Individual screen wallpapers have problem with scale factors

[tsujan]

Steps to Reproduce (for bugs)

1. Set the global Qt scale factor to 1.5 in LXQt Session Settings.
2. Choose "Individual wallpaper for each monitor" in Desktop Preferences.
3. Set up a double screen.

Then the wallpaper will be drawn incorrectly.

Possible Solution

Will fix it when I feel motivated -- it's boring.

System Information

Latest git LXQt.

[tsujan]

It's very likely that this is a Qt bug because desktop items also have wrong positions with multi-screen+ scaling but, as far as I checked, calculations are correct.