[weston] gl-renderer: add support of WL_SHM_FORMAT_YUV420

[Vincent ABRIOU]

Hi Daniel,

Coming back to the asymmetrical subsampling...
I am now able too support NV12 SHM pixel format and you are right about 
the subsampling which is not assymmetrical at all :).
I willl send a new series of patches to support both I420 and NV12 
taking into account your comments.

We can abandon this patch since the new series will come very soon.

Thanks
Vincent

On 08/04/2016 06:03 PM, Vincent Abriou wrote:
> Hi Daniel,
>
> On 08/04/2016 04:32 PM, Daniel Stone wrote:
>> Hi Vincent,
>>
>> On 4 August 2016 at 14:35, Vincent Abriou <vincent.abriou at st.com> wrote:
>>> This patch allow weston to accept WL_SHM_FORMAT_YUV420 buffers.
>>>
>>> In a gstreamer pipeline, the support of the WL_SHM_FORMAT_YUV420 by
>>> weston avoid pixel conversion between software decoders and waylandsink.
>>> Indeed, software decoders output I420 (YUV420 planar) that willYou
>>> match with WL_SHM_FORMAT_YUV420.
>>
>> Thanks for the patch. It would be nice if wl_shm used the same FourCC
>> codes as wl_drm though, i.e. this would be I420 rather than YUV420.
>>
>
> I use the WL_SHM_FORMAT_YUV420 defined in Wayland protocol. It is always
> a mental gymnastics to understand the match. But I don't know how to
> change it except by changing the wayland protocol it self.
>
>> You could save yourself some pain by unconditionally initialising
>> hsub/vsub/offset rather than in every format code though, and also
>
> I will propose a new patch to simplify this.
>
>> perhaps just flatten hsub/vsub into a single field, given that I don't
>> expect we'd support asymmetric subsampling through SHM any time soon.
>
> When I wrote the code, I was thinking about NV12. The 2nd plane UV size
> should be width * (height/2). It is less a component subsampling
> parameters than a plane width and height divider.
>
> Vincent.
>>
>> You should also trim the 'Change-Id' line from your patch, as we don't
>> use Gerrit upstream.
>>
>> Aside from that, looks good to me.
>>
>> Cheers,
>> Daniel
>>