Re: [PATCH v11 06/15] drm/vkms: Avoid computing blending limits inside pre_mul_alpha_blend

[Randy Dunlap <rdunlap@infradead.org>]

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@collabora.com>
>>> Signed-off-by: Louis Chauvet <louis.chauvet@bootlin.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..@pixel_count in stage_buffer are blended at @x_start..@x_start+@pixel_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.

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.

thanks.