Using gtk4, in C, how do I make the window background color transparent?

Platform
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4

Hi,

I’m not sure using a custom snapshot will work, as gtk will anyway automatically draw the background based on CSS theme before calling snapshot().

Why not embedding a small CSS style to unset the window’s background?

Here a working example in Python:

#!/usr/bin/env python3

import sys
import gi
gi.require_version('Gdk', '4.0')
gi.require_version('Gtk', '4.0')
from gi.repository import Gdk, Gtk

THEME = """
window.background {
    background: unset;
}
"""

class MyAppWindow(Gtk.ApplicationWindow):
    __gtype_name__ = __qualname__
    def __init__(self, **kwargs):
        super().__init__(default_width=200, default_height=200, show_menubar=False, **kwargs)
        button = Gtk.Button.new_with_label("Hello World!")
        button.set_halign(Gtk.Align.CENTER)
        button.set_valign(Gtk.Align.CENTER)
        self.set_child(button)
        self.present()

class MyApp(Gtk.Application):
    __gtype_name__ = __qualname__
    def __init__(self, **kwargs):
        super().__init__(**kwargs)
        self.connect('activate', self.on_activate)
    def on_activate(self, app):
        cssp = Gtk.CssProvider()
        cssp.load_from_string(THEME)
        d = Gdk.Display.get_default()
        Gtk.StyleContext.add_provider_for_display(d, cssp, Gtk.STYLE_PROVIDER_PRIORITY_APPLICATION)
        self.add_window(MyAppWindow())

if __name__ == '__main__':
    sys.exit(MyApp().run(sys.argv))