linux-kernel - Re: [PATCH v11 06/15] drm/vkms: Avoid computing blending limits inside pre_mul_alpha

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Message-ID: <Zv0LBo8OtRHJM029@louis-chauvet-laptop>
Date: Wed, 2 Oct 2024 10:57:42 +0200
From: Louis Chauvet <louis.chauvet@...tlin.com>
To: Randy Dunlap <rdunlap@...radead.org>
Cc: Rodrigo Siqueira <rodrigosiqueiramelo@...il.com>,
	Melissa Wen <melissa.srw@...il.com>,
	Maaara Canal <mairacanal@...eup.net>,
	Haneen Mohammed <hamohammed.sa@...il.com>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	David Airlie <airlied@...il.com>, Jonathan Corbet <corbet@....net>,
	Simona Vetter <simona@...ll.ch>, arthurgrillo@...eup.net,
	pekka.paalanen@...oniitty.fi,
	Simona Vetter <simona.vetter@...ll.ch>,
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
	linux-doc@...r.kernel.org, thomas.petazzoni@...tlin.com,
	jeremie.dautheribes@...tlin.com, miquel.raynal@...tlin.com,
	seanpaul@...gle.com, marcheu@...gle.com, nicolejadeyee@...gle.com,
	Pekka Paalanen <pekka.paalanen@...labora.com>
Subject: Re: [PATCH v11 06/15] drm/vkms: Avoid computing blending limits
 inside pre_mul_alpha_blend

On 01/10/24 - 20:54, Randy Dunlap wrote:
> Hi--
> 
> On 9/30/24 8:31 AM, Louis Chauvet wrote:
> > The pre_mul_alpha_blend is dedicated to blending, so to avoid mixing
> > different concepts (coordinate calculation and color management), extract
> > the x_limit and x_dst computation outside of this helper.
> > It also increases the maintainability by grouping the computation related
> > to coordinates in the same place: the loop in `blend`.
> > 
> > Reviewed-by: Pekka Paalanen <pekka.paalanen@...labora.com>
> > Signed-off-by: Louis Chauvet <louis.chauvet@...tlin.com>
> > ---
> >  drivers/gpu/drm/vkms/vkms_composer.c | 40 +++++++++++++++++-------------------
> >  1 file changed, 19 insertions(+), 21 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/vkms/vkms_composer.c b/drivers/gpu/drm/vkms/vkms_composer.c
> > index 931e214b225c..4d220bbb023c 100644
> > --- a/drivers/gpu/drm/vkms/vkms_composer.c
> > +++ b/drivers/gpu/drm/vkms/vkms_composer.c
> > @@ -24,34 +24,30 @@ static u16 pre_mul_blend_channel(u16 src, u16 dst, u16 alpha)
> >  
> >  /**
> >   * pre_mul_alpha_blend - alpha blending equation
> > - * @frame_info: Source framebuffer's metadata
> >   * @stage_buffer: The line with the pixels from src_plane
> >   * @output_buffer: A line buffer that receives all the blends output
> > + * @x_start: The start offset
> > + * @pixel_count: The number of pixels to blend
> 
> so is this actually pixel count + 1; or
> 
> >   *
> > - * Using the information from the `frame_info`, this blends only the
> > - * necessary pixels from the `stage_buffer` to the `output_buffer`
> > - * using premultiplied blend formula.
> > + * The pixels 0..@...el_count in stage_buffer are blended at @x_start..@...tart+@...el_count in
> 
> should these ranges include a "- 1"?
> Else please explain.

Hi Randy,

For the next version, I will use standard mathematical notation to clarify 
the "inclusiveness" of the interval: [0;pixel_count[

Thanks,
Louis Chauvet
 
> > + * output_buffer.
>