Bug Mouse position flickers in Editor fullscreen on non-primary monitor

So, in-Editor fullscreen was recently added which is great. But apparently it comes with some birth defects. I am not sure this is just a uGUI specific issue, but the example project I made use uGUI.

I have filed a bug report with case IN-21628. Unity 2022.2.20f1.

An example package is attached.

1. What happened
Mouse position is unreliable in Editor fullscreen on non-primary monitor. It jumps from the actual position to what looks like x2 position on my monitors. I have only tested on Windows.

2. How can we reproduce it using the example you attached

• Set primary monitor to 4K (3840x2160) and a secondary monitor to something else like 2K (1920x1080) in Windows settings.
• Import the attached package in a fresh 2022.1.20f project and open the scene 'EditorFullscreenBug'.
• Drag the game view to the second monitor and set 'Enter Play Mode' to fullscreen on the second monitor.
• Hit play and hover the second monitor.
• A pink square should flicker between two positions.

The square is positioned like this (but I get the same problem when using for example ICanvasRaycastFilter).

Code (CSharp):

1. using UnityEngine;
2. using UnityEngine.UI;
3.  
4. public class CustomImage : Image
5. {
6.     void Update()
7.     {
8.         rectTransform.position = Input.mousePosition;
9.     }
10. }

 

I don't think it's uGUI specific, just hit this bug when doing camera raycasts. Seems to be the input systems (both new and old) reporting wrong mouse coordinates when the mouse moves.