Adds the ability to disable/enable window interactions

[TheColorRed]

This allows the user to enable/disable interactions with the window. This is useful for displaying a dialog box that. This is useful in conjunction with always-on-top and PR #6675.

Example Slint:

mod dialog {
    slint::slint! {
        export component MyDialog inherits Window {
          skip-taskbar: true;

          width: 200px;
          height: 200px;
        }
    }
}

slint::slint! {
  import { Button } from "std-widgets.slint";

  export component AppWindow inherits Window {
    callback show-dialog;

    min-width: 200px;
    min-height: 200px;

    Button {
      text: "Click me!";
      clicked => {
        root.show-dialog();
        // root.disabled = true;
      }
    }
  }
}

Example Rust (Might be overkill 😃)

use std::sync::Arc;

pub fn main() -> Result<(), slint::PlatformError> {
    let app_window = AppWindow::new()?;
    let app = Arc::new(app_window);

    let window_ref = app.clone();
    app.clone().on_show_dialog(move || {
        let dialog = dialog::MyDialog::new().unwrap();
        window_ref.clone().window().set_disabled(true);
        let window_ref = window_ref.clone();
        dialog.window().on_close_requested(move || {
            window_ref.clone().window().set_disabled(false);
            slint::CloseRequestResponse::HideWindow
        });

        let _ = dialog.show();
    });

    app.clone().run()?;
    Ok(())
}

[ogoffart]

I'm wondering if that's really the right API to create modal dialog.
We might need a more complex API in rust/C++ to create modal dialog that prevent interaction on their parent. I think this is the typical usecase.

[hunger]

With wayland + portals we will also need a way to register external windows as "modal windows" on top of application windows. So maybe we can pass in a optional (os-) window handle or something instead of a bool?

E.g. file selection in a program using a portal can pop up a file dialog that logically belongs to the application asking for a file, but is actually a different process providing the window. That needs to be handled properly to make sure the right windows get selected when switching between applications.

Kai-Uwe blogged about KDE doing this recently: https://blog.broulik.de/2024/11/little-wayland-things/