[Mesa-dev] Sampling DRM_FORMAT_YUYV in GLSL

[Volker Vogelhuber]

Hi,

first sorry, for missing the subject in my mail to the mailing list, 
then thanks
for the hint with the "ext_image_dma_buf_import-sample_yuv". Unfortunately
things don't become clearer. In the samples as far as I can see, there 
is also
only one sampler defined in the shader. So how are the different planes 
accessed
in the shader? In the example only a simple copy is done:
gl_FragColor = texture2D(sampler, texcoords);
In the comment in intel_screen.c it says:

/* For YUYV buffers, we set up two overlapping DRI images and treat
     * them as planar buffers in the compositors.  Plane 0 is GR88 and
     * samples YU or YV pairs and places Y into the R component, while
     * plane 1 is ARGB and samples YUYV clusters and places pairs and
     * places U into the G component and V into A.  This lets the
     * texture sampler interpolate the Y components correctly when
     * sampling from plane 0, and interpolate U and V correctly when
     * sampling from plane 1. */

So how are the pixels transfered from the YUYV memory to the vec4 in the 
shader?
Do I have to calculate the chroma values by interpolating myself based 
on the
current texture coordinate? Or is it done automatically in some way? From my
experience the texture call only returns the values from plane0 which 
leads me to the
suspicion that I have to interpolate myself. But why is there then the 
plane 1 which
don't seem to be accessible in the shader?

BTW: I'm using the OES_EGL_image extension not the 
OES_EGL_image_external, so my
sampler is sampler2D not samplerExternalOES but that shouldn't make a 
difference should it?
And I use "texture" instead of "texture2D" because I'm on OpenGL 3.3, 
but that does not seem
to cause any differences.

On 09.05.2017 06:37, Tapani Pälli wrote:
> Hi;
>
> Take a look at Piglit test "ext_image_dma_buf_import-sample_yuv", 
> (https://cgit.freedesktop.org/piglit). Test creates EGLImage from dma 
> buf, binds to a texture and then samples this in a shader with 
> samplerExternalOES type from GL_OES_EGL_image_external extension.
>
>
> On 05/09/2017 01:57 AM, Volker Vogelhuber wrote:
>> I'm currently trying to render a V4L2 image with OpenGL
>> on an Intel Apollo Lake using Linux 4.10 and Mesa 13.
>> Supprisingly I noticed that importing a DMABUF with format
>> DRM_FORMAT_YUYV into OpenGL using
>>    eglCreateImage/glEGLImageTargetTexture2DOES
>> worked out of the box. But I noticed that there seem to be a split into
>> two textures when importing the buffer. At least the nplanes
>> variable in the __DRIimage's planar_format is set to 2 and in the
>> intel_screen.c there is a comment for __DRI_IMAGE_FOURCC_YUYV:
>> "For YUYV buffers, we set up two overlapping DRI images
>>    and treat them as planar buffers in the compositors."
>> So far so good, but how do I access the second texture in the GLSL
>> shader. I only created one texture object before calling
>> glEGLImageTargetTexture2DOES with the EGLImage I got from
>> eglCreateImage. And using the GLSL function texture( source, texCoord 
>> ) on this
>> texture samples only the Y and U channel, what seems obvious
>> as the first plane's texture is created as GL_RG texture.
>> Can anyone explain to me, how one accesses the second plane.
>> And if there is an example somewhere how the two planes
>> have to be sampled to convert the values back to RGB, it would
>> be nice if someone can send a link to such an example.
>>
>> Thanks
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>> mesa-dev at lists.freedesktop.org
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>>