Unity build changes its resolution after going to windowed mode and then back to fullscreen

Question

It seems to me that this behavior is incorrect (or at least illogical). Correct me if I'm wrong.

Repro (Unity 2020.3.26f1 LTS / default project settings):

• Run the build (in fullscreen by default):

• Go to windowed mode (Alt + Enter):

• Resize the window with the mouse so that its resolution is reduced (to 500x500 pixels):

• Go back to fullscreen mode (Alt + Enter):

Actual results:

• When going back to fullscreen mode resolution is being kept 500x500 pixels (the scene is rendered in 500x500 pixels, the text is blurry and the canvas is squared).
• Both Screen.currentResolution & Screen.width/height have 500x500 values.

Expected results:

• Fullscreen-mode should restore the game resolution back to 1920x1080 (as on the 1st screenshot before going to windowed-mode).
• Both Screen.currentResolution & Screen.width/height should have the values of 1920x1080.

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The problem caused by this behavior is that the user cannot return to full-screen mode with full display resolution after switching to windowed mode and changing the window size.

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Component script used in this test:

public class ResolutionInfo : MonoBehaviour
{
    public Text text;

    private Vector2 _resolution, _currentResolution;
    private bool _fullscreen;

    void Update()
    {
        Vector2 resolution = new Vector2(Screen.width, Screen.height);
        Vector2 currentResolution = new Vector2(Screen.currentResolution.width, Screen.currentResolution.height);

        if (_resolution == resolution && _currentResolution == currentResolution && _fullscreen == Screen.fullScreen)
            return;

        _resolution = resolution;
        _currentResolution = currentResolution;
        _fullscreen = Screen.fullScreen;

        text.text =
            $"FullScreen: {Screen.fullScreen}\r\n" +
            $"Screen.currentResolution = {Screen.currentResolution}\r\n" +
            $"Screen.width/height = {Screen.width}x{Screen.height}";
    }
}

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P.S. Screen.resolutions list added to the request from Arian Keshvari comment:

Answer 1

This is a bit late, but I ran into the same problem recently and plopped this script together after exploring the forums a bit. It should do the trick once attached to any component in your scene. Hope that helps and good luck!

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.UI;
public class ManageFullscreenSwitch : MonoBehaviour
{
    private int _fullscreenWidth = 0;
    private int _fullscreenHeight = 0;
    private int _fullscreenAspectRatio = 0;

    private bool _fullscreen = false;

    private void Start()
    {
        _fullscreen = Screen.fullScreen;
        SetFullScreenValues();
    }
    private void Update()
    {
        if (_fullscreen != Screen.fullScreen)
        {
            if (Screen.fullScreen)
            {
                RestoreFullscreenResolution();
            }

            _fullscreen = Screen.fullScreen;
        }
    }

    private void RestoreFullscreenResolution()
    {
        Screen.SetResolution(_fullscreenWidth, _fullscreenHeight, true, _fullscreenAspectRatio);
    }

    private void SetFullScreenValues()
    {
        // Set the screen width and height
        int systemWidth = Display.main.systemWidth;
        int systemHeight = Display.main.systemHeight;

        // Get a list of all supported resolutions
        Resolution[] supportedResolutions = Screen.resolutions;

        // Find the closest supported resolution to the native resolution
        Resolution closestResolution = supportedResolutions[0];
        int smallestGapInResolution = int.MaxValue;

        foreach (Resolution resolution in supportedResolutions)
        {
            int gap = Mathf.Abs(resolution.width - systemWidth) + Mathf.Abs(resolution.height - systemHeight);

            if (gap < smallestGapInResolution)
            {
                smallestGapInResolution = gap;
                closestResolution = resolution;
            }
        }

        _fullscreenWidth = closestResolution.width;
        _fullscreenHeight = closestResolution.height;
        _fullscreenAspectRatio = _fullscreenWidth / _fullscreenHeight;
    }
}