[ale] Raspian Screen Duplicating - How Hard Can It Be?

[Alex Carver]

Answering in reverse, if your projector and TV will have different 
resolutions then nothing is going to save you short of just making the 
Pi display at the lowest resolution of the two devices.

Simplest solution is an actual HDMI splitter and then you don't have to 
think about it.

But you can run this to get the current displays:
xrandr --current

Some posts suggest you can use the graphical screen setup tool (Screen 
Layout Editor) to overlap the monitors which will result in sharing 
content. Drag one monitor over the top of the other.


On 2024-01-01 12:48, Neal Rhodes via Ale wrote:
> 
> 
> Trying to stay retired, but a fella can't never get totally away from 
> the sea....
> 
> Needing to setup a PI 4B to simply display words for an Irish Pub Night 
> to both the onboard HDMI outputs.   One will go to a projector; the 
> other to a 40" TV.  Both HDMI.      Both need to stay in Sync.
> 
> I'm testing it now on a pair of 1920x1080 HDMI monitors. Both work fine 
> as independent monitors.
> 
> My notes on how to do this came from Bing AI, courtesy of Raspian 
> Forums, and seemed pretty simple:
> 
> Y_es, you can make both HDMI outputs on a Raspberry Pi 4 have the same 
> output on Raspbian. Here are the steps:_
> _ _
> _Use the xrandr command to mirror the displays1. Replace <projector> and 
> <desktop> with your display names:_
> _xrandr --output <projector> --same-as <desktop>_
> _In the example provided in the forum, <projector> was HDMI-2, and 
> <desktop> was HDMI-11._
> _To check the display names, run the following command when both 
> displays are attached1:_
> _xrandr --current_
> _ _
> _Please note that these steps should work by default on Raspberry Pi OS, 
> Bullseye2. If you encounter any issues, please let me know! I'm here to 
> help._
> 
> Alas, it ain't working.
> 
> eal at raspberrypi:~ $ xrandr
> Screen 0: minimum 16 x 16, current 3840 x 1080, maximum 32767 x 32767
> XWAYLAND0 connected 1920x1080+0+0 (normal left inverted right x axis y 
> axis) 510mm x 290mm
>     1920x1080     59.96*+
>     1440x1080     59.99
>     1400x1050     59.98
>     1280x1024     59.89
>     1280x960      59.94
>     1152x864      59.96
>     1024x768      59.92
>     800x600       59.86
>     640x480       59.38
>     320x240       59.52
>     1680x1050     59.95
>     1440x900      59.89
>     1280x800      59.81
>     720x480       59.71
>     640x400       59.95
>     320x200       58.96
>     1600x900      59.95
>     1368x768      59.88
>     1280x720      59.86
>     1024x576      59.90
>     864x486       59.92
>     720x400       59.55
>     640x350       59.77
> XWAYLAND1 connected 1920x1080+1920+0 (normal left inverted right x axis 
> y axis) 520mm x 290mm
>     1920x1080     59.96*+
>     1440x1080     59.99
>     1400x1050     59.98
>     1280x1024     59.89
>     1280x960      59.94
>     1152x864      59.96
>     1024x768      59.92
>     800x600       59.86
>     640x480       59.38
>     320x240       59.52
>     1680x1050     59.95
>     1440x900      59.89
>     1280x800      59.81
>     720x480       59.71
>     640x400       59.95
>     320x200       58.96
>     1600x900      59.95
>     1368x768      59.88
>     1280x720      59.86
>     1024x576      59.90
>     864x486       59.92
>     720x400       59.55
>     640x350       59.77
> neal at raspberrypi:~ $ xrandr --listmonitors
> Monitors: 2
>   0: +XWAYLAND0 1920/510x1080/290+0+0  XWAYLAND0
>   1: +XWAYLAND1 1920/520x1080/290+1920+0  XWAYLAND1
> neal at raspberrypi:~ $ xrandr --output 1 --same-as 0
> warning: output 1 not found; ignoring
> neal at raspberrypi:~ $ Xrandr
> bash: Xrandr: command not found
> neal at raspberrypi:~ $ xrandr --output XWAYLAND1 --same-as XWAYLAND0
> X Error of failed request:  BadMatch (invalid parameter attributes)
>    Major opcode of failed request:  139 (RANDR)
>    Minor opcode of failed request:  7 (RRSetScreenSize)
>    Serial number of failed request:  29
>    Current serial number in output stream:  30
> neal at raspberrypi:~ $ xrandr --output +XWAYLAND1 --same-as +XWAYLAND0
> warning: output +XWAYLAND1 not found; ignoring
> 
> The Screen Layout Editor shows displays as HDMI-A-1 and HDMI-A-2, so I 
> also tried...
> 
> neal at raspberrypi:~ $ xrandr --output HDMI-A-2 --same-as HDMI-A-1
> warning: output HDMI-A-2 not found; ignoring
> neal at raspberrypi:~ $ xrandr --output HDMI-2 --same-as HDMI-1
> warning: output HDMI-2 not found; ignoring
> 
> I don't see an option in xrandr to simply tell me what outputs it thinks 
> it has.
> 
> And, is there a better way of doing this?  Also considering that the 
> real use will involve beer, and the projector may have different 
> resolution from the TV?
> 
> regards,
> 
> Neal
> 
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