[Documentation] Splashscreen on linux does not support transparency

[Avasam]

Description of the issue

On linux, my splashscreen appears as follows, where the transparent parts are gray. They are transparent on Windows.

Here's the hard-cut transparency image I am using for reference:

I understand this could be a Linux limitation and/or the nature of the splashscreen being experimental. But this limitation is not currently documented: https://pyinstaller.org/en/stable/usage.html#splash-screen-experimental

Context information (for bug reports)

• Output of pyinstaller --version: 5.2
• Version of Python: 3.10
• Platform: Ubuntu 22.04
• How you installed Python: python.org/downloads
• Did you also try this on another platform? Does it work there? Yes Windows

Make sure everything is packaged correctly

• [x] start with clean installation
• [x] use the latest development version
• [x] Run your frozen program from a command window (shell) — instead of double-clicking on it
• [x] Package your program in --onedir mode
• [x] Package without UPX, say: use the option --noupx or set upx=False in your .spec-file
• [x] Repackage you application in verbose/debug mode. For this, pass the option --debug to pyi-makespec or pyinstaller or use EXE(..., debug=1, ...) in your .spec file.

A minimal example program which shows the error

N/A (program can be empty, just needs a spashscreen)

Stacktrace / full error message

N/A

Please also see https://github.com/pyinstaller/pyinstaller/wiki/How-to-Report-Bugs for more about what would use to solve the issue.

[rokm]

You're right; hard-cut transparency does not seem to be supported on linux. Sounds like a platform-specific limitation of Tcl/Tk.

And yeah, it would be nice if the docs contained a note about that - care to open a PR that adds one?