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RetinaDisplay - How to deal with HiDPI “Retina” displays.

On Linux with the standard X11 display system, no special measures are
needed and HiDPI “Retina” displays should just work like regular displays
as far as Psychtoolbox is concerned.

On Apple OSX, Psychtoolbox by default will emulate a standard resolution
display when used on a Retina display to keep old user code working which
was written before the era of Retina displays, or with Psychtoolbox
3.0.11 or earlier versions. If you want to make full use of the native
high resolution of your Retina display, use the imaging pipeline task
PsychImaging(‘AddTask’, ‘General’, ‘UseRetinaResolution’);. This will
expose the full resolution but also require more graphics performance
from your graphics card.

On MS-Windows the situation can be difficult, depending on the Windows
version and Matlab version in use, and potentially on what other
applications are running and their status with respect to HiDPI Retina
displays:

On Windows XP and earlier versions, stuff will just work, but your
application windows will look tiny when displayed on a Retina display.

On Windows Vista and Windows 7, Psychtoolbox disables the DWM (Desktop
Window Manager) by default for fullscreen onscreen windows. This will
ensure optimal display timing precision and avoid Retina display trouble,
essentially turning your system into a Windows XP system. DPI aware
applications will continue to display correctly in such a configuration,
but non DPI aware apps may appear tiny and difficult to use on Retina
displays. All versions of Matlab older than R2015b are not DPI aware and
will likely suffer from this problems.

On Windows 8 and later, Psychtoolbox can not disable the DWM. If you
display a Psychtoolbox window on a standard resolution display, stuff
will probably work. If you try to display on a HiDPI Retina display then
you will need to make sure that you either use GNU/Octave, or you use a
Matlab version that is DPI aware, ie., at least R2015b. You will probably
also have to make sure that no other non-DPI aware application is running
or at least not displaying on your stimulus monitor, as such applications
would trigger use of the DWM and thereby cause stimulus timing problems.

Additionally, on Windows 8 and later you must make sure that the
stimulation display is the designated “primary display”, so DPI settings,
which always apply to the primary display, thereby apply to your stimulus
display. Applications displayed on other than the primary display will be
subject to DWM scaling if those other displays do not have the same DPI
setting as the primary display. A running Matlab or Octave would trigger
harmful use of the DWM on such a non-matching display. In general it is a
good idea for timing precision to make your stimulus display the
designated primary display (this can be set in the display settings
control display, maybe via a “Make this my main display” checkbox).

If you must use a system setup with Retina display and a version of
Matlab, or of Windows 8 or later, that does not allow you to circumvent
or solve these problems, then there exists also the option to either
override Windows DPI settings (somewhere under display control panel,
advanced settings or “Make text appear bigger or smaller” - Try a Google
search to find it) - this would get rid of DPI related timing problems at
the expense of applications that display too small on your Retina
display. Another option is to disable DPI scaling for all applications
(including Matlab!) which are supposed to display on the HiDPI / Retina
display. This will avoid rescaling and triggering the DWM, at the expense
of a too small appearance of those applications GUIs on the Retina
display. You can do this by right-clicking on the applications icon, then
selecting the “Properties” item from the context menu, then selecting the
“Compatibility” tab in the property dialog. In that tab, check the field
called “Disable display scaling on high DPI settings”, then click “OK” to
apply the new settings and restart the application.

See also Psychtoolbox forum message #23414 for another oddity that one user
needed to do to fix HiDPI on a Windows multi-display setup:

https://groups.yahoo.com/neo/groups/PSYCHTOOLBOX/conversations/messages/23414

Windows is not only troublesome for proper visual stimulation and
stimulation timing in itself, it can be especially troublesome when used
with HiDPI / Retina displays. Therefore it might be a good idea to switch
to Linux, or if you have to use Windows, to stick to Windows-7, or if you
have to use a later Windows version, upgrade to Windows 10. It is
probably also a good idea to then limit yourself to a single display
setup and/or make sure that only DPI aware applications are running on
this setup.

Good luck!