[Mesa-dev] Sampling DRM_FORMAT_YUYV in GLSL

[Daniel Stone]

Hi Volker,

On 9 May 2017 at 12:32, Volker Vogelhuber
<v.vogelhuber at digitalendoscopy.de> wrote:
> On 09.05.2017 12:59, Philipp Zabel wrote:
>> You create two separate EGLImages, calling eglCreateImage once for each
>> plane. See for example:
>>
>> https://cgit.freedesktop.org/gstreamer/gst-plugins-bad/tree/gst-libs/gst/gl/gstglupload.c#n646
>>
>> or
>>
>> https://cgit.freedesktop.org/wayland/weston/tree/libweston/gl-renderer.c#n1536
>
> That assumes I have two planes available. But as mentioned the planes
> are created internally by dri2_create_image_dma_buf during my call of
> eglCreateImage.
> So from the API point of view I only have one FD from the V4L2 buffer that
> is of type
> FOURCC('Y','U','Y','V'). Passing that FD to eglCreateImage returns only one
> EGLImage.
> Although understanding gstreamer code is always a bit hard, I think in their
> case they have
> a mulit plane V4L2 buffer, where I only have a single plane buffer.

What Philipp is suggesting is that you import the same plane to an
EGLImage twice: once as DRM_FORMAT_RG8 and once as
DRM_FORMAT_ARGB8888. This gives you two EGLImages, which you bind to
two separate texture units / samplers: you sample the Y channel from
the DRM_FORMAT_RG8 image (ignoring the other channel), and you sample
the U and V channels from the DRM_FORMAT_ARGB8888 image (ignoring the
other two channels). This is what GStreamer and Weston do when
confronted with such a buffer, and it does work.

> That's why I wonder if there is a way to retrieve the "second" EGLImage
> after eglCreateImage
> has been called for the single V4L2 DMABUF file descriptor.

There is not a way to do this.

Cheers,
Daniel