Re: [PATCH/RFC 1/2] v4l: Add a global color alpha control

[Sylwester Nawrocki <s.nawrocki@samsung.com>]

Hi Laurent,

On 11/25/2011 01:57 PM, Laurent Pinchart wrote:
> On Thursday 24 November 2011 16:53:12 Sylwester Nawrocki wrote:
>> On 11/24/2011 03:00 PM, Laurent Pinchart wrote:
>>> On Thursday 24 November 2011 13:22:10 Hans Verkuil wrote:
>>>> On Thursday, November 24, 2011 13:06:09 Laurent Pinchart wrote:
>>>>> On Thursday 24 November 2011 12:49:00 Hans Verkuil wrote:
>>>>>> On Thursday, November 24, 2011 12:39:54 Sylwester Nawrocki wrote:
>>>>>>> On 11/24/2011 12:09 PM, Laurent Pinchart wrote:
>>>>>>>> On Thursday 24 November 2011 12:00:45 Hans Verkuil wrote:
>>>>>>>>> On Thursday, November 24, 2011 11:53:16 Sylwester Nawrocki wrote:
>>>> Well, if that's the case, then we already have an API for that
>>>> (http://hverkuil.home.xs4all.nl/spec/media.html#v4l2-window, field
>>>> global_alpha).
>>>>
>>>> It was my understanding that this is used with a mem2mem device where
>>>> you just want to fill in the alpha channel to the desired value. It's
>>>> not used inside the device at all (that happens later in the pipeline).
>>>
>>> OK, now I understand. Maybe the documentation should describe this a bit
>>> more explicitly ?
>>
>> I've modified the control description so now it is:
>>
>> V4L2_CID_ALPHA_COMPONENT
>> integer
>>
> 
> What about clarifying it further with something like
> 
> "When a mem-to-mem device produces a frame format that includes an alpha 
> component (e.g. _packed RGB image_ formats), the alpha value is not defined by 
> the mem-to-mem input data. This control lets you select the alpha component 
> value of all pixels in such a case. It is applicable to any pixel format that 
> contains an alpha component."

Thanks for the help. Since there are also mem-to-mem devices that account an input 
alpha when producing an output frame (e.g. S5P SoC G2D IP block supports alpha 
blending), I would change that to:


 "When a mem-to-mem device produces a frame format that includes an alpha 
 component (e.g. _packed RGB image_ formats) and the alpha value is not defined by 
 the mem-to-mem input data this control lets you select the alpha component 
 value of all pixels. It is applicable to any pixel format that contains an alpha
 component."

OR

 "When data format of a frame produced by a mem-to-mem device includes an alpha 
 component (e.g. _packed RGB image_ formats) and the alpha value is not defined
 by the mem-to-mem input data this control lets you select the alpha component
 value of all pixels. The control is applicable to any pixel format that contains
 an alpha component."

How do you think ?

> 
>> And the part below Table 2.6
>>
>> Bit 7 is the most significant bit. The value of a = alpha bits is undefined
>> when reading from the driver, ignored when writing to the driver, except
>> when alpha blending has been negotiated for a Video Overlay or Video
>> Output Overlay or when alpha component has been configured for a Video
>> Capture by means of V4L2_CID_ALPHA_COMPONENT control.
 
--
Thanks,
Sylwester