Background image is duplicated when running on multiple monitors

[will-hinson]

 * slick-greeter 2.0.2
 * Distribution - Arch Linux
 * Graphics hardware *and* driver used: AMD ATI Radeon RX 6700 with `amdgpu` driver
 * 64 bit

Issue
When running slick-greeter on multiple monitors with one monitor in portrait left orientation, the applied background image is displayed twice on the portrait monitor resulting in a doubling effect:

Steps to reproduce

• A three-monitor display configuration with a portrait monitor on the far right should be used. All three monitors should have a resolution of 1920x1080.
• The contents of slick-greeter.conf are as follows. (Note: monterey-4-blur.jpeg is this image and monterey-4-blur-darker.jpeg is this one.

  [Greeter]
  background=/usr/share/pixmaps/monterey-4-blur.jpeg
  theme-name=Adwaita-dark
  clock-format=%b %e %H:%M
  other-monitors-logo=/usr/share/pixmaps/monterey-4-blur-darker.jpeg
  draw-user-backgrounds=false
  only-on-monitor=DP-2
  

• A display-setup-script setting should be configured in lightdm.conf to point to a shell script with these contents:

#!/bin/sh
# NOTE: the portrait monitor is on HDMI-1. the landscape monitors are on HDMI-2 and DP-2
xrandr --output HDMI-2 --pos 0x411
xrandr --output DP-2 --primary --pos 1920x411
xrandr --output HDMI-1 --pos 3840x0 --rotate left

• Upon rebooting and loading slick-greeter, the errant display will appear.

Expected behaviour
I would have expected the display to look like this. Notice the lack of the duplicated background image on the portrait monitor:

Other information
The output of xrandr is:

