Using DMA buffer with QtWayland

[nedo99]

Hi,

I have built the Qt 6.4.0 from the sources and would like to run a wayland using DMA buffers, so not waylang-egl using QT_WAYLAND_CLIENT_BUFFER_INTEGRATION env variable like explained here: https://code.qt.io/cgit/qt/qtwayland.git/tree/README.

The error message I get when I set QT_WAYLAND_CLIENT_BUFFER_INTEGRATION=linux-dmabuf-unstable-v1 is that linux-dmabuf-unstable-v1 is not available, only waylang-egl.

I see that plugin is built as QT_FEATURE_wayland_dmabuf_client_buffer is set to 1 and running cmake on qtwayland module shows that dma libraries are detected:

Qt Wayland Drivers:
  EGL .................................... yes
  Raspberry Pi ........................... no
  DRM EGL ................................ yes
  libhybris EGL .......................... no
  Linux dma-buf server buffer integration  yes
  Shm emulation server buffer integration  yes
  Vulkan-based server buffer integration . no

Am I missing something or the approach, in this case, is wrong?

Looking forward to your reply.

Regards,
Nedim

[cordlandwehr]

Hi, I just checked on my Yocto development setup with Qt 6.4 that linux-dmabuf works as expected. So, I think we have to figure out where your configuration differs from mine. My compositor is started with

$> QT_WAYLAND_CLIENT_BUFFER_INTEGRATION=linux-dmabuf-unstable-v1 XDG_RUNTIME_DIR=/var/run qmlscene Compositor.qml -platform eglfs

which should be all that is needed to enable linux-dmabuf. The client test application is started with

$> XDG_RUNTIME_DIR=/var/run qmlscene Client.qml -platform wayland-egl

When now also setting WAYLAND_DEBUG=1, all the nice infos about "zwp_linux_dmabuf_v1..." are printed, so the protocol is definitely enabled.

Looking at the QtWayland config output, I see the very same summary

Qt Wayland Drivers:
  EGL .................................... yes
  Raspberry Pi ........................... no
  DRM EGL ................................ yes
  libhybris EGL .......................... no
  Linux dma-buf server buffer integration  yes
  Shm emulation server buffer integration  yes
  Vulkan-based server buffer integration . no

Thus, I expect that there is something wrong with your compositor startup. Can you check that the compositor is started the same way as noted above?