On 05/09/2017 12:14 PM, Volker Vogelhuber wrote:
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?
IMO that is a big difference as samplerExternalOES does the YUV2RGB
conversion and returns RGB values for you.
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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