Unexpected pixel jitter when using 2d stretch mode and keep stretch aspect

[Skullfurious]

Godot version:
3.2.3.stable.official

OS/device including version:
Windows 10 20H2, GTX 1080ti, R7 3800X

Issue description:
The bottom and right side of the Godot application jitter when being resized if you enable 2D Stretch mode with Aspect locking.

This only occurs on the bottom and right side. Left and top work as expected without jitter.

Steps to reproduce:
Under DIsplay -> Window:
Size
Width: 1280
Height: 720
Stretch
Mode: 2d
Aspect: keep
(This enables letterboxing like Celeste on ultrawide monitors)

Under Rendering -> Quality:
2d
Use Pixel Snap

Drag Window around and look at bottom / right side letter boxing.

Minimal reproduction project:
Demo.zip

i0BlRliFsh.1.mp4

WF3EdRtMQb.1.mp4

[Skullfurious]

i believe the issue starts at line 615
in window.cpp

https://github.com/godotengine/godot/blob/a6ec6521fae92a245c9d395efda01a120a44324d/scene/main/window.cpp

[Calinou]

@Skullfurious window.cpp only exists in the master branch, not 3.2.

Also, if you want to avoid any kind of pixel jitter, you need to enforce integer scaling using a script: godotengine/godot-proposals#1666

[Skullfurious]

The jitter doesnt come from the actual canvas resolution changing. Not demonstrated in the videos is the top and left sides not jittering. None of the pixels within the bounds of the viewport jitter.

The only jitter is when the letterboxing is shifting on the bottom and right side of the window.

ZfNhQrdRXA.1.mp4