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

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Message-ID: <Zv1wz-TNT36McwXp@louis-chauvet-laptop>
Date: Wed, 2 Oct 2024 18:11:59 +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 02/10/24 - 08:49, Randy Dunlap wrote:
> Hi Louis,
> 
> On 10/2/24 1:57 AM, Louis Chauvet wrote:
> > 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[
> 
> Hm, I can read that after a second or two.
> 
> My math classes always used:  [0,pixel_count)
> for that range, and that is what most of the internet says as well.

I'm french, and we use ]a;b[ notation at school :-)

Both are valids according to ISO80000-2, but I will change it for the next 
revision.
 
> or you could just stick with
>   The pixels from 0 through @pixel_count - 1 in stage_buffer are blended at @x_start
>   through @x_start through @x_start + @pixel_count - 1.
> 
> but after writing all of that, I think using range notation is better.

I also prefer ranges, way shorter to write, and easier to understand at 
first sight. 

> thanks.