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

[Randy Dunlap]

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@xxxxxxxxxxxxx>
>>>>> Signed-off-by: Louis Chauvet <louis.chauvet@xxxxxxxxxxx>
>>>>> ---
>>>>>  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.
> 
> 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.