4.0alpha: Stretch scale factor doesn't apply when using viewport stretch mode (while it does in 3.x)

[Calinou]

Godot version

4.0.alpha7

System information

Fedora 34, GeForce GTX 1080 (NVIDIA 510.60.02)

Issue description

In master, the stretch scale factor doesn't apply when using the viewport stretch mode (while it does in 3.5beta4). The stretch scale factor works as expected when using the disabled or canvas_items stretch modes.

cc @Ansraer, as they ported the stretch scale to 4.0 inhttps://github.com//pull/52170.

master behavior (incorrect)

simplescreenrecorder-2022-05-05_19.34.34.mp4

3.x behavior (correct)

simplescreenrecorder-2022-05-05_19.33.59.mp4

Steps to reproduce

• Use the viewport stretch mode (not disabled or canvas_items).

Minimal reproduction project

• master project: https://github.com/Calinou/godot-demo-projects/tree/multiple-resolutions-update-to-4.0/gui/multiple_resolutions
• 3.x project: https://github.com/godotengine/godot-demo-projects/tree/master/gui/multiple_resolutions

[Ansraer]

I am fairly certain it isn't supposed to work for viewport in 3.x. When I wrote the original PR there was a reason why I excluded that (see the PR messages), though I can't remember what it was right now.
What makes this even more confusing is that, despite what I wrote in the messages, according to git blame I did add code for viewport stretching in 3.x.

I suppose I could enable this in 4.x and see what happens.

[Calinou]

I do think the scale factor property should work when using the viewport stretch mode, as it gives more flexibility to the user. Working this around requires using a second viewport, which isn't great for usability (and performs worse).