Re: [FFmpeg-devel] [PATCH 1/8] swscale: fix sws_setColorspaceDetails after sws_init_context

[Michael Niedermayer <michael@niedermayer.cc>]

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On Fri, Oct 27, 2023 at 07:04:39PM +0200, Niklas Haas wrote:
> From: Niklas Haas <git@haasn.dev>
> 
> More commonly, this fixes the case of sws_setColorspaceDetails after
> sws_getContext, since the latter implies sws_init_context.
> 
> The problem here is that sws_init_context sets up the range conversion
> and fast path tables based on the values of srcRange/dstRange at init
> time. This may result in locking in a "wrong" path (either using
> unscaled fast path when range conversion later required, or using
> scaled slow path when range conversion becomes no longer required).
> 
> There are two way outs:
> 
> 1. Always initialize range conversion and unscaled converters, even if
>    they will be unused, and extend the runtime check.
> 2. Re-do initialization if the values change after
>    sws_setColorspaceDetails.
> 
> I opted for approach 1 because it was simpler and easier to reason
> about.
> ---
>  libswscale/swscale.c | 2 +-
>  libswscale/utils.c   | 5 +----
>  2 files changed, 2 insertions(+), 5 deletions(-)
> 
> diff --git a/libswscale/swscale.c b/libswscale/swscale.c
> index 90e5b299ab..46ba68fe6a 100644
> --- a/libswscale/swscale.c
> +++ b/libswscale/swscale.c
> @@ -1016,7 +1016,7 @@ static int scale_internal(SwsContext *c,
>      reset_ptr(src2, c->srcFormat);
>      reset_ptr((void*)dst2, c->dstFormat);
>  
> -    if (c->convert_unscaled) {
> +    if (c->convert_unscaled && !c->lumConvertRange && !c->chrConvertRange) {
>          int offset  = srcSliceY_internal;
>          int slice_h = srcSliceH;
>  
> diff --git a/libswscale/utils.c b/libswscale/utils.c
> index e1ad685972..455955e907 100644
> --- a/libswscale/utils.c
> +++ b/libswscale/utils.c
> @@ -1728,9 +1728,7 @@ static av_cold int sws_init_single_context(SwsContext *c, SwsFilter *srcFilter,
>      }
>  
>      /* unscaled special cases */
> -    if (unscaled && !usesHFilter && !usesVFilter &&
> -        (c->srcRange == c->dstRange || isAnyRGB(dstFormat) ||
> -         isFloat(srcFormat) || isFloat(dstFormat))){
> +    if (unscaled && !usesHFilter && !usesVFilter) {
>          ff_get_unscaled_swscale(c);
>  
>          if (c->convert_unscaled) {
> @@ -1738,7 +1736,6 @@ static av_cold int sws_init_single_context(SwsContext *c, SwsFilter *srcFilter,
>                  av_log(c, AV_LOG_INFO,
>                         "using unscaled %s -> %s special converter\n",
>                         av_get_pix_fmt_name(srcFormat), av_get_pix_fmt_name(dstFormat));
> -            return 0;
>          }
>      }

the av_log() message will be wrong if this path is unused

also this ties convert_unscaled to never do range conversion, if thats
intended, i guess thats ok. Otherwise that maybe is a restriction
we dont want to add.

thx

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

"I am not trying to be anyone's saviour, I'm trying to think about the
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