@iandaemon Not exactly. An arcade cocktail table and I installed dual monitors in them with a Raspberry Pi 4. My plan B is to use a VGA or HDMI splitter but I'd like to see if can be done with the dual HDMI outputs already available on the Raspberry Pi 4. Any ideas?

@red732 a shader could do this. eg: https://github.com/libretro/glsl-shaders/blob/master/misc/flip-horizontal.glsl

any arcade game that was available in such a cabinet probably has a system option to run it in a flipped mode - maybe in the service menu or dip switches. eg https://retropie.org.uk/docs/lr-mame2003/#service-menu

I'm just waiting for gamers to visit and play this cabinet as 2p.

I don't think mirroring would work, since the displays are of different resolutions. I think you can make the HDMI the primary display by adding display_default_lcd=0 to the config.txt, so if HDMI is detected, then the primary output would be switched to it.

@grant2258 Top post explains it a bit more. I can already get the game flipped on a CRT TV. I can't get Emulation Station flipped too. Flipped to work if viewed in a mirror.

@dankcushions said in RetroArch Mirror Mode:

is an ES issue? presumably once you've loaded the game, it's now a game issue. there doesn't seem much point in fixing it in ES if there's no a solution for the games as well. never mind if you load the command prompt/retropie-setup menu...

With HDMI, you can flip the screen horizontally (and I think vertically), to give an image of everything that will look the right-way around when viewed in a mirror.

With component/SCART output suitable for a CRT TV, you can use a RetroArch shader to get the image flipped and rotated so it works perfectly in a mirror too (see this forum post). This is good, but obviously, all the menus, the screensaver (easier to fix) and general RetroPie/ES menus are the wrong way around. It would be very nice to find a fix for that last piece of the puzzle.

@HorseWithForce said in RetroPie Screen Mirroring / Streaming / Casting:

Also the Retro Pi emulation wont start cause it tells me no display connected...

That's probably the reason why it's not working - there's no video device initialized. You didn't mention which Pi model are you using, but as a general solution, configure a video mode in /boot/config.txt and set hdmi_force_hotplug=1 as-well so that display detection is skipped.

As for using the solution on the RaspiOS Bullseye, it will not work due to the fact that the MMAL/DispmanX API is no longer supported with the new KMS ARM driver.

Just out of curiosity, why are you trying to use this solution, if you don't have a display attached to the Pi ? Wouldn't it be easier to install the emulators on your PC/Phone to play ?

@jonnykesh
Yes, I think providing the beta on the official site (the only source of retropie images for new users) could be a good idea, of course with a statement like
If you're using a Pi 3B+, a Stretch based image is necessary. Here is a compatible beta/RC image of retropie, use it at your own risks, and please report eventual bugs on the forum. Final image coming soon
It would (I think) avoid a lot of disappointment for new users with 3B+, as well as a big load of new similar topics here :)
It could also involve more people in beta testing, and thus help to stabilize the image.
Again, it's just my personal point of view.
I use Stretch image for 2 months now without major issue, and I assure you I've seen a huge lot of far less polished commercial (and furthermore expensive) products hitting GA :)

@TMNTturtlguy Well thankfully it was okay, my only irrational is that the mirror I use does go down sometimes, anyway I can check my mirror status or change my mirror in ssh?

@roquen probably not possible.

Do you want this for a console (NES, Genesis, Atari), or an arcade game (MAME, FBA)? If for a console, the answer is no. If for an arcade, the answer is maybe. Some arcade games utilized multiple screens for display, like the 6-player X-Men game. However those two screens were utilized by all players, not just one screen per player.

If you want to have one screen for one player and another screen for another player whole playing the same game, you should look into Retroarch Net Play. You'll need two RaspberryPi's, and they'll need to be connected to each other and then you can play over the network using two setups.

Actually, scratch that. You could just get an HDMI splitter and split the signal from the RaspberryPi. That way you don't have to fiddle with Net Play, but you get two screens with the same game being played​.