[PATCH] drm: document pre-multiplied assumptions

[Pekka Paalanen]

On Wed, 29 Sep 2021 09:54:14 +0000
Simon Ser <contact at emersion.fr> wrote:

> When a plane is missing the "alpha blend mode" property, KMS drivers
> will use the pre-multiplied mode.
> 
> Signed-off-by: Simon Ser <contact at emersion.fr>
> Cc: Daniel Vetter <daniel at ffwll.ch>
> Cc: Pekka Paalanen <ppaalanen at gmail.com>
> ---
>  drivers/gpu/drm/drm_blend.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_blend.c b/drivers/gpu/drm/drm_blend.c
> index ec37cbfabb50..eebb32ba84d7 100644
> --- a/drivers/gpu/drm/drm_blend.c
> +++ b/drivers/gpu/drm/drm_blend.c
> @@ -185,6 +185,9 @@
>   *		 plane does not expose the "alpha" property, then this is
>   *		 assumed to be 1.0
>   *
> + *	When a plane is missing this property, the plane uses the
> + *	"Pre-multiplied" equation.
> + *
>   * Note that all the property extensions described here apply either to the
>   * plane or the CRTC (e.g. for the background color, which currently is not
>   * exposed and assumed to be black).

Hi Simon,

thank you! :-D

I have no idea if that's correct though, but also nothing against it,
and it does help with what I ranted about in
https://lists.freedesktop.org/archives/wayland-devel/2021-September/041993.html
so is it appropriate to offer my

Acked-by: Pekka Paalanen <pekka.paalanen at collabora.com>

?


Thanks,
pq
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