Main window appears, disappears and re-appears on startup

Issue type

UI bug (incorrect info or interface appearance)

Description with steps to reproduce

1. Start MS. :)

Actual result: when the splash screen closes, the main window appears empty briefly, then suddently disappears and re-appears a bit later.
Expected result: Main window should not disappear once it appears.

Video demonstration at 0.5x speed:

https://github.com/user-attachments/assets/8628ce4d-dbc7-49ed-b357-41686e87fbb2

This behavior is the result of a couple of fixes and probably the latest Qt updates:

1. I made the main window appear as soon as the splash screen is closed, to fix issue 21148.

2. This lead to issue 29630 where the main window was showing its border but nothing else for a moment and then it appeared fully. The fix here was to make the main window transparent.

What happens now is that even though we set the transparency to 0.01, when we are showing the window Qt ignores the transparency, shows the window and then applies the transparency. This makes the window appear and disappear until the transparency is removed once the start up page loads. I suspect Qt's latest versions have started doing this weird thing.

I propose three possible routes we can go to fix this, each one of them with pros and cons. So the team needs to decide. Here are the possibilities:

1. Replace the transparency with 0.0 (currently it is 0.01). This makes a difference for Qt and the window is not shown in this case as it is transparent. PROs: the main window appears when the startup page has loaded, i.e. it appears when it is no longer empty. CONs: there is a noticeable gap between the closing of the splash screen and the appearance of the main window. For devs, this gap can even make them think for a moment that MS has crashed. :) Video demonstration:

https://github.com/user-attachments/assets/e5dc256c-f1a9-46a9-8861-396a757cc644

2. Remove the transparency and just show the main window. PROs: the main window appears as soon as the splash screen closes, there is no gap. CONs: the main window is blank for a (not very short) moment until the startup page loads. Video demonstration:

https://github.com/user-attachments/assets/8ac92326-6fc4-432b-a451-b098cee635a3

3. Set the transparency to 0.0 as in the first possibility, but delay the closing of the splash screen until the startup page has loaded and the main window is not empty. PROs: no gap between the splash screen and the main window and the main window appears populated. CONs: the longer period that the splash screen is shown gives the impression of a larger load time than before even though the total load time is the same. Also, any floating windows appear while the splash screen is showing (althogh on my machine it is not very noticeable). You can test this if you set your startup scenario to be to load a score and float one or more windows (e.g. the piano keyboard). Also other startup screens such as the Welcome screen, might be problematic and need to be tested. Video demonstration:

https://github.com/user-attachments/assets/28b23dff-1595-4439-8b28-29edeb0c14cd

Note that the release builds of MSS run faster than my debug builds, so these effects (empty screen or gap) are much less pronounced / noticeable.

It will be very interesting to know if this is a Windows-only thing or not.
Tagging @igorkorsukov (he added the transparency fix) and @avvvvve for now.

Supporting files, videos and screenshots

n/a

In which versions of MuseScore Studio is this issue present?

from around 4.6.5 onwards

Regression

Yes, this used to work in a previous version of MuseScore 4.x

Operating system

Windows 10

Additional context

No response

Checklist

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• I have verified that this issue has not been logged before, by searching the issue tracker for similar issues
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• I have attempted to identify the root problem as concisely as possible, and have used minimal reproducible examples where possible