kivy(sdl2) + x11vnc + headless

[Sato Takenori]

Hi,

Let me share what I have found in the context of the title.

I have developed a system to analyze road traffic with our own box,

which is placed outside, and based on Jetson TX2.

For various settings, the system's GUI is build with kivy.

And I have tested ways to manage the kivy app remotely(vnc).

Here're my findings.

1. in general, vnc operates on its own display(:x), and execute a X command remotely

2. in general, vnc executes even OpenGL command remotely

3. to fix 1 and 2, VirtualGL could be used

4. or take a different approach like x11vnc, which can operate on :0

5. 4 works(e.g. glxgears) even without attaching a physical monitor (the latest L4T comes with the following option in xorg.conf by default)

# Allow X server to be started even if no display devices are connected.

    Option      "AllowEmptyInitialConfiguration" "true"

6. but kivy won't work in 4 with the error "no available displays"

7. as below, SDL2(2.0.4~) checks if a physical display is available with xrandr

https://github.com/spurious/SDL-mirror/blob/b00ee82424a5a8198e2556f960e8a09bfe584b26/src/video/x11/SDL_x11modes.c#L498

8. some people in the Steam community say SDL2 had worked before(<= 2.0.0), but not today

9. there are many cheap HDMI dongle available, so which is ugly to use outside, but a possible workaround

I am not 100% sure, though. 

I would appreciate if you correct something wrong.

Thanks!