Dual 3.5" screen with Retropie (not mirrored images)

Hello,

So I'm trying to create this portable gaming system with a raspberry pie using the retropie emulator, but one requisite for it to work as I'd like is to have 2 different 3.5" screens showing different parts of the actual game total image.

For example I'd like to use the MAME emulator on the Retropie with Game and Watch emulator. The emulator shows one image where you can see both screens of the game and watch (on game and watch models that require 2 screens) but instead of having only one screen connected to the raspberry pie, I want to have 2 screens and spit the image, half goes on one screen and the other on another screen. And not only that, I'd like to crop exactly what part of the image I want to go on each screen.

Is this even possible??

Thanks for your help

shabaz over 2 years ago

Hi,

I think it would be possible, but would entail writing your own device driver (which has a learning curve), unless you get lucky and find a project where someone has already done the work (I'm not aware of any).

There are two discussions here concerning device drivers, so you can start seeing what sort of thing would be required:

Is there a way to incorporate Linux hardware drivers into Python projects on SBC's?

Calling embedded Linux kernel experts - how do you build a loadable kernel module from the Linux kernel driver repo

It would need a reasonably competent software engineer, because they would have to troubleshoot as they go (since there are not many 100% working tutorials on the device driver topic either, let alone even single display related).
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feiticeir0 over 2 years ago

I know that you can have two screens connected to the Raspberry PI 4, with an expanded desktop.

Don't know if retropie even supports this - probably check on their forums.

Regarding cropping the screen exactly where you want... That's another story.

If you find any solution, please share it here. Always love to see some challenges.
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shabaz over 2 years ago in reply to feiticeir0

Cropping would be easy for a device driver, since it will merely read half (or a configurable value) of the framebuffer for driving one 3.5" TFT, and read the other half for driving the other 3.5" TFT, and the application would not be aware that the content was being split and directed to two screens.

However, creating the device driver is unfortunately a task that has a learning curve : (
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cstanton over 2 years ago

rictrajano , which model of Raspberry Pi you're using for this matters greatly, as the Raspberry Pi 4 for example has two HDMI outputs you could use for this depending on the size of display you're wanting to use, you say 3.5" so you may struggle with using that in such a size but it's not impossible.

Previous models of Raspberry Pi will require some messing around with different types of screens from what I remember.
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shabaz over 2 years ago

By coincidence just saw this, linked to a Hackady article today:

https://www.youtube.com/watch?v=x1Y203vH-Dc&list=PLCGpd0Do5-I3b5TtyqeF1UdyD4C-S-dMa

It is a 30-episode video series walking through how to write a device driver.

I would say, if you can follow that, then by the end of it, it shouldn't be too hard to code a driver that can (say) drive a couple of SPI interfaced LCD screens, each one displaying part of the framebuffer.

However, the series contains many hours of video overall. You'd have to really want to do it, to sit through that. (Useful employable skill though, if it fits your desired career path).
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