ctx->blend, 0.0, 1.0) * (float)a;
>       } else {
> -        return (diff > ctx->similarity) ? 255 : 0;
> +        return (diff > ctx->similarity) ? a : 0;
>       }
>   }
>   
> -static uint16_t do_chromakey_pixel16(ChromakeyContext *ctx, uint16_t u[9], uint16_t v[9])
> +static uint16_t do_chromakey_pixel16(ChromakeyContext *ctx, uint16_t a, uint16_t u[9], uint16_t v[9])
>   {
>       double max = ctx->max;
>       double diff = 0.0;
> @@ -84,9 +84,9 @@ static uint16_t do_chromakey_pixel16(ChromakeyContext *ctx, uint16_t u[9], uint1
>       diff /= 9.0;
>   
>       if (ctx->blend > 0.0001) {
> -        return av_clipd((diff - ctx->similarity) / ctx->blend, 0.0, 1.0) * max;
> +        return av_clipd((diff - ctx->similarity) / ctx->blend, 0.0, 1.0) * (float)a;
>       } else {
> -        return (diff > ctx->similarity) ? max : 0;
> +        return (diff > ctx->similarity) ? a : 0;
>       }
>   }
>   
> @@ -131,13 +131,17 @@ static int do_chromakey_slice(AVFilterContext *avctx, void *arg, int jobnr, int
>   
>       for (y = slice_start; y < slice_end; ++y) {
>           for (x = 0; x < frame->width; ++x) {
> -            for (yo = 0; yo < 3; ++yo) {
> -                for (xo = 0; xo < 3; ++xo) {
> -                    get_pixel_uv(frame, ctx->hsub_log2, ctx->vsub_log2, x + xo - 1, y + yo - 1, &u[yo * 3 + xo], &v[yo * 3 + xo]);
> +            uint8_t *a = frame->data[3] + frame->linesize[3] * y;
> +            const uint8_t ao = a[x];
> +
> +            if (ao != 0) {
> +                for (yo = 0; yo < 3; ++yo) {
> +                    for (xo = 0; xo < 3; ++xo) {
> +                        get_pixel_uv(frame, ctx->hsub_log2, ctx->vsub_log2, x + xo - 1, y + yo - 1, &u[yo * 3 + xo], &v[yo * 3 + xo]);
> +                    }
>                   }
> +                a[x] = do_chromakey_pixel(ctx, ao, u, v);
>               }
> -
> -            frame->data[3][frame->linesize[3] * y + x] = do_chromakey_pixel(ctx, u, v);
>           }
>       }
>   
> @@ -163,15 +167,18 @@ static int do_chromakey16_slice(AVFilterContext *avctx, void *arg, int jobnr, in
>   
>       for (y = slice_start; y < slice_end; ++y) {
>           for (x = 0; x < frame->width; ++x) {
> -            uint16_t *dst = (uint16_t *)(frame->data[3] + frame->linesize[3] * y);
> -
> -            for (yo = 0; yo < 3; ++yo) {
> -                for (xo = 0; xo < 3; ++xo) {
> -                    get_pixel16_uv(frame, ctx->hsub_log2, ctx->vsub_log2, x + xo - 1, y + yo - 1, &u[yo * 3 + xo], &v[yo * 3 + xo]);
> +            uint16_t *a = (uint16_t *)(frame->data[3] + frame->linesize[3] * y);
> +            const uint16_t ao = a[x];
> +
> +            if (ao != 0) {
> +                for (yo = 0; yo < 3; ++yo) {
> +                    for (xo = 0; xo < 3; ++xo) {
> +                        get_pixel16_uv(frame, ctx->hsub_log2, ctx->vsub_log2, x + xo - 1, y + yo - 1, &u[yo * 3 + xo], &v[yo * 3 + xo]);
> +                    }
>                   }
> -            }
>   
> -            dst[x] = do_chromakey_pixel16(ctx, u, v);
> +                a[x] = do_chromakey_pixel16(ctx, ao, u, v);
> +            }
>           }
>       }
>