I've tracked down the origin of the 16384 limit. It's a combination of:
* Xorg treating all monitors as a single framebuffer; and
* The modesetting driver getting the maximum dimensions from the kernel via
drmModeResPtr; and
* The Intel kernel graphics driver limiting framebuffer sizes to 16384. This
Intel limitation is unavoidable if you want to use the laptop screen as part of
your desktop.
You can also see it in the log:
modeset(0): Allocate new frame buffer 16384x...
So I have a couple of suggestions for getting around it:
* Use a lower scaling factor or the default of 100%; or
* Remove one monitor from the system
** Changed in: mutter (Ubuntu)
Status: New => Invalid
** Also affects: xorg-server (Ubuntu)
Importance: Undecided
Status: New
** Changed in: xorg-server (Ubuntu)
Status: New => Won't Fix
** Also affects: linux (Ubuntu)
Importance: Undecided
Status: New
** Changed in: linux (Ubuntu)
Status: New => Opinion
** Summary changed:
- Triple 4K monitor setup with fractional scaling truncated
+ Xorg Triple 4K monitor setup with fractional scaling truncated at 16384 pixels
** Summary changed:
- Xorg Triple 4K monitor setup with fractional scaling truncated at 16384 pixels
+ Xorg multi-monitor setup truncated at 16384 pixels
** Tags added: multimonitor
** Tags added: hybrid i915 nvidia
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https://bugs.launchpad.net/bugs/2017323
Title:
Xorg multi-monitor setup truncated at 16384 pixels
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