[Mesa-dev] [PATCH 4/6] st/dri: handle emulated YUV texture sampling in query_dma_buf_modifiers

[Philipp Zabel]

On Fri, 2019-04-12 at 19:33 +0200, Lucas Stach wrote:
> The Mesa state tracker will emulate YUV texture sampling for drivers that
> don't support it natively by using multiple R8/RG88 samplers. Teach
> dri2_query_dma_buf_modifiers about this special case.
> This allows clients like GStreamer glupload or Kodi to properly query
> the supported dma-buf import formats, without the need to take a special
> code path for the emulated OES_external texture handling.
> 
> Signed-off-by: Lucas Stach <l.stach at pengutronix.de>
> ---
>  src/gallium/state_trackers/dri/dri2.c | 17 ++++++++++++++---
>  1 file changed, 14 insertions(+), 3 deletions(-)
> 
> diff --git a/src/gallium/state_trackers/dri/dri2.c b/src/gallium/state_trackers/dri/dri2.c
> index f139bd6722b9..4243a00cb38d 100644
> --- a/src/gallium/state_trackers/dri/dri2.c
> +++ b/src/gallium/state_trackers/dri/dri2.c
> @@ -1358,19 +1358,30 @@ dri2_query_dma_buf_modifiers(__DRIscreen *_screen, int fourcc, int max,
>     const struct dri2_format_mapping *map = dri2_get_mapping_by_fourcc(fourcc);
>     enum pipe_format format;
>  
> -   if (!map)
> +   if (!map || !pscreen->query_dmabuf_modifiers)
>        return false;
>  
>     format = map->pipe_format;
>  
> -   if (pscreen->query_dmabuf_modifiers != NULL &&
> -       (pscreen->is_format_supported(pscreen, format, screen->target, 0, 0,
> +   if ((pscreen->is_format_supported(pscreen, format, screen->target, 0, 0,
>                                       PIPE_BIND_RENDER_TARGET) ||
>          pscreen->is_format_supported(pscreen, format, screen->target, 0, 0,
>                                       PIPE_BIND_SAMPLER_VIEW))) {
>        pscreen->query_dmabuf_modifiers(pscreen, format, max, modifiers,
>                                        external_only, count);
>        return true;
> +   } else if (util_format_is_yuv(format) &&
> +              pscreen->is_format_supported(pscreen, PIPE_FORMAT_R8_UNORM,
> +                                           screen->target, 0, 0,
> +                                           PIPE_BIND_SAMPLER_VIEW)) {
> +      /* YUV format sampling can be emulated by the Mesa state tracker by
> +       * using multiple R8/RG88 samplers if the driver doesn't support those
> +       * formats natively, so we need a special case here to give a mostly
> +       * accurate answer to the modifiers query.
> +       */

"Mostly accurate" meaning that for IYUV this is correct, but for NV12 we
are assuming that the drivers will return the same modifiers for
PIPE_FORMAT_R8_UNORM as for PIPE_FORMAT_RG88_UNORM. As far as I can
tell, this is currently the case for all drivers that implement
query_dmabuf_modifiers.

Reviewed-by: Philipp Zabel <p.zabel at pengutronix.de>

regards
Philipp