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Windows 8.1 multi-DPI broken w/ Crimson

Question asked by orcinus on May 7, 2016
Latest reply on May 7, 2016 by orcinus

Previous NVIDIA user, switched to a Fury X recently.

My setup on both consists of the following:

- R9 Fury X

- 1 HD monitor (BenQ XL2420T)

- 1 4K monitor (Dell UP2414Q)

- Windows 8.1


The HD monitor is the primary, 4K monitor is the secondary.

It's an MST monitor, so is configured as an Eyefinity group (that's the only way to get it to work on a Radeon, on NVIDIA cards it's recognized as a two-stream monitor automatically and behaves as a single screen without additional configuration).


With a setup such as this, Windows 8.1 recognizes the screens have completely different physical resolutions (DPI) and adjusts the scaling appropriately - e.g. if the system scaling is set to 100%, it will automatically apply 100% to the HD monitor and 180% to the 4K monitor, so the physical size of the on-screen elements (where supported) retains the same *physical* size.


In other words, if you drag a window from the HD monitor to the 4K monitor, it will scale the window up, so it appears the same *physical* size on both.


This is not an NVIDIA feature, this is a Windows feature. It's fully automatic and cannot be tweaked manually.

It relies on detection of the monitor's physical size (i assume via EDID) and some hard-coded look up tables that round up to the nearest scale factor.


This feature, however, appears completely and utterly broken on Crimson (at least, haven't rolled back as far as Catalyst) - as in, dead, non-functional, kaput, inoperative. The 4K screen always retains the *exact same* scaling as the HD screen. My hunch tells me this has something to do with Eyefinity - i.e. it somehow fudges up the EDID and Windows see it as either the wrong physical size, or the wrong *reported* resolution.


This, allegedly, works fine on Windows 10, but it's irrelevant there, as on Windows 10, you can tweak the scaling for each screen independently.

You *cannot* do that on Windows 8.1. It's always automatic. Upgrading to Windows 10 is not an option for me, do not suggest it, do not ask why. It just isn't.


That said, any other suggestions on how to rectify this are very welcome