Overlay different X screens GTX1080

To get the best result of 4 projectors on a 210° screen they have to overlay.
We have a Linux workstation with 2 GTX1080.

With a splitter it is possible to connect all 4 projectors with on one graphikcard on one X screen, the overlay is working well, but then often there are some very big graphik faults while running a video via Vires VTD.

That’s why we tried to connect only 2 projectors with one graphikcard, but then you get different X screens and we can’t get the video maximized on the whole screen, even if we give the size of the screen to the window.

Are there any solutions?

I don’t fully get your setup, at first, you connected all four projectors to a single 1080 but were using splitters? What kind of splitters/connectors were you using? The 1080 should support four directly connected displays, why didn’t that work?
In your second attempt, did you use only two projectors, or all four but only two per gpu? In that case, you’ll have to enable Mosaic in your xorg.conf to get a single screen.
In screen or device section, set

Option "BaseMosaic" "true"

To have more info, lease run nvidia-bug-report.sh as root and attach the resulting .gz file to your post. Hovering the mouse over an existing post will reveal a paperclip icon.

I’m sorry, forget about the BaseMosaic option, Geforce type cards like the 1080 are limited to three displays in mosaic mode, only Quadro type cards support more.

Thank you for your answer.

Well I just have displayport cables coming down from the projectors and the GTX1080 only has 2 displayports, so I use 2 splitters to connect all 4 projectors. This configurations works, but the shown video sometimes has some faults on the screen. That’s why I thought it’s better to use both GPUs.

The secound setup was with all 4 projectors but only two on each GPU.

I don’t have nvidia -bug-report.sh on my workstation.

Did I got your secound answer right, with this GPUs it won’t work?

Mosaic won’t work with your GPUs, correct.
So for MultiGPU, there’s only Xinerama left, which is old and flakey, might or might not work, depending on software used and use case. You can try but shouldn’t put much time in it if it doesn’t work.
http://download.nvidia.com/XFree86/Linux-x86/340.104/README/xineramaglx.html
The better option IMHO is to use (active) converters or better DP splitters/hubs to connect all four projectors to one 1080.