External DMA to gpu

[Pekka Paalanen]

On Tue, 2 Oct 2018 15:06:14 +0200
Dirk Eibach <dirk.eibach at googlemail.com> wrote:

> Hi Pekka,
> 
> I finally got everything working. I am using gbm_bo_create() and
> gbm_bo_get_fd() to get a buffer that is filled by my grabber. Then I
> use eglCreateImageKHR() and glEGLImageTargetTexture2DOES() to display
> it.

Hi Dirk,

nice to hear!

I suppose that means you still do a copy from the gbm_bo/dmabuf into a
window surface? If you used zwp_linux_dmabuf manually from your Wayland
client, you could avoid even that copy. It has the same caveat as below
though.

> My only problem left is that glEGLImageTargetTexture2DOES() does only
> accept ARGB8888 and not RGB888, which means I have to waste a lot of
> PCIe bandwidth. Any ideas how to get around this? Or what would be a
> more appropriate place to post this question?

Yeah, I suppose support for true 24-bit-storage formats is rare
nowadays.

The format list advertised via zwp_linux_dmabuf, visible via e.g.
weston-info, can tell you what you could use directly. After all, a
Wayland compositor does the same EGLImage import as you do in the
simple case.

You could probably use the GPU to convert from 24-bit to 32-bit format
though, by importing the image as R8 format instead of RGB888 and
pretend the width is 3x. Then you could use a fragment shader to sample
the real R, G and B separately and write out a 32-bit format image for
display.


Thanks,
pq
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