linux-kernel - Re: [PATCH] drm/vkms: Use alpha value to blend values.

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Date:   Mon, 24 Aug 2020 23:15:01 -0400
From:   Rodrigo Siqueira <rodrigosiqueiramelo@...il.com>
To:     Sidong Yang <realwakka@...il.com>
Cc:     Haneen Mohammed <hamohammed.sa@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        Rodrigo Siqueira <Rodrigo.Siqueira@....com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        kernel-usp@...glegroups.com
Subject: Re: [PATCH] drm/vkms: Use alpha value to blend values.

Hi Sidong,

Thanks a lot for your patch and effort to improve VKMS.

On 08/18, Sidong Yang wrote:
> I wrote this patch for TODO list in vkms documentation.
> 
> Use alpha value to blend source value and destination value Instead of
> just overwrite with source value.
> 
> Cc: Rodrigo Siqueira <rodrigosiqueiramelo@...il.com>
> Cc: Haneen Mohammed <hamohammed.sa@...il.com>
> 
> Signed-off-by: Sidong Yang <realwakka@...il.com>
> ---
>  drivers/gpu/drm/vkms/vkms_composer.c | 14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/vkms/vkms_composer.c b/drivers/gpu/drm/vkms/vkms_composer.c
> index 4f3b07a32b60..e3230e2a99af 100644
> --- a/drivers/gpu/drm/vkms/vkms_composer.c
> +++ b/drivers/gpu/drm/vkms/vkms_composer.c
> @@ -77,6 +77,9 @@ static void blend(void *vaddr_dst, void *vaddr_src,
>  
>  	for (i = y_src, i_dst = y_dst; i < y_limit; ++i) {
>  		for (j = x_src, j_dst = x_dst; j < x_limit; ++j) {
> +			u8 *src, *dst;
> +			u32 alpha, inv_alpha;
> +
>  			offset_dst = dest_composer->offset
>  				     + (i_dst * dest_composer->pitch)
>  				     + (j_dst++ * dest_composer->cpp);
> @@ -84,8 +87,15 @@ static void blend(void *vaddr_dst, void *vaddr_src,
>  				     + (i * src_composer->pitch)
>  				     + (j * src_composer->cpp);
>  
> -			memcpy(vaddr_dst + offset_dst,
> -			       vaddr_src + offset_src, sizeof(u32));
> +			src = vaddr_src + offset_src;
> +			dst = vaddr_dst + offset_dst;
> +			alpha = src[3] + 1;
> +			inv_alpha = 256 - src[3];
> +			dst[0] = (alpha * src[0] + inv_alpha * dst[0]) >> 8;
> +			dst[1] = (alpha * src[1] + inv_alpha * dst[1]) >> 8;
> +			dst[2] = (alpha * src[2] + inv_alpha * dst[2]) >> 8;

Did you test your change with IGT? Maybe I missed something but looks
like that you're applying the alpha value but the value that we get is
already pre-multiplied.

Btw, It looks like that you and Melissa are working in the same feature,
maybe you two could try to sync for avoiding overlapping.

Finally, do you have plans to send your fix for
vkms_get_vblank_timestamp() function? That patch was really good and
removes a lot of warning generated during the IGT test.

Best Regards

> +			dst[3] = 0xff;
> +
>  		}
>  		i_dst++;
>  	}
> -- 
> 2.17.1
> 

-- 
Rodrigo Siqueira
https://siqueira.tech

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