GUI Scale 1x/2x and 3x/4x Behave Identically at 1080p Fullscreen #3891

Bug Description

When running Minecraft at 1920×1080 in fullscreen mode with Sodium installed, the GUI Scale setting does not behave correctly.

The available GUI Scale options are 1x, 2x, 3x, and 4x. However, 1x and 2x result in the same effective GUI size, while 3x and 4x also result in the same effective GUI size.

Reproduction Steps

Launch Minecraft with Sodium installed.
Set the resolution to 1920×1080.
Enable fullscreen mode.
Open the Video Settings and find the GUI Scale setting.
Set GUI Scale to 1x and observe the GUI size.
Change GUI Scale to 2x and compare the GUI size.
Repeat the test with 3x and 4x.
Expected Behavior
Each GUI Scale option should apply a different GUI scaling level when supported by the current resolution.

Actual Behavior
At 1920×1080 fullscreen:

1x and 2x have the same effective GUI scale.
3x and 4x have the same effective GUI scale.
This means that the four GUI Scale options effectively provide only two different GUI sizes.
Environment
Minecraft: 26.2
Sodium: 0.91
Java: 26.2
Resolution: 1920×1080
Display Mode: Fullscreen
GPU: Intel integrated graphics (Core i5-12500H)
Additional Information
The issue occurs when using 1080p fullscreen and appears to affect the GUI Scale setting specifically.

Log File

The latest.log does not contain any relevant errors or messages related to the GUI Scale issue.

Crash Report

N/A

Additional Testing

I also tested the issue with the Precise GUI Scalar mod.

With Precise GUI Scalar, I am able to adjust the GUI scale more precisely and get different GUI sizes. However, the GUI becomes blurry / has visible aliasing around text and UI elements when using the non-standard scaling values.

This suggests that the display resolution itself is not preventing the GUI from being scaled. The issue appears to be related specifically to how the standard GUI Scale options are calculated or applied in fullscreen at 1920×1080.

The original issue with Sodium remains:

1x and 2x result in the same effective GUI size.
3x and 4x result in the same effective GUI size.