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

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Message-ID: <9886cf09-8886-4757-86ca-f5e724d1cd88@infradead.org>
Date: Wed, 2 Oct 2024 09:37:01 -0700
From: Randy Dunlap <rdunlap@...radead.org>
To: 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 10/2/24 9:11 AM, Louis Chauvet wrote:
> 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 :-)

The one reference that I found to that notation was to a French author.
> 
> 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. 

Yes, thanks.