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

[Sidong Yang <realwakka@gmail.com>]

On Mon, Aug 24, 2020 at 11:15:01PM -0400, Rodrigo Siqueira wrote:
> 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@gmail.com>
> > Cc: Haneen Mohammed <hamohammed.sa@gmail.com>
> > 
> > Signed-off-by: Sidong Yang <realwakka@gmail.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;
> 

Hi, Rodrigo!

> 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.

Thanks for review.
Yes, this patch should be dropped and I should watch Melissa's patch.

> 
> 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.

Okay, I'll work for improve vkms_get_vblank_timestamp().
Thank you so much.

Sincerely,
-Sidong

> 
> Best Regards
> 
> > +			dst[3] = 0xff;
> > +
> >  		}
> >  		i_dst++;
> >  	}
> > -- 
> > 2.17.1
> > 
> 
> -- 
> Rodrigo Siqueira
> https://siqueira.tech