Hi Stéphane,
it is great to see that my problems are finally reproduceable by someone else 😉.
I did not describe it in details, but my PSX image was also shifted and scaled, so we share the same misbehaviour with our dual-screen setup.
Maybe this is an interesting finding - I just found it in Recalbox´s initrc:
# to disable a video output (multi-screen setup) and prevent ES to be stretcht on all screens,
# uncomment the line below, and replace output_name by the output that you want disable on ES start
# xrandr --output output_name --off
I need to try this out with Batocera…
EDIT: Adding xrandr --output DVI-D-1
to the xinitrc did not help here. With DVI-D-1 disconnected, ES still does not show up on my CRT, but clicking twice on the “B” button of the gamepad indeed starts an emulator, and this is being shown on the CRT.
And the PSX scaling also is still wrong, even though xrandr outputs the correct resolutions. And when I connect DVI-D-1, the image is being shown on both screens even when I had DVI-D-1 disabled via xrandr before. Changing the monitor index in the RetroArch settings also does not help - maybe it is also a core issue in this case because enabling overscan in the core settings is not being saved?
However, suprisingly, exiting RetroArch then shows (!) the EmulationStation menu, but it is shifted/scaled.
So it looks to me that there is something wrong with the X configuration or the drivers.
BTW.: Haven´t spoken french since school, so I needed to translate the other thread with Google translate - and unfortunately got only difficult-to-understand results. However, I read that you want to get a test image like you posted above. Quite easy: Create the appropriate image (e.g. 640×480 or 768×576), start Kodi and use the built-in image viewer. Regarding the VGA–RGB converter: Since it worked flawless with Batocera 5.26 and older cards, this also looks more like an X or kernel/driver issue to me.
Joerg