devcontainer, how to make X display work (mount graphics inside docker in visual studio code)

Normally I use this trick to make X work inside docker:

docker run --rm -it -v /tmp/.X11-unix:/tmp/.X11-unix -v $HOME/Videos:/videos -e DISPLAY=unix$DISPLAY --name knl kdenlive

I tried doing the same on a devcontainer:

{
    "name": "example_dockerized_environment",
    "dockerFile": "Dockerfile",
    "extensions": [
        "ms-vscode.cpptools",
        "twxs.cmake",
        "eamodio.gitlens"
    ],
    "mounts": [ "source=../,target=/home/project", "source=/tmp/.X11-unix, target=/tmp/.X11-unix"],
    "containerEnv": {
        "DISPLAY": "unix:0"
    },
    "runArgs": ["--privileged"]
}

As you can see, I passed unix$DISPLAY and also mounted X11-unix

But I get

root@5e6a10efbea6:/workspaces/leuze_lidar_volume/sdk/quanergy_client-master# ./visualizer --host localhost
ERROR: In /build/vtk6-YpT4yb/vtk6-6.2.0+dfsg1/Rendering/OpenGL/vtkXOpenGLRenderWindow.cxx, line 1466
vtkXOpenGLRenderWindow (0x2293740): bad X server connection. DISPLAY=Aborted (core dumped)

When I do echo $DISPLAY inside docker I see nothing. I tried doing

export DISPLAY=unix:0 then I get

root@5e6a10efbea6:/workspaces/leuze_lidar_volume/sdk/quanergy_client-master# ./visualizer --host localhost
ERROR: In /build/vtk6-YpT4yb/vtk6-6.2.0+dfsg1/Rendering/OpenGL/vtkXOpenGLRenderWindow.cxx, line 1466
vtkXOpenGLRenderWindow (0x281dcf0): bad X server connection. DISPLAY=unix:0. Aborting.


Aborted (core dumped)

I also see no /tmp.x11-unix inside the container:

root@5e6a10efbea6:/tmp# ls -la /tmp 
total 16
drwxrwxrwt 1 root root 4096 Mar 18 03:47 .
drwxr-xr-x 1 root root 4096 Mar 18 03:45 ..
srwxr-xr-x 1 root root    0 Mar 18 03:42 vscode-git-askpass-c2ca47727522d7940b4cce1d99fcc88d32ccfefc.sock
srwxr-xr-x 1 root root    0 Mar 18 03:47 vscode-git-ipc-f52b0dbfd870db22481ea656170b7615ea1e6497.sock
srwxr-xr-x 1 root root    0 Mar 18 03:45 vscode-ipc-032f3099-16ea-4f5d-8561-586571a4aea9.sock
srwxr-xr-x 1 root root    0 Mar 18 03:32 vscode-ipc-425af2fc-ddb1-4554-b93b-3a5bede4c52d.sock
srwxr-xr-x 1 root root    0 Mar 18 03:47 vscode-ipc-58739ccc-fb7d-4289-808e-21d31c703d1a.sock
srwxr-xr-x 1 root root    0 Mar 18 03:42 vscode-ipc-aa7aed50-92e4-4b2b-b17e-d70c1bba595e.sock
-rw-r--r-- 1 root root 2342 Mar 18 03:46 vscode-remote-containers-6a199ce05d20a43a350860289798f388414d648c.js
srwxr-xr-x 1 root root    0 Mar 18 03:46 vscode-remote-containers-ipc-6a199ce05d20a43a350860289798f388414d648c.sock
srwxr-xr-x 1 root root    0 Mar 18 03:46 vscode-ssh-auth-6a199ce05d20a43a350860289798f388414d648c.sock
drwxr-xr-x 2 root root 4096 Mar 18 03:46 vscode-typescript0
root@5e6a10efbea6:/tmp# 

this works:

{
    "name": "my_docker_environment",
    "dockerFile": "Dockerfile",
    "extensions": [
        "ms-vscode.cpptools",
        "twxs.cmake",
        "eamodio.gitlens",
        "ms-vscode.cmake-tools"
    ],
    "containerEnv": {
        "DISPLAY": "unix:0"
    },
    "mounts": [
        "source=/tmp/.X11-unix,target=/tmp/.X11-unix,type=bind,consistency=cached"
      ],
    "runArgs": ["--privileged"]
}

I don't recall if "runArgs": ["--privileged"] is needed but I guess no

You migth need to do

xhost local:root

on a terminal on the host before launching your app