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Re: Debian with HiDPI / 4K displays

On 08/08/2015 01:58 PM, Daniel Pocock wrote:

I recently started using a 4K display with Debian jessie and GNOME shell

The hardware setup was quite straightforward as I chose to buy a new

There is also an understated problem - DPI changing during a session, or even different monitors having different DPI in a multihead situation.

This seems to be particularly poorly supported, but is rather common.  My laptop is 1920x1080 in a 12.5" display, with approximately 176DPI.  The external monitor on its docking station is a more conventional DPI.

There are many questions here:

  • Simplest: When I use one monitor at the time, does the OS do the right thing with the only enabled display device changes to a device with a different DPI?  (No, it doesn't; there is no automatic DPI changing.)
  • Then: Does the OS do the right thing when there are two non-mirrored devices with differing DPIs?  (Not really)
  • Does the OS do the right thing when a connected device changes configured resolution, changing DPI?
  • Finally: Does the OS do the right thing when a display is mirrored across two devices with diverging DPIs?  What even IS the right thing here?  Probably stick with the DPI of the device that got in "first".  But what is that device when both an internal and external display are connected at boot?
(Note: DE here is XFCE)

There are many things that seem to not handle differences in DPI.  Fonts are just the start.  What about taskbars and taskbar icons, which become tiny at certain DPIs?  We seem to be using pixel heights in these a lot.


graphics card with 4K support and a relatively new monitor.  The
graphics card and monitor both support DisplayPort 1.2 so I just hook
them up with the standard cable.

The graphics card vendor supplies a proprietary driver but everything
else is currently running using the packages from jessie.

However, I've come up against the DPI issues.

The actual DPI is about 131x137 on a 32" display.

xdpyinfo reports 96x96

It looks like there has been a history of bug reports about DPI in both
the Xorg server itself and some individual applications.

Some web sites suggested using gnome-tweak-tool to change the window
scaling factor.  It only appears to accept integer values and changing
it from the default of 1 to 2 makes the fonts too big.

So, is there any strategy for HiDPI with Debian?  Is a BTS tag needed to
track such issues perhaps?  Or is it already dealt with in unstable and
people just have to wait for it?

My general feeling is that the 32" 4K display was a worthwhile purchase
and it definitely lets me improve my workflow.  For example, I can now
have all my communication tools (Icedove, IRC and others) arranged in a
single virtual desktop, none of them overlap each other and I don't have
to use alt-tab to switch between them.  In another virtual desktop I no
longer need to run Eclipse at full screen, I can just give it two thirds
of the screen and use the rest for testing things.  However, all fonts
are really tiny, they are readable and even pleasant to look at but I
would probably like to see them just a little bigger.



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