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

[Ville Syrjälä]

On Sat, Aug 31, 2019 at 06:25:46PM +0100, Sidong Yang wrote:
> Use alpha value to blend source value and destination value Instead of
> just overwrite with source value.
> 
> Signed-off-by: Sidong Yang <realwakka@xxxxxxxxx>
> ---
>  drivers/gpu/drm/vkms/vkms_composer.c | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/vkms/vkms_composer.c b/drivers/gpu/drm/vkms/vkms_composer.c
> index d5585695c64d..b776185e5cb5 100644
> --- a/drivers/gpu/drm/vkms/vkms_composer.c
> +++ b/drivers/gpu/drm/vkms/vkms_composer.c
> @@ -75,6 +75,9 @@ static void blend(void *vaddr_dst, void *vaddr_src,
>  	int y_limit = y_src + h_dst;
>  	int x_limit = x_src + w_dst;
>  
> +	u8 *src, *dst;
> +	u32 alpha, inv_alpha;

These could all live in a tighter scope.

Apart from that lgtm
Reviewed-by: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>

> +
>  	for (i = y_src, i_dst = y_dst; i < y_limit; ++i) {
>  		for (j = x_src, j_dst = x_dst; j < x_limit; ++j) {
>  			offset_dst = dest_composer->offset
> @@ -84,8 +87,14 @@ 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;
> +			dst[3] = 0xff;
>  		}
>  		i_dst++;
>  	}
> -- 
> 2.20.1
> 
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-- 
Ville Syrjälä
Intel