Psychtoolbox>Screen.{mex*} subfunction

screenNumbers=Screen(‘Screens’ [, physicalDisplays]);

Return an array of screenNumbers, corresponding to available logical or physical
displays.
Please note that the set of reported screens is only refreshed on first
invocation of Screen() after application startup or after a ‘clear all’. If you
replug or en-/disable displays, you must execute ‘clear all’ to force a
redetection of available displays. This is done for efficiency reasons to get
better realtime behaviour.
The meaning/mapping of screenNumbers to physical display devices on different
operating systems differs:
On Linux with X11 X-Server display system, screenNumber 0 - n correspond to
X-Screens 0 - n. As a single X-Screen can have multiple physical displays
assigned, there isn’t a one to one mapping by default. E.g., by default, all
displays are assigned to X-Screen 0, so a multi-display setup will only report
one screenNumber, the number 0. You can define arbitrary mappings with our setup
script XOrgConfCreator, to optimally suit your needs.
If this command is executed on Microsoft Windows in a multi-display
configuration, then the following rule applies: Screen 0 is always the first two
monitors assigned to the Windows desktop. Screens 1 to n are corresponding to
windows display monitors 1 to n. If you want to open an onscreen window only on
one specific display, or you want to query or set the properties of a display
(e.g., framerate, size, color depth or gamma tables), use the screen numbers 1
to n. If you want to open a window suitable for stereo display on a dual display
setup consisting of the first two monitors, use screen zero.
On OSX, numbers 0 - n correspond to logical displays 0 - n. When executed on OSX
with the optional ‘physicalDisplays’ flag set to 1, it will enumerate the set of
physical displays, which can be different from the set of logical displays that
is returned by default. E.g., in mirror mode or clone mode, there is only one
logical display, representing the mirror set of all mirrored physical displays.
This is mostly useful to set, e.g., gamma tables on a per display basis, even if
in mirror mode. Note that according to some user reports, reporting of the true
set of physical displays may have been broken by Apple in current macOS
versions: The set of reported logical and physical displays may be the same even
in mirror mode configurations, due to macOS operating system defects.

###See also: