Wrong mouse coordinates after window resize when using viewport stretch-mode canvas_items or viewport

[ZuBsPaCe]

Godot version

v4.0.dev (75697c0)

System information

Windows 10

Issue description

I want to position a Sprite2D at the global mouse position.

This works when setting stretch mode to disabled/keep-aspect, even when resizing the screen:

When I set stretch mode to canvas_items/keep-aspect, the mouse coordinates are sometimes wrong after I resize the window:

When I set stretch mode to viewport/keep-aspect, the mouse coordinates are always wrong after I resize the window:

Hints:

• I could not reproduce the Issue in 3.3.3-stable.
• Could be related to changes regarding stretch mode.
• If I use an Area2D, mouse_entered and mouse_exited signals are also affected.
• Issue 2d or viewport stretch mode does not scale mouse coordinates #34805 could be related. But it's in 3.2 and I'm not using ViewportContainer/Viewport at all.

Steps to reproduce

1. Add a Sprite2D scene with following code:

func _process(delta):
    position = get_global_mouse_position()

2. In the project settings select viewport/keep-aspect or canvas_items/keep-aspect.
3. Run the game.
4. Resize the window by dragging the top, right, bottom or left window border.

Minimal reproduction project

ViewportScalingGodot4.zip

[CosmicSpore]

This bug does exist in v3.3 (and also v3.2 at the very least) but in a slightly different way...
Instead of global_mouse_position() not returning proper coordinates, the same problem instead occurs with InputEvents, particularly with "event.global_position". In fact, ironically enough, using global_mouse_position() actually seems to FIX the bug in v3.3. (So I guess technically this could be considered a different bug? But it seems similar enough to me that I figured I would just post here.)

Steps to reproduce on 3.3:

1. Add Sprite to scene with the following code:

func _input(event):
    if event is InputEventMouse:
	position = event.global_position

2. In project settings select: Mode: 2D, Stretch: Keep Height (May occur with other settings as well)
3. Run
4. Resize the window

Minimal project:
TestTestTest.zip

I've had a longstanding issue with this and I could never figure out why it happened until I saw this ticket. It never occurred to me the problem may have been in the engine itself. So I started testing a couple things and thanks to @ZuBsPaCe, for posting this bug, I finally found a way to work around it properly in my project. :)

[Racinettee]

I'm not fully sure if its the same issue or not, but I think this might also affect UI elements in godot 4.
When using the ItemList in godot 4, and the viewport mode: after expanding the window or using a larger test_mode size, the UI elements cannot be clicked anymore.
I couldn't reproduce the issue on 3.3 using the above settings, but in godot 4 the viewport setting on its own causes the UI elements to seem to not get mouse input.

[Supergeek]

In 3.3.3-stable using a StretchShrink setting other than 1 on a ViewportContainer makes GetGlobalMousePosition() incorrect. If you set it back to 1 it works. For values higher than 1, the reported position appears to be offset by an amount that seems to scale with the screen scale. (Using Display->Window->Stretch Mode->Viewport.)

My personal workaround. (C# version)

var global_position = (viewportContainer.GetLocalMousePosition() / viewportContainer.StretchShrink) + camera.Position;

[Calinou]

Related to #50802.