[Libva] [PATCH 6/7] shaders: vpp: gen7: use yuv to rgb matrix to compute rgb values

[Lionel Landwerlin]

On 05/11/15 00:31, Zhao Yakui wrote:
> On 11/04/2015 11:27 PM, Lionel Landwerlin wrote:
>> ---
>>   src/shaders/post_processing/gen7/YUV_to_RGB.g4a   | 626 
>> ++++++++++++----------
>>   src/shaders/post_processing/gen7/pl2_to_rgbx.g75b | 528 
>> +++++++++---------
>>   src/shaders/post_processing/gen7/pl2_to_rgbx.g7b  | 528 
>> +++++++++---------
>>   3 files changed, 909 insertions(+), 773 deletions(-)
>>
>> diff --git a/src/shaders/post_processing/gen7/YUV_to_RGB.g4a 
>> b/src/shaders/post_processing/gen7/YUV_to_RGB.g4a
>> index 24616dc..6af651f 100644
>> --- a/src/shaders/post_processing/gen7/YUV_to_RGB.g4a
>> +++ b/src/shaders/post_processing/gen7/YUV_to_RGB.g4a
>> @@ -386,34 +386,36 @@
>>           mov   (8) fBUFFER_V(0, 0)<1>    r[a0.0, 1]<16;8,2>:ub
>>           mov   (8) fBUFFER_V(1, 0)<1>    r[a0.0, 17]<16;8,2>:ub
>>
>> -    add   (16) fBUFFER_U(0, 0)<1>    fBUFFER_U(0, 0)<8;8,1>    -128.0f
>> -    add   (16) fBUFFER_V(0, 0)<1>    fBUFFER_V(0, 0)<8;8,1>    -128.0f
>
> As far as I know, the value in fBUEER_U/V is still in [0 255] range.
> So I think that it still should be extraced by 128 before it is 
> normalized to [0..1].

Looking at the green component for example, given the following 
coefficients for Y, U and V :

CY = 1.0
CU = -0.344
CV = -0.714

This is what the current shader does :

green = ((Y + (U - 128) * CU + (V - 128) * CV) * 0.0039216) * 255

The shader in this patch does this :

green = (Y * 0.0039216 + (U * 0.0039216 - 128.0 / 255) * CU + (CV * 
0.0039216 - 128.0 / 255) * CV) * 255

This looks equivalent to me given that

128.0 / 255 ~= 128 * 0.0039216

we just distribute the [0..1] normalizing factor earlier.

It's possible to do what you suggest, but it would require more 
instructions.
Maybe I'm missing some precision stuff that is specific to the hardware?

>
>
>> +        mul   (16) fBUFFER_Y(0, 0)<1>      fBUFFER_Y(0, 
>> 0)<1>             0.0039216f
>> +        mul   (16) fBUFFER_U(0, 0)<1>      fBUFFER_U(0, 
>> 0)<1>             0.0039216f
>> +        mul   (16) fBUFFER_V(0, 0)<1>      fBUFFER_V(0, 
>> 0)<1>             0.0039216f
>

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