[BUG] The virtual pointer does not extend to second screen

[giampierosalvi]

Description
In multiple screen settings, the virtual pointer works well on the main screen, but only reaches a small part of the second screen.

To Reproduce
Start projecteur, start the virtual pointer either with a Logitech Spotlight or with "Show test..." and a normal mouse. At this point the background of the second screen changes showing an darker area (see screenshots). Move the pointer around in the first and second screen. On the second screen the pointer stops when reaching the edge of the darker area. Note that in normal mouse mode there is no problem moving the mouse pointer on any screen. Same behavior is observed if running QT_QPA_PLATFORM=wayland projecteur.

Expected behavior
It should be possible to use the virtual pointer on the whole surface of the second screen.

Desktop/Linux Environment (please complete the following information):

• Linux Distribution and Version: Ubuntu 26.04
• Desktop/Window Manager and Version GNOME 50
• Did you built Projecteur yourself?: n
• What is the output of projecteur -f ?:

Projecteur 0.10
  - git-branch: tag: v0.10, master
  - git-hash: a7b2649296f5f8b6793e0c38cdee93d36831404b
  - compiler: GNU 15.2.0
  - build-type: Debian
  - qt-version: (build: 5.15.18, runtime: 5.15.18)
  - device-scan: (errors: 0, devices: 0 [readable: 0, writable: 0])

• What is the output of projecteur -d ?:

Projecteur 0.10; device scan

 * Found 1 supported devices. (1 readable, 1 writable)

 +++ name:     'Logitech USB Receiver'
     userName: 'Logitech Spotlight (USB)'
     vendorId:  046d
     productId: c53e
     phys:      usb-0000:00:14.0-11
     busType:   BusType::Usb
     devices:   /dev/hidraw6, /dev/input/event3, /dev/input/event19, /dev/input/event5, /dev/input/event7
     readable:  true
     writable:  true

Screenshots
Screenshot of the second screen before activating the virtual pointer:

Screenshot of the second screen after activating the virtual pointer:

[giampierosalvi]

Update:
the problem can be fixed by running QT_QPA_PLATFORM=xcb projecteur, and by selecting "Enable multi-screen overlay".