Screen 0: minimum 320 x 200, current 4920 x 1920, maximum 16384 x 16384
DP-1 disconnected (normal left inverted right x axis y axis)
DP-2 connected primary 1920x1080+1920+411 (normal left inverted right x axis y axis) 598mm x 336mm
   1920x1080     60.00*+  59.96    50.00    59.94    59.93  
   1680x1050     60.00    59.95    59.88  
   1400x1050     74.76    59.98  
   1600x900      59.94    59.95    60.00    59.82  
   1280x1024     75.02    60.02  
   1440x900      60.00  
   1400x900      59.96    59.88  
   1280x960      60.00  
   1440x810      59.97  
   1368x768      59.88    59.85  
   1280x800      59.99    60.00    59.97    59.81    59.91  
   1152x864      75.00  
   1280x720      60.00    59.99    59.86    60.00    50.00    59.94    59.74  
   1024x768      75.05    60.04    75.03    70.07    60.00  
   960x720       75.00    60.00  
   928x696       75.00    60.05  
   896x672       75.05    60.01  
   1024x576      59.95    59.96    59.90    59.82  
   960x600       59.93    60.00  
   832x624       74.55  
   960x540       59.96    59.99    59.63    59.82  
   800x600       75.00    70.00    65.00    60.00    72.19    75.00    60.32    56.25  
   840x525       60.01    59.88  
   864x486       59.92    59.57  
   720x576       50.00  
   700x525       74.76    59.98  
   800x450       59.95    59.82  
   720x480       60.00    59.94  
   640x512       75.02    60.02  
   700x450       59.96    59.88  
   640x480       60.00    75.00    72.81    75.00    60.00    59.94  
   720x405       59.51    58.99  
   720x400       70.08  
   684x384       59.88    59.85  
   640x400       59.88    59.98  
   576x432       75.00  
   640x360       59.86    59.83    59.84    59.32  
   512x384       75.03    70.07    60.00  
   512x288       60.00    59.92  
   416x312       74.66  
   480x270       59.63    59.82  
   400x300       72.19    75.12    60.32    56.34  
   432x243       59.92    59.57  
   320x240       72.81    75.00    60.05  
   360x202       59.51    59.13  
   320x180       59.84    59.32  
HDMI-1 connected 1080x1920+3840+0 left (normal left inverted right x axis y axis) 598mm x 336mm
   1920x1080     60.00 +  74.97*   72.01    60.01    50.03    48.02    59.96    50.00    59.94    59.93  
   1680x1050     60.00    59.95    59.88  
   1400x1050     74.76    59.98  
   1600x900      59.94    59.95    60.00    59.82  
   1280x1024     75.02    60.02  
   1440x900      60.00  
   1400x900      59.96    59.88  
   1280x960      60.00  
   1440x810      59.97  
   1368x768      59.88    59.85  
   1280x800      59.99    60.00    59.97    59.81    59.91  
   1152x864      75.00  
   1280x720      60.00    59.99    59.86    60.00    50.00    59.94    59.74  
   1024x768      75.05    60.04    75.03    70.07    60.00  
   960x720       75.00    60.00  
   928x696       75.00    60.05  
   896x672       75.05    60.01  
   1024x576      59.95    59.96    59.90    59.82  
   960x600       59.93    60.00  
   832x624       74.55  
   960x540       59.96    59.99    59.63    59.82  
   800x600       75.00    70.00    65.00    60.00    72.19    75.00    60.32    56.25  
   840x525       60.01    59.88  
   864x486       59.92    59.57  
   720x576       50.00  
   700x525       74.76    59.98  
   800x450       59.95    59.82  
   720x480       60.00    59.94  
   640x512       75.02    60.02  
   700x450       59.96    59.88  
   640x480       60.00    75.00    72.81    75.00    60.00    59.94  
   720x405       59.51    58.99  
   720x400       70.08  
   684x384       59.88    59.85  
   640x400       59.88    59.98  
   576x432       75.00  
   640x360       59.86    59.83    59.84    59.32  
   512x384       75.03    70.07    60.00  
   512x288       60.00    59.92  
   416x312       74.66  
   480x270       59.63    59.82  
   400x300       72.19    75.12    60.32    56.34  
   432x243       59.92    59.57  
   320x240       72.81    75.00    60.05  
   360x202       59.51    59.13  
   320x180       59.84    59.32  
HDMI-2 connected 1920x1080+0+411 (normal left inverted right x axis y axis) 598mm x 336mm
   1920x1080     60.00 +  74.97*   72.01    60.01    50.03    48.02    59.96    50.00    59.94    59.93  
   1680x1050     60.00    59.95    59.88  
   1400x1050     74.76    59.98  
   1600x900      59.94    59.95    60.00    59.82  
   1280x1024     75.02    60.02  
   1440x900      60.00  
   1400x900      59.96    59.88  
   1280x960      60.00  
   1440x810      59.97  
   1368x768      59.88    59.85  
   1280x800      59.99    60.00    59.97    59.81    59.91  
   1152x864      75.00  
   1280x720      60.00    59.99    59.86    60.00    50.00    59.94    59.74  
   1024x768      75.05    60.04    75.03    70.07    60.00  
   960x720       75.00    60.00  
   928x696       75.00    60.05  
   896x672       75.05    60.01  
   1024x576      59.95    59.96    59.90    59.82  
   960x600       59.93    60.00  
   832x624       74.55  
   960x540       59.96    59.99    59.63    59.82  
   800x600       75.00    70.00    65.00    60.00    72.19    75.00    60.32    56.25  
   840x525       60.01    59.88  
   864x486       59.92    59.57  
   720x576       50.00  
   700x525       74.76    59.98  
   800x450       59.95    59.82  
   720x480       60.00    59.94  
   640x512       75.02    60.02  
   700x450       59.96    59.88  
   640x480       60.00    75.00    72.81    75.00    60.00    59.94  
   720x405       59.51    58.99  
   720x400       70.08  
   684x384       59.88    59.85  
   640x400       59.88    59.98  
   576x432       75.00  
   640x360       59.86    59.83    59.84    59.32  
   512x384       75.03    70.07    60.00  
   512x288       60.00    59.92  
   416x312       74.66  
   480x270       59.63    59.82  
   400x300       72.19    75.12    60.32    56.34  
   432x243       59.92    59.57  
   320x240       72.81    75.00    60.05  
   360x202       59.51    59.13  
   320x180       59.84    59.32